C 55.618: 23 Climate Monitoring and Diagnostics Laboratory No. 23 Summary Report 1994-1995 COo Growth Rate (ppm / yr) YEAR CH 4 Growth Rate (ppb / yr) — i — . i , i i i 84 85 86 87 88 89 90 YEAR 91 92 93 ..aKTMOftw ^ EN TOf^ U.S. Department of Commerce National Oceanic and Atmospheric Administration Environmental Research Laboratories Cover: Contour plots showing the temporal and spatial variations in the atmospheric increases of carbon dioxide (CO2, upper panel) and methane (CH 4 , lower panel). The cooler colors (blue, violet, black) represent periods of lower than average growth rates and the warmer colors (yellow, orange, red) represent high growth rate periods. These plots are derived from measurements of thousands of samples collected at the CMDL Cooperative Air Sampling Network sites. The variations in the growth rates of these climatically important gases are due to interannual variations in the imbalances between sources and sinks, and also to variations in atmospheric transport. Because the major sources and sinks for CO2 and CH4 are different, their patterns of growth rate variations are usually dissimilar. An exception to this is the period of low, and even negative growth rates of both gases in 1992-1993, a period when anomalous low temperatures were observed. These observations provide powerful constraints on attempts to model the global carbon cycle. [This figure was created by Ken Masarie and Catherine Mcintosh.] Climate Monitoring and Diagnostics Laboratory No. 23 Summary Report 1994-95 David J. Hofmann, Editor James T. Peterson, Editor Rita M. Rosson, Assistant Editor Boulder, Colorado September 1 996 Pennsylvania State University Libraries NOV 5 1996 Documents Collection U.S. Depository Copy U.S. DEPARTMENT OF COMMERCE Michael Kantor, Secretary National Oceanic and Atmospheric Administration D. James Baker, Under Secretary for Oceans and Atmosphere/Administrator Environmental Research Laboratories James L. Rasmussen, Director NOTICE Mention of a commercial company or product does not constitute an endorsement by NOAA Environmental Research Laboratories. Use for publicity or advertising purposes of information from this publication concerning proprietary products or the tests of such products is not authorized. For sale by the National Technical Information Service. 5285 Port Royal Road Springfield, VA 22161 Preface The Climate Monitoring and Diagnostics Laboratory (CMDL) is located in Boulder, Colorado, with observatories in Barrow, Alaska; Mauna Loa, Hawaii; Cape Matatula, American Samoa; and South Pole, Antarctica. It is one of twelve components of the Environmental Research Laboratories (ERL) within the Office of Oceanic and Atmospheric Research (OAR) of the National Oceanic and Atmospheric Administration (NOAA). CMDL conducts research related to atmospheric constituents that are capable of forcing change in the climate of the earth through modification of the atmospheric radiative environment, for example greenhouse gases and aerosols, and those that may cause depletion of the global ozone layer. This report is a summary of activities of CMDL for calendar years 1994 and 1995. It is the 23rd consecutive report issued by this organization and its Air Resources Laboratory/Geophysical Monitoring for Climatic Change predecessor since formation in 1972. From 1972 through 1993 (numbers 1 through 22), reports were issued annually. However, with this issue we begin a 2-year reporting cycle, which stems from a need to most efficiently use the time and financial resources of our staff and laboratory and from a general trend towards electronic media. In this respect, CMDL has developed a comprehensive internet home page during the past 2 years. There you will find information about our major groups and observatories, latest events and press releases, publications, data availability, and personnel. Numerous data graphs and ftp data files are available. The URL address is http://www.cmdl.noaa.gov. Information (program descriptions, accomplishments, publications, plans, data access, etc.) on CMDL parent organizations can best be obtained via the internet. Their URL addresses are ERL: http://www.erl.noaa.gov; OAR: http://www.oar.noaa.gov; NOAA: http://www.noaa.gov. In 1995, Eldon Ferguson retired from federal service and from the CMDL Director's position that he held from the formation of the Laboratory in 1990. On a personal note, we extend to him our best wishes for the future and our thanks for scientific guidance and direction in the past. In 1996, David Hofmann, the CMDL Chief Scientist since 1990, was appointed Director of CMDL. This report is organized into the following major sections: 1. Observatory, Meteorology, and Data Management 2. Carbon Cycle 3. Aerosols and Radiation 4. Ozone and Water Vapor 5. Nitrous Oxide and Halocompounds 6. Cooperative Programs These are followed by a list of CMDL staff publications for 1994-1995. Inquiries and/or comments are welcomed and should be addressed to: Director, R/E/CG NOAA/Climate Monitoring and Diagnostics Laboratory 325 Broadway Boulder, CO 80303-3328 (303)497-6074 e-mail: hofmann@cmdl.noaa.gov Eldon E. Ferguson, Climate Monitoring and Diagnostics Laboratory Director, 1990-1995. IV Contents Preface iii CMDL Organization, 1995 ix CMDL Staff, 1995 x CMDL Station Information xi 1. Observatory, Meteorology, and Data Management Operations 1 1.1. Mauna Loa Observatory 1 1.1.1. Operations 1 1.1.2. Programs 2 1.2. Barrow Observatory 9 1.2.1. Operations 9 1.2.2. Programs 9 1.3. Samoa Observatory 12 1.3.1. Operations 12 1.3.2. Programs 12 1.4. South Pole Observatory 14 1.4.1. Operations 15 1.4.2. Programs 14 1.5. Meteorological Measurements 17 1.5.1. Station Climatologies 17 1.5.2. Meteorology Operations 24 1.6. Data Management 26 1.7. References 28 2. Carbon Cycle 29 2.1. Overview 29 2.2. Carbon Dioxide 29 2.2.1. In Situ Carbon Dioxide Measurements 29 2.2.2. Flask Sample Carbon Dioxide Measurements 30 2.2.3. Carbon Dioxide Reference Gas Calibrations 31 2.2.4. Measurements of Stable Isotopes of CO2 33 2.2.5. The Airkit Sampler 34 2.2.6. Calibration of Measurements of Stable Isotopes of CO2 34 2.3. Methane 35 2.3.1. In Situ Methane Measurements 35 2.3.2. Discrete Sample Measurements of Methane 37 2.3.3. Measurement of 13C/12C of Methane 39 2.4. Carbon Monoxide 39 2.4.1. In Situ Carbon Monoxide Measurements 39 2.4.2. Flask Measurements of Carbon Monoxide 40 2.4.3. The MAPS Program 42 2.4.4. Carbon Monoxide Standards 42 2.5. Flask Measurements of SF 6 /N 2 42 2.6. Measurements on Tall Towers 43 2.7. Automated Aircraft Sampling 45 2.8. Data Management 47 2.9. Data Integration 47 2.10. Three-Dimensional Inverse Modeling 47 2.11. References 48 3. Aerosols and Radiation 50 3.1. Aerosol Monitoring 50 3.1.1. Scientific Background 50 3.1.2. Experimental Methods 50 3.1.3. Annual Cycles 51 3.1.4. Long-Term Trends 53 3.1.5. Results From 1994-1995 53 3.1.6. Aircraft Observations 56 3.1.7. Lidar Measurements at Mauna Loa 59 3.2. Solar and Thermal Atmospheric Radiation 60 3.2.1. Baseline Monitoring Activities 60 3.2.2. Solar Radiation Calibration Facility 62 3.2.3. Aerosol Optical Depth Remote Sensing 62 3.2.4. Mauna Loa UV Spectroradiometer 63 3.2.5. MLO Broadband UV 65 3.2.6. BSRN 65 3.2.7. WMO GAW Stations 65 3.2.8. Volcanic Radiative Fording and Induced Global Cooling 65 3.2.9. BRW Surface Radiation and Meteorological Measurements 66 3.3. References 67 4. Ozone and Water Vapor 69 4.1. Continuing Programs 69 4.1.1. Total Ozone Observations 69 4.1.2. Umkehrs 70 4.1.3. Surface and Tropospheric Ozone 71 4.1.4. Ozonesondes 74 4.1.5. Atmospheric Water Vapor 76 4.1.6. Atmospheric Transport 76 4.2. Special Projects 77 4.2.1. The Mauna Loa Ozone Profile Intercomparison 77 4.2.2. Ozone Vertical Profiles Over the North Atlantic 77 4.2.3. Water Vapor and Ozone Profiles at McMurdo, Antarctica 78 4.2.4. Flow Patterns for SMO Described with Clustered Trajectories 80 4.3. References 82 5. Nitrous Oxide and Halocompounds 84 5.1. Continuing Programs 84 5.1.1. Introduction 84 5.1.2. Flask Samples 84 5.1.3. RITS Continuous Gas Chromatograph Systems 87 5.1.4. LEAPS 89 5.1.5. Chlorofluorocarbon Alternative Measurements Program 90 5.1.6. Gravimetric Standards 95 5.2. Aircraft GC Project: SHOE/MAESA Mission 96 5.2.1. Overview 96 5.2.2. Transport in the Lower Stratosphere 96 5.2.3. Bromine Budget 99 5.3. LACE 101 5.4. Ocean Project: BLAST Cruises 101 5.5. STEALTH Project: Automated Four-Channel Field Gas Chromatographs 103 5.5.1. Overview 103 5.5.2. Tower GC at WITN in Cooperation with CCG 104 VI 5.6. Measurement of Air From South Pole Firn 105 5.7. References 109 Cooperative Programs 1 12 Evaluation of Arctic Meteorological Buoys G.F.Appell 112 Asian Transport of Aerosols to Mauna Loa Observatory, Spring 1994 T.A. Cahill and K.D. Perry 114 Ultrahigh Resolution Infrared Solar Spectra From Mauna Loa Observatory: New Results S.J. David, F.J. Murcray, A. Goldman, and R.D. Blatherwick 1 17 A Preliminary Comparison of 8 13 C Measurements in CO2 From Mace Head, Ireland A. Gaudry, P. Monfray, M. Trolier, C. Flehoc, P. Ciais, andS.G. Jennings 1 19 Measurement of Short Period Magnetic Pulsations at Barrow: A Key Location in the STEP Polar Network K.Hayashi 122 Total Nitrate Variation at Mauna Loa B.J. Huebert and L. Zhuang 123 Radionuclides in Surface Air at BRW, MLO, SMO, and SPO During 1994 and 1995 J. Kada and C.G. Sanderson 126 Global Distribution of Chloroform in the Marine Boundary Layer M.A.K. Khalil and R.A. Rasmussen 128 NSWC Pt. Barrow Geomagnetic Observatory D.S. Lenko, J.F. Scarzello, and D. Taylor 130 Exposure Experiment, South Pole J.E. Mak, CAM. Brenninkmeijer, andJ.R. Southon 131 Investigation of the Transfer Function Between Snow and Atmosphere Concentrations of Hydrogen Peroxide at South Pole J.R. McConnell and R.C. Bales 132 NDSC Stratospheric Ozone-Temperature-Aerosol Lidar IS. McDermid, E.W. Sirko, andT.D. Walsh 134 Antarctic UV Spectroradiometer Monitoring Program: Contrasts in UV Irradiance at the South Pole and Barrow, Alaska T. Mestechkina, C.R. Booth, J.R. Tusson IV, and J.C. Ehramjian 135 Gamma Radionuclide Deposition at SMO During Recent French Nuclear Weapons Testing on South Pacific Atolls M. Monetti 138 Early Morning UV-B During the 1994-1995 Record Low Ozone at Mauna Loa P.J. Neale, D.L. Correll, V.R. Goodrich, and D.R. Hayes, Jr 140 Advanced Global Atmospheric Gases Experiment (AGAGE) R.G. Prinn, R.F. Weiss, F.N. Alyea, DM. Cunnold, P.J. Fraser, L.P. Steele, and P.G. Simonds 142 The 13 C/ ,2 C of Atmospheric Methane P. Quay, J. Stutsman, and D. Wilbur 144 Aerosol Measurements on American Samoa D.L. Savoie and JM. Prospero 146 An Operational Intercalibration Experiment Between CMDL and CSIRO to Measure Several Atmospheric Trace Species L.P. Steele, R.J. Francey, R.L. Langenfelds, C.E. Allison, M.P. Lucarelli, P.P. Tans, E.J. Dlugokencky, T.J. Conway, P.C Novelli, K.A. Masarie, J.W.C White, and M. Trolier 148 USGS Barrow Observatory J. Townshend 150 The New ANSTO Radon Detector at MLO S. Whittlestone 151 A comparison of CO2 and 13 /12C Seasonal Amplitudes in the Northern Hemisphere T.P. Whorf, CD. Keeling, and M. Wahlen 153 Publications and Presentations by CMDL Staff, 1994-1995 157 Vlll CMDL Organization, 1995 The CMDL organization structure features five research areas organized according to scientific discipline as follows: (1) Carbon Cycle; (2) Nitrous Oxide and Halocompounds; (3) Ozone and Water Vapor; (4) Aerosols and Radiation; and (5) Observatory Operations. At the end of 1995, the laboratory staff consisted of 46 civil service personnel (excluding part-time student assistants), 34 CIRES/University of Colorado personnel, and two NOAA Corps officers as well as several visitors and people on special appointments. Laboratory Secretary Ann Thorne (303) 497-6074 Director, CMDL David Hofmann (303) 497-6966 Deputy Director James T. Peterson (303) 497-6668 Administrative Officer Sandra Howe (303)497-6070 Carbon Cycle Pieter Tans (303) 497-6678 Ozone and Water Vapor Samuel Oltmans (303) 497-6676 Nitrous Oxide and Halocompounds James W. Elkins (303) 497-6224 Observatory Operations and Data Management Barrow Observatory Daniel J. Endres (907) 852-6500 Aerosols and Radiation John Ogren (303)497-6210 Ellsworth Dutton (303)497-6660 Mauna Loa Observatory Russell C. Schnell (808) 933-6965 Samoa Observatory Mark A. Winey (684) 622-7455 South Pole Observatory Ricardo Ramos (303)497-6650 IX CMDL Staff, 1995 Director's Office David Hofmann, Director James T. Peterson, Deputy Director Sandra Howe, Administrative Officer Ann Thorne, Secretary Rita Rosson, Editorial Assistant Denise Theede, Program Support Technician Kay Villars, Administrative Assistant Special Projects Mark Bieniulis, CIRES Bradley Halter, CIRES Thomas Mefford, CIRES Kenneth Thaut, Electronic Technician Patrick Sheridan, CIRES Eldon Ferguson, Guest Scientist Aerosols and Radiation Division Ellsworth Dutton, Meteorologist John Ogren, Physical Scientist Jill Foose, Secretary Sharon Anthony, CIRES Michael Bergin, DOE Post Doc. Barry Bodhaine, Meteorologist Paul Breding, CIRES Rudy Haas, Mathematician Wen Huang, Physical Science Aid Thomas Kotsines, Engineering Technician David Longenecker, CIRES Lynn Mclnnes, NRC Post Doc. Brian Mohr, CCHE Intern Charles Myers, Engineering Aid Donald Nelson, Meteorologist James Rattling Leaf, AISES Intern Jay Shah, CIRES Herman Sievering, Guest Worker Ryan Spackman, CIRES Robert Stone, CIRES Shad Thaxton, CIRES James Wendell, Electronic Technician Brett Wightman, Physical Science Aid Ozone and Water Vapor Division Samuel Oltmans, Physicist Jill Foose, Secretary Kirsten Borbe, CIRES Mark Clark, CIRES Robert Evans, CIRES Eric Hackathorn, Engineering Aid Joyce Harris, Physical Scientist Bryan Johnson, CIRES Gloria Koenig, Physical Scientist Walter Komhyr, CIRES Jeffrey Lathrop, Physical Scientist Micheal O'Neill, CIRES Dorothy Quincy, CIRES Holger Vomel, CIRES Byron Wells, Physical Science Aid Carbon Cycle Division Pieter Tans, Chief Debra Hansen , Secretary Peter Bakwin, Physicist Thomas Conway, Research Chemist Wyatt Coy, CIRES Richard Dissly, NRC Post Doc. Ed Dlugokencky, Research Chemist Scott Durelle, CCHE Intern James Frelinger, Engineering Aid Laurie Geller, CIRES Student Douglas Guenther, CIRES Michael Hahn, Physical Science Aid Duane Kitzis, CIRES Patricia Lang, Physical Scientist Kenneth Masarie, CIRES John Miller, CIRES Paul Novelli, Res. Chemist Constance Prostko-Bell, CIRES Michel Ramonet, Guest Scientist Kirk Thoning, Physicist Tom Treloar, CIRES Michael Trolier, INSTAAR Lee Waterman, Research Chemist Ni Zhang, CIRES Conglong Zhao, CIRES Nitrous Oxide and Halocarbons Division James Elkins, Chief Debra Hansen, Secretary Thomas Baring, CIRES James Butler, Research Chemist Andrew Clarke, CIRES Nicholas Condon, CIRES Matthew Dicorleto, CIRES Raymond Dunn, CIRES Geoffrey Dutton, CIRES Arnold Hayden, CIRES Dale Hurst, NRC Associate Bryan Jordan, C.U. Work Study Frank Lee, AISES Intern Jiirgen Lobert, CIRES Loreen Lock, C.U. Work Study Michele McCarthy, C.U. Work Study Lynn Mclnnes, NRC Post Doc. Fred Moore, CIRES Richard Myers, Physical Science Technician Michael Perry, C.U. Work Study Robin Sam, CIRES Thomas Swanson, CIRES Thayne Thompson, Physicist Michael Volk, CIRES Shari Yvon, DOE Post Doc Observatory Operations Division Bernard Mendonca, Chief Linda Sachetti, Secretary Daniel Endres, Station Chief, Barrow Malcom Gaylord, Electronic Engineer Russell Schnell, Director, Mauna Loa Judith Pereira, Program Support Technician John Barns, Physical Scientist John Chin, Physicist Darryl Kuniyuki, Electronic Engineer Leslie Pajo, Data Clark Steven Ryan, Physical Scientist Robert Uchida, Electronic Technician Alice Wall, Physical Science Aid Alan Yoshinaga, Chemist Mark Winey, Station Chief, Samoa Alexis Brown, Environmental Engineer Gerald Yung, Elect. Engineer Ricardo Ramos, NOAA Corps, South Pole Jeffrey Otten, Engineering Technician Thomas Jacobs, NOAA Corps Katherine, McNitt, NOAA Corps CMDL Station Information Name: Latitude: Longitude: Elevation: Time Zone: Office Hours: Telephone Office hours: Fax: Barrow (BRW) 71.323 156.609 8m GMT -9 8:00am-5:00pm (907) 852-6500 (907) 852-4622 Mauna Loa (MLO) 19.539 155.578 3397 m GMT-10 8:00am-5:00pm (808)961-3788 (808)961-3789 Postal Address: Officer in Charge NOAA/ERL/CMDL Pouch 8888 Barrow, AK 99723 U.S. Dept. of Commerce NOAA - Mauna Loa Observatory P.O. Box 275 Hilo, HI 96720 Freight Address: Same as above U.S. Dept. of Commerce NOAA - Mauna Loa Observatory 154 Waianuenue Ave. Hilo, HI 96720 Name: Latitude: Longitude: Elevation: Time Zone: Office Hours: Telephone: Office hours: After hours: Fax: Samoa (SMO) -14.232 170.563 77 m GMT -11 8:00am-5:00pm 011 (684)622-7455 011 (684)699-9953 01 1 (684) 699-4440 South Pole (SPO) -89.997 -102.0 2841 m GMT +12 8:00 am -5:00 pm Relayed through CMDL Boulder Postal Address: U.S. Dept. of Commerce NOAA - CMDL Samoa Observatory P.O. Box 2568 Pago Pago, American Samoa 96799 Officer in Charge NOAA/CMDL Clean Air Facility S-257 South Pole, Antarctica PSC 468 Box 402 FPO AP 96598-5402 Freight Address: Same as above Same as above \ll 1. Observatory, Meteorology, and Data Management Operations 1.1. Mauna Loa Observatory r. c. schnell and the mlo staff 1.1.1. Operations Mauna Loa Observatory (MLO) continues to evolve in the scope of the measurements conducted, the way in which data are recorded and transmitted, and the number and form of the buildings on the site. With installation of the majority of the Network for the Detection of Stratospheric Change (NDSC) instrumentation completed at MLO, remote monitoring of stratospheric ozone concentrations, temperatures, and water vapor has become routine. At the surface, ultraviolet (UV) radiation is now monitored in a program that is designed and operated in a manner to set the world standard. Over the past 2 years essentially all the instruments of the core MLO continuous measurement programs, as well as the NDSC instruments, were connected to the Internet. In a number of cases these instruments are controlled and adjusted from locations other than Hawaii. Four new structures have been added to the MLO site over the past 2 years: a 3.7 m x 7.3 m building for the microwave ozone and microwave water vapor instruments, a similar building to accommodate visitors and their programs, a 3.7 m x 4.9 m tank storage building appended to the main observatory, and the Global Oscillation Network Group (GONG) 2.4 m x 6 m instrumented container. The GONG program, operated by the University of Arizona on space at MLO, is a study of the sun's core. The old Atomic Energy Commission (AEC) building was refurbished and a roof catchment water supply and a sink added. A new Network for the Detection of Stratospheric Change (NDSC) building, which was to be erected on the 4-acre (16,187 m 2 ) parcel to the east of the main MLO site, has been scaled back to a smaller structure to be erected south of the main observatory building. If all goes to plan, this 306.6 m 2 building will be completed by December 1996. At the Hilo facility, the refurbishing of the electronics shop and the addition of air conditioning to the room were major improvements as was the addition of an elevator linking the basement to the rest of the building. Installation of the FTS2000 telephone system in the Hilo offices with connections to the MLO site has reduced monthly telephone costs and expanded the number of lines available. MLO and cooperative/visitor programs now use 29 telephone lines in addition to the Internet. A note on Hilo's rain: Although Hilo has a reputation for having a lot of rain, in 1995 it had 2.5 m less than in 1994. But 1994 was a special year. On one day in August at sea level, Hilo had 45 cm of rain in 8 hours (greater amounts fell at higher elevations). In September, it had 50 cm in 7 hours. At the Cape Kumukahi, Hawaii (KUM) site, grid electric power was added to the tower, with a distribution panel providing 110 V, 220 V and recreational vehicle (RV) circuits. A 15 m x 15 m area was graded, filled, and security fenced to provide a site for mobile trailers and vans for future short-term research projects. The KUM tower now has four air sample lines running from near the top (18 m) to the base. Two of these lines are used for weekly trace gas and oxygen flask sampling and are purged continuously. No aerosol or radiation measure- ments are conducted at KUM at present. The largest nonroutine research activity of the past 2 years was the Mauna Loa Ozone Profile Intercomparison (ML03) program, summer 1995, in which various NDSC ozone-profiling instruments were intercompared. Preparations for the program included the construction of a building to house the University of Massachusetts Millitech microwave ozone profiler; installation of the NOAA/NIWA multispectra, UV radiometer system; and preparation of a pad area for two 16.7 m-long National Aeronautics and Space Administration/Goddard Space Flight Center (NASA/GSFC) ozone lidar trailers. The Jet Propulsion Laboratories (JPL) ozone lidar, also part of the study, had been in full operation at MLO for more than a year prior to the intercomparison. World standard Dobson no. 83, secondary standard no. 65, and the MLO station Dobson were operated prior to, and during, the intercomparison. During a 3-week intensive study period in August, daily ozonesonde launches were conducted from Hilo. Some balloons carried three ozonesondes to determine the variability between instruments. Ancillary ML03 measurements included aerosol/ temperature profiles with the NOAA lidars, infrared multispectral measurements with the University of Denver Fourier Transform Interferometer (FTIR) spectrometer, and twice-daily measurements from radiosondes launched from Hilo. A number of passes of a satellite carrying aerosol and ozone measurement instruments occurred during the intensive study period. In the staff arena, an MLO physical scientist spent from June to December 1994 at the Australian Baseline Station, Cape Grim, Tasmania, in an exchange with the Technical Officer from Cape Grim. All parties concerned, and their families, found the experience to be beneficial. The Technical Officer helped improve the MLO sulfate (S0 2 ) measurement program and quickly became a valued member of the MLO mountain crew. MLO recommends similar exchanges in the future. A staff member new to MLO in January 1995 has responsibilities for managing data flow and data archiving, and has rapidly become a valued addition and a capable computer operator. In May 1994, a motorcyclist was killed during a race on the MLO road when his brakes locked and he missed a turn in the road. This event, and the fact that the organizer of the weekly commercial bike rides down MLO was also killed in an unrelated bicycle accident in Kona, have dramatically reduced bicycle traffic on the MLO road. MLO was host to about 960 visitors in 1994-1995. Countries represented were from Japan, China, Canada, Germany, Burkina-Faso, Switzerland, France, Togo, Australia, Brazil, Russia, Iran, England, Denmark, Samoa, Mexico, Singapore, Italy, Holland, New Zealand, Norway, and Sweden. These visitors were in addition to guests from 21 states. Most of these visitors were given a guided tour and many left with at least one color reprint of the most up-to-date CMDL data plots MLO had available. Visitors to MLO from NOAA's higher level administra- tive community included the NOAA Administrator; NOAA Deputy Under Secretary; NOAA Associate Under Secretary; Director, Sustainable Development and Inter- governmental Affairs; outgoing Deputy Director, Environmental Research Laboratories (ERL); newly appointed Deputy Director, ERL; and Director, Oceans and Atmospheric Research Programs Office. Mauna Loa Mountain is still inflating and carbon dioxide (C0 2 ) gas releases from the summit caldera persist which means that an eruption may occur within a few years. Therefore, an escape plan and an equipment removal list have been drawn up. In essence, most equipment valued over $10,000 per item will be removed when it is predicted that lava will inundate MLO within 12 hours. 1.1.2. Programs Table 1.1 summarizes the programs in operation or terminated at MLO during 1994-1995. Relevant details of note on the respective programs are as follows: Carbon Dioxide The CMDL Siemens Ultramat-3 infrared (IR) C0 2 analyzer and the Scripps Institution of Oceanography (SIO) Applied Physics IR C0 2 analyzer were operated in parallel without major problems throughout 1994 and 1995. Routine maintenance and calibrations were undertaken on both instruments as scheduled. An electronic engineer from SIO upgraded the SIO C0 2 data acquisition system in 1994. Data are now recorded on a Brown strip chart recorder and stored on a personal computer (PC) hard disk and a floppy disk, which are mailed to SIO weekly. The CMDL C0 2 data acquisition system was modified on November 28, 1995, through the replacement of the original Control and Monitoring System (CAMS) data logger with a Unix CMDL Carbon Cycle Group (CCG) system connected to the Internet. Through computers in Boulder and in Hilo operators are able to monitor operation of the C0 2 analyzer and plot C0 2 concentrations in near-real time. The CCG has the capability of modifying the C0 2 measurement control software from Boulder. The venerable C0 2 strip chart recorder is now used only for viewing the weekly standard gas calibrations and weekly maintenance procedures. Outgassing from the volcanic vents at the Mauna Loa caldera and along the northeast rift zone at Mauna Loa continued to cause periodic observable disturbances in some of the C0 2 data records. As in prior years, these venting events occurred mostly between midnight and 0800 (local standard time (LST) of the following day, during the downslope wind regime. The erratic C0 2 concentration data resulting from these venting events were easily identified by visually scanning chart records or by utilizing a computerized data screening procedure, and thus they have been separated from the clean-air record without difficulty. Such venting episodes were detected mainly on the basis of criteria for C0 2 concentration, TABLE 1.1. Summary of Measurement Programs at MLO in 1994-1995 Program Instrument Sampling Frequency Gases co 2 CO C0 2 , CH 4 , CO, l3 C, 18 of C0 2 CH 4 SO, Siemens Ultramat-3 IR analyzerf 0.5-L glass flasks, through analyzer Trace Analytical RGA3 reduction gas analyzer no. R5f 2.5-L glass flasks, MAKS pump unit* 3-L evacuated glass flasks^ Carle automated GC no. 6 (removed 1 1/95) HP6890GCI (began 1 1/95) AIRKIT pump unit, 2.5-L glass flasks:]: (began 5/95) TECO model 435 pulsed-florescence analyzerf (began 6/94) Continuous 1 pair wk" 1 Continuous 1 pair wk" 1 1 pair wk" 1 1 sample (24 min)" 1 Continuous 1 pair wk" 1 Continuous TABLE Summary of Measurement Programs at MLO in 1994-1995 — Continued Program Instrument Sampling Frequency Gases - Continued Surface O3 Total O, 3 profiles CH3CCI3, CC1 4 CH3CCI3, CCI4, SF 6 , HCFC-22, HCFC-141b, HCFC-142b, CH 3 Br, CH 3 C1, CH 2 C1 2 , CHClj, C 2 HC1 3 , C 2 C1 4 , H-1301, H-1211, H-2402, HFC-134a CFC-1 1, CFC-12, CFC-1 13, N 2 0, CCI4, CH3CCI, N 2 Radon Aerosols Condensation nuclei Optical properties Aerosol light absorption (black carbon) Stratospheric and upper tropospheric aerosols Solar Radiation Global irradiance Direct irradiance Diffuse irradiance UV solar radiation Terrestrial (1R) radiation Turbidity Dasibi ozone meter! Dobson spectrophotometer no. 76! Dobson spectrophotometer no. 76! (automated Umkehr method) Balloonborne ECC sonde 300-mL stainless steel flasks 850-mL stainless steel flasks Column water vapor HP5890 automated GCt Shimadzu automated GCt Two-filter system Pollak CNC TSI CNCt Four-wavelength nephelometerf: 450, 550, 700, 850 nm three-wavelength nephelometer: 450, 550, 700 nm Aethalometert Lidar: 694.3 nm, 532 nm! Eppley pyranometers with Q, OG1, and RG8 filters! Eppley pyrheliometer with Q filter! Eppley pyrheliometer with RG8 filtert Eppley pyrheliometer with Q, OG1, RG2, and RG8 filtersf Eppley/Kendall active cavity radiometer! Eppley pyrgeometer with shading disk and Q filter! Yankee Environmental UVB pyranometer (280-320 nm)! Global downwelling IR pyrgeometer! J-202 and J-314 sunphotometers with 380-, 500-, 778-, 862 nm narrowband filters PMOD three-wavelength sunphotometer!: 380, 500, 778 nm; narrowband Two wavelength tracking sunphotometer: 860, 940 nm! Continuous 3 day" 1 , weekdays 2 day" 1 1 wk" 1 1 sample wk' 1 1 sample wk ' 1 sample h" 1 1 sample h" 1 Continuous integrated 30-min samples 1 day' 1 Continuous Continuous Continuous 1 profile wk"' Continuous Continuous 3 day 1 1 mo" 1 Continuous Continuous Continuous 3 day" 1 , weekdays Continuous Continuous Meteorology Air temperature Air temperature (30-70 KM) Temperature gradient Dewpoint temperature Relative humidity Pressure Aspirated thermistor, 2-, 9-, 37-m heights! Max.-min. thermometers, 2-m height Lidar Aspirated thermistors, 2-, 9-, 37-m heights! Dewpoint hygrometer, 2-m height! TSL 2-m height! Capacitance transducer! Mercurial barometer Continuous 1 day" 1 1 profile wk" 1 Continuous Continuous Continuous Continuous 5 wk- 1 TABLE 1.1. Summary of Measurement Programs at MLO in 1994-1995 — Continued Program Instrument Sampling Frequency Meteorology - Continued Wind (speed and direction) Precipitation Total precipitable water Precipitation Chemistry PH Conductivity Cooperative Programs C0 2 (SIO) C0 2 , 13 C, N 2 0(SIO) C0 2 , CO, CH 4 , '3C/ 12 C (CSIRO) CH 4 , CH3CCI3, CH3CI, F-22, F-12, F-ll, F-l 13, CO, C0 2 , N 2 0, CHC1,, CCl 4 (OGIST) 2 analyses (SIO) 2 analyses (URI) CH 4 ( 13 C/ 12 C) (Univ. of Washington) Total suspended particulates (DOE) Ultraviolet radiation (Smithsonian) Ultraviolet radiation (Univ. of Hawaii) Solar aureole intensity (CSU) Precipitation collection (DOE) Aerosol chemistry (Univ. of Calif.-Davis) Sulfate, nitrate, aerosols (Univ. of Hawaii) Radon (ANSTO) Network for Detection of Stratospheric Change (NDSC) Ultraviolet radiation (NOAA and NIWA, New Zealand) Stratospheric ozone profile, 20-70 km (Univ. of Mass, Amherst) Stratospheric ozone profiles (15-55 km), temperature (15-80 km), aerosol profiles (15-40 km) (JPL) Solar spectra (Univ. of Denver) 8.5-, 10-, and 38-m heightst Rain gauge, 20-cm Rain gauge, 20-cm§ Rain gauge, tipping bucket! Foskett IR hygrometer! pH meter Conductivity bridge Applied Physics IR analyzer! 5-L evacuated glass flasks* Pressurized glass flask sample Pressurized stainless steel flasks* 5-L glass flasks through tower line and pump unit* 3-L glass flasks through tower line and pump unit 35-L evacuated flask High-volume sampler Eight-wavelength UV radiometer: 290-325 nm; narrowband Robertson-Berger UV radiometer (erythema)! Multi-aperture tracking photometer: 2, 5, 10, 20, 30° fields of view (discontinued 9/94) Exposed collection pails Programmed filter sampler Filter system Aerosol scavenging of Rn daughters! (2-filter system after 4/95) UV spectrometer (290-450 nm), 1 nm resolution! Microwave spectroscopy, MillitechCorp, 1I0.8GH, UV lidar! FTIR spectrometer, automated! Continuous 5 wk" 1 1 wk' 1 Continuous Continuous wk" 1 wk- 1 Continuous 1 pair wk"' 1 mo" 1 3 wk- 1 3 (2 mo)" 1 2 (2 mo)" 1 2 mo" 1 Continuous (1 filter wk 1 ) Continuous Continuous Continuous Integrated monthly sample Integrated 3-day sample, 1 continuous and 1 downslope sample (3 days) ' Daily, 2000-0600 LST Continuous; integrated 30-min samples Continuous 3 profiles h' 1 3-4 profiles/wk"' 5 wk" 1 All instruments are at MLO unless indicated. *MLO and Kumukahi. !Data from this instrument recorded and processed by microcomputers. + Kumukahi only. §Kulani Mauka variability, and wind sector. The criterion for the C0 2 standard deviation screening was 1.0 ppm, which is the value suggested by Thoning et al. [1989]. The monthly occurrences of observable outgassing from volcanic vents on Mauna Loa for 1994 and 1995 are listed in Table 1.2, and the annual number of events for the past years are listed in Table 1.3. A paper was published in the American Geophysical Union (AGU) Monograph No. 92 concerning the outgassing history of Mauna Loa volcano as recorded in the MLO data record [Ryan, 1995]. In early 1993, the C0 2 emissions from the summit, as measured at MLO, began to increase after undergoing a steady exponential decline since the last eruption in 1984. The distribution of volcanic C0 2 with wind direction suggests that there is a new C0 2 source just outside the summit cauldera, high on the southwest rift. The average plume C0 2 concentration continued to increase through the end of 1995. Condensation nuclei and S0 2 in the volcanic plume also began to increase during this period. These changes may be an early precursor to the next eruption of Mauna Loa, which continues to inflate and which has produced a slightly greater frequency of shallow summit earthquakes since 1993. The weekly C0 2 , methane (CH 4 ), and other gas sampling programs, using flasks at MLO and at KUM, were carried out according to schedule throughout the year, without major problems. An AIRKIT sampling pump unit upgraded from the MAKS pump unit began its weekly operation on May 8, 1995, at KUM only. The flask types used and sampling procedure were the same as for the MAKS method. Carbon Monoxide A Trace Analytical RGA3 reduction gas analyzer for the continuous measurement of carbon monoxide (CO) mixing ratios was installed in May 1992 and continued to work well throughout 1995. The analyzer was replaced with a new, but essentially identical, unit on November 28, 1995, in an upgrade program. On the same date, system operations and chromatographic data logging were switched to a Hewlett Packard (HP) 35900E analog-digital converter system. This new installation is connected to the MLO-site Unix workstation. The system operates without using chart paper. Chromatograms stored on the workstation hard disk may be displayed on the computer monitor. Methane The Carle automated gas chromatograph (GC) system, Carle 6, was in continuous operation throughout the period providing CH 4 data from a grab air sample taken every 24 minutes. On November 28, 1995, the Carle 6 was replaced with the HP6890 GC, which is considered the best commercial GC available in the market. The system uses nitrogen carrier gas instead of helium, which has improved sensitivity in the measurement. A new analog-digital converter, HP35900E, which has the capacity of obtaining better precision, has replaced the original HP3393 integrator. The new CH 4 GC system is paperless; the chromatograms are stored in the CCG hard disk and can be displayed on the CH 4 computer monitor at the observatory. The CH 4 data continued to show clearly defined cycles of varying frequencies. The typical diurnal cycle was well correlated with upslope and downslope winds, with the marine boundary layer air having the higher CH 4 concentrations. Multiday or synoptic-scale CH 4 cycles were also observed, which apparently relate to different air mass source regions. Sulfur Dioxide An S0 2 monitoring program was developed in house during the spring of 1994, with measurements beginning at MLO on June 1, 1994. The measurement system is built around a TECO 435 pulsed-florescence analyzer with a PC controlling flows, monitoring temperatures and humidities, and acquiring data. The system runs on hourly cycles consisting of a 20-minute sample of ambient air through a Teflon line at 4 m, followed by a 10-minute zero-air sample, a 20-minute sample of air from a high-volume polyvinyl chloride (PVC) line at 34 m, and another 10- minute zero-air sample. A one-point, 1.2-ppb calibration is performed for 10 minutes every 12 hours by injecting a 10-ppm S0 2 -in-air standard into the 1000 L min-' high- volume flow. A six-point calibration is automatically run every 10 days over a range of concentrations between 125 ppt and 5 ppb. Injecting the calibration gas into the ambient air sample allows us to measure the effect of humidity on the loss of S0 2 in the sampling system. It also allows the use of a stable ppm-level calibration gas to perform sub-ppb calibrations. The system had a 95% data recovery rate in 1994-1995, with most of the downtime caused by an intermittent failure of the computer hard drive. Several system modifications were made, including the addition of humidity and temperature sensors in January and February of 1995. Data graphs are available over the Internet in Hilo in near-real time. One-minute-average measurements of zero air had a standard deviation of 35 ppt, yielding a 1-hour detection limit of about 10 ppt. The nightly average clean-air TABLE 1.2. Estimated Mauna Loa Venting Episodes (Total Time in Hours) at MLO in 19994 and 1995' Jan. Feb. March April May June July August Sept. Oct. Nov. Dec. Year 1994 4 1995 2 24 *Criteria: C0 2 SD >1.0 ppm; wind direction sector 135°-225 c ; wind speed >1.35 m s 1 . tNo data due to new system installation. TABLE 1.3. C0 2 Venting Events From 1988 Through 1995 Year Total Time (Hours) 1988 1989 1990 1991 1992 1993 1994 1995 200 X4 48 26 23 2H 24 9* ; No data for December due to new system installation. robin tank measurements were undertaken. System software was upgraded in August and a watchdog timer installed to cut down on computer lockups. In May 1995 a new computer system was installed. At that time the watchdog timer was removed because it never worked well, and Channel A was connected to P5 (AR/CH 4 ) to curb the C0 2 effect. In October 1995, new file transfer protocol (FTP) 4.0 software was installed and a more extensive hardware check of the GCs was carried out. During both of these major maintenance undertakings, round-robin tank measurements were made and precision checks completed. In general, the operation of the RITS computer has improved over the previous years with the installation of the new unit. baseline concentration of S0 2 at MLO as measured through the 4-m Teflon intake varied between 10 and 30 ppt. The high-volume PVC intake lost 5 to 10 ppt of S0 2 through dry deposition, and began to experience hygroscopic losses at relative humidities above 40%. During "Asian dust" events, which bring high concentrations of radon and anthropogenic gases, the S0 2 concentration increased to as much as 100 ppt. The volcanic plume from Mauna Loa (detected by high variability in the C0 2 concentration) contained up to 500 ppt S0 2 and had an S0 2 to C0 2 ratio of about 10 4 . The largest source of S0 2 was Kilauea volcano located 1 km above sea level on the south slope of Mauna Loa. Traces of its eruptive plume were frequently transported to MLO in the daytime upslope winds, producing S0 2 concentrations that occasionally exceed 50 ppb. On 15% of the nights in 1995, S0 2 from Kilauea was detected at concentrations between 100 ppt and 25 ppb in the downslope winds between midnight and 0700 LST. Ozone Monitoring The 1994-1995 MLO ozone monitoring program consisted of three measurement foci: continuous MLO surface ozone monitoring using a Dasibi model 1003- AH UV-absorption ozone monitor; total ozone three times a day and Umkehr ozone profile measurements two times a day using a computer-based automated Dobson instrument (Dobson no. 76); and ozone profile measurements based on weekly ascents of balloonborne electrochemical concentration cell (ECC) ozonesondes released from the National Weather Service (NWS) station at the Hilo airport. Ozonesondes were launched weekly whenever supplies were available from Boulder. In 1994 there were 45 ozonesonde flights. In 1995 there were 52 ozonesonde flights, which included an intensive period in August when daily flights were launched during an NDSC intercomparison with the Dobson ozone spectro- photometer, two ozone lidar systems, a microwave ozone profiler, and a variety of related instruments operated at MLO. Radon By the end of 1995, the CMDL Department of Energy (DOE) radon program had collected 5 complete years of data. The radon instrument has performed reliably, the only problems being a broken drive belt and periodic replacement of the filter paper roll. A radon calibration source was purchased in 1995, and the instrument calibration was found to be within 5% of the source value. Daily average radon between 0000 and 0700 LST is shown in Figure 1.1, along with a 90-day running mean. The principal source of radon is soil. Radon has a half-life of 3.8 days. The amount of atmospheric radon reaching Mauna Loa during baseline conditions is a function of both the amount of continental radon injected into the free troposphere and its travel time across the Pacific Ocean. The yearly radon cycles seen in Figure 1.1 are similar to those measured for dust particles and anthropogenic gases and aerosols at MLO. There is a late-winter/spring maximum that is caused by the fast transport of air coming from Asia, and a late-summer/autumn minimum that occurs when air has spent long periods over the tropical Pacific. The 5-year record is beginning to show interannual variability. The average radon concentrations in the spring of 1991 and 1992 were higher than those of later years. 800 Halocarbons and Nitrous Oxide The Radiatively Important Trace Species (RITS) system for measuring halocarbons and nitrous oxide had its semiannual maintenance in March 1994 and August 1994. Besides the normal checks, precision checks and round- Fig. 1.1. Daily average radon at MLO measured by the CMDL- DOE radon instrument between 0000 and 0700 LST (downslope air) with a 90-point running mean (darker line). The annual peaks in the mean define the spring Asian dust season when fast air transport brings continental air and Gobi Desert dust to the observatory. The mean annual cycle of radon varied from a high of 270 mBq nr 3 in March to a low of 70 mBq nr 3 in August. This is a factor of 4, which is two radon half-lives or about 7.5 days. If the seasonal variation in radon is entirely due to variations in air mass transport time across the Pacific, it follows that the average transit time of continental air to MLO is 1 week less in the spring than in late summer. Aerosol Monitoring Condensation nucleus counter. The Thermo Systems Incorporated (TSI) unit is a continuous-expansion con- densation nucleus counter (CNC) in which condensation occurs in butyl alcohol vapor in a chamber and single- particle counting statistics are used as a basis for calculating condensation nuclei (CN) concentrations. The instrument has continued to display higher counts than the Pollak CNC since its return from the manufacturer in 1991. Nephelometer. The four-wavelength nephelometer continues to run without too much downtime. A three- wavelength nephelometer with much better resolution was installed and activated in April 1994. These two units will operate in parallel for a couple of years sampling the same air stream before the older instrument will be retired. Aethalometer. The aethalometer performed satis- factorily during 1994-1995. A new computer and program was set up in September 1994. A dual-head pump was installed in November 1994 to increase the air sample flow rate. Lidar. Ruby lidar (694 nm) observations of stratospheric aerosols were continued throughout 1994- 1995, adding to the MLO lidar database extending back to late 1974. The only significant modification to the instrument, following the major changes in 1993 (486 computer for data acquisition and automatic control of the laser), was rotating the entire lidar 90° in the building in April 1995. This was undertaken to provide more room for the new YAG lidar described below in this section. The lidar reorientation resulted in the ruby lidar telescope being positioned closer to the outgoing beam (from 122 cm to 79 cm), thereby increasing the low-altitude signal strength. The data are still being acquired with the 10- MHz, 8-bit Biomation unit and the operating conditions (PMT voltages, data-taking delays, number of shots) are unchanged. Data analysis was improved to better account for signal- induced noise generated by the strong signal at low altitudes. A nonlinear fit of the signal background improved the aerosol profile between 30 and 45 km where it should converge to zero (backscatter ratio of one). The same extinction-to-backscatter ratio (50) and standard atmosphere that have been used in the past were maintained. The entire record of aerosol profiles is not currently available in a database, although the integrated backscatter is. Reanalysis of raw signals from 1984 to 1990 to add to the overall database was started in 1995 and has continued to the present. In March 1994 the first aerosol profiles were taken with the new Nd:YAG laser-based lidar. The laser (Spectra Physics GCR-6, 30 Hz) emits 39 W at 1064 nm and has frequency doubling and tripling to produce 532 nm and 355 nm wavelengths. The 532 nm wavelength is the only wavelength used for measurements. A single mirror (61- cm diameter) focuses light onto a liquid light guide that carries the illumination to three PMT detectors. The detectors are electronically gated at low altitudes to reduce signal-induced noise. All channels are photon counted and have dynamical ranges of 10 MHz. Channel one detects the full signal for stratospheric and mesospheric altitudes and channel two detects a few percent of the signal for the troposphere. A third channel detects a Raman-shifted wavelength from nitrogen to obtain molecular density in the presence of aerosols. Besides producing a much better measurement than the ruby lidar, the new system is largely built with equipment that is readily available and serviceable. A second 61-cm mirror was installed for detection of the 1064 nm wavelength in the future. The aerosol analysis for the new system is quite similar to the ruby lidar procedures (with changes in Rayleigh scattering cross sections) but simpler because of the much larger dynamic range of the electronics. A significant difference in the systems is that the Nd:YAG lidar obtains accurate data above the aerosol layer (35-45 km), which may then be used as an aerosol-free altitude. The ruby lidar analysis assumes an aerosol-free reference altitude below that altitude (around 15 km), which is not always a valid assumption. The Nd:YAG measurement is now used to correct the reference for the ruby lidar. The 532 nm signal is also used to measure atmospheric temperatures from 33 to 70 km by assuming the ideal gas law, hydrostatic equilibrium, and pure Rayleigh scattering. The temperature is initialized at 80 km using a MAP85 model calculated for 19.5°N with seasonal dependence. See sections 3.1.2-3.1.7 for results of the observations. Solar Radiation The set of solar radiation instruments at MLO remained unchanged from previous years. In March 1994 the Physikalisch-Meteorologisches Observatorium Davos (PMOD) (World Radiation Center) sunphotometer filters were exchanged and their spectral characteristics measured in Boulder. Hand-held sunphotometers continued to be calibrated at MLO, with 34 calibrations performed in 1994 and 38 made in 1995. In September 1995, a new data acquisition and control system was installed in the solar dome. The system is based on an HP data acquisition unit and a persona) computer, and is tied to the Internet. It automatically operates the dome shutter and adjusts the azimuthal position of the dome based on calculations of the sun position and feedback from a shaft encoder on the dome drive motor. After overcoming a few initial problems, the system has performed well. UV Radiation Monitoring In July 1995 a spectral UV monitor was installed at MLO. The instrument was originally developed and operated at the National Institute for Water and Atmosphere (NIWA) in Lauder, New Zealand, and then moved to MLO when a newer instrument was built to replace it. The monitor measures the global UV spectrum between 290 and 450 nm in 0.2 nm steps with a bandpass of 1.15 nm. It is calibrated with mercury and standard lamps every week. An absolute standard lamp calibration is made several times per year. Early results from this program are presented in section 3 of this Summary Report. Computers/Network Many changes to the MLO network/computer systems have occurred during the 1994-1995 period, both in the number of computers in the network and the sophistication of the operation. The "nerves" of the mountain system were expanded with the installation of fiber optic lines connecting the main building to the Radon Building, Solar Dome, University of Denver FTIR and NOAA/NIWA UV Building, Microwave Ozone Building, National Center for Atmospheric Research/High Altitude Observatory (NCAR/HAO) Facility, GONG Observatory site, and the new Visitor Building. At the Hilo site, fiber optic lines were installed to link NCAR/HAO's Hilo office and the Smithsonian Institution Observatory to MLO's Internet server. To control the overall network, two Windows NT servers were installed as nodes, one at the Hilo office and the other at the MLO mountain site. "Trusts" were created with the NT server in CMDL, Boulder, which in effect allows the MLO and CMDL network administrators access to some of each other's network control software. This facilitates data transfer for the ozonesonde, surface ozone, and solar dome programs. CMDL measurement programs and projects connected to the network in 1994-1995 include the aethalometer, S0 2 , radon, RITS, carbon cycle species, and the NOAA/NIWA UV systems. NDSC programs added were the University of Denver FTIR and the University of Massachusetts microwave ozone system. The JPL lidar group, already on the network from the previous year, added six more computers to the network. Other groups affiliated with the MLO facility also enhanced their network utilization as NCAR/HAO added six computers at the mountain site and one at Hilo, GONG added two computers, and the Smithsonian Observatory added two computers and a printserver. MLO computers for the staff have all been upgraded to 486s and Pentiums (six 486s and four Pentiums), and two 486 computers were installed at the observatory, one for staff and one for visitor programs. Surge protection devices and UPSs were installed at all locations to protect servers, computers, and other network devices. New telephone and data lines were installed in 1995 giving MLO access to the Centernet and FTS2000. This resulted in an increase of eight voice and data lines split between MLO and Hilo at no increase in monthly expenses. An MLO home page located at http://mloserv. mlo.hawaii.gov has been set up on the Internet. This page contains some information on the observatory, staff, and a few data plots. Software upgrades were numerous and varied; some of interest to users of MLO data and the MLO network: the VAX was upgraded with a newer operating system and other software, a server was set up for remote prints, and an anonymous FTP set up for public file transfers. Excursion software has been upgraded for use with Windows 95. The operating system for client machines is slowly being converted from Windows For Workgroups to Windows 95. Eudora is now being used for e-mail by the entire staff because it is much easier to use than the VAX mailer. The Time and Attendance program has been upgraded twice over the past 2 years. A network monitoring program has been implemented to aid in troubleshooting the network. PCanywhere is being used for testing the remote control of a test computer with the view of developing methods of controlling more routine MLO functions from a keyboard in Hilo. MLO receives trajectory plots and meteorological data on a daily basis from Boulder automatically over the Internet. Radiosonde data from NWS are being archived weekly on our VAX. A small electronic database has been created for MLO publications, which includes scanned abstracts. Meteorology The old meteorological system and the planetary boundary layer (PBL) Met system were deactivated and removed in October 1993. They were replaced with a computer-based system, the "New Met System," which measures temperatures at the 2-, 9-, and 37-m levels, dewpoint at the 2-m level, and wind speeds and directions at the 8.5-, 10-, and 38-m levels. This new system has operated unaltered and with high reliability to date. Precipitation Chemistry The MLO modified program of precipitation chemistry collection and analyses was continued throughout 1994- 1995 within the basic MLO operational routine. This program consists of collection of a weekly integrated precipitation sample from the Hilo NWS station and collection of precipitation event samples at MLO. Analyses of these samples are undertaken in the Hilo laboratory for pH and conductivity. Cooperative Programs MLO Cooperative Programs are listed in Table 1.1. In September 1994 the Colorado State University (CSU) sunphotometer program was discontinued. The Australian Nuclear Science and Technology Organization (ANSTO) radon monitor underwent a major upgrade in April 1995 which resulted in an increase in sensitivity, a decrease in the response time, simpler operation, and more reliable performance. 1.2. Barrow Observatory D. Endres 1.2.1. Operations Data collection continued at the Barrow Observatory, Barrow Alaska (BRW) without any major interruptions during 1994-1995. Data collection system upgrades improved the quality of data for several programs and allowed remote access to data by personnel in Boulder. A second 486 computer was added to the station inventory allowing access to the Internet and, by using PC/TCP software, allowing access to email. The Control and Monitoring System (CAMS) units reached the end of their useful life and replacement data acquisition systems were installed. The future of the distant early warning (DEW) Line site remains in question with the only certainty being a reduction in personnel. At this time it is uncertain how changes may affect operations at BRW. Assurances were given by the Air Force that any changes made at the DEW Line will have the smallest possible impact on the observatory while meeting the changing needs of the Air Force. For the second time in the 23-year history of BRW, the exterior of the main building was painted during the summer of 1994. Plans are still in the works for other much needed upgrades to the building. A new pump enclosure was built at the end 1995 to help the sound abatement program at the observatory. Sound levels were measured at 85 dB at one time and have been reduced to 66 dB. A further reduction is expected when the enclosure is finished and all pumps are installed. On two separate occasions snow and/or ice blocked the sampling stack and had to be cleaned. Cleaning was done by removing the cap at the bottom of the stack and tapping the stack near the top with a long pole. This dislodged the blockage and allowed the normal volume of air to pass through the stack. A change in personnel occurred in April 1994 when the technician left for a position in Boulder. A replacement arrived shortly before his departure and assumed the technician duties in a very smooth transition. The station chief celebrated his tenth year at BRW during 1994 and in 1995 was asked to serve on the Barrow Restoration Advisory Board. This Board is concerned with the cleanup of toxic waste spills by the Navy and the Air Force at the old National Arctic Research Laboratory site and the DEW Line site. Vehicles ran well with the sole exception of a cracked piston in one of the snow machines. It was repaired and the snow machine was returned to service without interruption to the daily routine. The Naval Surface Warfare Center donated a snow machine to the station in the summer of 1995. The NOAA housing was connected to the city water supply during the summer of 1995. Water no longer must be hauled in by truck; the storage tank at the CMDL unit will be removed. During 1994-1995 BRW was visited by 158 registered guests. Among these were Congressional staff members, the NOAA Administrator, and researchers from China, Japan, and Russia. There were several visits by personnel from the National Science Foundation (NSF), the Arctic Research Consortium of the U.S. (ARCUS), and the U.S. Air Force and Navy. 1.2.2. Programs Aerosols The Thermo Systems Incorporated (TSI) condensation nucleus counter (CNC) uses butyl alcohol to saturate particles and passes them through a laser diode to count CN. The instrument continued to run well throughout the year. Problems were found, however, in noise levels in the signal. There appears to be a possible ground loop problem causing noise on the Campbell Scientific, Inc. (CSI) data recorder. On two separate occasions the optics and air path were cleaned of debris buildup and the alcohol was drained due to moisture absorption. The nephelometer measures backscatter at four wavelengths. It ran well this period except for the ball valve in the blower system. A shaft made of inferior plastic broke and the change between filtered air and ambient air could not take place. Station personnel machined a new part at the local high school and the unit was returned to operation the next day. Problems with the noise mentioned above was also found in the nephelometer signal. Solar Radiation The CSI data acquisition system (DAS) operated well all year with the only problem being a shorted input channel. Signal lines were moved to another terminal and the data flow continued with only a minor interruption. Blowers were installed on the pyranometers and pyrgeometers during 1994. They ran well during the 1994-1995 season and helped keep the snow and ice from building up on the domes. The air flow across the domes and the dry BRW air combined to sublimate any ice buildup that did occur. Instruments are taken off line each year in November and installed again in February of the following year. During this downtime any calibrations that are needed are performed in Boulder and repairs made as needed. During the 1995 winter season, all instruments were returned to Boulder with the exception of the up-facing and down- facing pyrgeometer infrared instruments which were left online. The filter wheel normal incidence pyrheliometer (NIP), normally kept in the Dobson dome, was also returned to Boulder. Carbon Cycle Carbon Dioxide Nondispersive Infrared Analyzer. The Siemens Ultramat 5-E continues to be the station instrument and ran well the entire period. Data trends continue to show the normal seasonal variations in BRW data. Highs of up to 370 ppm and lows to 340 ppm were noted. A static discharge damaged the electronics in the Linseis chart recorder. The recorder was taken out of service for approximately 3 weeks while replacement parts were ordered. Future plans call for replacing the CAMS DAS with a Hewlett Packard (HP) UNIX-based workstation. The strip chart recorder will be taken out of service as well. These changes are being planned for sometime during the spring of 1996. Methane. A Carle GC uses flame ionization to measure CH 4 . Data is recorded by an HP integrator and stored on floppy disks. Noise in the data for a short time was the only problem encountered. Data trends continue as in past years with data ranging between highs of over 1950 ppbv and lows of 1750 ppbv. Growth exhibited a slightly negative trend in 1994. Carbon Monoxide. A Trace Analytical gas chromatograph (GC) has been in continuous operation since 1991. CO mixing ratios range between approximately 150 ppbv and 250 ppbv. Flask data are available since 1990. The system ran well during the entire period with no significant downtime. Data are measured by an HP A/D, processed on an HP integrator, recorded on an HP floppy disk drive, and sent to Boulder for final analysis. Flask Samples. Flask samples were collected as scheduled based on availability of flasks. The carbon dioxide (C0 2 ), methane (CH 4 ), carbon monoxide (CO) and isotopic data from the flask samples can be found in sections 2 and 5 of the report. No major problems were encountered. has had minimal problems during its entire 10-year lifetime, but parts have become too hard to find and a replacement needed to be found. Ozone Surface Ozone. Surface ozone, as measured by the Dasibi, continues to be one of the long-term staples of the BRW measurement regime. The Dasibi was temporarily affected by the blockage of the stack with snow. A new display and logic board was installed when the old board malfunctioned. Otherwise the system ran without major problems. Dobson. BRW continues to operate Dobson no. 91. Long-term trends in the data continue as in past years with seasonal highs in the spring and lows occurring in the fall. Values in April can be as high as 440 Dobson Units (DU) and lows in September can be as low as 290 DU. The Dobson is not run during the winter months due to lack of sunlight, but the calibration regime is continued to assure proper functioning when the sun rises the next year. Observations are usually made from February until October. Meteorology A new data collection system was installed during April 1994. The new system replaces the aging CAMS DAS and is a ruggedized 486 computer rack mounted for ease of use. Metrabyte modules are used as an interface between the sensors and DAS. The new system was connected to the BRW local area network (LAN) and data are available to the CMDL Meteorological group on demand. Data are transferred to Boulder once per day and a quick look for quality control assures a higher level of confidence in the data. Calibrations are performed twice each year, once in the spring and once in the fall, to assure correct operation of all sensors. Temperature probes are checked and corrected, if needed, to 0.2°C. Alignment of the wind sensor is checked and the speed accuracy is traceable to NIST standards. CAMS As mentioned previously, the MET CAMS was replaced during April 1994. The aerosol solar radiation (ASR) CAMS was replaced during 1993. The only programs still running on CAMS are the C0 2 and the Dasibi. Plans call for replacing the CO, early in 1996. The CAMS system Nitrous Oxide and Halocarbons Gas Chromatographs. The HP DAS was replaced with a 486-based system during the summer of 1995. The new system was connected to the LAN and allows access to the data by Boulder personnel. The new system is considerably more reliable than the HP computer used in the past. New data handling schemes are possible that were not with the HP-based system. The GC's remain unchanged. Currently there is an HP-5890 and a Shimadzu GC-8A onsite running every half hour, alternating between calibration gas and ambient air. Flask Samples. Flask samples were collected as scheduled and available. Data show a very distinct leveling of the chlorofluorocarbon-1 1 and -12 (CFC) mixing ratio. This is attributed to the Montreal Protocol, which phases out production of certain CFCs. A detailed list of the chemicals analyzed by the CMDL Nitrous Oxide and Halocompounds Group (NOAH) can be found in Table 1.4. Cooperative Projects A comprehensive list of all BRW cooperative projects and affiliation is given in Table 1.4. Only projects with special problems or unusual occurrences are mentioned here. TABLE 1 .4. Summary of Measurement Programs at BRW in 1 994- 1 995 Program Instrument Sampling Frequency Gases CO, C0 2 , CH 4 , CO, and 13 C/ 12 C and 18 0/ 16 Oof C0 2 CH 4 Surface O^ Total O, C0 2 N 2 0, CFC- 1 1, CFC- 12, CFC- 1 13, CH,CC1 V CC1 4 Siemens Ultramat 5E analyzer 3-L glass flasks 0.5-L glass flasks, through analyzer 0.5-L glass flasks, P 3 pump unit Carle automated GC Dasibi ozone meter Dobson spectrophotometer no. 91 Siemens Ultramat 5E analyzer 300-mL stainless steel flasks Continuous 1 pair wk" 1 1 pair wk -1 1 pair wk -1 1 sample (12 min)" 1 Continuous 3 day-' Continuous 1 sample mo" 1 10 TABLE 1.4. Summary of Measurement Programs at BRW in 1994-1995 — Continued Program Instrument Sampling Frequency Gases - Continued N 2 0, CFC- 1 1 , CFC- 12, CFC- 113, CH3CCI3, CCI4, SF 6 , HCFC-22, HCFC-141b, HCFC-142b, CH,Br, CH3CI, CH 2 C1 2 , CHCI3, C 2 HC1 3 , C 2 C1 4 , H-1301, H-1211, H-2402, HFC- 134a CFC-11,CFC-12, CFC-113, N 2 CC1 4 . CH3CCI3 N 2 CO 850-mL stainless steel flasks HP5890 automated GC Shimadzu automated GC Trace Analytical GC 1 sample mo" 1 sample h" 1 1 sample h" 1 1 sample (6 min)' Aerosols Condensation nuclei Optical properties Black carbon Pollak CNC T.S.I. CNC Four-wavelength nephelometer Aethalometer 1 day"' Continuous Continuous Continuous Solar Radiation Global irradiance Direct irradiance Albedo Terrestrial (IR) Radiation Upwelling and downwelling Eppley pyranometers with Q and RG8 filters Tracking NIP Eppley pyrheliometer with Q, OG1 RG2, and RG8 filters Eppley pyranometer Eppley pyrgeometers Continuous Continuous Discrete Continuous Continuous Meteorology Air temperature Dewpoint temperature Pressure Wind (speed and direction) Precipitation Thermistor, 2 levels Max. -min. thermometers Dewpoint hygrometer Capacitance transducer Mercurial barometer R.M. Young aerovane Rain gauge, tipping bucket Continuous 1 day' 1 Continuous Continuous Discrete Continuous Cooperative Programs Total surface particulates (DOE) Precipitation gauge (USDA) Magnetic fields (USGS) Various trace gases (OGIST) C0 2 , ,3 C, N 2 (SIO) CH 4 (Univ. of Calif., Irvine) Earthquake detection (Univ. of Alaska) 13 CH 4 ( 13 C/ 12 C) (Univ. of Washington) 14 CO (Univ. of Washington) UV monitor (NSF) Magnetic fields (NAVSWC) Sound Source (DOE) Ice Buoys (NOS) 2 in air (Univ. of Rhode Island) Magnetic micropulsations (Univ. of Tokyo) Aerosol chemistry (Univ. of Alaska) High-volume sampler (1 filter wk 1 ) Nipher shield, Alter shield, 2 buckets 3-Component fluxgate magnetometer and total field proton magnetometer Declination/inclination magnetometer sample Stainless steel flasks 5-L evacuated glass flasks Various stainless steel flasks Seismograph 35-L stainless steel flasks A 150 aluminum cylinders filled to 2000 psi UV spectrometer 3 He sensors RASS Ice buoys 3-L glass flasks Magnetometer and cassette recorder High-volume sampler Continuous 1 mo -1 Continuous 6 sets mo -1 1 set wk -1 (3 flasks set" 1 ) 1 pair wk -1 1 set (3 mo) -1 Continuous, check site 1 wk" 1 1 (2 wk) 1 1 (3 wk) 1 1 scan per 0.5 hour Continuous 1 hr 1 Continuous 1 pair (2 wk) -1 Continuous 3 wk" 1 11 DOE/ARM. The Department of Energy (DOE) Atmospheric Radiation Measurement (ARM) Laboratory is planning a long-term program of atmospheric radiation monitoring to collect data for use in climate models. The largest single unknown is the effect of cloud cover on the climate. BRW has been chosen as one of three sites worldwide to monitor these variables. Since late 1993, in cooperation with the North Slope Borough, Department of Wildlife Management, DOE has been testing an active Radio Acoustic Sounding System (RASS). Its impact on wildlife near the site is monitored. NOAA/Navy Joint Ice Center. In CMDL Summary Report No. 22 a brief discussion of this project was given. Since that time new buoys and a new DAS have been added to the project. Phone access to the data is now possible. This project has yielded much useful data as to the type of buoy and the problems encountered with arctic deployment. University of Tokyo. A new data recorder was installed in 1995 and this project was reactivated. The recorder, with high gain amplifiers, is connected to a set of three search coil sensors that point to magnetic north, magnetic east, and vertical. Magnetic micropulsations of 0.001-5 Hz are recorded and the tapes are sent to the University of Tokyo for analysis of magnetic storm effects. Each week during the tape change, a time check to the nearest second is performed and the system is checked during the week for proper functioning. University of Alaska, Fairbanks. A trace metals project was reactivated this time period. This is the reactivation of the former University of Rhode Island (URI) filter project discontinued in 1988. A filter is connected to a hi-vol pump and samples are collected three times per week. Filters are sent to the University of Alaska where they are stored for future analysis for trace metals associated with arctic haze. At the present time no analysis is being performed. 1.3. Samoa Observatory M. WlNEY 1.3.1. Operations The environmental engineer position with the Samoa Observatory, American Samoa (SMO) was vacated in October 1995 after 2 years of service. The replacement electronic engineer was selected with arrival due in 1996. Internet access for the SMO local area network (LAN) was made possible by the installation of a modem router; however, e-mail services will be the only feature taken advantage of due to the high cost of a phone call and the poor quality of the telephone lines in Samoa. Hopes were high when the phone company replaced the old cable that runs 915 m from the observatory to the main phone line; unfortunately, there was no noticeable improvement. Due to ongoing deterioration of the remote Ekto sampling building, plans were made to replace it with a permanent, concrete wall structure. This new building will be just a little larger than the old one and located as close as possible to the existing walk-up tower. Construction began in November 1995 with an expected completion date of June 1996. Termites continued to be a problem at house T-7. The garage was torn down and replaced with a carport because termites devoured most of the old structure. The house was also infested and had to be fumigated again; this slows down the feeding process but does not stop it. Both of the aging observatory vehicles were replaced with new trucks. This resulted in much less time being spent by the staff dealing with the constant vehicle problems. The standby generator allowed the observatory to continue operation through many blackouts. No major problems were encountered and the small ones were easily handled by the staff. The observatory continues to be a favorite tourist attraction because of the beautiful views. The observatory is also a favorite with local science teachers who bring their classes on field trips. Visitors are always welcomed and given a tour if they wish to learn more about the observatory's function. 1.3.2. Programs Table 1.5 summarizes the programs at SMO for 1994- 1995. Further descriptions of some of the programs follow. Carbon Dioxide The Siemens analyzer has traditionally been one of the most trouble-free instruments at SMO. However, when it broke down and defied local attempts to fix it, the analyzer made a round trip to Boulder for repair and was back in service in less than a month. The air-intake line on the mast broke in 1994 and again in 1995. The problem is probably wind-induced vibration in the tubing thus causing it to crack. The AirKit flask air sampler was put into service for an intercomparison with the older Martin and Kitzis Sampler (MAKS) unit. Eventually the MAKS unit will be retired in favor of the AirKit's built-in condenser that removes moisture from the air. Surface Ozone The Dasibi began the period in good condition with the Control and Monitoring System (CAMS) still responsible for the digital data collection. CAMS had a few problems that were eventually dealt with but a fair amount of data will have to be entered by hand from the chart recording. A new PC-based data system was received, but several problems prevented it from being hooked up. In May 1995 the Dasibi overheated and blew some circuits; onsite repair was not feasible, therefore, a replacement was obtained. Unfortunately, the replacement was also a used instrument with its own set of troubles. As of the end of 1995, the Dasibi was not working properly. 12 TABLE 1.5. Summary of Measurement Programs at SMO in 1994-1995 Program Instrument Sampling Frequency Gases C0 2 C0 2 , CH 4 C0 2 , CH 4 , CO, and '-'C, 18 of CO, Surface 3 Total 3 N 2 0, CFC-11, CFC-12, CFC-113, CH 3 CC1 3 , CCI4 N 2 0, CFC-11, CFC-12, CFC-1 13, CH3CCI3, CC1 4 , SF 6 , HCFC-22, HCFC -141b, HCFC-142b, CH 3 Br, CH 3 C1, CH 2 C1 2 , CHC1 3 , C 2 HC1 3 , C 2 C1 4 , H-1301, H-1211, H-2402, HFC- 134a CFC-11, CFC-12, CFC-113, N 2 0, CC1 4 , CH 3 CC1 3 N 2 Aerosols Condensation nuclei Siemens Ultramat-5E analyzer 0.5-L glass flasks, through analyzer 2.5-L glass flasks, MAKS pump unit 2.5-L glass flasks, AirKit Dasibi ozone meter Dobson spectrophotometer no. 42 300-mL stainless steel flasks 850-mL stainless steel flasks HP5890 automated GC Shimadzu automated GC Pollak CNC TSI CNC Continuous 1 pair wk" 1 I pair wk" 1 1 pair wk' 1 Continuous 4 day 1 1 sample wk" 1 1 sample wk" 1 1 sample h" 1 1 sample fr 1 1 day 1 Continuous Solar Radiation Global irradiance Direct irradiance Diffuse irradiance Meteorology Air temperature Dewpoint temperature Pressure Wind (speed and direction) Precipitation Eppley pyranometers with Q and RG8 filters Continuous Eppley pyrheliometer with Q filter Continuous Eppley pyrheliometer with Q, OG1, Discrete RG2, and RG8 filters Eppley pyrgeometer with shading disk and Q filter Continuous Thermistors (2) Continuous Polished mirror Continuous Capacitance transducer Continuous Mercurial barometer 1 wk -1 Bendix Aerovane Continuous Rain gauge, tipping bucket Continuous Rain gauge, plastic bulk 1 day 1 Cooperative Programs C0 2 , 13 C, N 2 (SIO) GAGE project: CFC- 1 1 , CFC- 1 2, N 2 0, CH3CCI3, CC1 4 (SIO) Various trace gases (OGIST) Bulk deposition (DOE) Total suspended particulates (DOE) Total suspended particulates (SEASPAN) CH 4 ,( 13 C/ 12 C ratio) (Univ. of Wash.) Light hydrocarbons (UCI) 2 (URI) 2 (SIO) 5-L evacuated glass flasks HP5880 gas chromatograph Stainless steel flasks Plastic bucket Ion exchange column High-volume sampler High-volume sampler 30-L pressurized cylinder 1-L evacuated stainless steel flasks 2.5-L glass flasks 3-L glass flasks 1 set wk" 1 (3 flasks set 1 ) 1 h 1 1 set wk -1 (3 flasks set 1 ) Continuous (1 bucket mo -1 ) Continuous ( 1 filter mo" 1 Continuous (1 filter wk 1 ) Continuous (1 filter wk 1 ) Biweekly 3-4 flasks qtr 1 2 pair mo -1 2 sets mo -1 (3 flasks set 1 ) SIO - Scripps Institution of Oceanography OGIST - Oregon Graduate Institute of Science and Technology UCI - University of California, Irvine URI - University of Rhode Island 13 Total Ozone The Dobson worked well with only one small problem when the high voltage power supply had to be replaced. The data acquisition program was updated and continues to work well. The dome is aging fast in the corrosive sea-air and will have to be replaced soon. Ozonesonde Balloons Ozonesonde balloon launches were restarted in August 1995 after a break of several years. At the airport the National Weather Service made their balloon inflation facility available, including the use of hydrogen gas to fill the balloons. Releases were made weekly. Nitrous Oxide and Halocompounds The old Hewlett Packard (HP) data acquisition computer was replaced with a PC-based system. This was done in May 1995. Some problems were solved and some new ones were born. The good news was that system crashes were almost completely eliminated. The most perplexing problem was a lack of readable chromatograms. Good data was being produced and saved but for some reason the printouts were no good. The new computer came with a network board and software installed, however, reliable communication has yet to be achieved. This could be due to the long, 200 m run of coaxial cable from the main building to the remote site where the computer is located. As in the past, several site visits were made by CMDL personnel from Boulder. This regular, close attention is one good reason why this program is so successful. Aerosols In January 1995 data acquisition was switched from CAMS to the new solar radiation system. This was a big improvement. The Pollak performed well for the most part; the only problems encountered were with the ammeter. Apparently these ammeters are becoming scarce and servicing old ones is a delicate operation. The main blower that provides the steady flow of air from the top of the pipe to the instruments inside failed. The failure was not noticed for several months. A new blower was installed April 1994. With the construction of a new sampling building in November 1995, occasional heavy activity near the air intake for the aerosol instruments had a noticeable effect on the data. Solar Radiation A new data acquisition system was installed January 1995. This was a major improvement with several benefits including 24-hour access via modem to real time data. Another benefit was the elimination of the chore of packaging and mailing the data to Boulder. An Eppley pyrgeometer with a Q dome and a shading disk mounted to a tracker to measure diffuse irradiance was put online August 1995. Meteorology A major overhaul of the meteorological system occurred in July 1994. A new data acquisition system was installed and all of the old sensors were replaced with new ones. As with the new solar radiation system, data will be available in Boulder at any time via modem. Unfortunately, this convenient feature was hampered by the poor quality of the telephone communication system in Samoa. The new system performed flawlessly for several months then gradually became afflicted by resets and hangups. This problem was never satisfactorily solved; the most likely suspect was excessive noise on the 485- communication line connecting all the sensors to the computer. CAMS By the end of 1995, carbon dioxide (C0 2 ) was the only program still using CAMS for data acquisition. The C0 2 CAMS unit has done a fine job but some day it too will be retired in favor of a more modern system. Cooperative Programs SIO GC. The Scripps Institution of Oceanography (SIO) gas chromatograph (GC) Nafion dryer used to dry the incoming air sample was upgraded. The new system is self-recharging thus eliminating the chore of replacing cartridges periodically. SEASPAN. The SEAREX South Pacific Aerosol Network (SEASPAN) wind sensor cable was replaced with a new one; the old one had several splices that were suspected of degrading the signal. The wind speed transducer was also upgraded. DOE. The Department of Energy (DOE) wet/dry rooftop collection bucket was replaced with an ion exchange column in August 1995. At the same time, the frequency at which samples were shipped out was increased to once per week. This was done in response to the decision in France to resume nuclear testing at Muroroa Atoll near Tahiti. 1.4. South Pole Observatory T. Jacobs 1.4.1. Operations The CMDL South Pole Observatory (SPO) is located at the geographic South Pole at an elevation of 2835 m above sea level with an average temperature of -49°C. SPO is part of Amundsen Scott Station, which is managed by the National Science Foundation (NSF) Office of Polar Programs. Most CMDL projects are housed in the Clean Air Facility (CAF), an elevated building located upwind of the main South Pole Station. Construction of a replacement facility began in October 1995; the new building should be complete and ready for occupation by January 1997. Because the surface wind at the South Pole blows predominantly from the grid northeast, the SPO "Clean Air Sector" includes the area grid north of the CAF between grid 340 degrees and grid 110 degrees. Excursions into the Clean Air Sector are generally prohibited, with few exceptions. SPO's meteorological instruments are mounted on the walk-up Met. Tower, which was located 100 m from the eastern side of the CAF. In November of 1995 the tower was moved to accommodate construction of the new CAF. 14 Operations for the balloon program take place in three locations: the main station science building, the cargo arch, and the Balloon Inflation Tower (BIT). The cargo arch is used to inflate plastic balloons, that are too large to inflate and launch from the BIT. Amundsen Scott Station is supplied by air. Because airplanes can only land at the Pole during the relatively warm months of October through February, the station is physically "closed" for 8 months each year. A midwinter "airdrop" took place in June of 1994 and 1995. Air samples collected during the austral winter cannot be returned for analysis until the following spring. Data are transferred digitally via satellite throughout the year. In January 1994, Amundsen Scott Station established a satellite link to the Internet, greatly facilitating the transfer of data. During 1994 and 1995 there were occasional power outages and frequent "brownouts" because of an increasing demand for electrical power at the Pole. Within the CAF, science demands continue to exceed the "clean" power supplied by the building's uninteruptable power supply (UPS). The University of Rome lidar was replaced by a similar instrument, owned and operated by the University of Illinois. 1.4.2. Programs Table 1.6 is a summary of the measurement programs at SPO during 1994 and 1995. Operational highlights are as follows. Carbon Cycle The Siemens continuous carbon dioxide (CO2) analyzer ran continuously without significant problems. Sample flask pairs were filled through the analyzer once per week and through a portable Martin and Kitzis Sampler (MAKS) unit twice per month. Aerosols The Meteorology Research, Inc. (MRI) four-wavelength nephelometer "hung" occasionally for unknown reasons. Discrete observations with the Pollak condensation nucleus counter (CNC), taken twice daily, generally agreed, as expected, with data from the Thermo Systems Inc. (TSI) CNC. Solar and Terrestrial Radiation During the summer, all Eppley pyranometers, pyrgeometers, and the tracking normal incidence phyrheliometer (NIP) ran continuously without significant problems. Discrete observations with the filter wheel NIP took place three times daily during especially clear conditions. In November 1995, a pyranometer equipped with a sun blocking disk was installed on the roof of the CAF. After sunset each March, the short-wave instruments were taken off-line for the winter. Ozone and Water Vapor The Dasibi ultraviolet absorption ozone monitor ran continuously without remarkable problems. Discrete observations with the Dobson ozone spectrophotometer took place three times daily during the summer and again during the darkest winter months using the full moon as a light source. The ozonesonde program ran well during 1994 and 1995. Rubber balloons were launched from the balloon inflation tower (BIT) platform; the larger plastic balloons were inflated in the cargo arch and launched from the cargo yard. Launches usually occurred once per week except during the months of stratospheric ozone depletion (August-November) when the schedule was increased to every 3 days and then to every other day. Nitrous Oxides and Halocarbons The two Shimadzu Mini-2 electron capture gas chromatographs were inspected and upgraded in January 1994 and November 1994. Sample flask pairs were filled with ambient air twice per month whenever flasks were available. Meteorology The meteorology system was upgraded in January 1994 with all new sensors and a new data acquisition system. Manual weather observations took place daily at midnight universal time (UT). Data Acquisition The aerosol Control and Monitoring System (CAMS) unit was taken off-line during summer 1994. Cooperative Programs SIO. The Scripps Institution of Oceanography (SIO) conducts long-term monitoring of C0 2 , 13 C/ I2 C ratio, and N 2 0. Twice per month, three evacuated glass flasks were exposed to ambient air. SIO. Three glass flasks were pressurized with ambient air on the first and fifteenth of each month for the long- term monitoring of 2 and N 2 . DOE. The Department of Energy (DOE)conducts long- term monitoring of the spatial and temporal distribution of specific and anthropogenic radionuclides in surface air. The DOE pump ran continuously without significant problems; filters were replaced each week. OGIST. Oregon Graduate Institute of Science and Technology (OGIST) monitors seasonal trends in the amount of chlorine-and bromine-containing trace gases in the Antarctic. Two flasks per week were filled with ambient air. CSIRO. CSIRO monitors the ratio 13C/ 12 C in atmospheric C0 2 for use in a 2-D global carbon cycle model. One glass flask was pressurized with ambient air every 2 weeks. SUNY. Five air-filled cylinders remained on platforms approximately 800 m downwind of the main station for the quantification of the production rate of radiocarbon by galactic cosmic rays. The cylinders were inspected and cleared of snow once per month; no other operations were required for State University of New York (SUNY) . . University of Arizona. An unsuccessful attempt was made to run a continuous meter during the winter of 1994 for the monitoring of H 2 2 in the air/snow interface. In the summer of 1994 CMDL began collecting surface snow and micropit snow samples once per week. 15 TABLE 1.6. Summary of Measurement Programs at SPO in 1994-1995 Program Instrument Sampling Frequency Gases C0 2 CO,, CH 4 Surface 3 Total 3 Ozone profiles Water vapor N 2 O t CFC- 1 1 , CFC- 1 2, CFC- 113, CH3CCI3, CCI4 N 2 0, CFC-11, CFC- 12, CFC- 113, CH3CCI3, CCI4, SF 6 , HCFC-22, HCFC-141b, HCFC-142b, CHjBr, CH3CI, CH 2 C1 2 , CHCI3, C 2 HC1 3 , C 2 C1 4 , H-1301, H-1211.H-2402, HFC-134a CFC- 1 1 , CFC- 1 2, CFC- 113, N 2 0, CH3CCI3, CCI4 Siemans IR analyzer 2.5-L glass flasks, through analyzer 2.5-L glass flasks, MAKS pump unit Dasibi ozone meter Dobson spectrophotometer no. 82 Balloonborne ECC sonde Balloonborne sonde 300-mL stainless steel flasks 850-mL stainless steel flasks Shimadzu automated GCs Continuous 1 pair twice mo -1 1 pair twice mo -1 Continuous 3 day 1 1 wk 1 , summer, autumn, winter; 1 (3 day) 1 , spring 10 times yr 1 1 sample mo -1 1 sample mo 1 1 sample h _1 Aerosols Condensation nuclei Optical properties Pollack CNC TSI CNC Four-wavelength nephelometer 2 day 1 Continuous Continuous Solar Radiation Global irradiance Direct irradiance Albedo Eppley pyranometers with Q and RG8 filters Eppley pyranometer with Q filter Net radiometer Eppley pyrheliometer with Q, OG1, RG2, and RG8 filters Eppley pyrheliometers with Q and RG8 filters Eppley pyranometers with Q and RG8 filters filters, downward facing Continuous, summer Continuous, summer Continuous, summer 2 day 1 Continuous, summer Continuous, summer Terrestrial (IR) Radiation Upwelling and downwelling Eppley pyrgeometers Continuous Meteorology Air temperature Pressure Wind (speed and direction) Frost-point temperature Platinum resistor, 2- and 20-m heights Capacitance transducer Mercurial barometer Bendix Aerovane Hygrometer Continuous Continuous 1 time wk" 1 Continuous Continuous Cooperative Programs C0 2 , l3 C, N 2 0(SIO) Total surface particulates (DOE) Various trace gases (OGIST) Interhemispheric 13 C/ 14 C (CSIRO) 2 , N 2 (Scripps) H 2 2 (Univ. of Arizona) Isotope production (SUNY) 5-L evacuated glass flasks High-volume sampler Stainless-steel flasks 5-L glass flasks Air sampling pump and flasks Snow sample collection Pressurized cylinders 2 mo -1 (3 flasks sample 1 ) Continuous (4 filters mo 1 ) 1 week -1 (2 flasks set ''), summer only 1 or 2 flasks mo -1 1 mo- 1 (3 flasks set 1 ) 1 time wk -1 N/A; checked once mo" 1 Id 1.5. Meteorological Measurements T. Mefford (Editor), M. Bieniulis, B. Halter, and J. Peterson 1.5.1. Station Climatologies Introduction The climatology of surface meteorological observations at the four CMDL observatories is based on hourly average measurements of the resultant wind direction and speed, barometric pressure, ambient and dewpoint temperatures, and the precipitation amount. The 19-year station climatologies are an important record for the interpretation of measured values of aerosols, trace gases, atmospheric turbidity, and long-term changes in the records themselves. The records also serve to outline periods of local contamination. The sensors in use were selected for their high accuracy and their ability to withstand the extreme conditions of the polar region. Data is recorded as 1- minute average values so that the variability within the hourly averages can be determined. To the extent that is practical. World Meteorological Organization (WMO) siting standards [WMO, 1969] are followed. Thermometers are also positioned at the top of the sampling towers at BRW, MLO, and SPO to measure the temperature gradient to determine the stability of the surface boundary layer. The Control and Monitoring System (CAMS) was replaced with a PC-based meteorological data acquisition system at BRW in April 1994, MLO in October 1993, SMO in June 1994, and SPO in January 1994. A detailed description of the new data acquisition system can be found in [Peterson and Rosson, 1994]. Table 1.7 describes the sensor disposition as of December 3 1 , 1995. Barrow Descriptions of the BRW station and its climate are given in previous CMDL Summary Reports [e.g., DeLuisi, 1981]. Wind roses of hourly average resultant wind direction and speed are presented in 16 direction classes and 4 speed classes (Figure 1.2). Winds from the "clean air" sector, north-northeast to southeast occurred 58.8% of the time in 1994 and 62.8% in 1995 as compared to 62.1% for the 17- year climatology period of 1977 through 1993 (Figure 1.3). Wind speeds that were greater than 10 ms' 1 for 1994 (9.1%) and 1995 (6.8%) were both lower than the 17-year climatology (12.1%). The average speed of 5.5 ms-' in 1994 (Table 1.8) was the second lowest average while the 5.0 ms -1 in 1995 set the lowest average in the 19 years at the station. This could have been caused by lowering of the new anemometer to 9.5 m from 16.5 m on April 15, 1994, when the new system was installed. The average temperature of -13.1°C in 1994 was 0.5°C colder than the 17-year average (Table 1.8). In 1995, the average of -11.4°C was 1.2°C warmer than the 17-year average. June 1994 set a new record low temperature and December 1994 tied its lowest record. In 1995, April tied its record high and September set a new record high. A temperature of -44.4°C set the new record low temperature for March. The barometric pressure for 1994 was close to normal; however, 1995 was 2.0 hPa above the 17-year average. The summertime precipitation measured 85 mm in 1994 and 53 mm in 1995. Mauna Loa The climatology of MLO is best understood when it is considered in two distinctive wind direction regimes, the night (downslope) period (1800-0559 Hawaiian Standard Time (HST)) and the day (upslope) period (0600-1759 HST). The 17-year night and day wind roses illustrate the two distinct wind patterns (Figure 1.4). Night Regime. The 17-year wind rose (Figure 1.4) shows that 91.2% of all winds observed had a southerly component. The percentage of occurrence of southerly winds in 1994 was 94.2% (Figure 1.5) and 90.9% in 1995 (Figure 1.6). Pressure gradient controlled winds (WS>10 ms -1 ) from predominately westerly and south-easterly TABLE 1 .7. CMDL Meteorological Sensor Deployment December 3 1 , 1 995 BRW MLO SMO SPO Serial Elevation, Serial Elevation, Serial Elevation, Serial Elevation, Sensor No. in No. in No. in No. in Primary anemometerf 14584 10.5 13864 10.0 15945 13.7 14583 10.0 Secondary anemometerf 13865 38.2 Pressure transducer} 374199 9.5 374198 3398.4 374200 78.5 358960 2841.0 Mercurial barometer 641 9 5 278 3398.4 961 78.5 215 2841.0 Air temperature A§ 2.2 2.0 14.0 2.0 Air temperature B§1 16.3 37.4 22.0 Air temperature C** 2.0 2.0 12.8 2.0 Dewpoint temperature G0001 2.0 G0004 2.0 G0008 12.8 G0007 2.0 Rain gauge ~4 0.8 -4 tPropeller Anemometer, model no. 05105, R. M. Young Company, Traverse City, Michigan. ^Pressure Transducer, model no. 270, Setra Systems, Acton Massachusetts. Heights of all pressure sensors are given with respect to MSL §Platinum Resistance Probe, Logan 4150 Series, Logan Enterprises, Liberty, Ohio. ^Thermometer, positioned at the top of the local sampling tower to facilitate an estimation of boundary layer stability. **Hygrothermometer, Technical Services Laboratory model no. 1088-400, Fort Walton Beach, Florida. 17 BARROW UI --... WIND ROSE 1994 "'""•--.... ""••■,. >., w I | i Jk£2j CALM 1 -H 1 j 1 1 1 p- "o / / / j / / ■■-■' ...* WIND SPEED (M/S) .5 s WS < 5 E2SE3 5 » WS < 10 $ WIND FREQ [ IWS « 10 BARROW 1995 E WIND ROSE ■w- & X ..*' ■$ WIND FREQ Fig. 1.2. Wind rose of surface winds for BRW for 1994 (left) and 1995 (right). The distribution of resultant wind direction and speed are given in units of percent occ-urrence. Wind speed is displayed as a function of direction in three speed classes. BARROW 1977-93 M. WIND ROSE m ••& JV WIND SPEED (M/S) .5 s WS < 5 r/MV/MU 5 t WS < 10 I i ws 10 $ WIND FREQ Fig. 1.3. Wind rose of surface winds for BRW for 1977-1993. The distribution of resultant wind direction and speed are given in units of percent occurrence for the 17-year period. Wind speed is displayed as a function of direction in three wind classes. directions occurred 5.0% of the time in 1994 and 8.4% in 1995 while the 17-year record shows a 6.1% occurrence. The annual average wind speed for both 1994 and 1995 was not significantly different from the long-term mean (Tables 1.9 and 1.10). The upslope or northerly component winds (north-northwest through east-northeast) that occurred 2.0% of the time in 1994 and 1.9% in 1995, are the result of daytime, upslope flow extending into the early evening hours. Day Regime. The 1994 and 1995 wind roses (Figures 1.5 and 1.6) indicate that winds from the west-northwest through east-northeast occurred 58.4% and 55.4% of the time respectively, compared with the expected occurrence of 58.5% indicated by the 17-year climatology. Pressure gradient controlled winds (WS>10 ms-') occurred 4.1% of the time in 1994 and 8.7% in 1995 while the 17-year average shows an expected occurrence of 5.7%. In 1994, the pressure gradient winds, which are usually associated with storms, followed the expected pattern of fewer occurrences during the day regime. In 1995, these winds had approximately the same number of occurrences in the day and night regimes. The day wind rose is more uniformly distributed in the light wind classes than the night wind rose. This is due to the occurrence of variable wind directions during the transition periods at dawn and dusk, most of which are included in this regime. The average ambient temperature for 1994 and 1995 (Tables 1.9 and 1.10), combining both the day and night records, was 7.8°C and 8.4°C respectively, both considerably higher than the long-term average of 7.0°C. September 1995 set a new record high temperature for the IK TABLE 1.8. BRW 1994 and 1995 Monthly Climate Summary Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Year Prevailing wind direction Average wind speed (m s' 1 ) Maximum wind speed* (m s" 1 ) Direction of max. wind* (deg.) Average station pressure (hPa) Maximum pressure* (hPa) Minimum pressure* (hPa) Average air temperature (°C) Maximum temperature* (°C) Minimum temperature* (°C) Average dewpoint temperature (°C) Maximum dewpoint temperature (°C) Minimum dewpoint temperature (°C) Precipitation (mm) Prevailing wind direction Average wind speed (ins' 1 ) Maximum wind speed* (m s" 1 ) Direction of max. wind* (deg.) Average station pressure (hPa) Maximum pressure* (hPa) Minimum pressure* (hPa) Average air temperature (°C) Maximum temperature* (°C) Minimum temperature* (°C) Average dewpoint temperature (°C) Maximum dewpoint temperature (°C) Minimum dewpoint temperature (°C) Precipitation (mm) ENE ESE ENE 8.8 7.2 5.9 17 20 13 67 95 73 1028.5 1026.5 1016.1 1050 1050 1036 1003 1003 995 -23.0 -23.2 -28.1 -14 -2 -11 -35 -36 -40 -26.0 -25.6 -30.9 -16 -4 -13 -38 -39 -43 ENE E ENE 4.8 5.1 5.4 13 16 15 104 50 112 1010.4 1025.5 1023.6 1025 1042 1040 986 1002 1002 -24.3 -26.8 -27.4 -4 -7 -3 -44 -46 -44 -26.6 -29.4 -29.9 -5 -8 -3 -49 -50 -49 ENE ENE W 4.2 6.1 4.0 13 12 9 72 64 270 1020.1 1014.6 1011.3 1036 1025 1023 1006 998 1001 -17.8 -7.7 -0.3 -2 2 9 -33 -18 -11 -19.7 -9.1 -1.3 -4 8 -36 -19 -12 2 1 ENE ENE NE 5.2 5.4 3.8 13 13 9 226 58 258 1014.9 1017.5 1012.7 1024 1036 1028 997 1003 1000 -13.7 -4.5 1.2 2 2 16 -35 -11 -6 -15.2 -4.9 -0.9 -37 -12 -7 1 15 1994 E ESE NE ENE 4.3 5.0 5.6 4.3 12 13 14 13 90 231 264 71 1010.0 1009.2 1012.3 1009.5 1024 1030 1027 1022 995 995 998 991 3.6 5.5 -3.2 -13.0 17 20 7 -3 -3 -3 -12 -31 2.5 3.7 -5.0 -14.4 11 15 7 -3 -3 -9 -13 -34 15 4S 3 1995 E ENE ENE ENE 5.1 4.3 5.7 6.6 12 9 13 14 74 246 72 64 1012.4 1011.2 1011.2 1013.3 1022 1025 1030 1025 1003 999 990 1001 2.8 1 7 1.7 -7.2 17 14 16 -1 -2 -3 -4 -27 4 1.4 0.4 -8.9 11 10 10 -2 -6 -5 -6 -28 28 5 3 ENE NE ENE 6.0 4.4 5.5 19 14 20 66 210 95 1006.9 1006.5 1014.3 1032 1025 1050 980 987 980 -22.9 -27.2 -13.1 -6 -7 20 -36 -44 -44 -25.1 -29.7 -15.1 -7 -7 15 -40 -48 -48 16 85 ENE ENE ENE 4.2 4.8 5.0 16 16 16 292 72 50 1020.7 1019.8 1016.0 1036 1034 1042 1001 1002 986 -15.1 -24.5 -11.4 -2 -12 17 -29 -35 -46 -16.1 -26.2 -12.8 -2 -12 11 -31 -37 -50 53 Instrument heights: wind, 10.5 m; pressure, 9.5 m (MSL); air temperature, 2.2 m; dewpoint temperature, 2.0 m. Wind and temperature instruments are on a tower 25 m northeast of the main building. *Maximum and minimum values are hourly averages. 19 MAUNA LOA 1977-93... - # WIND SPEED (M/S) -.5 « WS < 5 EiimiiJ5 « WS < 10 [ )ws 10 HL WIND ROSE E ..-*" ■$ WIND FREQ MAUNA LOA 1977-93 ,-•• # WIND SPEED (M/S) — — .5 * WS < 5 i5 i IS < 10 ]WS » 10 %.. WIND ROSE -E X "x ■■$ WIND FREQ Fig. 1.4. Wind roses of the surface winds for MLO for 1977-1993 night (left) and day (right). The distribution of resultant wind direction and speed are given in units of percent occurrence for the 17-year period. Wind speed is displayed as a function of direction in three speed classes. MAUNA LOA 1994 JL WIND ROSE m i \ i {--- -E WIND SPEED (M/S) .5 * WS < 5 V////////A F* S WS < 10 10 $■■ WIND FREQ MAUNA LOA 1994 HL WIND ROSE #■ E # WIND SPEED (M/S) 5 « WS < 5 TMwav/M ** i WS < 10 I iws » 10 M $ WIND FREQ Fig. 1.5. Wind roses of the surface winds for MLO for 1994 night (left) and day (right). The distribution of resultant wind direction and speed are given in units of percent occurrence. Wind speed is displayed as a function of direction in three speed classes. 20 MAUNA LOA 1995 '"". UL WIND ROSE V w I- WIND SPEED (M/S) — 5 » WS < 5 vzzzzzzms * ws < 10 Hws < 10 E ■■$ WIND FREQ MAUNA LOA 1995 $ .... WIND ROSE 4 1 ( f j h™J CALM ! t PS! 2 4 * Jb\/ / //III X """■■■-... ! '...--*"")< / / / / \ "'■•••. X ..."""■-.,.." ..-"- ....%"' / .. • ' WIND FREQ .--■"' * WIND SPEED (M/S) — — .5 » WS < 5 ■•-C^: $ 1 iws » 10 Fig. 1.6. Wind roses of the surface winds for MLO for 1995 night (left) and day (right). The distribution of resultant wind direction and speed are given in units of percent occurrence. Wind speed is displayed as a function of direction in three speed classes. month. The January 1994 and November 1995 average wind speeds set new minimums for the month. The barometric pressure for 1994 and 1995 (679.7 hPa and 680.0 hPa respectively) were both lower than the long- term average pressure of 680.5 hPa. July 1994 and March 1995 each tied its record minimum pressure for those months and April 1995 set a new record minimum for the month. The precipitation amounts for 1994 and 1995 (438 mm and 188 mm respectively) were both significantly lower than the long-term average amount of 500 mm. The 1995 amount is the lowest amount ever received at the station. Samoa A comparison of SMO's 1994 and 1995 wind roses (Figure 1.7) to that of the 17-year period (Figure 1.8) shows a lower percentage (57.7%) of "clean air" sector winds (north-northwest through southeast) in 1994 while 1995 shows a higher percentage (61.2%) than the long-term average of 59.8%. The occurrence of winds in the 10 ms _1 or greater class was 6.7% in 1994 and 3.9% in 1995 while the expected occurrence based on the 17-year record is 4.9%. The average wind speed for both 1994 and 1995, 4.8 ms _1 (Table 1.11) is close to normal. The monthly average for May 1995 set a new minimum record for the month. The average ambient temperature for 1994 and 1995 was 27.3°C and 27.0°C respectively, which are both very close to the 17-year average of 27.1°C. Five new record highs were set in 1994 that occurred during the months of February through June with a new record low occurring during the month of June. In 1994, temperatures during the first 7 months were above their monthly means and the other 5 months were below their respective monthly means. The average barometric pressure for 1994 and 1995 (Table 1.11) was 1.2 hPa and 1.9 hPa above the 17- year average of 999.3 hPa at Cape Matatula respectively. The months of January and June in 1995 both tied the record maximum pressure for the month. The amount of precipitation in 1994 measured near normal amounts during the first 6 months of the year while the last 6 months were wetter than normal. In 1995, the precipitation amount was again near normal for the first 6 months; however, the last 6 months were drier than normal. South Pole The distribution of the surface wind direction in 1994 and 1995 (Figure 1.9) shows a higher percentage of "clean air" sector (grid north-northwest through east-southeast) winds (95.0%) in 1994 while 1995 showed a lower percentage (92.4%) from the than the 17-year average (93.9%) (Figure 1.10). A lower percentage of winds in the 10 ms-> class (3.5% in 1994 and 3.1% in 1995) were observed as compared to the 17-year average (4.0%). The average wind speeds for 1994 and 1995 were very close to the long-term average of 5.4 ms' 1 . May 1995 tied its maximum wind speed record. The monthly average wind speed for January 1995 set a new minimum for the month. The average temperature for 1994 (-49.5°C) and 1995 (-49.7°C) were both colder than the 17-year average of - 49.0°C. September 1994 set a new record maximum and July 1995 tied its record maximum temperature for the month. January 1995 tied its record minimum temperature for the month. The minimum temperature of -74°C for 1994 occurred in May and September while the minimum of - 77°C in 1995 occurred in September. The annual average station pressures for 1994 (679.7 hPa) and 1995 (679.6 hPa) (Table 1.12) were both above the 17-year average of 679.1 hPa. June 1994 tied its record high pressure for the month and July 1995 set a new record high pressure. 21 TABLE 1.9. MLO 1994 Monthly Climate Summary Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Year Night Prevailing wind SW SW SW SSE SSE SSE SSE SSE SSE SSE SSE SSE SSE direction Average wind 3.7 4.3 4.8 4.1 4.4 3.4 5.9 4.1 3.9 3.3 5.4 6.5 4.5 speed (m s' 1 ) Maximum wind 12 12 13 12 13 10 16 14 13 9 13 17 17 speed* (m s" 1 ) Direction of max. 248 241 129 150 148 157 153 154 155 166 158 143 143 wind* (deg.) Average station 678.1 677.9 679.1 679.6 680.2 680.4 680.6 680.9 680.0 679.6 679.8 680.3 679.7 pressure (hPa) Maximum pressure* 682 682 684 683 683 684 683 684 683 683 682 684 684 (hPa) Minimum pressure* 675 673 672 676 678 678 677 678 677 676 677 677 672 (hPa) Average air 4.0 3.7 4.7 5.5 6.5 7.1 7.7 7.1 6.7 6.5 4.8 6.0 5.9 temperature (°C) Maximum temperature* 10 9 12 11 12 15 13 13 11 10 10 11 15 (°C) Minimum temperature* 1 1 2 4 3 3 3 1 2 (°C) Average dewpoint -16.7 -8.6 -14.3 -17.6 -13.5 -11.1 -6.1 -3.7 -3.9 -12.1 -9.0 -22.8 -11.7 temperature (°C) Maximum dewpoint 4 5 4 4 7 9 8 9 8 6 4 -3 9 temperature (°C) Minimum dewpoint -32 -24 -30 -29 -30 -29 -24 -16 -18 -29 -29 -32 -32 temperature (°C) Precipitation (mm) 38 23 22 1 13 Day 4 7 31 140 Prevailing wind NW NNW NW NNW NNW NNW ESE NNW NNW NNW SE SE NNW direction Average wind 3.9 4.3 4.4 3.5 3.7 2.8 5.0 3.7 3 1 2.7 4.5 5.8 4.0 speed (m s' 1 ) Maximum wind 12 12 15 13 13 8 15 13 11 10 13 16 16 speed* (m s" 1 ) Direction of max. 259 214 104 141 153 106 142 147 152 160 142 124 124 wind* (deg.) Average station 678.1 677.9 679.1 679.7 680.3 680.6 680.8 681.0 679.9 679.6 679.7 680.3 679.8 pressure (hPa) Maximum pressure* 682 683 684 683 682 684 683 683 683 683 683 684 684 (hPa) Minimum pressure* 675 673 672 677 678 678 677 678 677 676 677 677 672 (hPa) Average air 7.3 6.5 8.3 9.8 10.6 11.2 11.4 11.2 10.3 10.4 7.9 10.2 9.7 temperature (°C) Maximum temperature* 12 13 16 15 15 17 16 15 15 15 14 16 17 (°C) Minimum temperature* 2 3 4 5 4 4 3 1 2 (°C) Average dewpoint -11.7 -5.7 -8.9 -9.6 -6.1 -4.4 -1.6 -0.3 0.6 -5.9 -4.6 -18.4 -6.5 temperature (°C) Maximum dewpoint 6 6 6 8 8 9 9 9 10 8 7 2 10 temperature (°C) Minimum dewpoint -32 -24 -30 -28 -28 -27 -22 -18 -21 -26 -27 -31 -32 temperature (°C) Precipitation (mm) 29 42 38 10 19 56 58 12 34 298 Instrument heights: wind, 10.0 m; pressure, 3398.4 m (MSL); air temperature, 2.0 m; dewpoint temperature, 2.0 m. Wind and temperature instruments are on a tower 15 m southwest of the main building. *Maximum and minimum values are hourly averages. 22 TABLE 1.10. MLO 1995 Monthly Climate Summary Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Year Night Prevailing wind SE WSW WSW SW SE SE SSE SE SSE SE SSE SSE SE direction Average wind 5.4 7 6.5 6.1 4.5 t.4 3.8 $.9 3.5 4.3 3.8 4.4 4.8 speed (m s" 1 ) Maximum wind 17 15 16 16 13 12 11 11 11 15 13 14 17 speed* (m s" 1 ) Direction of max. 249 241 224 224 241 164 169 164 141 140 152 160 249 wind* (deg.) Average station 680.0 677.4 678.7 678.4 680.2 681.1 680.6 680.3 680.9 680.1 680.4 680.8 679.9 pressure (hPa) Maximum pressure* 683 681 684 682 684 684 683 683 684 684 684 684 684 (hPa) Minimum pressure* 677 673 669 672 677 678 678 678 678 677 677 676 669 (hPa) Average air 5.8 4.2 5.7 5.7 6.5 8.8 8.1 7.3 8.5 6.9 5.6 5.5 6.6 temperature (°C) Maximum temperature* 11 11 13 11 11 14 14 13 14 13 10 11 14 (°C) Minimum temperature* 1 -1 -1 2 5 2 2 3 1 2 1 -1 (°C) Average dewpoint -12.8 -15.0 -15.0 -12.5 -12.7 -15.9 -11.2 -13.1 -15.2 -14.7 -5.5 -12.3 -13.0 temperature (°C) Maximum dewpoint 5 3 1 5 8 7 8 7 7 6 6 6 8 temperature (°C) Minimum dewpoint -30 -38 -30 •32 -28 -25 -24 -27 28 -29 -24 -31 -38 temperature (°C) Precipitation (mm) 5 18 5 1 1 3 Day » 12 3 49 Prevailing wind wsw WNW W NNW NNW NE NE NE NE NNW NNW NNW NNW direction Average wind 5.1 7 1 6.5 6.5 4.7 3.8 3.6 3.5 3.1 3.8 3.0 3.4 4 5 speed (m s"') Maximum wind 17 14 17 16 13 10 14 12 13 13 13 12 17 speed* (m s ) Direction of max. 248 297 233 233 251 144 148 155 125 147 155 234 2-18 wind* (deg.) Average station 680.0 677.5 678.8 678.4 680.3 681.2 680.8 680.5 681.0 680.2 680.3 680.7 680.0 pressure (hPa) Maximum pressure* 683 682 684 682 684 683 684 683 684 683 684 685 685 (hPa) Minimum pressure* 677 673 670 673 677 678 678 678 678 677 678 676 670 (hPa) Average air 9.4 7.6 9.7 9.7 10.6 13.0 11.7 11.2 12.2 10.5 8.9 9.0 10.3 temperature (°C) Maximum temperature* 16 15 17 15 16 17 16 17 19 17 14 15 19 (°C) Minimum temperature* 1 -1 1 2 3 7 5 4 5 2 2 2 -1 (°C) Average dewpoint -10.4 -10.9 -10.6 -7.9 -4.7 -7.7 -2.8 -3.8 -5.8 -7.1 -2.2 -7.7 -6.8 temperature (°C) Maximum dewpoint 5 4 6 6 9 8 9 10 9 7 8 6 10 temperature (°C) Minimum dewpoint -30 -38 -30 -30 -26 -24 -22 ■27 -26 -2') -23 -31 -38 temperature (°C) Precipitation (mm) 7 16 7 10 11 8 16 9 10 25 14 140 Instrument heights: wind, 10.0 m; pressure, 3398.4 m (MSL); air instruments are on a tower 15 m southwest of the main building. *Maximum and minimum values are hourly averages. temperature, 2.0 m; dewpoint temperature, 2.0 m. Wind and temperature 23 SAMOA 1994 S ..; WIND ROSE m E * WIND SPEED (U/S) .5 « WS < 5 V////////A Fi f WS < 10 L"" _.rjws 10 ■■$ ...-•' WIND FREQ SAMOA 1995 ..$ ; WIND ROSE # WIND SPEED (U/S) -5 « WS < 5 Y/W////M fi C WS < 10 I I WS a 10 ■$ Fig. 1.7. Wind rose of surface winds for SMO for 1994 (left) and 1995 (right). The distribution of resultant wind direction and speed are given in units of percent occurrence. Wind speed is displayed as a function of direction in three speed classes. SAMOA 1977-93 fiL WIND ROSE W ! t ! !~ -•! \ E- WIND SPEED (U/S) .5 « WS < 5 rp7777P7m ^ t WS < 10 10 jWS ■•$ WIND FREQ Fig. 1.8. Wind rose of surface winds for SMO for 1977-1993. The distribution of resultant wind direction and speed are given in units of percent occurrence for the 17-year period. Wind speed is displayed as a function of direction in three speed classes. 1.5.2. Meteorology Operations New Dewpoint Sensors and Electronics Upgrade Three new hygrothermometers and transmit logic boards from Technical Services Laboratory (TSL) were purchased for the BRW, SMO, and SPO observatories. The model 1088-400 replaced the model 1063-104 at BRW in August 1995, at SMO in December 1995, and at SPO in November 1995. The new model hygrothermometer was installed at MLO when the new data acquisition was initially installed in October 1993. The upgrade improvements include tighter tolerances in the electronic components for greater data accuracy, better radiation shielding of the temperature sensors, and a higher volume of ambient air flow past the temperature sensors to minimize the effects of heat buildup in the sensor housing. SPO Meteorological Sampling Tower Relocation and Sensor Recalibrations Prior to moving the meteorological sampling tower, all of the SPO meteorological sensors listed in Table 1.7, except for the Setra pressure transducer, were removed and located on the grid north (upwind) railing of the clean air facility (CAF). The alignment of the wind direction sensor was approximate. From November 9 through November 22, 1995, the tower was disassembled, moved from a location at approximately 100 m along a grid 110° from the current CAF to a location approximately 183 m grid northeast of the CAF, and reassembled. The new location will put the tower approximately 91 m at grid 340° from 24 TABLE 1.11. SMO 1994 and 1995 Monthly Climate Summary Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Year 1994 Prevailing wind SE NW SSE NW SE SSE SE si; SSE SE si-: SSE SE direction Average wind 3.8 3.1 3.5 3.7 4 6 6.5 5 5 7.3 4.8 3.7 6.5 4 4.8 speed (m s 1 ) Maximum wind 9 8 14 14 12 13 13 15 II 12 14 11 15 speed* (m s" 1 ) Direction of max. 310 140 334 315 144 138 146 145 112 113 138 151 145 wind* (deg.) Average station 998.7 999.3 999.5 999.1 1001.0 1001.8 1001.2 1002.8 1002.7 1001.8 1000.3 997.8 1000.5 pressure (hPa) Maximum pressure* 1003 1003 1004 1003 1005 1006 1004 1007 1007 1005 1004 1003 1007 (hPa) Minimum pressure* 991 996 992 994 996 998 998 997 999 998 994 992 991 (hPa) Average air 28.7 29.5 29.1 28.2 27.7 26.9 26.3 25.5 25.9 26.4 26.8 27.3 27.3 temperature (°C) Maximum temperature* 35 37 36 36 34 34 29 27 2X 29 29 30 37 (°C) Minimum temperature* 23 23 24 23 21 23 23 23 23 23 23 24 21 (°C) Average dewpoint 23.2 23.5 23.8 23.6 22.4 22.8 23.0 21.7 22.8 24.0 23.8 25.0 23.3 temperature (°C) Maximum dewpoint 26 25 26 26 25 25 26 25 25 26 26 27 27 temperature (°C) Minimum dewpoint 21 22 22 20 20 19 18 15 17 21 20 23 15 temperature ( C C) Precipitation (mm) 215 121 181 288 283 84 233 1995 200 65 299 201 332 2503 Prevailing wind SSE SE ESE SSE SSE SE SE SE SE SSE SSE E SSE direction Average wind 5.9 3.1 3.2 3.1 3.4 6.6 6.1 6 1 6 9 5.7 4.1 2 1 4.8 speed (m s" 1 ) Maximum wind 14 10 8 10 12 11 15 13 13 13 12 6 is speed* (m s" 1 ) Direction of max. 322 138 323 118 156 153 124 164 130 130 87 64 124 wind* (deg.) Average station 998.7 1000.1 1000.6 1000.0 1001.0 1002.9 1002.5 1002.9 1003.7 1001.8 1000.2 999.0 1001.2 pressure (hPa) Maximum pressure* 1005 1004 1005 1003 1004 1007 1006 1007 1007 1006 1005 1005 1007 (hPa) Minimum pressure* 992 995 996 997 997 999 999 999 1000 998 995 995 992 (hPa) Average air 27.2 27.7 27.8 27.3 27.1 27.2 26.8 26.4 26.4 26.3 26.8 27.6 27.0 temperature (°C) Maximum temperature* 29 30 29 30 30 29 28 30 29 28 29 30 30 (°C) Minimum temperature* 24 24 24 23 23 24 24 23 23 24 23 25 23 (°C) Average dewpoint 23.9 24.4 24.6 23.9 24.0 23.4 23.5 23.3 22.7 22.9 23.9 23.8 23.7 temperature (°C) Maximum dewpoint 26 27 26 26 26 26 25 25 25 25 26 27 27 temperature ( C C) Minimum dewpoint 21 21 22 20 22 20 21 20 17 20 22 21 17 temperature ( C C) Precipitation (mm) 288 128 192 258 1X3 85 143 273 119 103 149 39 1960 Instrument heights: wind, 13.7 m; pressure, 78.5 m (MSL); air temperature, 14.0 m; dewpoint temperature, 12.8 m. Wind and temperature instruments are on Lauagae Ridge, 110 m northeast of the main building. *Maximum and minimum values are hourly averages. 25 SOUTH POLE 1994 JL w : i WIND ROSE WIND SPEED (M/S) .5 « WS < 5 r/»/w//A 5 i WS < 10 I IWS > 10 E- .M % WIND FREQ SOUTH POLE 1995 ...m WIND ROSE W E ..-*" WIND SPEED (M/S) — 5 i WS < 5 wmmm 5 * WS < 10 I IWS » 10 S -*' .-■■"" .---"'' WIND FREQ Fig. 1.9. Wind rose of surface winds for SPO for 1994 (left) and 1995 (right). The distribution of resultant wind direction and speed are given in units of percent occurrence. Wind speed is displayed as a function of direction in three speed classes. SOUTH POLE 1977-93 I... WIND ROSE # & # WIND SPEED (M/S) — 5 i WS < 5 v/mma 5 i WS < 10 10 ]ws WIND FREQ Fig. 1.10. Wind rose of surface winds for SPO for 1977-1993. The distribution of resultant wind direction and speed are given in units of percent occurrence for the 17-year period. Wind speed is displayed as a function of direction in three speed classes. the new CAF. Nearly two full 2-m sections were buried under snow at the old location. The increase in snow height at the old location was 267 mm per year on average since 1983. The move resulted in a gain of 3 to 3.4 m of tower height and an ability to use all 24 m of the tower. During this time, the new TSL 1088-400 hygrothermo- meter was put into operation and calibrated. The platinum resistance probes (RTDs) were calibrated by using an ice bath at 0°C. From November 22 through December 2, 1995, a new cable for the RS-485 data communications line was prepared, and hardware for the AC power and the meteorological sensors was installed on the tower at the new location. The azimuth orientation of the anemometer was set by using a solar azimuth alignment tool and tables of solar position. Table 1.13 describes the sensor heights before and after the move of the sampling tower. 1.6. Data Management During 1994, the meteorological data acquisition system operated 96.9% of the time and during 1995 operated 93.8% of the time. The meteorological data acquisition system gathers data from sensors that operate continuously at each of the four CMDL observatories. The performance was monitored by comparing the number of data points recorded against that expected for the year. Table 1.14 shows the performance of each system during 1994 and 1995. Due to the remoteness of the observatories, power outages are common and the main reason for data loss. 26 TABLE 1.12. SPO 1994 and 1995 Monthly Climate Summary Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Year 1994 Prevailing wind N ENE N E N NE ENE NE E NNE NNE ENE NNE direction Average wind 5.3 4.7 6.2 4.7 5.8 62 6.0 5.8 6.6 5.7 4.3 3.4 5.4 speed (m s ) Maximum wind 11 1(1 12 10 13 11 12 12 1 3 10 l > 7 14 speed* (m s" 1 ) Direction of max. 359 5 13 40 7 214 20 359 M) 17 25 116 214 wind* (deg.) Average station 688.3 680.0 674.7 681.9 674.8 691.2 675.4 670.9 676.8 677.3 685.1 680.9 679.7 pressure (hPa) Maximum pressure* 697 687 684 696 693 705 691 687 697 693 693 690 705 (hPa) Minimum pressure* 679 669 664 666 661 677 660 653 651 663 675 672 651 (hPa) Average air -28.3 -44.0 -53.7 -57.3 -58.3 -54.9 -62.5 -58.5 -56.9 -51.3 -37.4 -28.7 -49.5 temperature ( C C) Maximum temperature* -23 -35 -37 -38 -35 -37 -45 -37 -31 -34 -27 -22 -22 (°C) Minimum temperature* -37 -55 -64 -70 -74 -68 -72 -73 -74 -63 -47 -34 -74 (°C) Average dewpoint -31.3 -51.1 -59.5 -62.2 -59.3 -59.7 -65.9 -61.0 -56.7 -57.3 -44.5 -34.1 -52.6 temperature (°C) Maximum dewpoint -24 -42 -42 -42 -39 -41 -50 -41 -34 -38 -33 -26 -24 temperature (°C) Minimum dewpoint -52 -63 -71 -71 -71 -71 -71 -71 71 •70 -56 -41 71 temperature (°C) Precipitation (mm) 1995 Prevailing wind E N NNE N ESE E NE E ESE ENE N N N direction Average wind 3.0 5.1 5.7 6.2 5.8 5.1 6.2 5.4 4.8 6.6 5.3 3.6 5 2 speed (m s" 1 ) Maximum wind 7 10 11 13 14 10 15 12 11 13 10 8 15 speed* (m s" 1 ) Direction of max. 351 22 23 340 9 4 28 36 6 11 3 6 28 wind* (deg.) Average station 681.9 682.1 682.0 676.6 671.9 680.5 686.2 676.3 671.4 679.3 683.7 683.6 679.6 pressure (hPa) Maximum pressure* 691 692 690 691 688 697 705 695 685 692 693 692 705 (hPa) Minimum pressure* 675 673 670 655 662 666 673 660 662 669 673 678 655 (hPa) Average air -31.3 -40.3 -52.6 -58.3 -59.0 -58.6 -55.6 -61.8 -64.6 -48.9 -37.9 -27.3 -49.7 temperature (°C) Maximum temperature* -24 -28 -40 -44 -37 -39 -34 -49 -50 -31 -27 -20 -20 (°C) Minimum temperature* -38 -51 -66 -74 -76 -72 -68 -74 -77 -66 -49 -33 -77 (°C) Average dewpoint -38.2 -46.0 -58.1 -63.8 -65.6 -63.7 -61.7 -70.1 -71.8 -54.3 -42.3 -31.1 -54.7 temperature (°C) Maximum dewpoint -27 -32 -44 -49 -42 -43 -37 -54 -55 -35 -30 -23 -23 temperature ( C C) Minimum dewpoint -47 -60 -73 -81 -85 -79 -75 -81 -86 -73 -55 -37 -86 temperature (°C) Precipitation (mm) Instrument heights: wind. 10.0 m; pressure, 2841 m (MSL); air temperature, 2.0 instruments were on a tower 100 m grid east-southeast of the CAF until November 9, northeast of the CAF. *Maximum and minimum values are hourly averages. m; dewpoint temperature, 2.0 m. Wind and temperature 1995, when the tower was moved to a location 183 m grid 27 TABLE 1.13. SPO Sensor Instrument Heights Before and After Tower Move Instrument Height Before Move (m) Height After Move (m) Primary anemometer Pressure transducer Air temperature A Air temperature B Air temperature C Dewpoint temperature Non-aspirated temperature 10.0 2841.0 1.1 20.0 1.6 1.6 1.4 10.0 2841.0 2.0 22.0 2.0 2.0 2.0 Heights are in meters above snow surface, except for barometric pressure, which is with respect to MSL. Refer to Table 1.7 for sensor information. TABLE 1.14. CMDL Meteorological Operations Summary, 1994-1995 Expected Number Percent Data Number of Missing Station of Data Points Capture Data Points 1994 BRW 3,006,720* 99.08% 27,678 MLO 6,832,800 94.48% 377,222 SMO l,955,520t 99.27% 14,215 SPO 3,985,9201: 94.95% 1995 201,128 BRW 4,204,800 99.40% 25,115 MLO 6,832,800 95.85% 283,394 SMO 3,679,200 84.08% 585,716 SPO 4,204,800 95.88% 173,093 ^Expected number of data points as of April 15, 1994. tExpected number of data points as of June 21, 1994. +Expected number of data points as of January 20, 1994. Hardware failure, system restarts, and system maintenance are the other reasons for data loss. At BRW, during the winter periods, rime, snow, and ice occasionally would build up on the sensors and have to be removed by station personnel. At MLO, high winds caused electrostatic buildup in the wind direction module at 38 m. High winds also caused damage to the 38 m anemometer nose cone and propeller shaft assembly. At SMO, the hygrothermometer failed. The biggest cause of data loss was due to the buildup of corrosion on the sensor connector pins and moisture getting into the RS-485 communications line. This produced noise in the communications that the data acquisition system was not able to handle. At SPO the fuse in the meteorological crate, which houses the Setra pressure transducer and the module for the non-aspirated platinum resistance probe, blew several times due to station power failures. The plastic junction box for the anemometer, which houses a circuit board, disintegrated due to the extreme cold of SPO. Periods of high winds at SPO caused static buildup along the sensors and data lines. The solution was to temporarily disconnect the AC power that would reset the modules. On at least two separate occasions, the static buildup damaged electrical com- ponents, requiring their replacement with spare parts on hand at the station. Data is transferred to Boulder on a daily basis via the Internet. Preliminary hourly averages of wind direction and speed, barometric pressure, ambient and dewpoint temperature, and precipitation amounts are sent to the station personnel. Each month a climatic summary is prepared from edited data and distributed within CMDL and to each of the observatories. Recently, parts for the aerosol solar radiation (ASR), C02, and M03 CAMS have become very difficult to purchase. As a result, CAMS is in the process of being decommissioned. Since 1993, the CAMS system has been gradually replaced with more sophisticated data acquisition systems. These new systems are also gradually getting on the Internet so that the data can be transferred to Boulder more quickly than was possible with the CAMS system. Acknowledgment. We wish to thank Gary Herbert and Ken Thaut (both retired) who were responsible for the installation of the new meteorological data acquisition systems at MLO in 1993, BRW, SMO, and SPO in 1994, and for their dedication to the CMDL meteorology program. 1.7. References DeLuisi, J. (ed.), Geophysical Monitoring for Climatic Change No. 9 Summary Report 1980, 163 pp., NOAA Environmental Research Laboratories, Boulder, CO 1981. Peterson, J.T., and R.M. Rosson (eds.). Climate Monitoring and Diagnostics Laboratory No. 22 Summary Report 1993, 152 pp., NOAA Environmental Research Laboratories, Boulder, CO, 1994. Ryan, S., Quiescent outgassing from Mauna Loa Volcano 1958- 1994, in Mauna Loa Revealed: Structure, Composition, History, and Hazards, Geophysical Monograph 92, edited by J.M. Rhodes and J. P. Lockwood, Am. Geophys. Union, Washington, D.C., 95-1 15, 1995. Thoning, K.W., P.P. Tans, and W.D. Komhyr, Atmospheric carbon dioxide at Mauna Loa Observatory, 2, Analysis of the NOAA GMCC data, 1974-1985, J. Geophys. Res., 95(D6), 8549-8565, 1989. World Meteorological Organization (WMO), Guide to Meteorological Instrumentation and Observing Practices, No. 8, Tech. Paper 3, 347 pp., World Meteorological Organization, Geneva, 1969. 2S 2. Carbon Cycle P.P. Tans (Editor), P.S. Bakwin, T.J. Conway, R.W. Dissly, E.J. Dlugokencky, L.S. Geller, D.W. Guenther, D.F. Hurst, D.R. Kitzis, P.M. Lang, K.A. Masarie, J.B. Miller, P.C. Novelli, C. Prostko-Bell, M. Ramonet, K.W. Thoning, M. Trolier, L.S. Waterman, N. Zhang, and C. Zhao 2.1. Overview The overall goal of the work by the Carbon Cycle Group (CCG) is to improve our understanding of what determines the atmospheric burden of the major trace gases involved in the carbon cycle: CO2, CH 4 , and CO. Concern about global climate change, and possible future management of the problem, is the driving force behind the work. The anthropogenic influence on all three gas species is large, but natural cycles are involved as well. Two methods were employed from the start of the Geophysical Monitoring for Climatic Change program, the forerunner of CMDL. Continuous measurements in remote clean air locations, namely the four CMDL observatories, and the collection of weekly or bi-weekly discrete flask samples in pairs, also at remote clean air locations. Initially the samples were analyzed only for C0 2 . Methane was added in 1983, CO in 1988, isotopic ratios of CO2 (in collaboration with the University of Colorado/Institute for Arctic and Alpine Research (CU/INSTAAR)) in 1990. Information on the sources and sinks of the trace gases is obtained from their rates of increase and from their spatial distributions. The link between sources and observed mixing ratios is provided by numerical models of atmospheric transport operating in both two and three dimensions. Since we are working "backwards" from observed concentrations, this problem is in the class of so- called inverse problems. The greatest limitation is sparseness of data, especially in regions close to important sources and sinks. Therefore the Carbon Cycle Group has gradually expanded the spatial coverage of the cooperative air sampling network, as well as added isotopic ratio measurements since different sources/sinks may be characterized by distinctive isotopic "signatures." To overcome the limitation of having only measurements from the marine boundary layer, remote from many important source areas, two new approaches were initiated. One is to continuously measure a number of chemical species and atmospheric physical properties at different heights on very tall towers. Mixing ratios in the continental planetary boundary layer are highly variable and their interpretation is more difficult, requiring much more auxiliary data, than the "traditional" marine air samples. The second new approach is to obtain discrete air samples from low-cost airplanes in automated fashion from the boundary layer up to about 8 km altitude. These samples are then sent back to the laboratory in Boulder for analysis. The use of this method, especially over North America, will be greatly expanded to provide significant regional-scale constraints on the budgets of carbon species. The global air samples also provide a unique resource for narrowing the uncertainties of additional atmospheric problems. In collaboration with the Nitrous Oxide And Halocompounds (NOAH) group of CMDL, the species N 2 (a greenhouse gas) and SF 6 were added to the suite of flask measurements, and other species are under investigation. The development of a method to routinely measure the l3 C/ 12 C ratio of CH 4 , in collaboration with INSTAAR, is at an advanced stage. Since the global coverage of our sampling is unmatched, CMDL plays an active role in bringing together the measurements from many different laboratories around the world. Towards this end, measurements of field samples as well as reference gas standards are intercompared. The link with the Commonwealth Scientific and Industrial Research Organization (CSIRO) in Australia is particularly strong in this regard. For C0 2 and CO, calibrated reference gases are provided under the auspices of the World Meteorological Organization (WMO). At the "product" end, a common database for C0 2 has been assembled without significant calibration or methodo- logical discrepancies, incorporating the measurements of a number of laboratories, called GLOBALVIEW-C02. Its intended use is for three-dimensional (inverse) modeling. Plans are to maintain and enlarge the database, as well as assemble similar ones for CH 4 , isotopic ratios, etc. Data records and monthly means can be obtained for each site from the CMDL World Wide Web page (www.cmdl.noaa.gov); the ftp file server's "pub" directory (ftp.cmdl.noaa.gov), from the WMO World Data Center for Greenhouse Gases (Tokyo), and from the Carbon Dioxide Information Analysis Center (Oak Ridge, Tennessee). 2.2. Carbon Dioxide 2.2.1. In Situ Carbon Dioxide Measurements The mixing ratio of atmospheric C0 2 was measured with continuously operating nondispersive infrared (NDIR) analyzers at the four CMDL observatories during 1994 and 1995 as in previous years. Monthly and annual mean C0 2 concentrations (in the WMO 1993 mole fraction scale (X93)) are given in Table 2.1. These values are provisional, pending final calibrations of station standards. Preliminary selected monthly average C0 2 mixing ratios for the entire record through 1995 are plotted versus time for the four observatories in Figure 2.1. The C0 2 in situ systems operated during 1994 and 1995 at 94.0% and 91.2% at BRW; 94.2% and 95.1% at MLO; 91.0% and 78.7% at SMO; and 90.9% and 92.9% at SPO. The maximum percentage expected is 95.8% based on missing data due to reference gas calibrations during the year. The majority of the loss of data at SMO in 1995 was due to a failure in the C0 2 NDIR analyzer in November that lasted until late December. A new data acquisition and control system was installed at MLO in December 1995. This system uses a Hewlett-Packard Unix workstation for controlling not only the C0 2 NDIR measurements, but the CH 4 and CO in situ gas chromatograph systems as well. Data are downloaded from MLO to Boulder daily over the Internet, as well as recorded on optical disks at MLO for backup. New data 29 TABLE 2.1. Provisional 1994 and 1995 Monthly Mean C0 2 Mixing Ratios From Continuous Analyzer Data (micromol/mol, abbreviated as ppm, relative to dry air WMO X85 mole fraction scale) Month BRW MLO SMO SPO 1994 Jan. 361.83 358.01 357.00 355.48 Feb. 363.76 358.82 357.37 355.45 March 365.04 359.74 357.10 355.51 April 364.26 361.13 357.35 355.63 May 364.07 361.49 356.76 355.76 June 362.76 360.60 357.02 356.04 July 354.37 359.20 357.60 356.46 August 349.03 357.23 357.32 357.14 Sept. 350.41 355.44 357.33 357.52 Oct. 357.37 355.89 357.63 357.56 Nov. 360.80 357.42 358.16 357.52 Dec. 364.28 358.74 358.59 357.40 Year 359.83 358.64 1995 357.44 1975 1980 1985 1990 356.46 Jan. 364.49 359.74 358.54 357.22 Feb. 366.13 360.59 359.30 357.23 March 366.27 361.59 359.31 357.40 April 366.60 363.05 359.03 357.40 May 365.78 363.56 359.43 357.63 June 364.01 363.08 359.28 357.87 July 356.53 361.57 359.50 358.35 Aug. 351.49 358.91 359.31 358.78 Sept. 355.24 357.94 359.17 359.10 Oct. 357.90 357.78 359.47 359.29 Nov. 363.80 359.21 359.89 359.39 Dec. 366.94 360.45 360.15 359.40 Year 362.10 360.62 359.36 358.26 3/0 1 ' i ' ■ ' ■ i ■ ■ ■ ■ i . , , . 1 O Barrow fit ~ —A— Mauna Loo tin j 360 -+- Samoa □ South Pole *4p - 1 1 " 350 ] ? Jv 11 f A mMMT^] l! f — 340 ihmMm^n 330 i Mppn | - 3?0 - * 1 ■ i ■ 1995 Fig. 2.1. Preliminary selected monthly mean C0 2 mixing ratios expressed in micromol/mol at the four CMDL observatories acquisition and control systems will be installed at the remaining observatories during 1996. In addition to the new data system, the C0 2 NDIR analyzer was fitted with smaller optical cells, 60 mm in length compared with the original 180 mm length cells. The glass H 2 cryotrap was relocated between the inlet air pumps and the gas manifold with a smaller auxiliary cryotrap added in between the gas manifold and the NDIR analyzer. With this setup, the first cryotrap dried only the ambient air samples, and the second cryotrap dried the reference gases and the dried ambient air. The volume of gas that the reference gases need to flush away after each gas change was greatly reduced so that lower flow rates were possible. The flow rate was reduced to -150 cc min -1 from 300 cc min" 1 . 2.2.2. Flask Sample Carbon Dioxide Measurements Measurements of the distribution and variations of atmospheric C0 2 continued during 1994 and 1995 using samples collected throughout the CMDL global air sampling network. In January and February 1994, sampling began at Easter Island, Chile (29°09'S, 109°26'W; site code: EIC) and Ny-Alesund, Svalbard (78°54'N, 11°53'E; ZEP), respectively. The flask sampling at Easter Island is through the cooperation of the Chilean Meteorological Service. Ny-Alesund is a collaboration with the Stockholm University in situ C0 2 measurement program and is intended to study the North Atlantic/subarctic marine sink for C0 2 . In September 1994, flask sampling began near Ushuaia, Argentina (54°52'S, 68°29'W; TDF) in support of the new Global Atmosphere Watch (GAW) observatory. In October 1994, sampling was initiated at Constanta, Romania (44°10'N, 28 C 41'E; BSC) on the western shore of the Black Sea, and the sampling program on Terceira Island, Azores (38°46'N, 27°23'W; AZR) was revived after a 2-year interruption. In September 1995 flask sampling began at Assekrem, Algeria (23°11' N, 5°25'E; ASK) in cooperation with the GAW observatory at Tamanrasset, Algeria. Finally, in November 1995 CCG began receiving samples collected in the Negev Desert, Israel (31°08'N, 34°53'E; WIS) in cooperation with the Weizmann Institute of Science. These new sites are shown with the rest of the air sampling network in Figure 2.2. Annual mean mixing ratios for 41 sites for 1993, 1994, and 1995 are given in Table 2.2. The 1995 values are based on preliminary editing and data selection. Air samples were collected in evacuated flasks at 5 degree latitude intervals over the Pacific Ocean aboard the California Star (OPC) during 1993 through 1995. In 1995 sampling began on a second ship, the Brisbane Star (OPB). Annual averages calculated from merged data from both ships (POC) are given for 14 latitude intervals in Table 2.3. Flask samples were also collected from ships in the South China Sea (SCS). Annual averages for seven 3 degree latitude intervals are given in Table 2.4. The globally-averaged C0 2 growth rate determined from the air sampling network data is shown in Figure 2.3. The C0 2 growth rate declined from a high of =2.6 |imol (abbreviated ppm) per year in 1987 to a low of =0.6 ppm yr 1 in 1992. The growth rate in 1994 was above the 1981- 1995 average of =1 .4 ppm yr 1 , and in 1995 the growth rate was still above the decadal average. 30 90°N 60°N 30°N o°- 30°S 60°S 90°S 90°N 60°N -30°N 30°S -60°S i 1 1 ■ r 100°E 140°E 180° 140°W 100°W 60°W 20°W 20°E 60°E 1 00°E 90°S Fig. 2.2. Network of continuing measurements by the Carbon Cycle Group. A two-dimensional model was developed to use the flask C0 2 data, together with measurements of the l3 C/ 12 C ratio in CO2 from the same air samples, to partition CO2 sources and sinks into terrestrial and marine components as a function of latitude [Ciais et al., 1995a]. An application of this model to data through 1993 attributed a large fraction of the northern hemisphere sink to the terrestrial biosphere [Ciais et al., 1995b]. This is an important result because it is not known which processes account for this sink and also because carbon stored as biomass has the potential to be returned to the atmosphere on short time scales. A preliminary application of the model through 1995 shows that the total global C0 2 sink in 1992 was a factor of 2 larger than in 1995. This analysis also showed significant interannual variations in both the marine and terrestrial components of this sink. 2.2.3. Carbon Calibrations Dioxide Reference Gas The calibration of C02-in-air reference gas tanks continued in 1995; 407 tanks were calibrated using the NDIR analyzer. All C0 2 -in-air reference gas tanks used by CMDL are filled with clean dry ambient air from Niwot Ridge, Colorado, in aluminum tanks. A manometric system was developed for performing primary calibrations of the absolute mole fraction of C0 2 in a carrier (air) gas. The manometric apparatus itself is principally made of glass. It consists essentially of a 6-L glass flask connected by means of a manifold to a 10-mL glass small volume. A pressure gauge of quartz spiral Bourdon tube type as a primary manometer in the manometric system is used to measure the C0 2 and the carrier gas pressures precisely. The apparatus is enclosed in an oven. The temperature of the oven is uniform and controlled to an accuracy of 0.0 1°C during the calibration process. The quartz spiral pressure gauge is regularly calibrated with a dead-weight pressure calibration tester. To begin the manometric calibrating process the glass manometric chamber, including the 6-L large volume, the manifold, and 10-mL volume, are evacuated to a residual pressure of less than 1 millitorr. A sample of air from a cylinder to be analyzed is dried at -70°C to remove water vapor and then fills the evacuated glass chamber to the ambient pressure. After the sample air in the chamber has come to equilibrium, the temperature is measured by platinum resistance thermometers, and pressure is measured by the quartz spiral gauge. The sample air from the chamber is then slowly pumped out through two liquid nitrogen traps, freezing out C0 2 , N 2 0, and residual water vapor. Upon completion of the extraction, the C0 2 frozen in the traps is dried with a dry ice-alcohol mixture and then transferred to the small 10 mL volume by placing liquid nitrogen around it. After the 10-mL small volume containing the collected pure C0 2 (and N 2 0) is thawed, the temperature and pressure are continuously measured 31 TABLE 2.2. Provisional 1993-1995 Annual Mean C0 2 Mixing Ratios From Network Sites TABLE 2.3. Provisional 1993-1995 Annual Mean C0 2 Mixing Ratios from Pacific Ocean Cruises Code CO, (ppm) Station 1993 1994 1995 ALT Alert, N.W.T., Canada ASC Ascension Island AZR Terceira Island, Azores BAL Baltic Sea BME Bermuda (east coast) BMW Bermuda (west coast) BRW Barrow, Alaska BSC Constanta, Romania CBA Cold Bay, Alaska CGO Cape Grim, Tasmania CHR Christmas Island CMO Cape Meares, Oregon CRZ Crozet Island EIC Easter Island, Chile GMI Guam, Mariana Islands GOZ Gozo Island, Malta HBA Halley Bay, Antarctica HUN Hegyhatsal. Hungary ICE Vestmanaeyjar, Iceland IZO Izana Observatory, Tenerife KEY Key Biscayne, Florida KUM Cape Kumukahi, Hawaii MBC Mould Bay, Canada MHT Mace Head, Ireland MID Midway Island MLO Mauna Loa, Hawaii NWR Niwot Ridge, Colorado PSA Palmer Station, Antarctica QPC Qinghai Province, China RPB Ragged Point, Barbados SEY Mahe Island, Seychelles SHM Shemya Island, Alaska SMO American Samoa SPO South Pole, Antarctica STM Ocean Station M SYO Syowa Station, Antarctica TAP Tae-ahn Peninsula, S. Korea TDF Tierra del Fuego, Argentina UTA Wendover, Utah UUM Ulaan Uul, Mongolia ZEP Ny-Alesund, Svalbard 357.7 355.8 [] 359.9 356.8 357.3 358.2 357.8 354.5 357.4 358.5 355.3 356.6 [] 355.1 [] 357.3 357.5 358.4 357.1 357.8 356.7 357.5 356.9 357.4 355.1 357.3 356.7 356.0 357.7 355.6 354.8 357.5 354.5 360.4 357.1 359.8 357.3 [] 361.9 358.8 359.8 359.6 [] 359.1 356.1 [] 361.7 356.9 355.7 358.5 359.6 356.9 362.2 359.0 358.6 359.3 359.1 359.9 358.6 359.2 358.5 359.5 356.4 359.3 358.0 356.5 360.6 357.4 356.2 359.2 356.1 361.2 [] 361.2 359.3 359.2 361.1 359.2 359.5 364.4 361.3 361.0 361.9 364.6 361.4 357.9 [] [] 357.9 357.6 360.6 362.2 358.1 366.6 360.1 361.4 362.1 360.9 361.3 360.7 360.9 360.6 361.2 358.1 [] 360.2 358.1 360.9 359.2 357.7 360.4 358.1 363.6 [] 361.2 360.3 361.0 Square brackets indicate insufficient data to calculate annual mean. The 1994 and 1995 annual means have been adjusted upward by 0.25 ppm to correct for a systematic loss of CO ; in the flask analysis apparatus. while equilibrium is reached. Because the volume ratio of the small and the large volumes is known accurately, the molar ratio of the C0 2 in the original air sample can be calculated with the virial equation of state, taking real gas compressibility into account, and correcting for the N 2 contribution. From December 1995 to February 1996, the C0 2 concentrations of three cylinders with C0 2 -in-air mixtures were determined by the manometric calibration system. The results of the tests are presented in Table 2.5. For C0 2 (ppm) Latitude 30°N 25°N 20°N 15°N I0°N 5'N Equator 5°S 10"S 15°S 20"S 25°S 30"S 35°S 1993 1994 1995 357.7 359.4 360.8 357.7 359.5 361.4 357.1 359.6 361.0 357.6 359.7 360.7 357.8 359.2 361.1 357.7 359.5 361.0 357.5 359.1 360.6 357.0 358.9 360.4 356.7 358.3 360.2 356.2 357.8 359.5 355.8 358.1 359.0 355.4 357.6 358.5 355.4 356.9 358.4 355.5 357.0 358.6 TABLE 2.4. Latitude Provisional 1993-1995 Annual Mean C0 2 Mixing Ratios from South China Sea C0 2 (ppm) 21°N 18'N 15°N 12"N 9°N 6°N 3'N 1993 1994 1995 361.1 360.4 362.0 360.2 360.3 362.2 357.8 360.2 362.3 359.9 360.0 361.2 357.9 359.9 362.3 357.9 359.8 361.5 359.2 359.8 361.1 n 1 1 1 1 1 1 1 I i r j i i i u 82 83 84 8586 87 8889909192 93949596 Fig. 2.3. Global C0 2 growth rate. 32 TABLE 2.5. Results of Tests Using Manometric Calibration System Date Cylinder Serial No. Manometric C0 2 Average Standard Deviation NDIR Difference (NDIR-MANO) Dec. 6, 1995 71568 386.33 Dec. 6, 1995 71568 386.30 Dec. 8, 1995 71568 386.37 Feb. 1, 1996 56797 352.67 Feb. 2, 1996 56797 352.78 Feb. 5, 1996 56797 352.83 Feb. 13, 1996 56797 352.62 Feb. 16, 1996 56797 352.77 Feb. 17, 1996 56797 352.77 Feb. 19, 1996 56797 352.76 Feb. 20, 1996 56797 352.62 Feb. 20, 1996 56797 352.77 Feb. 21, 1996 56797 352.63 Feb. 21, 1996 56797 352.89 Feb. 23, 1996 114997 314.97 Feb. 24, 1996 114997 314.95 Feb. 26, 1996 114997 315.02 Feb. 28, 1996 114997 314.90 Feb. 28, 1996 114997 315.02 Feb. 29. 1996 114997 315.08 386.33 0.035 386.25 -0.08 352.74 0.090 352.77 0.03 314.99 0.063 315.05 0.06 C0 2 concentrations in umol/mol. comparison, the CO2 mole fractions measured by a NDIR analyzer using reference gases calibrated by the Scripps Institution of Oceanography (SIO) are also shown in the table. The reproducibility of the manometric system indicated in Table 2.5 as the standard deviation is about ±0.06 u.mol for a total of 20 measurements. The largest mean difference of measurements between the NDIR and the manometric system is 0.08 umol for the three C0 2 -in-air mixture cylinders. 2.2,4. Measurements of Stable Isotopes of CO z Since 1990, the Stable Isotope Laboratory at INSTAAR has been measuring the stable isotopic composition of C0 2 from flask samples from the CMDL global air sampling network. The natural ratio of l3 C to ,2 C is about 1.1% everywhere, but biogeochemical processes (such as photosynthesis or atmosphere-ocean exchange) can sustain small but readily measurable differences in that ratio between different carbon reservoirs. For example, plants discriminate against 13 C during photosynthetic uptake, therefore the 13 C/ 12 C ratio in plant carbon (and, by derivation, in soils and fossil fuels) is depleted relative to the atmosphere, typically by about 20%o (per mil, or parts per thousand) — which in turn leaves the atmosphere subtly enriched in 13 C. Observing such a 13 C signature allows exchanges of C0 2 with the biosphere to be distinguished from oceanic fluxes because the latter do not carry a significant isotopic signature [e.g., Keeling et al„ 1995]. The 18 composition of atmospheric CO? ultimately derives from its equilibration with liquid water, providing a link between the global carbon and hydrologic cycles. For example, C0 2 exposed to water within the leaves of plants, but diffusing out of the leaf before being incorporated, carries the isotopic signature of leaf water back to the atmosphere. Because C0 2 "remembers" the 18 signature of the water reservoir it has most recently visited, this tracer may prove to be useful in quantifying the gross annual uptake of C0 2 by photosynthesis and its release by respiration. INSTAAR currently measures 8 13 C (the normalized difference between the isotopic ratios of a sample and standard) and 8 18 in C0 2 for almost all of the CMDL network flasks, having begun with a selection of only six sites and two ships in 1990. The growth of the effort, reflected by the number of sites and flasks measured each year, is shown in Figure 2.4. Each measurement is made by first cryogenically extracting C0 2 from about 750 standard cm- 1 of dried air, then measuring the relative abundance of isotopic species of masses 44, 45, and 46 using a triple-collector isotope-ratio mass spectrometer [Trolier et al., 1996]; precisions of 0.03% o and 0.06% o are obtained for 8 I3 C and 8 I8 respectively. Small numerical corrections account for the presence of N 2 trapped with C0 2 and for the presence of isotopic species including 17 0. The isotopic data are fully integrated into the Carbon Cycle Group's trace gas data base. A sample of the isotope data is given in Figure 2.5, which shows time series of C0 2 mixing ratio, S 13 C, and 8 18 from Barrow, Alaska, from 1990 through 1995. There is a striking anticorrelation between the seasonal cycles of mixing ratio and 8 I3 C, reflecting the strong influence of the annual cycle of photosynthesis and respiration imposed on the atmosphere by the terrestrial biosphere in the northern hemisphere. Whereas the mixing ratio shows an increasing long-term trend due to the use of fossil fuels, the trend of 8 13 C is to lighter values, reflecting the depletion in l3 C of fossil fuel relative to the atmosphere. The seasonal cycle of 8 18 lags behind CO? and 8 I3 C, and while its interannual variability shows no steady trend, it can change its level dramatically from year to year, most likely because of the large exchanges of CO? between biosphere and atmosphere that are subject to efficient oxygen isotope exchange. 33 60 40 20 - 6000 4000 2000 M NOAA I cu I @ u NOAA (b) CU O o u 100 80 60 40 - 20 6"C <5"0 (c) t 1990 991 992 1993 Year Fig. 2.4. Statistics of the isotope measuring effort. The extent of the NOAA C0 2 monitoring program is shown for comparison. Solid bars represent land sites, hatched bars represent latitude bands from shipboard sampling, (a) Number of sites measured during each year, (b) Number of flasks analyzed each year, (c) Percentage of "good" flask pairs for 5 13 C and 8 18 0. I Q Q O o Point Barrow 380 ©Retoinec! + Non-bockground 4 * ft. t 340 1 *l * t Try \^f <0 o en -1.0 - -3.0 Fig. 2.5. Time series of C0 2 (upper panel), 8 13 C of C0 2 (middle panel), and 8 18 (lower panel) from Point Barrow, Alaska. The INSTAAR isotope data were recently described in detail [Trolier et al., 1996]. The INSTAAR S 13 C time series, though beginning only in 1990, were used in concert with the longer 8 13 C time series from Cape Grim, Australia, obtained by CSIRO, to identify a global flattening of the long-term 5 13 C trend during 1988-1992 [Francey et al., 1995a]. The decadal average trend observed during the 1980s, about 0.025%o yr l , was apparently offset during these years by anomalously high uptake of C0 2 by the global biosphere. Similarly, the INSTAAR 8 13 C data, supplemented by CSIRO data from the southern hemisphere, definitively identify a strong northern hemisphere biospheric sink equivalent to nearly half the annual anthropogenic source during 1992 and 1993 [Ciais et al., 1995b]. Interpretive work using the 8 18 data is underway. In addition to these scientific analyses, the measurements are actively intercompared with other atmospheric monitoring laboratories measuring C0 2 isotopic composition [Francey et al., 1995b; Gaudry et al., 1996]. INSTAAR recently obtained a more precise isotope- ratio mass spectrometer, a VG Optima, for analyzing the CMDL flasks. The instrument is currently being tested and it will come on-line for flask analysis during 1996. This instrument will be devoted entirely to analysis of atmospheric samples and will allow us to focus more attention on calibration. It is expected that the Optima will improve the analytical precision by about a factor of 3. 2.2.5. The Airkit Sampler Field testing of a new prototype air sampling apparatus began at SMO in September 1994 and Cape Kumukahi, Hawaii (KUM) in May 1995. The new Airkit (Air Kitzis sampler) differs from the currently used MAKS (Martin and Kitzis Sampler) in two important ways: (1) It has a thermoelectrically cooled condenser to remove water vapor from the air stream, and (2) It has a microprocessor to control the sampling process so that collecting the sample is more automated and less subject to operator error. The effect of drying the air sample is most dramatic for the measurement of 18 0/ 16 in C0 2 (Figures 2.6 and 2.7). In samples collected at humid, tropical locations without drying, the 18 0/ l6 measurements are highly variable and consistently more depleted in 18 due to the exchange of oxygen atoms between C0 2 and H 2 molecules. It was established through systematic tests at INSTAAR [Gemery, 1993] that the exchange takes place during storage in the flasks when the relative humidity of the air sample is above 50%. Overlapped sampling with the Airkit and MAKS at SMO and KUM shows that this effect is eliminated with the Airkit and that the measurement of other species is not affected by the drying (Table 2.6). The pair agreement improves from 0.73% c (la) to 0.09%c. 2.2.6. Calibration of Measurements of Stable Isotopes of C0 2 The INSTAAR stable isotope data are reported as isotopic composition relative to VPDB-C0 2 for both 8 11 C and 8 I8 0. Calibration of this record has two distinct facets. The first relies on comparatively precise intercomparisons of samples of C0 2 extracted from air. Carbon dioxide from individual flask samples is always 34 o -2 -4h -6 ♦ AIRKIT + MAKS TABLE 2.6. Comparison of Airkit to MAKS Sampler 1993 1994 1995 YEARS 1996 Fig. 2.6. Oxygen- 18 in flask samples from Cape Matatula, Samoa. The majority of the "wet" samples were rejected due to poor pair agreement. The few fortuitously retained pairs tend to be isotopically "light." Since samples have been dried with the Airkit, however, a first glimpse of the true 8 18 signature of C0 2 at equatorial latitudes from the CMDL network has been seen. compared with C0 2 from a "working reference" cylinder. The isotopic composition of the working reference cylinder itself is currently tracked on a monthly basis by comparison with a suite of secondary reference cylinders. The second facet of calibration consists of the comparison of the isotopic scale established by the reference cylinders to accepted international standards ("absolute" calibration). These measurements require the comparison of CO2 derived from different materials using different preparation systems and to date have been subject to larger uncertainties. Both carbonate standards (NBS-19, NBS-20, and INSTAAR laboratory standards) and water standards (V-SMOW, SLAP, and laboratory standards) have been used for absolute calibrations. Comparisons among the reference cylinders, though few in the early years of the program, have expanded to provide a fairly strong constraint on the consistency of the 4 2 ■ 1 1 1 x t ..„....■.. -2 -4 -6 -8 -in ♦ AIRKIT + MAKS 1 1 1 1993 1994 1995 YEAR 1996 Fig. 2.7. Oxygen-18 in flask samples from Cape Kumukahi, Hawaii. The comparison between Airkit and MAKS is very similar to Samoa. Species No. Pairs Airkit Minus MAKS Site Average Standard Deviation Units KUM CO, 31 -0.07 0.40 PPm SMO co 2 4X -0.04 0.18 ppm KUM CH 4 33 0.19 1.99 ppb SMO CH 4 53 0.42 2.35 ppb KUM CO 28 -2.01 2.49 ppb SMO CO S3 0.05 1.19 ppb KUM 8'3C 29 0.02 0.05 permil SMO 5"C 47 0.02 0.14 permil KUM 6 ls O 7 0.67 0.82 permil SMO 8 18 15 1.08 1.06 permil Summary of the differences between retained pairs for simultaneous Airkit and MAKS samples. There are no significant differences between Airkit samples and the MAKS samples except for 8 I8 0, where the retained MAKS pairs are considerably depleted in l8 at both KUM and SMO. working reference gas scales for 8 I3 C and 8 18 0. Working reference gas cylinders are used for up to 3 years; transitions between working reference cylinders provide the unfortunate possibility of a step shift in calibration. Such shifts could be too subtle to detect by too-seldom and too-noisy comparisons with carbonates and waters but can be tracked by other cylinders (provided, of course, that the suite of cylinders is not drifting in parallel). Figure 2.8 shows a summary of the calibration data available for the INSTAAR isotope data for 8 13 C and 8 18 0. The central feature of these plots are the scales defined by the sequence of working reference gases shown by solid lines plotted for each cylinder during its lifetime. This scale determines the values that are assigned to individual flask samples. Dotted lines represent the cylinders' values outside their period of use as the working reference. The relative values of any two working reference cylinders are determined by extensive inter- comparison preceding the transition. Also shown are the values for the working cylinders determined from other reference gases (open symbols) and carbonate or water standards (closed symbols); error bars (la) are shown where more than one determination is made in a month. Uncertainties clearly persist, particularly for the absolute assignment of the 8 18 scale. The assigned scales are to some extent based on subjective evaluations of the reliability of different calibration methods. However, drifts and step shifts within the working reference scales seem unlikely beyond (pessimistically) 0.02U%c for 8 ,3 C and0.04% c for8 18 O. 2.3. Methane 2.3.1. In Situ Methane Measurements Quasi-continuous in situ measurements of atmospheric CH 4 continued at MLO and BRW. Details of the measurement techniques and analysis of the in situ data through early 1994 were published in late 1995 [Dlugokencky et al., 1995]. Daily averaged CH 4 mole fractions (in nanomol/mol or 10" 9 mole/mole; abbreviated ppb) are plotted in Figure 2.9 for BRW (a) and MLO (b). 35 C CO -7.4 ■7.6 ■7.8 ■8.0 ■8.2 ■8.4 0.5 ■0.5 ■1.5 ■2.5 desi-002 o-r _|| desi-001 ■UO-CO ,^ , J ^ _ oo , t edda-001 thor-001 tnor-001 • ethl-00 y aBj ff^r iggjgg^l I " desi-002 lucy-001 riki-00 "rf" eddo-001 thor-001 1990 1991 1992 1993 1994 1995 Year Fig. 2.8. Calibration of the NOAA-CU data set. The upper panel shows calibrations for 8 13 C, the lower for 5 18 0. Reference gases are identified by cylinder name. Monthly means of calibrations of reference gases are plotted using open symbols; where more than one determination was made in a month, error bars are plotted at twice the standard deviation of the monthly values. Mean values for working reference gases are plotted as thick solid lines, for secondary reference gases as thin lines. Calibrations of the working reference scale using primary isotope reference materials are plotted as solid symbols (NBS-19, squares; NBS-20, diamonds; SMOW, circles). The data have been edited for instrument malfunction using a rule-based expert system [Masarie et al., 1991], but were not selected for meteorological conditions. High CH 4 values at BRW are due to emissions from local sources. Limitations of the unselected data sets have been discussed previously [Dlugokencky et al., 1995]. Previously it was reported that the precision of the measurements (-0.2%) was limited in part by variations in laboratory temperature which affects the flow rate of H 2 to the FID [Peterson and Rosson, 1993]. On December 1, 1995, a new analytical system was installed at MLO ushering in a new era of high precision in situ CH 4 measurements at MLO. Main components of the system are an HP 6890 GC with FID, an HP 35900E analog-to- digital converter (A/D), a temperature controlled box for the sample valve, and a HP UNIX workstation. A similar system will be installed at Barrow during Spring 1996. The gas chromatography has not changed significantly from what was used previously, except that the carrier gas was switched to N 2 to improve sensitivity. Two columns are used to separate CH 4 from air, and flame ionization is used for detection. Column head pressure and flow rates a n Q X 2000 900 1800 CL Q_ r o 1800 750 700 -H h— i h- i i I i i _, , , , ■_ y 1994 1995 YEAR Fig. 2.9. Daily mean CH4 mixing ratios in 10 -9 mole/mole (abbreviated ppb) for (a) BRW and (b) MLO for 1994 and 1995. The data have not been selected for meteorological conditions, but have undergone a quality control step to ensure that the analytical instrument was working optimally when they were obtained [Masarie et al.. 1991], for the FID gases are controlled electronically by the GC. The signal from the FID is amplified by an electrometer and sent to the A/D. Previously the A/D was included in a stand-alone integrator. The new HP 35900E A/D is 24-bit (versus 16 bit for the integrator), so it does not limit the measurement precision. Integration is now done on the UNIX workstation using an algorithm developed by SIO and incorporated into a program developed by the Carbon Cycle Group called GCPLOT. This program allows integration and display of chromatograms, and it is a powerful diagnostic that can be used to troubleshoot problems with the CH 4 chromatography and GC system. This integration system is also paperless; about 1 -month's worth of chromatograms are stored on the workstation hard disk, and these can be displayed on the computer monitor with GCPLOT. A typical chromatogram is shown in Figure 2.10. The peak at about 78 seconds is the air disturbance. The CH 4 peak response (at retention time = 124 seconds), from the baseline to the top of the peak, is -16.8 mV. Peak-to-peak noise is -8 u.V. Previously, peak height was used to calculate CH 4 mole fractions since height resulted in about a factor of 3 better precision than peak area response. With the new integration algorithm, peak area yields slightly better precision than height; therefore, peak area is now being used as the quantitative measure of CH 4 peak response. Using area is preferable to height because it gives a linear response over a larger range of mixing ratios. The mole fractions are calculated as before; the peak area 36 o o 4. Ox 3.5x10 3.0x10 2.5x10 60 80 100 120 140 160 180 200 Time (seconds) Fig. 2.10. Typical CH4 chromatogram from MLO obtained with the new analysis system. A/D sampling rate was 10 Hz. On the y-axis, there are 10 5 counts mV 1 . Signal-to-noise is -2000, based on a peak height of 16.8 mV and peak-to-peak noise of ~8uV. The retention time for CH 4 is 124.3 seconds, and the full- width-at-half-max is 8 seconds. from the sample is ratioed to the average peak area of the bracketing standard gas injections. This ratio is then multiplied by the assigned value for the standard gas cylinder. By only using the injections of standard gas, this calculation can be used to assess the instrument precision as described in the following paragraph. The preceding improvements have lead to an overall improvement in precision at MLO of a factor of 4. Typical relative precision is 0.04 to 0.07% (or <1 ppb CH 4 for ambient levels of about 1700 ppb). In Figure 2.1 1, relative differences between measurements of standard gas and the assigned value for the standard gas cylinder ("Relative 0.10 Jn° 0.05 0.00 -0.05 -0.10 2 10 12 14 Hour 16 18 20 22 24 Fig. 2.11. Relative measurement precision, assessed as the difference between measurements of standard gas and the assigned value of the standard gas cylinder, plotted for a 24-hour period. The relative instrument precision on this day, based on la for each measurement of reference gas, was 0.03% (plotted as the dashed lines). This corresponds to a precision, in mole fraction, of ±0.6 ppb for each measurement. Precision") are plotted for a 24-hour period. The relative precision for this day (assessed as la) was 0.03% (0.6 ppb). The new system is controlled by a program run on the UNIX workstation. This program chooses between ambient and standard gas flows from the stream selection valve, switches the gas sample valve to start the run, and records the digitized chromatogram. A VXI bus acts as the interface between the UNIX workstation and other system components. Various other programs that can be used to look at the results are also available at the workstation. 2.3.2. Discrete Sample Measurements of Methane During 1994-1995, the determination of the global distribution of atmospheric CH 4 continued from 46 sampling sites of the Carbon Cycle Group's cooperative air sampling network. Provisional annual mean values for 1994-1995 are given in Table 2.7. The effects of the eruption of Mt. Pinatubo on the growth rates of trace species such as CH 4 , CO2, CO, and N 2 still remain an area of great interest to our group. Studies of perturbations in growth rate that are associated with a specific event such as the eruption can be a useful tool in understanding the trace gas budgets. The eruption of Mt. Pinatubo on June 15, 1991, injected 20 Mt S0 2 and 3-5 km 3 of ash into the upper troposphere and lower stratosphere, and CH 4 and CO mixing ratios in the tropics immediately increased. The increased growth rates were short-lived as CH 4 [Dlugokencky et al., 1994a] and CO [Novelli et al., 1994] growth rates showed dramatic decreases later during 1992 and 1993. In Figure 2.12a, CH 4 zonal means for the latitude zone 30-90°S are plotted (open triangles) along with a function fitted to the zonal means (dashed line) of the form: f(t) = a, + a 2 1 + a 3 1 2 + ^[a 2l+2 sin(27rit) + a 2i+3 cos(27rit)]. ( 1 ) i = l Equation (1) is used to approximate (or model) the average trend and seasonal cycle for atmospheric CH 4 . Starting in late 1991, there is a significant departure of the "model" from the zonal means. The solid line is the deseasonalized trend (see Dlugokencky et al., 1994b for details of the curve fitting process). Its derivative, the instantaneous CH 4 growth rate, is shown in Figure 2.12b. The largest perturbation in CH 4 growth rate observed in this time series was during late- 199 1 and early 1992. The CH 4 growth rate is due to a relatively small imbalance between sources and sinks; therefore, the perturbation in 1991 could be due to either a change in one or more sources or a change in the sink. The major sink for CH 4 is reaction with hydroxyl radical OH + CH 4 -» H 2 + CH 3 . (2) In the clean marine troposphere, most OH formation is initiated through photolysis of O3 to give electronically excited oxygen atoms O3 + hv (330 > X > 290 nm) -* O('D) + 2 (3) 37 TABLE 2.7. Provisional 1994 and 1995 Annual Mean CH 4 Mixing Ratios From the Air Sampling Network Code Station 1994 CH 4 (ppb) 1995 CH 4 (ppb) ALT Alert. N.W.T., Canada 1809.8 1811.3 ASC Ascension Island 1684.0 1690.4 AZR Terceira Island, Azores [] 1783.2 BAL Baltic Sea 1828.6 1853.7 BME Bermuda (east coast) 1773.1 1780.5 BMW Bermuda (west coast) 1765.3 1771.0 BRW Barrow, Alaska 1821.4 1822.3 CBA Cold Bay, Alaska 1801.9 1804.2 CGO Cape Grim, Tasmania 1671.8 1679.8 CMO Cape Meares, Oregon 1788.5 [] CRZ Crozet Island [] 1679.3 GMI Guam, Mariana Islands 1731.3 1741.2 GOZ Dwejra Point, Gozo, Malta 1798.2 1804.2 HUN Hegyhatsal, Hungary 1853.3 1870.7 ICE Heimaey, Iceland 1799.1 1806.8 ITN WITN, Grifton, N. Carolina 1817.1 1817.0 IZO Izana Observatory, Tenerife 1754.0 1757.2 KEY Key Biscayne, Florida 1751.1 1765.1 KUM Cape Kumukahi, Hawaii 1753.7 1756.8 LEF WLEF, Park Falls, Wisconsin [] 1825.4 MBC Mould Bay, Canada 1812.0 1816.8 MHT Mace Head, Ireland 1793.2 1792.3 MID Midway Island 1763.5 1772.8 MLO Mauna Loa, Hawaii 1736.7 1739.7 NWR Niwot Ridge, Colorado 1764.9 1774.0 PSA Palmer Station, Antarctica 1672.4 1679.1 QPC Qinghai Province, China 1777.8 1782.2 RPB Ragged Point, Barbados 1740.5 1740.2 SEY Mahe Island, Seychelles 1696.3 1700.7 SHM Shemya Island, Alaska 1801.4 1804.8 SMO American Samoa 1679.3 1684.8 SPO South Pole, Antarctica 1671.2 1678.1 STM Ocean Station M 1803.2 1807.0 SYO Syowa Station, Antarctica 1671.5 1678.9 TAP Tae-ahn Peninsula, S. Korea 1830.5 1821.3 UTA Wendover, Utah 1779.1 1783.7 UUM Ulaan Uul, Mongolia 1802.1 1803.0 ZEP Ny-Alesund, Svalbard 1806.1 1815.2 Square brackets indicate insufficient data to calculate annual mean. Most O('D) is quenched to ground state O atoms, but a small fraction reacts with water, OCD) + H^O -> 20H (4) The photolysis rate coefficient for formation of O('D), jOjfOCD)), is a function of the actinic flux in the appropriate wavelength region, the ozone cross section, and the quantum yield (for O('D) formation). Anything that affects the flux of radiation in the wavelength region 330 > I > 290 nm, also affects the CH 4 sink. The large increase in CH 4 growth rate in 1991 is consistent with decreased actinic flux in the wavelength region 290-330 nm due to UV absorption by SO2 and enhanced scattering by sulfate aerosols. In Figure 2.13, the change in j0 3 (0('D)) calculated with a radiative transfer model is plotted. Initially, direct absorption of UV radiation by S0 2 lead to a 1 2% decrease in j0 3 (0( ' D)). 84 85 86 87 88 89 90 91 92 93 94 YEAR Fig. 2.12. (a) Zonally-averaged CH 4 mixing ratios for 30-90°S (symbols). The dashed line is a function (Eq. (1)) fitted to the zonal means to approximate the long-term trend and average seasonal cycle. The solid line is the deseasonalized trend; it is a combination of the polynomial in Eq. (1) and the result of the 650-day cutoff filter, (b) Instantaneous, smoothed growth rate for atmospheric CH 4 in the latitude zone 30-90°S. The curve is calculated as the derivative of the solid curve in (a). fr? L :> - ~\ - -5 - /""' S0 2 & Aerosol 10 ■ / Aerosol Only 15 - 1 199' I 992 YEAR Fig. 2.13. Relative change in j0 3 (0('D)) after the eruption of Mt. Pinatubo. The solid line includes the effects of direct absorption by S0 2 and scattering by sulfate aerosol; the dotted line includes aerosol only. The change is plotted relative to a 10- year climatological background. 38 This effect was relatively short-lived due to the short lifetime (-30 days) for SC>2- Later, UV scattering from sulfate aerosol produced by oxidation of the S0 2 maintained lower than normal values for j for more than 1 year after the eruption. It is suggested that the decreased UV flux led to a decreased steady-state concentration of atmospheric OH in the tropics and midlatitudes of the southern hemisphere, and this led to the observed perturbation in CH 4 growth rate. Of more general interest are the far reaching effects of the eruption of Mt. Pinatubo on trace gas budgets. In the case of CH 4 , it has been suggested previously that Mt. Pinatubo resulted in initially enhanced growth rates during 1991 and early 1992. Cooler temperatures resulting from the eruption [Dutton and Christy, 1992] also likely led to decreased CH 4 emissions from natural wetlands in the northern hemisphere [Hogan and Harriss, 1994], which in turn may have been largely responsible for the large observed decrease in CH 4 growth rate during late- 1992 and 1993 in the high northern latitudes. This is consistent with isotopic measurements of COi that suggest that the biosphere was a larger than normal sink for fossil C0 2 during 1992 and 1993 through either increased photo- synthesis or decreased respiration [Ciais et al., 1995b], either of which could result from short-term variations in temperature or precipitation as a result of the eruption. 2.3.3. Measurement of 13 C/ 12 C of Methane Although many sources of CH 4 have been identified, the uncertainty in individual source terms remains large. In order to explain trends in the CH 4 growth rate, such as the period of almost no growth in 1992 and 1993 [Dlugokencky et al., 1994a,b] a more precise under- standing of the CH 4 budget is needed. The global measurement of the stable carbon isotopes of CH 4 (8 I3 C) afford an excellent means of furthering our understanding of the CH 4 budget. The three primary processes that produce CH 4 (bacterial fermentation, fossil fuel extraction, and biomass burning) all have different characteristic isotopic "signatures." Thus, global measurement of 8 13 C used together with a transport and chemistry model will allow for a more accurate characterization of sources than is currently possible. A system is under development for the automated analysis of small (20 mL) air samples for 8 13 C. The technique employed is gas chromatography coupled with isotope-ratio mass spectrometry. Methane is chromatographically extracted from air, cryofocused, combusted to produce CO2, and then admitted to the mass spectrometer. The total analysis time, including reference gas analysis, is less than 30 minutes per sample. The automation, small sample size, and short analysis time are key design elements so that these isotopic measurements may be easily incorporated into our cooperative air sampling network. For our sample, the shot-noise limited precision would be 0.01%c; therefore, the goal of a precision of 0.1%c is attainable even with such a small sample size. To date, our best precision for five replicate samples of air from Niwot Ridge is 0.1 6%c (one standard deviation) (Figure 2.14). (5 13 C of Metharie From Niwot Ridge CD CD 0_ en o O cr> c c c D a> > o CD cr o pi <0 -4 1 . | i , , , , 1 1 -6 - - -8 - O O -10 O V O -12 - - (7 = 0.16 Per Mille ■ -14 - -16 1 1 1 1 1 1 1 I 1 ■ ' 2 4 6 Sample Number Fig. 2.14. Reproducibility of repeated measurements of 13 C of methane in the same air. 2.4. Carbon Monoxide 2.4.1. In Situ Carbon Monoxide Measurements In situ measurements of CO continued at BRW and MLO during 1994 and 1995. For the analysis, a Reduction Gas Analyzer (RGA) (Trace Analytical, Inc.) was used. This measures CO using the gas chromatography-mercuric oxide reduction technique (previously described in Peterson and Rosson, 1993). The instruments operating at both observatories are identical and provided CO concentrations for four to five air samples per hour. The CO content of air samples was quantified by comparison to standards that reflected the range of concentrations seen at each site: 80 to 220 ppb at BRW and 60 to 180 ppb at MLO. All standards were referenced to the CMDL CO reference scale 39 [Novelli et ai, 1991]. To account for a nonlinear detector response common to the RGAs, a 3-point linear calibration (three standards) was used. This approach fits a linear regression to the two standards closest in instrument response to that of the sample, the regression coefficient, then used to calculate the sample CO mixing ratio. Preliminary CO hourly-average mixing ratios measured at BRW and MLO during 1994 and 1995 are presented in Figure 2.15. These data have not been filtered for instrument performance or selected for background conditions. Work is currently underway to develop an expert system, based upon chromatographic parameters, that will automatically identify and flag periods when the instrument was not operating satisfactorily. The unselected time series, show features of the local and regional atmosphere. The timing of the seasonal cycles agrees well with that previously reported at these sites [Seiler et al., 1976; Novelli et al., 1992]. Maximum CO mixing ratios occur in late winter/early spring and the minimum occurs in summer. Periods of low variability are interrupted by short-term increases or decreases. These events reflect both the impact of local sources and the transport of air parcels from other locations. The annual mean CO mixing ratio determined from the in situ measurements made at BRW during 1994 and 1995 were 141.9 and 138.6 nanomol/mol, abbreviated as ppb, respectively. The annual means at MLO were 88.9 and 88.4 ppb. Breaks in the time series of about 2 weeks extent, occurred at MLO in 1995 due primarily to problems related to data storage. In spite of the high frequency variation seen in the in situ record, the annual average CO mixing ratios agree well with those determined from weekly flask samples that are collected to represent background conditions (Table 2.8). Comparison of CO mixing ratios determined using the in situ measurements to those measured from weekly flask samples provide a means to assure the quality of the former. There is strong confidence in the flask measurements because CMDL has better control over the characteristics of the analytical system and the stability of the CO standards used for flask analysis. Figure 2.16 compares CO mixing ratios measured in weekly flask TABLE 2.8. Preliminary 1994 and 1995 Mean CO Mixing Ratios From Land Sites Station Annual Mean CO (ppb) Code 1994 1995 ALT Alert, Canada 140.6 126.4 ASC Ascension Island 74.0 74.0 BAL Baltic Sea 177.2 175.7 BME Bermuda (East) 126.1 122.4 BMW Bermuda (West) 124.0 117.4 BRW Pt. Barrow, Alaska 141.6 131.3 CBA Cold Bay, Canada 139.5 126.5 CGO Cape Grim, Tasmania 51.3 51.7 CHR Christmas Island 73.9 [] CMO Cape Meares, Oregon 151.0 [] EIC Easter Island, Chile 55.6 57.7 GMI Marianas Island, Guam 90.5 94.5 GOZ Gozo, Malta 169.3 165.0 HUN Hegyhatsal, Hungary 225.1 241.1 ICE Vestmanaeyjar, Iceland 137.4 [] ITN Grifton, N. Carolina 182.0 171.6 IZO Izana, Tenerife 103.9 101.1 KEY Biscayne, Florida 103.1 [] KUM Cape Kumukahi, Hawaii 110.7 102.2 MBC Mold Bay, Canada 140.0 129.3 MHT Mace Head, Ireland 137.2 124.1 MID Midway Island 116.9 116.3 MLO Mauna Loa, Hawaii 95.1 90.2 NWR Niwot Ridge, Colorado 121.7 119.2 PSA Palmer Station [] 48.6 QPC Qinghai Prov., China 131.2 127.8 RPB Ragged Point, Barbados 93.9 89.7 SEY Seychelles 82.4 79.2 SMO American Samoa 58.1 57.7 SYO Syowa, Antarctica 47.9 NA TAP Tae-ahn Peninsula, S. Korea 226.1 204.4 UTA Wendover, Utah 132.2 123.4 UUM Ulaan Uul, Mongolia 161.6 141.4 ZEP Ny-Alesund, Spitzbergen [] 132.6 Square brackets indicate insufficient data to calculate an annual mean. NA indicates annual mean not yet available. 450 i mr Kji^M p\ BRW 00" Fig. 2.15. Preliminary in situ hourly average CO mixing ratios during 1994-1995 at (a) BRW and (b) MLO. samples of air to the corresponding hourly mean mixing ratio determined in situ. The results from the two sampling approaches agree well (r 2 values > 0.97). There is no significant difference between the flask concentrations and those measured in situ at BRW. However, the slight positive Y intercept in the regression of the MLO data suggests a small positive offset. It is unlikely that this is due to the calibration gases, because all standards were referenced against the CMDL working standards. If the instrument zero has increased (as observed before with these instruments) and is not accounted for, the calculated in situ CO mixing ratios could be slightly underestimated. 2.4.2. Flask Measurements of Carbon Monoxide Carbon monoxide mixing ratios were measured in a subset of flasks collected as part of the cooperative air sampling network. It was previously reported [Novelli et al., 1992] that the stability of CO in a container is dependent upon the flask materials and geometry. Only 40 240 (a) 220 ' . ' 2% * \ 9 180 160 \ V \ ? u 140 t \ /% * off* 120 \ • i '„ * 100 ■ : Si * * « "V^ % m 94 94 2 94-4 94 6 94 8 95 95 2 95 4 95 6 95.8 96 YEAR 160 O f. q ° (b) ISO - " o 14.) D <■ 130 " ° u 120 1 °» 1,/ iV ;i -a ■ o u 110 ; 8° &° 1 ■ v.. i / ' B 100 90 K. ■ ' e o, '?« V^'' u ° * ,-'-, rf 80 "" .1. * Ofl'o 960 70 60 h.2 ^ "« -%--8* ° 94 942 94.4 94.6 94.8 95 95.2 954 95.6 95.8 96 Fig. 2.16. Comparison of CO hourly averages measured in situ to those measured using flask sampling at (a) BRW and (b) MLO. glass flasks fitted with glass piston stopcocks were used to measure CO. Over the lifetime of the CO program, the number of sampling locations has gradually increased as new sites in the network are started and the type of flasks used at older sites are converted to glass flasks for CO measurements. Analysis of air from flasks for CO and H 2 were made on a semiautomated RGA. The response characteristics of the instrument used for flask analysis were nonlinear for CO over the range of atmospheric values. Therefore, a multipoint calibration (six to eight standards) was used to quantify the sample CO content [Peterson and Rosson, 1993; Novelli et al., 1994]. The precision of the CO method, estimated as the difference of mixing ratios determined for each flask in a simultaneously collected pair of flasks, was typically better than 2 ppb. A data selection routine flagged flask pairs having a difference of greater than 3 ppb. As before, hydrogen was referenced to an arbitrary scale. A set of H 2 standards was prepared using gravimetric methods in collaboration with the NOAH Group. The H 2 working standards are now being evaluated against the gravimetric standards. Table 2.8 provides the land-based sites at which CO was measured in 1994 and 1995, and, whenever possible, the 1994 and 1995 annual mean values for these sites are shown. Samples for CO were also collected on trans- Pacific and South China Sea cruises; the annual mean CO mixing ratios are presented in Tables 2.9 and 2.10. These mean values were calculated from a curve fit to the total time series [Thoning et al., 1989]. Over the past several years new sites located near areas of human activity have been added to the CMDL air sampling network and these are expected to represent the regionally-polluted atmosphere. Comparison of these sites to "background" sites located at similar latitude illustrates the impact of economic development on atmospheric composition and are important constraints on models of global trace gas budgets. The difference in CO levels at two sites in Europe: Mace Head, Ireland (MHT), and the middle of the Baltic Sea (BAL), show the effect of human activities on regional-scale surface CO levels. MHT is a coastal site (53°20'N, 9°54'W), and winds are typically off the north Atlantic. BAL, located about 2000 km to the northeast (55°30'N, 16°40'E), is polluted from combustion of fossil fuels in Europe. Carbon monoxide time series TABLE 2.9. Preliminary 1994 and 1995 Mean CO Mixing Ratios From Combined Pacific Ocean Cruises Annual Mean CO (ppb) Site 1994 1995 N35 N30 N25 N20 N15 N10 N05 000 S05 S10 S15 S20 S25 S30 S35 119.3 125.4 108.6 106.6 105.4 89.6 70.2 66.1 65.4 63.3 58.0 58.5 55.6 52.2 123.3 114.2 [] 100.1 96.4 83.5 73.5 66.3 66.5 61.9 58.1 55.8 54.9 54.5 55.1 A description of the CMDL shipboard measurement program is given in Lang et al. [1992]. Typically samples are collected at a frequency of one per 1.5-2 weeks. TABLE 2.10. Preliminary 1994 and 1995 Mean CO Mixing Ratios From South China Sea Cruise Annual Mean CO (ppb) Site 1994 1995 N21 N18 N15 N12 N9 N6 N3 190.0 147.3 147.3 138.5 142.8 145.9 145.3 172.0 [] 130.9 126.0 126.4 Approximately four samples per month were collected in each latitude bin. 41 measured at BAL is much noisier and mixing ratios are consistently higher than at MHT. In winter, CO mixing ratios at BAL are often 100 ppb greater than those at MHT, while in the summer the difference is 25 to 75 ppb. At BAL carbon dioxide (C0 2 ), another combustion product, was also enhanced relative to mixing ratios observed at MHT. However, there are also times when the CO and CO2 differences between the two sites are quite small, suggesting that BAL experiences periods of relatively unpolluted air. Similarly, comparison of CO mixing ratios measured as part of the shipboard sampling programs in the Pacific and in the South China Sea (Tables 2.9 and 2.10) show the effects of human activities on CO in the boundary layer. Whereas the Pacific cruises sample air representative of the background marine boundary layer, the SCS cruises encounter pollution from the highly developed coast of southeastern Asia. CO mixing ratios along coastal Asia are typically 50 to 100% greater than those found in the Pacific. At the lower latitude SCS sites, isentropic back- trajectories suggested that during periods in October 1994, air was transported to these sites from areas in the southern hemisphere where fires had been observed. The high levels of CO seen in these regions may then result from both fossil fuel combustion in industrialized areas plus emission of CO from biomass burning in less developed areas. 2.4.3. The MAPS Program As part of the CMDL collaboration with the Measurement of Air Pollution from Satellites (MAPS) program (National Aeronautics and Space Administration- Langley Research Center), nearly real-time data from BRW and MLO were provided to the MAPS team during April and October 1994. Because the MAPS instrument provides a maximum signal in the middle troposphere [Reichle et al., 1990], measurements from mountain sites above the boundary layer were used as a quick test of the radiances measured by the space-borne instrument and the associated retrieval calculations. During March to November 1994, a CO instrument was installed at Niwot Ridge, Colorado, and the CMDL aircraft program flew vertical profiles above the site during the MAPS missions. These data have proved very valuable in the validation of the MAPS measurements. The MAPS measurements have also been compared with other ground based and aircraft measurements supported by a program of reference gas standard intercomparisons (section 2.4.4). CMDL coordinated the correlative measurements team for the 1994 flights of MAPS. This team provided MAPS with CO data from more than 60 sites worldwide. These data were used to validate measurements made by MAPS and to provide a unique picture of CO in the lower troposphere during April and October 1994. 2.4.4. Carbon Monoxide Standards The primary CMDL CO standards were prepared gravimetrically during 1988-1989 and then propagated to a set of working standards [Novelli et al., 1991]. These working standards were re-evaluated using a new set of gravimetric standards in March 1992. Comparisons of values assigned to working standards using the original gravimetrics, those produced in 1992, and the working standards themselves, suggest that the accuracy of propagation and stability of the scale has been within about 1% [Novelli et al., 1994]. It is now well known that CO standards used by one laboratory can be significantly different from those used in another [Weeks et al., 1989]. Therefore, it has been difficult to combine CO measurements made by different laboratories. Under the MAPS program, an inter- comparison of CO measurements made by 11 laboratories in 8 countries was organized. The round-robin inter- comparison was organized with four standards having approximate mixing ratios of 50, 100, 150, and 200 ppb in air (levels that represent the range of global CO mixing ratios in the unpolluted atmosphere). The experiment began in July 1993 and was completed in October 1995. The participating laboratories used either gas chromatography with HgO reduction detection or gas filter correlation radiometry and standards from several sources, including CMDL, National Institute of Standards Technology (NIST), the Fraunhofer Institute (Germany), and the Chemical Instrument Testing Institute (Japan). Differences between participants ranged to 20%. These could not be explained solely by differences in calibration gases and indicate the effect of different calibration procedures and instrument configuration on the results. 2.5. Flask Measurements of SF 6 /N 2 This project is a collaborative effort between the CCG and NOAH groups within CMDL funded by the Atmospheric Chemistry Project of NOAA's Climate and Global Change Program. A custom built gas chromatograph-electron capture detection (GC-ECD) system was installed to measure N 2 and SFg in the air samples collected from the CCG air sampling network. This GC uses technology developed in the NOAH Group, which is the same as that used for the tower GCs and ACATS-IV (see Elkins, et al., 1996, for further instrumental details). Near the end of 1995 this system was used to analyze flasks from a subset of sites in the CCG network; eventually all of the sites in the network will be phased in. A primary goal of the N 2 measurement program is to gain a better understanding of the budget of this compound. Both the natural and the anthropogenic sources of N 2 are poorly quantified, and the effectiveness of in situ field measurements is limited due to the extremely heterogeneous nature of N 2 emissions. These CCG flask measurements will complement the already existing background measurements made by NOAH in several ways: The CCG network has more continental sites that will give a closer look at the land-based N 2 sources. The CCG network also includes regular ocean cruise sampling that will help us better understand the oceanic source of N 2 and the effect that El Nifio/QBO phenomenon has on this natural N 2 source. More generally, the increased spatial coverage of the CCG network will improve our ability to use inverse modeling techniques to derive N 2 sources and sinks on a more regional level, as has been done for C0 2 [Tans, et al., 1989; 1990]. There are several motivations for the SFg flask measurement program. (For more details on SF 6 sources, analysis, calibration, and CMDL references, see the NOAH section 5.1.2 of this report). The global mean growth rate of this strong greenhouse gas will be elucidated from the 42 NOAH baseline station flask sampling. With the CCG flask measurements, however, the more detailed variations in this compound's atmospheric distribution can be looked at. Because of its extreme inertness in the atmosphere and its well-understood sources, SF 6 is a nearly ideal tracer of atmospheric dynamics. To this end, the SF 6 flask data can be used to help keep track of interannual variations in interhemispheric mixing and to better characterize the "geographical history" of the air masses being sampled at our CCG network sites. Since it is a purely anthropogenic compound, the spatial and temporal variations that are observed in SF 6 will aid in the ability to interpret the variations that are observed in the carbon gases and N 2 0, which all have a combination of biogenic and anthropogenic sources. Initial findings show that, as expected, the continental sites (such as HUN, UTA, LEF; see Table 2.7 for acronyms) have SF 6 levels that are on average =0.2 picomol/mol (abbreviated as ppt) higher than the marine sites (which are at =3.5 ppt), and some of our coastal and near shore sites (MHT, RPB, BME) show regular incursions of polluted continental air. Long-term flask storage tests were conducted for N 2 using our standard glass flasks with Teflon o-rings filled with humidified air. After 1 year, a loss of =1.0 ppb of N 2 was measured most likely due to slow diffusion into the flasks' Teflon o-ring. Because the goal is to try to discern gradients about 1-3 ppb, this may rule out the use of N 2 data from flasks that have a long delay time between sample collection and analysis, primarily high latitude southern hemisphere sites. Similar long-term storage tests for SF 6 are currently being conducted. 2.6. Measurements on Tall Towers The Carbon Cycle Group initiated the Tall Towers Program as a component of the effort to incorporate regionally representative continental sampling sites into the global network of C0 2 , CH 4 , and CO observations. The CCG approach is to utilize the tallest existing towers (television transmitters up to 610 m) to get away from the influence of sources and sinks in the immediate vicinity of the tower in order to examine the sources of variance of C0 2 , CH 4 , and CO mixing ratios in the continental boundary layer. These sources of variance include atmosphere/biosphere exchange, boundary layer dynamics, horizontal transport, fossil fuel and biomass combustion, and other anthropogenic sources (e.g., landfills, wastewater treatment, and natural gas leakage for CH 4 ). Observations of C0 2 mixing ratio at the WITN TV tower (610 m) in eastern North Carolina began in June 1992 and are ongoing. A description of the site and surrounding area, and of the experimental setup is given and initial results are discussed in Bakwin et al. [1995]. Measurements are carried out at 51, 123, and 496 m above the ground. Daily mean C0 2 mixing ratios at each of the three measurement levels on the North Carolina tower and smooth curve fits to the data [Thoning et al., 1989] are shown in Figure 2.17. A seasonal cycle of 15-20 ppm amplitude is apparent in the daily mean data from 496 m but is damped in measurements made closer to the ground. The seasonal cycle of C0 2 near the ground is masked by a large diurnal cycle driven by photosynthesis and respiration [Bakwin et al., 1995]. The nighttime buildup of C0 2 near the ground due to respiration, is especially pronounced in summer and "fills in" the seasonal i i_ 7/1/92 1/1 7/1/93 1/1/94 7/1/94 1/1/95 7/1/95 1/1/% Fig. 2.17. Daily mean C0 2 mixing ratios at 51, 123, and 496 m on the North Carolina tower. In the top panel the data for each day are shown as points, and the vertical axes for each observation height are offset. In the lower panel the smooth curve fits are plotted on the same scale for comparison. The smooth curve fit to daily mean data from 396 m above the ground on the Wisconsin tower is also shown. drawdown of C0 2 . Observations well above the level of the nocturnal inversion, as can be obtained from tall towers, are necessary to quantify C0 2 mixing ratios typical of the whole planetary boundary layer (PBL). To determine the annual growth rate for C0 2 mixing ratios at the 496 m level, a trend curve is fitted through the data in Figure 2.17 as described by Thoning et al. [1989]. The annual growth rates for 1993, 1994, and 1995 were found to be 1.7, 2.0, and 2.0 ppm yr 1 , respectively. These growth rates are larger by about 0.3-0.6 ppm yr 1 than those for the whole northern hemisphere in each year. The reason for this accumulation of C0 2 over the region, relative to the whole northern hemisphere, is not known. In October 1994 CCG began observations of CO, CH 4 , N 2 0, and a suite of halocompounds at 51, 123, and 496 m on the North Carolina tower by automated in situ gas chromatography. The GC design and operating parameters are discussed in section 5.2.2 of the 1993 CMDL Summary Report [Peterson and Rosson, 1994]. Measurements of N 2 and halocompounds are discussed in Section 5.2.4 of this report. Figure 2.18 shows daily mean CH 4 and CO mixing ratios for 496 m plotted with flask data from Bermuda, giving a comparison of the continental tower site with a "background" marine site at approximately the same latitude. Mixing ratios of CO at the tower are consistently 40-60 ppb higher than at Bermuda, likely reflecting fossil fuel combustion sources proximate to the tower. Emission of CO and C0 2 from the average mix of fossil fuel combustion in the United States occurs with a molar ratio of around 0.020 (20 ppb/ppm) [Bakwin et al., 1994; J. Logan, Harvard University, personal communication, 1993], so our observations indicate that C0 2 mixing ratios at the tower are enhanced year-round by roughly 2-3 ppm relative to "background" air due to regional fossil fuel combustion. Mixing ratios of CH 4 at the tower are enhanced by 20-60 ppb throughout the year, probably also mainly due to anthropogenic sources [Bakwin et al., 1995]. In October 1994 measurements began at the WLEF TV transmitter tower in northern Wisconsin (45.95"N, 43 1994 1995 1995 1995 1 995 1995 1995 1996 1996 Nov Jan Mai May Jul Sep Nov Jan Mai Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 94 94 94 95 95 95 95 95 95 95 95 95 95 95 95 Fig. 2.18. Daily mean CH 4 and CO mixing ratios at 496 m on the North Carolina tower (points) and flask data from the CCG Bermuda sites BME and BMW (open circles). Each time series is fit with a smooth curve as described by Thoning et al. [1989], Fig. 2.19. Shaded regions indicate the inner 50% of daily average C0 2 mixing ratios for each month from 30, 76, and 396 m on the Wisconsin tower. 90.28°W, base height 472 m above sea level). The tower is 447 m tall and is located in the Chequamegon National Forest. The region is a heavily forested zone of low relief. The Chequamegon National Forest covers an area of about 3250 km 2 , and the dominant forest types are mixed northern hardwoods (850 km 2 ), aspen (750 km 2 ), and lowlands and wetlands (600 km 2 ). Much of the area was logged, mainly for pine, during 1860-1920 and has since regenerated (J. Isebrands, USDA Forest Service, personal communication, 1994). The regional population density is very low, and there is limited industry. Carbon dioxide mixing ratios are measured at 11, 30, 76, 122, 244, and 396 m above the ground. Wind speed and direction, temperature, and humidity at 76, 122, and 396 m, and barometric pressure, rainfall, incident photosynthetically active radiation (PAR) and net radiation at the surface. Intermittently (so far) vertical fluxes of C0 2 are also measured at 76 and 396 m using eddy correlation. The flux measurements have been discontinuous because of instrumental problems, but steps have recently been taken to improve reliability. In June 1995 an automated GC was installed at the Wisconsin tower for measurements of CH 4 and CO. The method of analysis is similar to that used at the North Carolina tower (Table 5.3 of Peterson and Rosson [1994]), and every 30 minutes one measurement is obtained at each of 30, 76, and 396 m above the ground. The smooth curve fit to the Wisconsin tower C0 2 daily mean mixing ratios from 396 m above the ground is shown in Figure 2.17 to allow comparison with the North Carolina tower. Mixing ratios at the Wisconsin and North Carolina towers are similar in winter, but the summertime draw-down is 3-4 ppm deeper and at least 1 month narrower at Wisconsin. The inner 50% (by month) of daily averages for C0 2 data from 30, 76, and 396 m is displayed in Figure 2.19, and monthly statistics for CH 4 and CO on the Wisconsin tower are presented in Figure 2.20. Figure 2.21 shows an example of C0 2 , CH 4 , and CO mixing ratios, and C0 2 fluxes at the Wisconsin tower for September 1-2, 1995. During the daytime the PBL is well mixed to heights well above the top of the tower (e.g., 1400-1600 m on these 2 days, W. Angevine, NOAA Aeronomy Laboratory, unpublished data) and the trace gas mixing ratios show little vertical gradient. At night a shallow inversion forms and C0 2 and CH 4 mixing ratios increase rapidly near the ground due to surface sources. Surface fluxes of C0 2 calculated from data obtained for 76 and 396 m are generally in good agreement. The eddy fluxes show net uptake of C0 2 by the forest in the afternoon of up to around 0.4 ppm m s _1 or 7 kg (C) ha -1 h _1 . At night the forest releases C0 2 as is also indicated by the vertical profiles. In the future, plans are to measure C0 2 fluxes continuously and to be able to determine the annual net C0 2 balance of the forest. Some additional results from the flux measurements are presented by Davis et al. [1996]. JO 18 a. Q- u J3 20 <> a. O 120 u : ti+ ft ft tit tit ft ■ ■ " 236 236 236 236 236 236 - ■ " ■ ■ « ■ I ■ " ■ 1 g II O 1 -!!! tti ffi r4 a* -■ 236 236 23? 236 236 236 Au.j Sep Oct Month, 1995 Fig. 2.20. Monthly statistics of CO and CH 4 measurements at the Wisconsin tower. Circles and asterisks are means ±1 standard deviation. The crosses indicate medians (horizontal bars) and upper and lower quartiles (vertical bars). The numbers across the bottom of the plot indicate sampling level (2, 3, and 6 refer to 30, 76, and 396 m, respectively). 44 410 ,— ^ fc Q. 390 □. fN 370 CI t ) 3b0 , — , in V b • 0.3 F n CL 0.0 X u. -0.3 o o u 140 CL 120 Q. mn U u HO 1910 „ 1850 X o 1790 J 12 24 MO 36 4? 48 Local Time (hours) Fig. 2.21. lime series of mixing ratios and surface fluxes of C0 2 and mixing ratios of CO and CH 4 measured on the WLEF tower in Wisconsin on September 1-2, 1995. Surface fluxes are calculated from eddy correlation measurements at 76 and 396 m above the ground. Mixing ratio measurements made below those levels are used to account for divergence of the fluxes in the vertical. F 50 CL CL 40 _^ 0) 30 "D 03 1— 20 CD CM 10 o o _o IfaO CL CL ' — ' ^_, L_ inn 0) "O Cfl 1— O 50 m- X o # * * X ■T+it * * * * o *-95% of the C0 2 that accumulates in the nocturnal stable layer in summer is biogenic (respiration). In December the maximum gradients for C0 2 and CH 4 are much smaller, only about 2 ppm and 17 ppb, but the maximum gradient for CO (28 ppb) is larger than in August. These observations likely reflect the nearly complete shutdown of biogenic sources of C0 2 and CH 4 in winter. Mixing ratio gradients for CO may be higher in winter due to increased combustion activity and shallower mixing depths for the nocturnal PBL than in summer. Fig. 2.22. Statistics of vertical gradients (30 m-396 m) for C0 2 , CH 4 , and CO, binned by hour, for August 1995. Crosses indicate means (horizontal bars) ± the 95% confidence interval (vertical bars), circles indicate medians, and asterisks indicate upper and lower quartiles. The leftmost panel on each plot gives statistics for the mean daily vertical gradients. The winter-summer comparison of vertical gradients indicates that the main source of CH 4 in the region surrounding the Wisconsin tower is biogenic (Figure 2.21). Future plans are to determine CH 4 fluxes at the Wisconsin tower using measurements of C0 2 fluxes (by eddy correlation) and vertical profiles of CO2 and CH 4 . In contrast, our results for the North Carolina tower imply that the main regional CH 4 sources are associated with anthropogenic activity [Bakwin et al., 1995], 2.7. Automated Aircraft Sampling The aircraft sampling project has been in continuous operation at the Carr, Colorado [40.9°N, 104. 8°W] site since November 1992. Until April 1995, profiles of 20 samples each were taken on a biweekly basis. After April, 45 E 4 CL Q. ^ 3 c -O 2 CO CD c\ O o * X * :::°otf**+t +. |t]i o o ********°Q°fQot*°**** _l L_ .Q 30 Q. D. ^•^ 20 C CD "O 10 m CD n- X o -10 X X - X XX X * X < > X < - > * X < X * X * X ) i > ( X ■■*■ V '■( -t ) r ( -( 1 I* c -1 ) c r > < ) "c r< < * X -Jit- X X X * c )- ) ™ ( . <> ■ * X X * X ■ * * * 1 1 1 1 1 1 1 1 Q. 40 Q. C CD 20 03 X X o X * * XX X XX X i _ X I w X »-- a 11444- * * "- JX L « .. u hr -l|T_ VliVlillVUi JUV.VIVJ, I • \1 • > \- VI III W 1 I *- I I I 1 W U I IIUIIUUUIl ■ 1 I V' %-> «- I •> II' --ill chemical species prognosed by the model. This parameter has typical unites of m 2 g" 1 caused by the the long-range transport of pollution and mineral dust from Asia. Little seasonality is seen in CN concentrations at MLO, however, indicating that the smallest particles (<0.1 u.m diameter), which usually dominate the CN concentration, are not enriched during these long-range transport events. Little seasonality is seen in the results from SMO, while at SPO the high a sp levels observed in the late winter are due to the long-range transport of sea salt in the upper troposphere from stormy regions near the Antarctic coast to the interior of the continent. Previous reports describing the baseline aerosol data sets include BRW: Bodhaine [1989] and Quakenbush and Bodhaine [1986]; MLO: Massey et al. [1987]; SMO: Bodhaine and DeLuisi [1985]; and SPO: Bodhaine et al. [1986, 1987] and Bodhaine and Shanahan [1990]. 52 2000 C ' BRW ISOO 1 E 1000- o ; 500- 1976-1995 A I 41 800 : MLO 1974 -1995 | soo ; E 400 L - u 200 ft H H H H H Hi 900 : smo 600 E 400 o : r 200 H H 1977-1995 - JAN MAR MAY JUL SEP NOV ANN Fig. 3.1a. Annual cycles of CN concentration for baseline stations at BRW, MLO, SMO, and (SPO Monthly median values are shown. Box-whisker plots illustrate the upper and lower quartiles (box), and 5th and 95th percentiles (whiskers). Values representing the entire year period, for all years, are also presented (ANN). Based on only 2-3 years of measurements, the annual cycles for the regional stations are very uncertain, therefore, it is premature to discuss the causes of the observed variability. The proximity of the regional sites to North American pollution sources is apparent in the results, however, with monthly median values that in some cases are over 2 orders of magnitude higher compared to values from the baseline stations. 3.1.4. Long-Term Trends Long-term trends in CN concentration, a sp , and angstrom exponent are plotted in Figure 3.2a-c for the baseline stations. The trends are plotted for the annual geometric average as well as for the geometric averages for the months with the lowest and highest median values observed in the annual cycle plots. Interpretation of the results are complicated by two changes in instrumentation: (a) replacement of the nephelometer at MLO in 1985 and (b) the replacement of the CN counters with butanol-based instruments at MLO in 1988; at SPO in 1989; at BRW 1.5-10' 1.0-10 4 50-10 3 o 6000 ,4000 E o ""2000 4000 BNO 1994-1995 i NWR 1994-1995 ; y ? t 11 T ■ 2000 WSA 1992-1995 9 T V JAN MAR MAY JUL SEP NOV ANN Fig. 3.1b. Annual cycles of CN concentration for regional stations at Bondville, Illinois (BND), Niwot Ridge, Colorado (NWR), and Sable Island, Nova Scotia (WSA). inl990; and SMO in 1992. The two types of CN counters have different lower-size detection limits, which means that any change in the long-term record will depend on the presence of particles not detected by one of the counters. This is the likely cause for the fact that obvious step changes in CN concentration are seen at MLO and SPO, but not at BRW and SMO. As discussed in the 1988 Summary Report [Elkins and Rosson, 1989], rj sp values at MLO were generally higher since the installation of the new nephelometer in 1985 and have not reached the low values previously observed in winter. The increasing trend in a sp at MLO is caused by higher winter values in the latter part of the record and the reason is believed to be instrumental. A modern, high- sensitivity three-wavelength nephelometer was deployed at MLO in 1994, and future comparison of the results from the two nephelometers is expected to quantify any biases introduced by the older, less-sensitive instrument. All data reported here are from the older instrument, however. 3.1.5. Results From 1994-1995 Daily Mean Values of Aerosol Properties Figures 3.3a-g show the daily mean values at each monitoring station for total number concentration (CN), aerosol scattering coefficient at 550 nm (0" sp ) and the angstrom exponent for the 550/700 nm wavelength pair from January 1, 1994, to December 31, 1995. Significant day-to- day variability in CN concentration, aerosol scattering coefficient, and angstrom exponent can be seen in the figures. The daily variability of these parameters is due to several factors, including changes in local meteorology, 53 .30 £T 20 E 10 BRW 1976-1995 ; 1 IT Uiiliiiy 10 s _* 6 i 4 2 : MLO 1974-1995 : k U U U 1 1 1 1 1 H 40 30 6 20 u 10 20 15 S 1.0 •J OS 00 SMO T T y v t t v ? v ri 197; -199 • SPO 1979-1996 9 9 0; 200 150 £ 100 50 40 £- 30 E ^20 10 • BND 1994-1995 • 6 1 M J H 1 1 j 4 ( I • NWR !A 4 1994-1995 HI 4 1 100 : wsa 1992-1995 : 80 - E 60 r ■i u — 40 L j 20 1 M M I i i J i 1 M M 9i - JAN MAR UAY JUL SEP NOV ANN Fig. 3.1c. Annual cycles of G sp at 550 nm for baseline stations at BRW, MLO, SMO, and SPO and for regional stations at BND, NWR, and WSA. : BRW 1975-1995 MLO 1974-1995 1 OS E0.o -0.5 -10 SMO 1977-1991 25 20 -1.5 S 10 OS 00 : WSA Al T V 1992-1995 : i, li T1 JAN MAR UAY JUL SEP NOV ANN Fig. 3. Id. Annual cycles of angstrom exponent (a, 550/700 nm) for baseline and regional stations. aerosol sources, transport time from source regions, and processing of aerosols during transport. It is worthwhile to point out that the data editing procedure for 1995, as seen in the CN plots from the edited stations, results in a more stringent acceptance of data. This can be clearly seen in the Barrow CN plot that shows significantly more breaks in the 1995 data because of the rejection of a greater amount of data compared with the previous year. The more rigorous approach to data screening for 1995 and after, generally results in less day-to-day variability in the CN concentrations, which is likely becaue of the fact that data resulting from local pollution are more completely excluded. Aerosol Intensive Properties Figure 3.4 shows box/whisker plots of the variability in the daily averages of three different intensive aerosol 54 " BRW MAR JUN ANN " MLO 4 - APR DEC ANN 10- SEP MAY ANN 0.8 SPO SEP ; 0.6 - 4 . '; A - £ 0.4 02 -- X /A _ NOV ANN ■i no 1974 1979 1964 1990 1995 2000 1974 1979 1984 1990 1995 2000 Fig. 3.2a. Long-term trends in CN concentration for baseline stations, showing months with the lowest and highest median values, and annual averages for each year (ANN). Fig. 3.2b. Long-term trends a S p at 550 nmfor baseline stations, showing months with the lowest and highest median values and annual averages. properties measured at Sable Island: the angstrom exponent (550/700 nm wavelength pair) for submicrometer particles, the fraction of scattering caused by submicrometer particles, and the fraction of the light that is scattered into the backwards hemisphere. The data were classified into three cases: "clean" conditions when both N tot and a sp (550 nm, D p < 1 (im) are below the lower quartile for the entire data set, "dirty" conditions in which N tot and G sp are above the upper quartile, and all "other" periods that do not meet the previously defined criteria (for example periods with low N tot and high a sp values). For comparison, the fine/total scattering fraction is plotted for Bondville (BND) (data for the other intensive properties are not available at BND prior to 1996). It can be seen that the values of the angstrom exponent increase for more polluted periods suggesting that the submicrometer aerosol shifts systematically towards smaller particles as the degree of pollution increases. This is also reflected in size- segregated measurements of light scattering, which show that a larger fraction of the total scatter is due to the submicrometer aerosol as the air becomes more polluted, reaching a median value of 84% at BND. In the cleanest cases at Sable Island, only 28% (median value) of the light scattering is caused by submicrometer particles; the remainder is presumably caused by larger sea salt particles. Submicrometer particles contribute a larger fraction to the total for each quartile at Bondville, suggesting the continental aerosol is always heavily influenced by fine aerosol pollution. Aerosol number concentrations and values of a sp for the submicrometer aerosol are consistently higher at Bondville than at Sable Island (Figure 3.1b,c). The backscatter fraction, on the other hand, exhibits relatively little dependence on the degree of pollution. Linear regression of the angstrom exponent with the fraction of submicrometer scattering (Figure 3.5) demon- strates that the two variables are highly correlated, suggesting that most of the variance in the angstrom exponent is controlled by the relative abundance of submicrometer particles. This challenges the traditional notion that the angstrom exponent can be interpreted as the slope of a power-law aerosol size distribution and better supports a bimodal model of the size distribution where the 55 2 - 1 - MAR JUN At*i 1974 1979 1984 1990 1995 2000 Fig. 3.2c. Long-term trends for a (550/700 nm) for baseline stations, showing months with the lowest and highest median values and annual averages. 200 400 Days since January 1, 1994 Fig. 3.3a. Daily means of aerosol properties (CN concentration, o sp , and a) for SPO for 1994, 1995. 200 400 6O0 angstrom exponent is a measure of the relative amounts of material in the two modes. 3.1.6. Aircraft Observations A special version of the CMDL aerosol instrumentation package used at the regional aerosol monitoring sites was developed for use on research aircraft. This effort was undertaken to extend our measurement capability into the vertical dimension and to greatly increase geographic coverage as well. This airborne aerosol package includes a three-wavelength nephelometer with backscatter shutter, a light absorption photometer, a condensation nucleus counter, and a multi-filter sampler, all interfaced to a laptop computer for instrument control and data logging. As is done on the ground, the sample air is heated as necessary to maintain a relative humidity below 40%, and multijet impactors are used to restrict the size-range of particles sampled (on the aircraft, only particles smaller than 1 urn aerodynamic diameter are sampled). Addi- Fig. 3.3b. Daily means of CN concentration for SMO for 1994, 1995. tionally, wing-mounted probes permit the determination of aerosol-size distributions. These instruments constitute a comprehensive airborne aerosol measurement platform capable of determining a wide suite of aerosol chemical, optical, and microphysical properties. Measurements of the optical properties of submicrometer aerosol particles were measured from the NOAA WP-3D Orion research aircraft during the summer 1995 Southern Oxidants Study. The majority of the flights were in the midwest and southeastern United States at altitudes below 5 km and provide a survey of the vertical and horizontal variability of the aerosols that dominate the direct aerosol radiative forcing of climate. Some flights were conducted over Colorado, allowing comparison of these aerosol properties between the humid East and arid West. Figure 3d 2000 1500 r ! ioo( z o 500 Wlup c 16 12 E 2 8 » o 4 ill 200 400 600 x.mi> ?00 200 400 Days since January 1, 1994 600 Fig. 3.3c. Daily means of aerosol properties for MLO for 1994 1995. 2O00 1500 r I 1000 500 A V M k V U 200 400 600 200 400 Days sines January 1 . 1 994 600 ?00 400 600 200 400 600 200 400 Days since January 1, 1994 600 Fig. 3.3e. Daily means of aerosol properties for WSA for 1994, 1995. 200 400 600 200 100 Fig. 3.3d. Daily means of aerosol properties for BRW for 1994, 1995. Fig. 3.3f. Daily means of aerosol properties for NWR 1994, 1995. 57 400 0.4 0.6 Fine/TotaJ Scattering Ratio 200 Fig. 3.3g. Daily means of aerosol properties for BND 1994, 1995. WSA dean WSA other WSA Arty Fig. 3.5. Linear regression of a versus the fraction of submicrometer scattering for WSA. 3.6 shows the vertical profiles measured over Colorado of a, w , b, and a sp (denoted by B sp in the figure legend). The data in Figure 3.6 were obtained over a large area of the state, and some of the variations are due to horizontal inhomogeneity. Nevertheless, the results show fairly constant values of u) , b, and a throughout the lower tropo- sphere. The increased variability above 5 km results from the very low (and hence imprecise) values of the primary measured variables, leading to large variations in para- meters that are defined as ratios of the primary variables. The single-scattering albedo varies in the range 0.88-0.95, and the hemispheric backscattering fraction is 0.15-0.18. A similar vertical profile over the southeastern United States is seen in Figure 3.7 in spite of much higher values of light scattering (note the scale change for a sp ) than were observed over Colorado. Once again, values at the higher altitudes are much less reliable because of the low values of the scattering and absorption coefficients. In the boundary layer, the single-scattering albedo is 0.95 and the hemispheric backscattering fraction is 0.11. These values are somewhat different from the values obtained over Colorado, suggesting systematic differences in aerosol composition and size distribution in the two regions. However, the differences may also be due to day-to-day variations in the aerosol. Figure 3.8 shows the horizontal variability observed in the boundary layer on the transit flight from Colorado to Tennessee. As was the case for the vertical dimension, the derived parameters (co , b, a) are relatively constant in spite of large changes in the primary measured variables. WSA clean WSAolher WSA dirty single scatter albedo -* - backAotai scatter Angstrom exponent • Bsp(iE-SAn) Fig. 3.4. Aerosol intensive properties (a, fraction of submicrometer scattering, and backscatter fraction) for WSA and BND. The data from Sable Island were separated according to clean, dirty, and other cases. Fig. 3.6. Vertical profile of aerosol properties over Colorado, June 6, 1995. SS -•-single scatter albedo -*- back/total scatter -•-Angstrom exponent • Bsp(1E-4*n) Fig. 3.7. Vertical profile of aerosol properties over the southeastern United States July 1, 1995. latitude - single scatter albedo • Angstrom exponent - backAotal scatter Bsp(lE-4/m) Fig. 3.9. North-south transect, midwest United States July 10, 1995. Finally, Figure 3.9 shows the latitudinal variability that was observed in the boundary layer over the mid- western U.S. (Tennessee-Indiana), where the values of co and b are identical to the boundary layer values shown in Figure 3.8. Slightly more variability is seen in the single- scattering albedo (0.89-0.96), but the hemispheric backscattering fraction is once again nearly constant (0.12). In all four cases, the angstrom exponent stays in the range 2.0-2.5. Although instrumental noise is a limiting factor, the observed variability in a may be due to variations in the aerosol size distribution with the larger values of a corresponding to cases with smaller particle sizes. Taken as a whole, the results of this study yield values for the single-scattering albedo in the range 0.88-0.96, with more variation observed from day-to-day than from place-to-place (horizontally or vertically). Similar conclusions can be drawn for the hemispheric backscattering fraction (0.11-0.18) and the angstrom exponent (2.0-2.5), although b in the boundary layer was always below 0.13 except for the one vertical profile over Colorado. Although it is difficult to draw general conclusions from a 1 -month study, the results suggest that ground-based measurements of the light scattering and absorption coefficients of submicrometer, continental ^.0 • 20- *"' __♦ • ♦ 1.0- 0.5- • — o— — m~ ,*■ •^ o 0.0- ■ * \ -^4- 1 X| *■ *> t -105 -100 -95 -90 -85 «- single scatter albedo longitude _+_ back/total scatter ►-Angstrom exponent -*- Bsp (1E-4/m) particles can be used to derive values of the single- scattering albedo, hemispheric backscattering fraction, and angstrom exponent representative of the dry aerosol throughout the lower troposphere. 3.1.7. Lidar Measurements at Mauna Loa Vertical profiles of tropospheric and stratospheric aerosols are regularly determined at MLO with two different lidar systems. Section 1.1.2 (Aerosol Monitoring, page 7, this report) describes the instruments and analysis techniques, and the new Nd:YAG lidar. The integrated aerosol backscatter (IABS) data at 694 nm in Figure 3.10 show that no volcanic eruptions injected large amounts of aerosols that were detectable in the stratosphere at MLO latitudes in 1994-1995. The decay of Mt. Pinatubo's aerosols continued, and by the end of 1995, the lowest levels of IABS in the past 16 years were in evidence. A small increase and decay in stratospheric aerosols just prior to the Mt. Pinatubo eruption may have been related to the eruption of Kelut which was observed by the Stratospheric Aerosol and Gas Experiment (SAGE) instrument. A similar small increase in the IABS data in the fall of 1994 may be observed in Figure 3.1 1 at 532 nm and 694 nm. The 532-nm data are from the new Nd:YAG 1E-05 Year Fig. 3.8. East-west transect, Colorado to Tennessee, June 19, 1995. Open symbols denote free tropospheric measurements. Fig. 3.10. Integrated aerosol backscatter for 1980-1995 at 694 nm (ruby lidar) from 15.8 to 33 km. 59 0.00035 -g" 0.00030 S5 0.00025 :■ § 0.00020 ■ | 0.00015 8 0.00010 i Q < 0.00005 -■ 0.00000 1994 1995 1996 Fig. 3.11. Integrated aerosol backscatter for 1994-1995 at 532 and 694 nm (ruby lidar) from 15.8 to 33 km. lidar. This increase coincides with an eruption of Rabaul in New Guinea. The increase abruptly disappears in December 1994 coincident with the air mass above the observatory switching abruptly from tropical to midlatitude air. In September 1994 the Lidar In-space Technology Experiment (LITE) was flown in the Space Shuttle. The lidar made aerosol measurements at 1064, 532, and 355 nm from the upper stratosphere into the troposphere. LITE observing times were concentrated over the Atlantic and Europe, but during two overflights of MLO, correlative measurements were made at 532 nm. For the first overflight (September 14), the profiles agree well throughout the stratosphere. On the second flight (September 16) the profiles agree (within calculated error) below 23 km. However, the MLO lidar observed higher aerosol backscatter at elevations from 23 to 33 km although the MLO lidar exhibited the same general features in the profile as the satellite instruments. The MLO lidars, as part of the Network for the Detection of Stratospheric Change (NDSC), participated in an aerosol analysis intercomparison (August 1995) conducted within the lidar group of NDSC to validate the analysis methods used by NDSC lidars. In the study, raw signals and radiosonde data were provided to participants to be used in their respective analysis routines. Pre- liminary results show good agreement between MLO analysis and the benchmark data. Atmospheric temperature profiles have been measured with the MLO lidar over altitudes from 33 to 70 km beginning in July 1994. A blind intercomparison of temperature profiles made between the NOAA lidar and three other NASA lidars during the ML03 campaign was undertaken in August 1995; the results and analysis have not been released to date. 3.2. Solar and Thermal Atmospheric Radiation E. Dutton (Editor), B. Bodhaine, R. Haas, D. longenecker, d. nelson, r. stone, and j. wendell 3.2.1. Baseline Monitoring Activities The CMDL surface radiation monitoring project began in 1973 with the intent to provide supporting information for baseline climate monitoring activities and to determine trends and variations in the surface radiation budget induced by changing atmospheric composition because of anthropogenic activity. Then, trends predicted in the measured radiation quantities due to anthropogenic sources were near or below the level of detectability for the available instrumentation. However, other sources of variability in the surface radiation budget were also not adequately known or understood; thus the measurements could contribute to the most basic understanding of the natural and changing surface radiation budget. Such contributions included definition of diurnal and annual cycles, effects of cloudiness, variation on daily to decadal time scales, effects of major volcanic eruptions, unexpectedly high concentrations of anthropogenic pollution in the Arctic, effects of constituent variations on narrowband irradiance (e.g., ozone and ultraviolet (UV) changes), and possible anthropogenic modification to cloudiness. In addition to research conducted by CMDL, the surface radiation measurements contribute to several global data bases. Global data bases are needed to evaluate the radiation and energy budget necessary to diagnose the climatic time scale general circulation of the atmosphere. Observations also contribute to satellite- based projects where surface measurements serve to verify spot estimates and to allow features of the intervening atmosphere to be deduced. A major goal of the monitoring program is to obtain a record, as long and complete as possible, of surface radiation parameters which will permit examination of the record for all scales of natural and modified variability. Of particular interest is the determination of the magnitude, representativeness, and possible consequences of any observed changes. To this end, the CMDL radiation group maintains complete and continuous surface radiation budget observations at several globally diverse sites with various ancillary supporting observations. The following describes those projects, particularly recent changes and results. CMDL Baseline Observatories The four main CMDL baseline observatories have been involved in the radiation project since the early 1970s. The different environments and conditions among the sites have resulted in different programs evolving at each site. The basic measurements made at all sites include both the downward global and direct components of solar radiation. By late 1995, solar diffuse radiation measurements had been added to each of the sites permitting more accurate determination of global radiation from the sum of vertical direct and diffuse. Broadband thermal infrared measurements were added in the last 10 years. At sites where the surrounding terrain is representative of a larger regional area (SPO and BRW), the upward solar and thermal infrared irradiances are also measured. The solar radiation records acquired at these sites constitute some of the longest known U.S. records of their kind acquired under research conditions. In 1994 a major upgrade to the observing network was accomplished with the conversion to a commercial data-logging system that provides 13-bit accuracy and precision, resistance and voltage mea- surements, and onsite processing of the data. The raw data are routinely transmitted over phone lines or Internet to the central data processing facility in Boulder where data editing, final calibrations, graphical inspection, and archiving are performed. 60 Basic Measurements The basic measurements currently conducted at each of the four baseline observatories for the past 20 years include normal-direct and downward-broadband solar irradiance, downward solar irradiance in the 0.695 urn to 2.8 urn band, and wideband spectral direct solar irradiance. Downward broadband thermal irradiance measurements were added at BRW, MLO, and SPO in more recent years as well as upwelling irradiance measurements at SPO and BRW. The wideband spectral direct observations are obtained manually under clear sky conditions while the others are sampled at 1 Hz with 3-minute averages recorded on computer media. Preliminary data from all CMDL radiation sites are generally available on the Internet within a few days of acquisition in the radiation section on the CMDL Home Page (www.cmdl.noaa.gov). Filter Wheel NIP The wideband spectral direct solar irradiance measurements are made with a filter wheel normal incidence pyrheliometer (FWNIP). The data from these observations are compared to a higher spectral resolution radiative transfer model [Bird and Riordan, 1986]. The model is based on Beer's law and has only one level (surface). The aerosol optical depth and precipitable water are adjusted within the model to obtain a best match with the FWNIP observations. This provides a low precision, but a relatively stable estimate of mean visible aerosol optical depth and water vapor at the four baseline observatories. The accuracy of the method of obtaining aerosol optical depth and water vapor is limited by the dependence on the absolute values of the extraterrestrial solar spectrum and instrument calibration, unlike typical applications in sunphotometery. The aerosol data record from this observational project is shown through 1995 (Figure 3.12). MLO Apparent Transmission The transmission of direct broadband solar irradiance through the atmosphere above MLO is monitored using a quantity known as the apparent transmission. This quantity is computed by taking the average of three ratios of direct solar irradiance where each ratio is the quotient of the irradiance at an integer air mass divided by the irradiance at the next smaller integer air mass as first defined by Ellis and Pueschel [1971] and used by Button et al. [1985] and others. The apparent transmission is stable over time because it is independent of a radiometer calibration value and also, therefore, quite sensitive to small changes in transmission that can be due to aerosols, ozone, or water vapor. Previous st udie s \Bodhaine et al., 1981; Dutton et al, 1985] have shown that in monthly averages, aerosols tend to dominate observed changes in the apparent transmission such that the major observed excursions in the record given in Figure 3.13, are because of aerosols. The major observable features in Figure 3.13 are the effects of several volcanoes, particularly Agung in 1963, El Chichon in 1982, Mt. Pinatubo in 1991, and an annual oscillation caused primarily by the springti me transp ort of Asian aerosol over~ihe site [Bodhaine et al., 1981]. Figure 3.13 is complete through 1995 and most recently shows that the recovery from the eruption of Mt. Pinatubo was not yet complete in 1995. The fact that the MLO apparent transmission record still indicates a Mt. Pinatubo residual 11 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 YEAR Fig. 3.12. Monthly average aerosol optical depth as determined from the filter wheel NIP for the four primary observatories. Note that these derived values are not as accurate as determined by some other techniques but are inherently stable and relatively complete over the period of record as compared to other attempts to remotely sense these quantities at these stations. is evidence of the sensitivity of the measurement since it is known from other measurements by CMDL and others, that the optical depth of Mt. Pinatubo in 1995 was very low (about 0.005 at 500 nm). Boulder Atmospheric Observatory (BAO) Tower Observations of upwelling and downwelling solar and thermal irradiances at the top of the 300-m BAO tower, located near Erie, Colorado, began in 1985. Nearly continuous observations of these quantities, hourly resolution until 1992 and 3-minute thereafter, have been maintained since 1985. The data provide a unique view of surrounding agricultural land in that the data are more representative than typical surface-based solar radiation budget observations. The data from the site were used in 60 62 64 66 68 70 72 74 76 78 80 82 84 Year 90 92 94 96 98 Fig. 3.13. Monthly average apparent solar transmission above Mauna Loa, Hawaii. The effects of major volcanic eruptions and the annual transport of Asian aerosol is most evident. 61 several recent publications [Nemesure et al., 1994; Cess et al., 1995; Dutton and Cox, 1995; Garrett and Praia, 1996; and several earlier papers]. Since 1990, observa-tions of direct solar and downwelling solar irradiances have been made near the base of the tower. This site has contributed data to the World Climate Research Program (WCRP) Baseline Surface Radiation Network (BSRN). Kwajalein Observations of direct solar, downwelling solar, and thermal IR irradiance began in Kwajalein in 1989. Kwajalein is a small, <4 km 2 , island in the tropical Pacific. Data obtained at this location are virtually free of any effects of the island and, therefore, are often taken as representative of the open ocean in that region. Data from Kwajalein were used in several recent publications including Dutton [1993], Whitlock et al. [1995], and Bishop et al. [1996] . Substantial upgrades to the Kwajalein radiation measurement array are planned for 1996 including spectral direct and diffuse, broadband diffuse, disk-shaded pyrgeometer, UV-B, Photo- synthetically Active Radiation (PAR), and improved solar tracking capability. Data from Kwajalein have been submitted to the BSRN data archive. Bermuda Observations of downwelling solar and thermal IR began on the east end of Bermuda in 1990 on the National Aeronautics and Space Administration (NASA) tracking station site. The rather small size and elongated shape of the island in the lower midlatitude westerlies is believed to have a minimal influence on the irradiance measurements, although some clouds of orographic origin are known to exist there in the summer months under certain synoptic meteorological conditions. Data from Bermuda were submitted to the BSRN data archive and have been used by Whitlock et al. [1995] and Bishop et al. [1996] in satellite comparison and validation studies. 3.2.2. Solar Radiation Calibration Facility Routine Operations Calibration support for the four CMDL baseline observatories and the BSRN sites at Kwajalein, Bermuda, and BAO during 1994 and 1995 was carried out by the CMDL Solar Radiation Calibration Facility (SRCF). Calibrations and characterizations of pyranometers and pyrheliometers were performed as needed, and field exchanges of recalibrated instruments were completed. Improved diffuse-sky measurements were implemented at the SRCF with the addition of ventilated tracking disk systems designed for the Eppley automated solar trackers used by CMDL. The improved diffuse measurements, together with automated cavity operation for the collection of solar direct beam data, have enabled more accurate characterizations and calibration procedures requiring accurate determination of solar components (direct beam and diffuse sky). Standards Activities The CMDL reference cavity radiometers were compared with reference cavities from other organizations during 1994 and 1995. A cavity intercomparison was held at the National Renewable Energy Laboratory in Golden, Colorado, October 8-10, 1994. In 1995 the CMDL references were taken to the World Radiation Center in Davos, Switzerland, for participation in the WMO- sponsored eighth International Pyrheliometer Comparison (IPCVIII). These comparisons are typically conducted every 5 years and allow reference instruments from all of the WMO regions to document their performance relative to a standard group of instruments maintained at the World Radiation Center. Seventy-seven reference instruments from 37 countries participated in IPCVIII from September 25 to October 13, 1995. Participation in IPCVIII of the CMDL reference cavities (TMI67502 and AHF28553) maintains the historical traceability of the NOAA standards to the World Radiometric Reference maintained in Davos and the World Radiation Center. All solar radiation measurements made by CMDL are thus traceable to the world reference. Instrument Development Activities Efforts began during 1995 to add observational capability to the BSRN sites at Kwajalein, Bermuda, and BAO. Dual ventilated shade disk systems were acquired, tested, and deployed to BAO during 1995 with installation at Bermuda and Kwajalein scheduled for early 1996. The dual shade disk systems attach to the Eppley solar trackers and enable a pyranometer and pyrgeometer to be continuously shaded and ventilated. Improvements in solar tracking accuracy for these sites was also achieved by implementing a more accurate solar position algorithm in the tracker control program, precision leveling of the solar tracker during installation and setup, and a solar position detector designed and built by CMDL was added to the solar tracker. Tracking accuracies of better than 0.1 degrees are achievable with these improvements. These improvements are scheduled for installation at the Kwajalein, Bermuda, and BAO sites in 1996. In addition, software was added to the tracker control computer that allows remote access to the tracker control program via modem. This capability, together with the solar position detector data, will allow monitoring of tracker performance at the remote sites and tracker control from Boulder if necessary. Installation of an automated self-calibrating cavity radiometer system in the refurbished MLO solar dome was also completed during the latter part of 1995. A new Eppley automated cavity system was purchased for this application with the goal of incorporating its operation and control in the dome control computer system. When this is completed, continuous direct-solar-beam data will be available from MLO in addition to the NIP data that have been collected since 1958. Special Projects In addition to the routine CMDL monitoring support for the four baseline observatories. The SRCF provided support, resources, training, and logistics assistance in other areas such as the World Meteorological Organization/Global Environmental Fund/Global Atmos- pheric Watch (WMO/GEF/GAW) baseline station network. 3.2.3 Aerosol Optical Depth Remote Sensing Remote sensing of aerosol optical depth is carried out in several projects in CMDL. Derivation of low precision aerosol optical depth from wideband filtered pyrheliometer observations is described in a previous section. Traditional narrow-band sunphotometery measurements are 62 currently made routinely at MLO and Sable Island, Nova Scotia. The CMDL radiation group also maintains a few calibrated handheld sunphotometers of an older but reliable design for use in various short-term field programs. Such field programs have recently included, ACE-1, TOGA CORE, Antarctic dry valley studies, Arctic aircraft flights, and visits to BSRN sites. CMDL will begin to deploy commercial versions of the Multi-Filter Rotating Shadowband Radiometer (MFRSR) from which not only can spectral optical depth be derived but also spectral diffuse and total spectral irradiance fields. As part of a world-wide aerosol optical depth network, the GAW and BSRN programs are awaiting delivery of several multi- channel sunphotometers from the WRC. The automated solar observatory at MLO, which houses the primary CMDL sunphotometer, was upgraded during 1995. The antiquated computers used for dome control and data acquisition were replaced with a single 486-PC. The dome operates, as before, opening and closing each day with both the internal spar and dome tracking the sun while constantly monitoring precipitation and wind speed to determine shutdown conditions. Instruments on the spar include the CMDL PMOD01 sunphotometer, two dual- channel water vapor meters, an active cavity radiometer, and a backup pyrheliometer. Aerosol optical depth data are obtained at three wavelengths: 380, 500, and 778 nm. One value per day per wavelength is derived from the Langley plot technique. The most recent summary of data from this project was given by Dutton et al. [1994]. 3.2.4. Mauna Loa UV Spectroradiometer A research-grade UV spectroradiometer was installed at MLO in July 1995. Because Mauna Loa (mountain) extends above the marine boundary layer, and because of the diurnal upslope-downslope wind circulation, mornings at MLO often exhibit unusually clear skies, providing an excellent site for solar radiation measurements. The instrument described here was developed and operated by the National Institute for Water and Atmosphere at Lauder, New Zealand [McKenzie et al, 1991, 1992]. The solar radiation measured at the earth's surface depends on the transmission of the atmosphere, the earth-sun distance, and the irradiance of the sun. The atmospheric transmission in the UV portion of the spectrum is controlled primarily by total ozone, and, since ozone is affected by anthropogenic influences, solar UV irradiance arriving at the earth's surface is controlled by both natural and anthropogenic effects. Ozone con- centration, in turn, is also affected by changes in solar UV. The UV-A region of the spectrum (320-400 nm) is virtually unaffected by ozone absorption; the UV-B (280-320 nm) is strongly affected by variations in ozone; and the UV-C (<280 nm) is almost entirely absorbed before it reaches the surface. An excellent review of this subject was given by Stamnes [1993]. The data presented here are the first spectroradiometer measurements at MLO. Because of the long Dobson spectrophotometer ozone measurement record at MLO (1957-present), a unique opportunity now exists to obtain well-calibrated UV spectroradiometer measurements and to compare them with the ozone measurements. Past studies show that short-term variations of UV-B irradiance are inversely correlated with variations in total ozone [McKenzie et al, 1991; Hofmann et al., 1996]. A description of the MLO site and instrumentation, and the first 3 months of data are presented. Although this time period was insufficient to observe long-term trends, it is expected that sufficient variation will occur to observe the inverse relation between UV and ozone. Instrumentation The UV spectroradiometer, built around a commercially available Jobin-Yvon DH10 double monochromator, is interfaced with a computer to provide automatic control and data acquisition [McKenzie et al., 1992]. A 17-mm diameter custom-made Teflon diffuser, designed to minimize cosine error, is mounted as a horizontal incidence receptor and views the whole sky. A shadow disk may be added in order to separate the diffuse and direct radiative components. The spectral range of the instrument is 290-450 nm, and the bandpass is about 1 nm. The gratings are driven by a stepper motor under computer control, and a complete scan requires about 200 seconds. The irradiance signal is sampled every 0.2 nm using a photomultiplier as a detector. The instrument is mounted in a weatherproof insulated enclosure (painted white) located on a concrete pad at the MLO site. The interior of the enclosure is temperature controlled using a Peltier heater/cooler unit. The computer control and data logging system are located in a small building near the instrument. Calibration of the spectroradiometer is performed onsite using a standard 1000-W FEL quartz-halogen lamp with calibration traceable to the National Institute of Standards. Calibrations are performed at approximately 6-month intervals using a precision optical bench. A stability test using a 45-W lamp and a wavelength check using a mercury lamp are performed weekly. The expected long-term accuracy of the spectroradiometer system is expected to be better than ±5%. A detailed error analysis for this instrument was given by McKenzie et al. [1992]. Observations The spectroradiometer is programmed to begin measurements at dawn and perform scans at 5° solar zenith angle intervals throughout the day beginning and ending at 95°, except that during the middle of the day the system switches to a scan every 15 minutes. In addition, a scan is performed each midnight to give "dark" values. A typical clear sky scan is shown in Figure 3.14. The solid curve gives total (direct + diffuse) irradiance for July 16, 1995, at a solar zenith angle of 45°. The long-dashed line shows the effective action spectrum accepted for calculating the erythema spectrum used to estimate the effect of UV radiation on human skin [McKinlay and Diffey, 1987]. Note that the effective action spectrum is a dimensionless quantity normalized to 1 for X < 298 nm. The short-dashed line in Figure 3.14 shows the erythemal spectrum for that scan, obtained by multiplying the total irradiance by the effective action spectrum. The erythema can then be calculated by integrating over the erythemal spectrum. In this example the erythema is 17.5 (iW cm -2 . This is the quantity commonly measured by broadband instruments designed to monitor erythema. At smaller solar zenith angle, the irradiances can be much higher, and erythemal irradiances in excess of 45 uW cm -2 have been measured at MLO. For the following analyses, UV spectroradiometer data for 45° solar zenith angles were chosen for clear mornings 63 1 x >N / \ v - 1 \ : f 16 July 1995 (DOY 197) " i J 9:15:44 HST v - . f SZA 45" "••--«._ Dobson ozone 251 OU ' Retrieved ozone 254 DU Erythema 17.5(iWcnr 2 Total Irradiance Erythema - - - Ertective Action Spaclrum : | 270 330 340 360 360 Wavelength (nm) Fig. 3.14. Example of a Mauna Loa UV spectrum obtained on a clear morning (July 16, 1995) at a solar zenth angle of 45° (solid line). A point is plotted every 0.2 nm. Also shown is the erythema spectrum (short-dashed) for this scan obtained by weighting the UV spectrum by the effective action spectrum (EAS) (long-dashed). The EAS is a dimensionless quantity normalized to 1 for X < 298 nm. The erythema for this scan is 17.5 uW cm- 2 . Hnm — hiHHMfr— ^HUfH: 22 E 20 c 'c 18 5l5nm jW — Hm^f-h^** SO c 45 40 03 c 002 001 190 32 30 320 nm - 28 26 11 "=] 10 e 06 OS 200 210 220 230 240 Day of Year 1995 at MLO. Clear mornings at MLO were determined by examining other solar radiation records for MLO. For each scan, 1-nm averages were formed centered at each 1-nm wavelength. In order to quantify changes in UV related to changes in ozone, and to display data as a time series, all spectral irradiance data were adjusted for the eccentricity of the earth's orbit around the sun. All Dobson spectrophotometer total ozone data were taken directly from the MLO observer notes. Retrieved ozone values were obtained from the UV spectroradiometer data using the method of Stamnes et al. [1991], which uses the irradiance ratio I340/I305 t0 infer total ozone. Erythemal radiation data were obtained from the spectroradiometer data by applying the effective action spectrum weighting function and integrating over wavelength as discussed previously. Analyses The radiative amplification factor (RAF) is defined as the percent change of UV irradiance divided by the percent change of total ozone, a quantity that was introduced to estimate the effects of ozone depletion on the incident UV radiation. In this work, RAFs were calculated using the power law formulation from Madronich [1993]: RAF = -Aln(I)/Aln(03), where I is UV irradiance. Referring again to Figure 3.14, it is seen that irradiance decreases by 5 orders of magnitude over the wavelength range 290-320 nm. All of the variability seen in the data is real and some of it is due to solar structure, such as the obvious calcium lines between 390 and 400 nm. As discussed previously, the 290-320 nm range is most strongly influenced by atmospheric ozone. Figure 3.15 shows a time series over the period DOY 192-253, 1995, of 1-nm means of UV irradiance data for a solar zenith angle of 45° over the 295- to 320-nm wavelength band (5-nm intervals). Only data for clear days are shown, giving 27 data points; however, the Fig. 3.15. One-nm averages of spectral irradiance on 27 clear sky mornings at MLO for selected wavelengths at a solar zenith angle of 45° (lower), corresponding erythema calculated using the EAS (middle), and total column Dobson ozone compared with ozone retrieved from the spectroradiometer data (top). The ozone retrieval uses I340/I305 as described by Stamnes et al. [1991]. Error bars shown are 2-o estimates including calibration, noise, and wavelength errors. Note that DOY 190 = July 9, 1995. individual data points are connected by straight lines for continuity. Although this 3-month time series is not long enough to show a significant trend, significant variations in both UV irradiance and total ozone occurred. During this time period, stability tests showed that the instrument was operating well within the expected limits of calibration uncertainty. The error bars show estimated 2-a errors that include calibration, noise, and wavelength errors calculated similar to that shown by McKenzie [1982]. The calculated erythema radiation correlates strongly with irradiance at the shorter wavelengths as expected. Total ozone values retrieved from the spectroradiometer data correlate well with Dobson total ozone but show a systematic difference of about 4 Dobson Units. However, this is better than 2% agreement and could be improved by optimizing the retrieval algorithm for MLO. RAFs, shown as a function of wavelength in Figure 3.16, are negligible for wavelengths longer than about 325 nm and increase for shorter wavelengths. This erythema RAF of about 1.4 for MLO is larger than the values of 1.1-1.2 reported for other locations [McKenzie et al., 1991] but is not significantly different because of the large error bars. Based on the previous discussion of the MLO UV spectroradiometer program, the following can be concluded: (a) The UV spectroradiometer has operated properly at MLO and is producing excellent data within expected calibration limits. The CMDL program plans to 64 MLO Spectroradiometer 45° Solar Zenith Angle 1-nm Averages 290 295 300 305 310 315 320 325 330 335 340 345 Wavelength (nm) Fig. 3.16. Radiative amplification factor (RAF) as a function of wavelength. Note that the erythema RAF is 1.37, equivalent to a wavelength of about 308 nm. continue these measurements as a long-term project in an effort to detect any possible long-term UV spectral trends and to relate these to ozone trends, (b) UV irradiance variations are strongly correlated (inversely) with Dobson total ozone variations, with the highest correlation coefficients at the shortest wavelengths. Erythema calculated from the spectroradiometer is also strongly correlated with ozone. (c) The RAFs of about 1.4 measured at MLO are higher than those previously measured at other sites but may not be significant because of the large error bars, (d) In this limited data set, no significant UV irradiance trend is evident. 3.2.5. MLO Broadband UV A UV broadband horizontal incidence instrument (Yankee UVB-1, SN 950208) was installed at MLO on July 7, 1995. This instrument was interfaced with the station solar radiation data acquisition system to provide 3-minute mean data. The UVB-1 has a spectral response over the wavelength range 280-330 nm and uses a fluorescent phosphor to convert UV light to visible light, which is then detected by a solid-state photodiode. All opu<-a! components are thermally stabilized at 45°C using a thermostatically controlled heater. The UVB-1 will undergo annual factory calibrations, and its calibration will be checked by comparison with the MLO spectro- radiometer that commenced measurements at the site at about the same time. The performance of the broadband UV radiometer relative to the spectral measurements will be used to assess the information content of broadband UV measurements at other CMDL sites. 3.2.6. BSRN CMDL has established an active role in the management of the WCRP BSRN. In addition to supplying data from five CMDL sites to the BSRN archive, CMDL provides the international manager for the program. BSRN is intended to acquire and supply surface radiation data of superior quality for global energy budget and satellite studies. Several instrumentation upgrades are still required at the CMDL observatories to fully comply with BSRN specifications. Recent improvements to the CMDL radiation sites that move in the direction of more complete BSRN compliance are new data loggers and tracking shadow disks for pyranometers and pyrgeometers. In addition, observations of wideband UV-B and PAR as well as spectral diffuse/total irradiance were added at some sites and will be added to more as funding and manpower allow. Considerable effort is put into data processing and analysis for the purpose of passing final data on to the BSRN archive. 3.2.7. WMO GAW STATIONS The CMDL radiation project participated in an effort to establish surface solar radiation programs at the GAW observatories. This effort involved the development of solar radiation monitoring systems, calibration capability, and personnel training for five sites. By the end of 1995, four of the five GAW sites had operational solar radiation monitoring programs. The four operational sites are located in Algeria, China, Tierra del Fuego, and Indonesia. A fifth site in Brazil is under preparation. Each site is equipped with pyrheliometers and pyranometers to monitor direct solar beam, global horizontal and diffuse-sky radiation, plus an automated cavity radiometer system for calibration. All sensors for the GAW sites were characterized and compared to CMDL standards prior to deployment to each site and site calibrations are performed using an automated cavity radiometer that enables the sites to maintain traceability to the absolute scale and the world radiometric reference. Instrumentation for the site was purchased with funds through the World Bank, Global Environmental Fund. Personnel from each site were trained in Boulder for a period of 1 month and some assistance from Boulder was provided in establishing some of the sites. Three of the four sites have been visited by CMDL personnel (China, Tierra del Fuego, and Indonesia); future collaboration between CMDL and these new monitoring sites is anticipated. Data from the sites is under the control of the individual site scientists and are to be sent to GAW archives and to Boulder for inspection and brief analysis. 3.2.8. Volcanic Radiative Forcing and Induced Global Cooling The zonal mean global radiative forcing due to the eruptions of El Chichon (1982) and Mt. Pinatubo (1991) was computed based on near global coverage aerosol optical depth estimates made from satellite [Dutton and Cox, 1995]. These events provide two case studies of the viability of our global observational network and our ability to assess the impact of a major radiation budget altering event. Aerosol optical properties were derived from Mie inverted aerosol size distributions based on surface measured spectral aerosol optical depth. Comparisons between optical properties derived from Mie inversions and those using in situ measured size distributions show little difference between the two in computed volcanic radiative forcing. The computed global zonal mean radiative forcing was used in a simple global thermal mass model to estimate the hemispheric tropospheric cooling, with close agreement to Microwave Sounding Unit (MSU) temperature observations following Mt. Pinatubo, but with poor agreement after El Chichon. The anomalous sea-surface temperature conditions of 1982-1983 are most likely responsible for the thermal model's failure to track observed temperatures. Previously, Dutton and Christy [1992] suggested that the observed volcanic aerosol and radiative forcing following El Chichon and Mt. Pinatubo might be responsible for observed (MSU) and predicted [Hansen et 65 al., 1992] global cooling following these two major eruptions. 3.2.9. BRW Surface Radiation and Meteoro- logical Measurements Measured surface radiation budget components for BRW have been compiled for 1994. From hourly-averaged data, daily and monthly means were produced and merged with ancillary meteorological data for each year, and monthly statistics were computed. These data were published by Stone et al. [1996] which also contains a description of CMDL's monitoring program at BRW and the data processing techniques used. Tables of daily values, monthly statistical summaries, and corresponding plots show annual cycles of several measured and derived radiation variables collated with meteorological data. These data include the four components that constitute the net surface radiation balance, i.e., the upward and downward solar (or shortwave) and the upward and downward thermal infrared (or longwave) irradiances and also direct-beam solar irradiance and surface albedo, derived from the ratio of the reflected to incident radiation. Figure 3.17 is a sample of the data for 1994 showing daily mean time series of the net surface radiation components, the direct beam irradiance, and derived quantities. Daily average total-sky cover, averaged from three hourly National Weather Service (NWS) observations made in Barrow, is also included. Coincident meteorological data Fig. 3.17. Daily average surface irradiance (W nr 2 ) observations and sky cover (cloudiness in tenths of total sky), for Barrow, Alaska, 1994. (not shown) are displayed similarly in the report to facilitate correlative analyses. In addition to the printed report, the 1992, 1993, and 1994 daily data are accessible digitally through the Internet via connection to the CMDL World Wide Web home page. Radiation measurements at BRW show a dramatic increase in net irradiance each spring in late May or early June coinciding with the maximum average daily solar gain at the surface. Snow melt typically occurs during the second week in June [Dutton and Endres, 1991] evidenced by a dramatic decrease in surface albedo (Figure 3.17). Monthly mean net radiation generally peaks in July, which tends to be the least cloudy of summer months. The downwelling thermal irradiance reaches a maximum, on average, during August, which is typically the cloudiest summer month and often the warmest. The data acquisition section (1.5) of this Summary Report gives a description of the BRW meteorology program as well as climate summaries for 1994 and 1995. Year-to-year variations in the net radiation balance at BRW are found to be greatest during the winter months when the longwave components dominate and day-to-day values correlate well with transient weather events. Increased cloudiness, relatively warm temperatures, and westerly winds weaken the surface-based temperature inversion and warm the surface. In fact, clouds tend to radiatively warm the surface most of the year when it is snow covered. Clear periods during winter are coldest and are usually associated with (northeasterly) outflow of air from a quasi-persistent polar anticyclone and relatively calm winds resulting in strong surface-based temperature inversions [Kahl, 1990]. Understanding the links between conditions at BRW and the central Arctic, such as ice distributions in the Beaufort and Chukchi Seas and/or the frequency of cyclones in the central Arctic [e.g., Serreze et al., 1995; Maslanik et al., 1996] is the focus of ongoing research. For instance, an inspection of the 1992-1994 sky-cover record compared with Kahl's [1990] analysis suggests that spring cloudiness has increased significantly in recent years. Because clouds can dramatically influence radiative flux at the surface at this time of year, the net radiation balance may also be affected. A comparison of the 1992-1994 BRW radiation measurements with an earlier record [Maykut and Church, 1973] suggests that this has occurred [Stone et al., 1996]. In turn, these changes may be associated with decreasing sea ice concentrations upwind of Barrow [Maslanik et al., 1996] and/or regionally changing circulation patterns that affect the Arctic hydrologic cycle [e.g., Serreze, et al., 1995]. Only through continuous monitoring of polar processes and analyses of correlative data sets will we begin to understand the complicated feedback mechanisms that determine polar climates; these in turn affect global circulation patterns [Fletcher, 1970]. BRW is strategically situated to investigate Arctic climate interactions because it is sensitive to processes that occur throughout the region. Useful discussions on how synoptic-scale systems influence the Barrow climate are given in Halter and Peterson [1981], Halter and Harris [1983], and Harris and Kahl [1994]. CMDL will continue its monitoring efforts as part of the BSRN [Wielicki et al., 1995]. In addition, the U.S. Department of Energy (DOE) is constructing a Cloud and Radiation Testbed (CART) facility nearby as part of their Atmospheric Radiation Measurement (ARM) Program [Wielicki et al., 1995; 66 Stokes and Schwartz, 1994], and an ambitious field experiment to investigate the Surface Heat Budget of the Arctic (SHEBA) is being organized to take place in the Beaufort Sea. The addition of DOE/ARM remote sensing and other sophisticated ground-based instruments in the vicinity of BRW will greatly enhance our ability to assess the unique radiative properties of the Arctic atmosphere and thus improve parameterizations needed for model studies. In addition, through comparative analyses of the combined BRW, DOE/ARM, and SHEBA data sets, critical aspects of Arctic climate will be further investigated. 3.3. References Bishop, J. KB., W.B. Rossow, and E.G. Dutton, Clouds, aerosols, and the temporal and spatial variability of surface solar irradiance. J. Geophys. Res., in press, 1996. Bodhaine, B.A., Barrow surface aerosol: 1976-1987, Atmos. Environ., 23(11), 2357-2369, 1989. Bodhaine, B.A., and J.J. DeLuisi, An aerosol climatology of Samoa, J. Atmos. Chem., 3, 107-122, 1985. Bodhaine, B.A., J.J. DeLuisi, J.M. Harris, P. Houmere, and S. Bauman, Aerosol measurements at the South Pole, Tellus, 38B, 223-235, 1986. Bodhaine, B.A., J.J. DeLuisi, J.M. Harris, P. Houmere, and S. Bauman, PIXE analysis of South Pole aerosol, in Nuclear Instruments and Methods in Physics Reserach, B22, pp. 24 1 - 247, Elsevier, Holland, 1987. Bodhaine, B.A., B.G. Mendonca, J.M. Harris, and J.M. Miller, Seasonal variations in aerosols and atmospheric transmission at Mauna Loa Observatory, J. Geophys. Res., 86(C8), 7395- 7398, 1981. Cess, R.D..M.H. Zhang, P. Minnis, L. Corsetti, E.G. Dutton, B.W. Forgan, DP. Garber, W.L. Gates, J.J. Hack, E.F. Harrison, X. Jing, J.T. Kiehl, C.N. Long, J. -J. Morcrett, G.L. Potter, V. Ramanathan, B. Subasilar, C.H. Whitlock, D.F. Young, and Y. Zhou, Absorption of solar radiation by clouds: Observations versus models, Science, 267, 496-499, 1995. Charlson, R.J., S.E. Schwartz, J.M. Hales, R.D. Cess, J. A. Coakley, Jr., J.E. Hansen, and D.J. Hofmann, Climate forcing by anthropogenic aerosols, Science, 255, 423-430, 1992. Dutton, E.G., An extended comparison between LOWTRAN7- computed and observed broadband thermal irradiances: Global extreme and intermediate surface conditions, J. Atmos. Ocean. Tech.. 10, 326-336, 1993. Dutton, E.G. and S.K. Cox, Tropospheric radiative forcing from El Chichdn and Mt. Pinatubo: Theory and observations, Colorado State University, Dept. of Atmos. Science Paper No. 586, Fort Collins, CO, 209 pp., 1995. Dutton, E.G., and D.J. Endres, Date of snowmelt at Barrow, Alaska, U.S., Arc. Alp. Res.. 23(1), 115-119, 1991. Dutton, E.G. and J.R. Christy, Solar and radiative forcing at selected locations and evidence for global lower tropospheric cooling following the eruptions of El Chichon and Pinatubo, Geophys. Res. Lett., 23, 2313-2316, 1992. Dutton, E.G., J.J. DeLuisi, and A. P. Austring, Interpretation of Mauna Loa atmospheric transmission relative to aerosols, using photometric precipitable water amounts, J. Atmos. Chem., 3, 53-68, 1985. Dutton, E.G., P. Reddy, S. Ryan, and J.J. DeLuisi, Features and effects of aeosol optical depth observed at Mauna Loa, Hawaii: 1982-1992, J. Geophys. Res., 99(D4), 8295-8306, 1994. Elkins, J.W., and R.M. Rosson (Eds.), Geophysical Monitoring for Climatic Change No. 17, Summary Report 1988, 142 pp., NOAA Air Resources Laboratory, Boulder, CO, 1989. Fletcher, JO., Polar ice and the global climate machine, Bull. Atomic. Sci., 40-47, 1970. Ellis, H.T., and R.F. Pueschel, Solar radiation: Absence of air pollution trends at Mauna Loa, Science, 172, 845-346, 1971. Garratt, J. R., and A.J. Prata, Downwelling longwave fluxes at continental surfacaes-a comparison of observations with GCM simulations and implications for the global land-surface radiation budget, J. Clim., 9(3), 646-655, 1996. Halter, B.C., and J.M. Harris, On the variability of atmospheric carbon dioxide concentration at Barrow, Alaska during winter, J. Geophys. Res., 88, 6858-6864, 1983. Halter, B.C., and J.T. Peterson, On the variability of atmospheric carbon dioxide concentration at Barrow, Alaska during summer, Atmos. Environ., 15, 1391-1399, 1981. Hansen, J.E., A. Lacis, R. Ruedy, and M. Sato, Potential climate impact of Mount Pinatubo eruption, Geophys. Res. Lett., 19, 215-218, 1992. Harris, J.M., and J.D.W. Kahl, Analysis of 10-day isentropic flow patterns for Barrow, Alaska: 1985-1992, J. Geophys. Res.. 99(D12), 25,845-25,855, 1994. Hofmann, D.J., S.J. Oltmans, G.L. Koenig, B.A. Bodhaine, J.M. Harris, J. A. Lathrop, R.C. Schnell. J. Barnes, J. Chin, D. Kuniyuki, S. Ryan, R. Uchida, A. Yoshinaga, P.J. Neale, D.R. Hayes, Jr., V.R. Goodrich, WD. Komhyr, R.D. Evans, B.J. Johnson, DM. Quincy, and M. Clark, Record low ozone at Mauna Loa Observatory during winter 1994-1995: A consequence of chemical and dynamical synergism? Geophys. Res. Lett., 23, 1533-1536, 1996. Kahl, J.D., Characteristics of the low-level temperature inversion along the Alaskan Arctic coast, Int. J. Climatoi, 10, 537-548, 1990. Madronich, S., The Atmosphere and UV-B Radiation at Ground Level, in Environmental UV Photobiology, edited by A. R. Young et al.. Plenum Press, New York, 1-39, 1993. Maslanik, J. A., M.C. Serreze, and R.G. Barry, Recent decreases in summer Arctic ice cover and linkages to anomalies in atmospheric circulation, Geophys. Res. Lett., submitted, 1996. Maykut, G.A., and P.E. Church, Radiation climate of Barrow, Alaska, 1962-66, J. Appl. Meteorol.. 12, 620-628, 1973. McKenzie, R. L., W. A. Matthews, and P. V. Johnston, The relationship between erythemal UV and ozone, derived from spectral irradiance measurements, Geophys. Res. Lett., 18, 2269-2272, 1991. McKenzie, R. L., P. V. Johnston, M. Kotkamp, A. Bittar, and J. D. Hamlin, Solar ultraviolet spectroradiometry in New Zealand: Instrumentation and sample results from 1990, Appl. Opt., 31, 6501-6509, 1992. McKinlay, A.F., and B.L. Diffey, A reference action spectrum for ultraviolet induced erythema in human skin, J. Int. Comm. Ilium, 6, 17-22, 1987. National Research Council (NRC), Aerosol Radiative Forcing and Climate Change, in Panel on Aerosol Radiative Forcing and Climate Change, Board on Atmospheric Sciences and Climate, Commission on Geosciences, Environment, and Resources, National Academy Press, Washington, DC, 161 pp., 1996. Nemesure, S., R.D. Cess, E.G. Dutton, J.J. DeLuisi, Z. Li, and H.G. Leighton, Impact of the shortwave radiation budget of the surface-atmosphere system for snow-covered surfaces, J. Clim., 7, 579-585, 1994. Quakenbush, T.K., and B.A. Bodhaine, Surface aerosols at the Barrow GMCC observatory: Data from 1976 through 1985, NOAA Data Rep. ERL ARL-10, 230 pp., NOAA Air Resources Laboratory, Silver Spring, MD, 1986. Radke, L.F., C.A. Brock, R.J. Ferek, and D.J. Coffman, Summertime arctic hazes, paper A52B-03 presented at the American Geophysical Union Fall Annual Meeting, San Francisco, December 3-7, 1990. Serreze, M.C, J. A. Maslanik, JR. Key, R.F. Kokaly, and DA. Robinson, Diagnosis of record minimum in Arctic sea ice area during 1990 and associated snow cover extremes, Geophys. Res. Lett., 22(16), 2183-2186, 1995. Stamnes, K., The stratosphere as a modulator of ultraviolet radiation into the biosphere, in Surveys of Geophysics, 14, Kluwer, Netherlands, 167-186, 1993. 67 Stamnes, K., J. Slusser, and M. Bowen, Derivation of total ozone abundance and cloud effects from spectral irradiance measurements, Appl. Opt., 30, 4418-4426, 1991. Stokes, G.M., and S.E. Schwartz, The Atmospheric Radiation Measurement (ARM) Program: Programmatic background and design of the cloud and radiation test bed, Bull. Amer. Meteorol. Soc, 75, 1201-1221, 1994. Stone, R.S., T. Mefford, E.G. Dutton, D. Longenecker, B. Halter, and D. Endres, Barrow, Alaska, surface radiation and meteorological measurements: January 1992 to December 1994, NOAA Data Report, ERL CMDL-ll, NO A A Environmental Research Laboratories, Boulder, CO, 81 pp., 1996. Whitlock, C.H., T.P. Charlock, W.F. Staylor, R.T. Pinker, I. Laszlo, A. Ohmura, H. Gilgen, T. Konzelman, R.C. DiPasquale, CD. Moats, S.R. LeCroy, and N.A. Ritchey, First global WCRP shortwave surface radiation budget dataset. Bull. Amer. Meteorol. Soc, 76, 905-922, 1995. Wielicki, B.A., R.D. Cess, M.D. King, D.A. Randall, and E.F. Harrison, Mission to planet earth: Role of clouds and radiation in climate, Bull. Amer. Meteorol. Soc, 76(11), 2125-2153, 1995. 68 4. Ozone and Water Vapor S. Oltmans (Editor), D. Hofmann, J. Harris, B. Johnson, R. Evans, G. Koenig, J. Lathrop, M. O'Neill, H. Vomel, D. Quincy, W. Komhyr, M. Clark, and E. Hackathorn 4.1. Continuing Programs 4.1.1. Total Ozone Observations Total ozone observations continued throughout 1994 and 1995 at 15 of the 16 stations that comprise the U.S. Dobson spectrophotometer network (Table 4.1). Of the 16 stations, 5 were operated by CMDL personnel, 5 by NWS, 2 are domestic cooperative stations, and 4 are foreign cooperative stations. All stations are either fully or semiautomated. In addition, a Brewer spectrophotometer was operated on a nearly continuous basis at Boulder. The Peruvian station was still out of operation at the end of 1995, although a new baseline monitoring station is under construction. Operations will likely start in late 1996. In May 1995 the Fresno instrument and shelter were moved 30 miles southwest of Hanford, California. The Bismarck instrument and shelter were moved about 150 m in August 1994. Provisional daily total ozone amounts applicable to local apparent noon for the stations listed in Table 4.1 were archived at the World Ozone Data Center (WODC), 4905 Dufferin Street, Ontario M3H 5T4, Canada, in Ozone Data for the World. Table 4.2 lists the monthly mean total ozone amounts measured at the various stations for 1994 and 1995. (Monthly means are computed for stations where observations were made on at least 10 days each month.). Ten Dobson ozone spectrophotometers in the CMDL network as well as 29 others were calibrated during 1994 and 1995. Tables 4.3 list all the instruments calibrated and the resulting calibration difference expressed as a percent ozone difference. This percent difference is between ozone calculated from the test and the standard instrument measurements with the ADDSGQP observation type at a u value of 2, and a total ozone value of 300 Dobson Units (DU), before any repair or calibration adjustment is made. The table also lists the place of the calibration and the standard instrument used. The Mauna Loa Observatory, Hawaii (MLO) instrument D076 failed mechanically in February 1994. This automated instrument was repaired and back in service in May 1994. During the repair the left side mirror was replaced due to a deteriorating surface. CMDL participated in an international Dobson spectrophotometer calibration at Izana Observatory (Tenerife, Spain) in June 1994 and at Arosa, Switzerland (LKO) in July 1995 as part of its role as the World Center for Dobson Calibrations. Instruments for Mexico City, Mexico; Comodoro Rivadavia, Argentina; and Montevideo, Uruguay, were calibrated in Boulder during this period. A representative from the Czech Hydrological and Meteorological Institute assisted with the latter two instruments. These were new instruments from Ealing Opto-Electronics. Reevaluation of more than 400 station-years of total ozone data from 25 CMDL (and its predecessor organizations) Dobson spectrophotometer stations was completed in 1995. Corrections were based on field instrument calibrations made throughout the years with World Primary Standard Dobson Instrument no. 83 [Komhyr et al., 1989]. This instrument's long-term ozone measurement precision has been maintained since the early 1960s at ±1% by means of Langley calibration TABLE 4.1. U.S. Dobson Ozone Spectrophotometer Station Network for 1994-1995 Station Period of Record Instrument No. Agency Bismarck, North Dakota Jan. 1, 1963-present 33 NOAA Caribou, Maine Jan. 1, 1963-present 54 NOAA Wallops Is., Virginia July 1, 1967-present 38 NOAA; NASA SMO Dec. 19, 1975-present 42 NOAA Tallahassee, Florida May 2, 1964-Nov. 30, 1989; ss NOAA; Florida State University Nov. 1, 1992-present Boulder, Colorado Sept. 1, 1966-present 01 NOAA Fairbanks, Alaska March 6, 1984-present 63 NOAA; University of Alaska Lauder, New Zealand Jan. 29, 1987-present 12 NOAA; DSIR MLO Jan. 2, 1964-present 76 NOAA Nashville, Tennessee Jan. 2, 1963-present 79 NOAA Perth, Australia July 30, 1984-present XI NOAA; Australian Bureau Meteorology SPO Nov. 17, 1961-present 82 NOAA Haute Provence, France Sept. 2, 1983-present ^ NOAA; CNRS Huancayo, Peru Feb. 14, 1964-Dec. 31, 1992 N7 NOAA; IGP BRW June 6, 1986-present 91 NOAA Fresno, California June 22, 1983-March 13, 1995 94 NOAA Hanford, California March 15, 1995-present 94 NOAA 69 TABLE 4.2. Provisional 1994 Monthly Mean Total Ozone Amounts (M-Atm-CM) Station Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. 1994 Bismarck, North Dakota 361 367 372 351 327 322 319 302 286 294 286 300 Caribou, Maine 340 382 390 377 369 338 324 324 316 299 293 304 Wallops Is., Virginia 320 343 347 325 355 327 309 302 292 281 255 270 SMO 241 242 244 237 237 241 240 244 244 248 251 242 Tallahassee, Florida 289 291 306 308 338 321 322 299 - - 241 269 Boulder, Colorado 321 331 333 34 1 315 295 299 280 277 274 265 276 UAF-G1, Alaska - [371] 420 408 380 347 312 278 - - - - Lauder, New Zealand 277 267 262 265 289 315 337 361 370 360 341 302 MLO 244 256 - - 279 271 268 265 258 256 238 220 Nashville. Tennessee 321 323 339 328 334 322 313 304 296 277 252 276 Perth, Australia 266 262 265 257 269 291 294 300 309 317 307 278 SPO 266 253 [245] [231] [277] [231] [239] [226] - 132 269 316 Haute Provence, France 326 373 314 382 352 332 320 305 31 1 295 273 293 Huancayo, Peru Station closed BRW - - 457 445 379 346 310 293 - - - - Fresno, California 314 324 325 332 333 1995 303 305 292 269 275 280 Bismarck, North Dakota 334 358 341 347 347 321 311 282 286 290 292 297 Caribou, Maine 349 382 357 372 348 323 320 304 302 - 311 325 Wallops Is., Virginia 307 344 316 325 316 323 312 297 288 267 299 284 SMO 242 243 243 244 243 247 245 250 259 262 251 251 Tallahassee, Florida 267 282 284 288 302 313 302 308 294 266 277 263 Boulder, Colorado 296 290 304 328 325 299 281 276 284 270 276 275 UAF-GI, Alaska - [349] 365 367 341 326 300 302 268 326 - - Lauder, New Zealand 277 267 282 273 280 302 335 336 361 348 328 287 MLO 217 223 254 268 280 274 262 262 261 255 254 239 Nashville, Tennessee 321 323 339 328 334 322 313 304 296 277 252 276 Perth, Australia 272 257 268 276 268 282 295 292 312 311 306 273 SPO 287 270 [231] [256] [255] [245] [246] [223] - 120 192 257 Haute Provence, France 293 319 333 340 340 331 322 329 304 277 283 303 Huancayo, Peru Station closed BRW - [354] 407 386 339 345 304 300 269 [260] - - Handford, California 293 292 315 316 338 330 298 292 286 272 264 285 Monthly mean ozone values in square brackets are derived from observations made on fewer than 10 days per month. observations conducted periodically at MLO and with standard lamps. Procedures used in reevaluating the data are described in detail in Komhyr [1993], Seasonal and annual downward trends in ozone during 1979-1995, determined from the reevaluated data for five U.S. mainland stations (Caribou, Maine; Bismarck, North Dakota; Boulder, Colorado; Wallops Island, Virginia; and Nashville, Tennessee) and for MLO and Samoa Observatory, American Samoa (SMO), are shown in Table 4.4. Also included in the table are the ozone trends measured at Fresno, California, during 1985-1995. The statistical method used in determining the trends (G. C. Reinsel, University of Wisconsin-Madison) was similar to that employed by the 1988 Ozone Trends Panel [WMO, 1988] whereby solar cycle and ozone QBO effects are removed from the data. Note that the downward trend in ozone, averaged over the five contiguous U.S. stations with the longest records, is largest at -5.45% per decade for spring (March-May) months and smallest at -1.6% per decade for autumn (September to November) months. On an annual basis, the downward ozone trend at these sites averages -3.58% per decade. These trends exhibit a slight recovery from values determined from 1979-1993 data that encompassed record low ozone values over the U.S. during the winter of 1992-1993 [Komhyr et al., 1994]. For the earlier time period, the average five-station downward ozone trend for spring months (not shown) was -5.79% per decade and -3.8% per decade on an annual basis. Downward trends in ozone measured nearer the equator at MLO and SMO are significantly smaller. 4.1.2. Umkehrs Umkehr observations made with the Automated Dobson Network instruments continued in 1994 and 1995 at Boulder; Haute Provence, France; Lauder, New Zealand; MLO; Perth, Western Australia; and at the University of Alaska's Geophysical Institute. Umkehr processing is set to resume early in 1996. Processing will begin with MLO, followed by Lauder and the other stations in a 70 TABLE 4.3. Dobson Ozone Spectrophotometers Calibrated in 1994-1995 Instrument Calibration Calibration Standard Station Number Date Correction (%) Number Place J 994 Lisbon, Spain D013 Aug. 2, 1990 +0.7% 65 Izana Observatory Oslo, Norway D056 Aug. 21, 1986 +0.5% 65 Izana Observatory Potsdam, Germany D064 Aug. 2, 1990 +0.6% 65 Izana Observatory Huancayo, Peru D087 May 15, 1985 +0.9% 65 Izana Observatory Natal, Brazil D093 May 20, 1986 +2.9% 65 Izana Observatory Buenos Aires, Argentina D097 July 15, 1992 +0.1% 65 Izana Observatory El Arenosillo, Spain D120 Aug. 9, 1990 + 1.3% 65 Izana Observatory Ushuaia, Argentina D131 None N/A 65 Izana Observatory Tallahassee, Florida D058 Sept. 9, 1991 -.3 83 Boulder Boulder, Colorado D06I Aug. 27, 1992 0.0% 65 Boulder MLO D076 June 13, 1993 N/A 83 Boulder SPO D080 May 26, 1988 0.5% 83 Boulder BRW D091 May 26, 1989 0.0% 83 Boulder Fresno, California D094 June 26, 1989 1.0% 83 Boulder Mexico D.F Mexico D098 August 1978 1995 -0.3% 83 Boulder RA VI Spare IS None N/A 65 LKO Arosa Vindeln, Sweden 30 May 10, 1990 +0.7% 65 LKO Arosa United Kingdom 3 2 May 1995 N/A 6 5 LKO Arosa Uccle, Belgium 40 Aug. 1, 1990 +2.0% 65 LKO Arosa United Kingdom, Standard 41 Aug. 2, 1990 + 1.2% 6 5 LKO Arosa Sestola, Italy 48 Nov. 12, 1980 +2.4% 65 LKO Arosa Bordeaux, France 4') July 10, 1990 +0.3% 65 LKO Arosa Reykjavik, Iceland 50 Aug. 2, 1990 + 1.1% 65 LKO Arosa Arosa, Switzerland 62 Aug. 7, 1992 + 1.7% 65 LKO Arosa Belsk, Poland 84 Aug. 2, 1990 +0.2% 65 LKO Arosa l'Obs. Haute Provence, France 85* July 10, 1990 +0.7% 65 LKO Arosa Denmark 92* Aug. 2, 1990 + 1.0% 65 LKO Arosa Arosa, Switzerland 101 Aug. 2, 1990 +2.1% 6 5 LKO Arosa Hohenpeissenberg, Germany 104 Aug. 2, 1990 + 1.6% 65 LKO Arosa Moscow, Russia 107 Aug. 5, 1990 + 1.4% 65 LKO Arosa Budapest, Hungary 110 Aug. 2, 1990 +0.5% 65 LKO Arosa Tsukuba, Japan, Standard 116* June 29, 1992 +0.6% 65 LKO Arosa Bucharest, Romania 121 Aug. 5, 1990 Not consistent 65 LKO Arosa Bismarck, North Dakota D033 Oct. 1, 1993 + 1.5 83 Boulder Caribou, Maine D034 Sept., 9. 1991 +0.3 83 Boulder Wallops Island, Virginia D038 Sept. 16, 1991 + 1.0 83 Boulde Nashville, Tennessee D079 Aug. 14, 1991 +0.6 81 Boulder Comodoro Rivadavia, D133 New Dobson N/A 83 Boulder Argentina Montevideo, Uruguay D134 New Dobson N/A 83 Boulder collaborative effort with the University of Alabama, Huntsville. Since the reprocessing of the total ozone from these stations will have been completed, the updated calibration tables and ozone values will be incorporated into the Umkehr processing. Under conditions of high stratospheric aerosol loading, which was the case following the eruption of Mt. Pinatubo, reliable ozone profiles can be obtained from the Umkehr technique only by correcting for aerosols. Such conditions prevailed through 1992 at most of the sites. The effort with University of Alabama, Huntsville, will include the application of proper aerosol corrections to the profile data. 4.1.3. Surface and Tropospheric Ozone At least 20-year records of observation are now available for each of the four CMDL baseline sites. Records at Bermuda, Barbados, and Niwot Ridge are at least 5 years in length. At Westman Islands, Iceland, observations began in 1992. For several years, data were being obtained from Mace Head, Ireland, in a cooperative program as part of the Atmosphere/Ocean Chemistry Experiment (AEROCE). Data continues to be received from Mace Head but CMDL is no longer actively involved in that measurement program. The aging complement of surface 71 TABLE 4.4. Annual and Seasonal Trends January 1979-December 1993 Latitude Ai nuial Dec .-Feb. March-May June-Aug. Sept .-Nov. Station Trend Std. Error Trend Std. Error Trend Std. Error Trend Std. Error Trend Std. Error Caribou, Maine 46.9°N -4.00 0.71 -4.84 1.73 -5.64 1.12 -3.34 0.79 -1.52 1.16 Bismarck, North Dakota 46.8°N -3.30 0.63 -3.25 1.43 -5.69 1.01 -2.00 0.93 -1.62 0.95 Boulder, Colorado 40.0°N -3.85 0.61 -3.97 1.23 -6.50 1 .22 -2.68 0.75 -1.51 0.98 Wallops Is., Virginia 37.9°N -3.67 0.68 -4.79 1.33 -4.77 1.28 -2.66 0.78 -2.10 1.18 Nashville, Tennessee 36.3°N -3.09 0.70 -4.08 1.25 -4.62 1.35 -2.03 0.92 -1.23 1.22 Fresno, California* 36.8°N -3.81 1.37 -3.18 2.00 -3.84 3.00 -3.52 1.71 -4.74 1.31 MLO 19.5°N -0.53 0.77 -1.55 1.15 -0.51 1.44 -0.20 0.94 0.08 0.74 SMO 14.3°S -1.66 0.66 -1.48 0.96 -2.13 0.80 -1.42 1.09 -1.61 0.85 Average over first five stations -3.58 -4.19 -5.45 -2.54 -1.60 ozone monitors, some of which are 20 years old, has experienced a number of breakdowns. Significant blocks of data were lost at Barbados and SMO during 1994 and 1995. The extent to which tropospheric ozone may have changed since preindustrial times and over the past 20 years is of significant interest. Surface ozone measurements using modern instruments were made only during the past 25 years. Some quantitative measurements using wet chemical techniques were made in Europe in the 1950s [Staehelin et al., 1994], and one set of measurements dates from the turn of the century [Volz and Kley, 1988]. These measurements show that over Europe ozone in the lower troposphere at least doubled from the beginning of the measurements to the early 1980s. Many of the more recent measurements (since 1970) show that at least over Europe, and probably over other areas in the midlatitudes of the northern hemisphere, tropospheric ozone continued to increase through the 1970s and early 1980s [Oltmans et al., 1995]. An analysis of most of the recent data sets from surface stations (some located above the boundary layer) suggests that over at least the past decade there has been a significant slowing in tropospheric ozone growth at midlatitudes of the northern hemisphere [Oltmans et al., 1995]. Most other regions show no evidence for tropospheric ozone increases over the past 20 years and in some cases, such as South Pole Observatory, Antarctica (SPO), significant decreases are evident. The four CMDL baseline observatory surface ozone data records are among the longest available. The annual averages and long-term trends at each location are shown in Figure 4.1. The numerical trend displayed in the figure is a linear regression of the monthly mean observations. At Barrow Observatory, Barrow, Alaska (BRW) there was a significant upward trend prior to 1990, primarily due to summer increases. Smaller annual averages over the last 5 years have driven the trend downward to show an overall small but insignificant increase. The lower amounts in the 1990s are consistent with the results seen in the ozonesonde record at the Canadian stations [Tarasick et al., 1995]. At MLO the overall record beginning in 1974 shows a small but significant increase. At the two e Barrow, Alaska 70°N -©-©- 0.18 ± 0.24 %/year Hm i.i.i.i.i.i.i, 76 7i 82 84 90 92 94 96 Mauna Loa 19°N 0.35 + 0.22 %/year 3397 m J I I I I I I I I , I I I L. 76 78 82 84 86 90 92 94 96 : American '.. . ffi ft.©..© Samoa © © ft> 14°S •.i.i. ty © w w ^ -0.26 ± 0.38 © %/year i i 1 82 m i 76 78 80 82 84 86 90 92 94 96 South Pole 90°S -0.70 + 0.20 %/year 2835 m J — i — I i I i I i I , i.i .i, 76 78 80 82 84 90 92 94 96 Year Fig. 4.1. Annual average surface ozone mixing ratios in parts per billion (ppbv) for BRW, MLO, SMO, and SPO. The solid line is a linear trend fit to the monthly anomalies. The trend and 95% confidence levels in percent per year are also shown. 72 southern hemisphere sites there are long-term decreases. The monthly ozone means for each of the four CMDL At SMO this decrease is not significant but at SPO a large baseline sites for the period of observation are given in and significant decline is evident. This is most apparent Table 4.5. For MLO the means are for the hours 0000- after 1986. This decline at SPO was discussed in the 1993 0800 LST, which falls within the time of downslope flow Summary Report [Peterson and Rosson, 1994]. at the observatory. TABLE 4.5. Monthly Mean Surface Ozone Mixing Ratios (ppbv) Year Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec BRW 1973 - - 22.3 15.8 15.6 19.3 15.1 18.8 23.3 30.8 30.2 34.8 1974 28.7 27.4 - - 23.3 22.0 17.7 18.1 26.1 31.6 32.8 30.9 1975 27.4 29.9 32.7 22.5 23.4 23.7 19.7 19.2 23.0 30.3 28.3 26.3 1976 29.2 31.2 24.4 9.7 11.3 24.1 18.6 18.1 20.3 31.6 30.7 29.1 1977 31.3 32.9 20.8 4.7 20.2 24.5 21.1 20.8 22.4 25.6 33.6 28.0 1978 32.1 32.2 31.0 21.7 22.0 24.1 21.4 22.3 23.6 32.8 29.6 30.3 1979 33.9 31.1 22.6 19.7 25.1 22.5 18.9 18.5 21.1 33.2 32.2 29.3 1980 33.5 33.6 24.5 19.6 18.1 24.7 20.3 19.1 27.9 25.6 34.3 30.0 1981 30.5 27.9 24.5 23.8 26.9 26.1 19.8 23.2 26.2 31.3 34.6 30.9 1982 31.6 31.1 22.5 12.2 15.3 27.1 24.5 23.3 29.7 34.6 36.2 34.5 1983 27.9 34.2 25.9 21.6 21.4 20.4 23.6 22.4 28.2 33.5 30.8 33.0 1984 26.8 19.9 21.5 6.8 16.4 25.5 21.9 22.1 24.3 35.7 38.3 32.2 1985 31.8 28.7 - - 20.2 28.0 21.2 25.0 28.8 31.4 33.0 33.4 1986 35.5 28.0 20.5 13.9 17.4 24.7 20.4 21.6 25.0 30.3 34.6 31.4 1987 31.1 27.2 22.0 15.0 24.0 30.9 23.3 25.6 31.1 32.5 38.8 36.4 1988 36.4 30.9 22.7 23.8 22.2 26.2 21.7 23.8 26.9 31.6 34.2 31.4 1989 30.2 36.8 32.9 24.6 20.2 24.3 19.9 21.0 31.4 34.8 35.0 35.8 1990 32.3 29.0 27.1 19.5 24.6 23.6 21.1 25.5 32.5 33.1 34.3 32.4 1991 31.6 30.2 16.8 14.3 29.4 25.4 24.4 31.6 28.3 27.5 29.8 27.3 1992 29.1 27.8 27.4 15.5 16.9 19.4 18.3 18.8 23.9 27.2 28.6 26.0 1993 26.1 26.5 14.7 17.5 20.6 22.4 16.3 19.1 24.1 29.1 30.3 31.8 1994 31.4 29.7 21.7 10.9 11.3 25.6 21.5 19.4 29.6 31.7 34.7 31.4 1995 33.0 28.5 18.0 18.8 22.4 27.6 MLO 20.5 21.3 25.4 35.1 32.2 28.0 1973 - - - - - - - - - 36.5 33.4 36.0 1974 34.5 42.8 51.8 51.8 49.6 40.8 38.0 31.5 31.2 31.9 29.6 31.9 1975 31.4 38.9 47.5 51.7 48.7 47.3 43.3 43.7 34.1 31.5 29.6 - 1976 37.3 41.6 36.7 41.2 39.3 35.6 32.2 30.0 25.6 30.9 39.3 37.5 1977 - 35.8 48.5 41.6 46.4 41.5 29.2 28.9 - - 39.0 33.2 1978 36.1 39.2 45.0 49.2 37.2 31.8 33.5 29.2 31.9 28.8 27.7 33.6 1979 39.5 36.6 48.5 50.3 48.5 43.7 36.7 29.4 37.4 31.0 38.2 41.6 1980 41.0 42.1 45.0 53.8 47.1 42.0 35.8 38.6 27.4 36.8 38.4 34.5 1981 43.5 42.2 52.1 61.1 60.8 38.6 39.1 37.0 35.9 37.8 38.3 39.9 1982 35.1 40.7 48.8 52.5 54.3 39.3 31.6 30.2 32.4 32.9 36.7 45.7 1983 46.8 53.6 59.1 63.4 56.7 47.6 44.4 32.2 31.0 38.6 34.3 40.2 1984 40.4 40.5 48.4 - 47.1 46.8 37.8 33.8 36.9 31.0 31.8 37.6 1985 43.2 41.6 52.4 50.7 48.4 43.9 40.3 36.9 31.4 33.2 36.2 38.1 1986 39.9 40.0 43.2 46.4 47.2 45.4 31.3 38.7 24.3 38.1 30.2 41.6 1987 38.4 40.5 50.0 - - - - 36.3 31.9 34.4 40.5 33.4 1988 44.8 43.3 50.3 53.1 47.5 32.3 41.2 33.5 34.2 30.0 29.5 36.1 1989 40.7 37.4 40.6 48.4 45.9 35.8 37.1 38.5 38.6 24.8 35.0 40.7 1990 37.8 38.3 49.6 52.0 55.0 43.3 36.7 35.3 30.5 38.1 28.8 39.6 1991 45.3 41.8 48.4 56.9 55.5 41.5 39.2 33.1 31.5 33.9 32.6 33.3 1992 40.2 42.8 53.8 61.0 46.9 49.5 38.8 30.6 26.3 24.9 29.2 32.2 1993 42.2 41.3 50.0 63.3 55.2 50.6 38.0 30.6 26.6 35.3 42.7 38.3 1994 43.3 37.5 48.5 57.9 48.7 35.4 30.1 29.8 33.5 41.4 40.5 45.5 1995 34.4 42.0 51.1 50.5 52.1 44.6 34.6 45.8 42.1 36.7 30.7 35.5 73 TABLE 4.5. Monthly Mean Surface Ozone Mixing Ratios (ppbv) - Continued Year Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. SMO 1976 9.9 9.1 8 8 8.3 11.2 13.5 17.6 21.7 17.9 15.2 12.4 13.2 1977 11.0 X 6 8 8 9 2 12.2 20.7 19.9 20.7 15.9 16.7 15.2 15.0 1978 10.2 9.2 9 2 8.4 13.6 15.9 22.8 15.9 17.7 18.6 13.9 13.3 1979 10.5 8.3 8.1 12.5 15.1 17.2 18.6 19.7 19.3 18.8 13.8 14.8 1980 9.8 7.9 8.5 11.6 15.1 19.3 16.8 21.8 17.7 - 11.4 9.7 1981 9 4 4.4 9 5 9.3 14.0 17.0 20.0 16.4 15.1 15.3 10.9 11.8 1982 8.2 9.1 6.7 7.3 14.0 16.9 16.7 16.1 20.2 13.5 17.0 12.2 1983 8.9 6.3 9.4 11.5 11.2 18.3 19.8 20.8 13.0 15.3 13.0 8.5 1984 7.4 7.1 8 5.7 17.3 18.4 18.7 17.6 14.5 17.2 14.7 . 1985 10.3 10.0 7.3 11.2 11.8 17.1 20.2 17.7 17.1 14.0 14.9 10.7 1986 8.4 8.6 8 4 7.2 - 14.0 20.3 21.3 14.5 16.6 12.9 12.7 1987 8 1 6.4 6.5 13.6 16.3 20.1 20.7 24.8 17.1 20.2 10.1 11.9 1988 7 4 8.4 8 1 9.9 11.8 13.9 21.6 17.1 18.3 15.8 13.3 9.1 1989 9.3 8.0 9 12.1 10.6 19.6 21.5 20.1 19.4 16.1 18.8 13.8 1990 11.4 111 11.3 10.8 16.7 16.1 20.0 19.3 13.4 12.7 13.2 13.2 1991 6.7 8.7 6.6 7.9 13.8 14.4 20.9 20.0 23.2 15.1 12.2 15.4 1992 12.2 - 12.1 - 11.7 18.5 15.2 13.7 12.2 13.9 13.0 9.9 1993 9.4 9.6 9.1 - - - - - - - - . 1994 8 9 8.3 9.4 6.9 12.7 18.0 SPO 18.1 22.5 13.6 10.1 13.7 8 1974 - - - - - - - - - - - 28.7 1975 24.6 25.7 24.9 29.4 35.7 34.9 35.3 34.4 35.1 36.2 33.9 31.6 1976 26.2 21.3 21.9 25.2 29.4 31.7 34.4 33.6 26.6 25.2 25.8 24.9 1977 23.5 22.0 21.5 26.7 31.5 33.1 34.2 36.0 33.1 29.9 26.7 30.8 1978 27.4 24.3 - - - 33.1 34.8 34.3 33.5 31.8 33.0 31.3 1979 25.1 22.2 23.6 29.6 33.1 34.7 37.9 34.5 33.1 34.4 - 25.1 1980 24.9 22.5 22.3 26.9 29.3 33.3 35.0 34.4 33.0 29.1 26.8 23.2 1981 21.3 19.6 20.1 24.6 29.0 32.5 35.3 37.7 37.8 37.6 35.3 29.5 1982 - 21.5 24.0 31.5 33.6 35.5 36.4 34.9 33.1 28.5 27.7 24.5 1983 21.3 20.5 21.2 27.3 30.6 33.1 34.3 32.7 33.4 30.6 27.8 25.6 1984 20.5 20.1 21.3 29.0 34.2 36.1 37.5 36.1 35.9 31.5 34.0 28.2 1985 22.7 19.3 22.0 24.4 30.5 36.6 36.7 34.4 32.3 28.3 26.7 24.8 1986 18.3 20.1 21.9 27.1 34.4 36.3 38.7 38.2 36.9 33.0 29.4 25.4 1987 20.0 17.8 19.3 23.5 28.0 30.9 29.7 - - - 24.4 26.0 1988 18.9 21.5 23.7 27.4 31.0 34.1 34.0 33.0 33.9 31.1 29.5 25.3 1989 22.9 19.7 18.7 25.4 35.3 35.4 36.2 36.0 35.5 24.2 28.6 23.4 1990 20.2 20.2 23.1 24.5 27.6 31.2 32.3 30.1 28.8 27.0 27.4 23.7 1991 23.8 19.9 18.9 23.8 26.8 30.9 31.8 34.1 27.7 27.2 22.8 22.1 1992 18.0 17.9 16.9 22.4 29.7 33.5 34.9 34.4 28.5 25.8 26.7 29.3 1993 23.4 20.1 17.5 23.1 26.4 29.7 30.7 30.3 29.1 27.5 29.7 22.9 1994 25.0 19.7 21.1 24.4 27.7 33.1 34.1 33.5 31.6 27.3 29.3 26.8 1995 25.3 18.0 18.0 19.8 24.0 28.3 34.5 33.0 21.8 26.3 29.2 26.4 Monthly means are computed from daily (24-hr) averages. 4.1.4. OZONESONDES Table 4.6 summarizes the 1994-1995 CMDL ozonesonde project involvment. This includes supplying receiving stations and all ozonesonde supplies, training where needed, personnel launching ozonesondes at several of the sites, and final data processing. The CMDL long-term stations at Boulder, Colorado; Hilo, Hawaii; and SPO, continued operating at one launch per week in 1994 and 1995, with SPO increasing to three per week during the ozone-hole period. The SPO minimum total ozone, measured by ozonesondes, reached 102 and 98 DU in 1994 and 1995, respectively. The minimum profiles and the predepletion profiles are shown in Figure 4.2. Severe depletion was observed in the 14- 20 km region (nearly 100%) but did not extend down to the 10-14 km region as it did in 1993 when a record low of 91 DU was measured [Hofmann et al., 1994]. This extended ozone-depletion layer in the lower stratosphere, observed in 1992 and 1993, was due to the effects of the Mt. Pinatubo volcanic aerosol layer [Hofmann and Oltmans, 1993]. By 1994, the Mt. Pinatubo volcanic layer had decayed to background levels over McMurdo Station, Antarctica [Deshler et al., 1996]. 74 TABLE 4.6. Summary of 1994-1995 Ozonesonde Projects Ozonesonde 1994 1995 Sites Totals Dates Totals Dates Project Station (weekly) Boulder 52 Full year S2 Full year NOAA long term MLO 52 Full year 62 Full Year NOAA long term + ML03 SPO 69 Full year 69 Full Year NOAA long term McMurdo 65 Feb. 3-Dec. 2S 6 Jan. I-Feb. 12 NSF and NOAA Tahiti - 24 July 31 -Dec. 29 PEM-Tropics SMO - 16 Aug. 1-Dec. 14 PEM-Tropics Intensives (- daily) Azores 30 May 5-June 3 42 June 2-July 27 AEROCE Bermuda 10 Jan 21-May 31' 55 April 17-July 27 AEROCE Maryland - 12 April 13-May 16 AEROCE Rhode Island - 7 April 18-May 15 AEROCE Newfoundland - 20 April 12-Aug. 3 AEROCE Nashville 14 Ship Cru ses June 27-July 21 Southern Oxidant Study Indian Ocean - 21 Feb. 12-April 14 NSF R/V Malcom Baldrige Pacific Ocean - 17 Oct. 17-Dec. 11 ACE R/V Discoverer Totals 278 418 PEM-Tropics - Pacific Exploratory Mission in the Tropics (a global tropospheric experiment). SOUTH POLE STATION 1994 SOUTH POLE STATION 1995 35 02 SEP 94 282 DU 05 OCT 94 102 DU 35 30 25 20 15 10 ■ i. .1 ... -V-, 22 AUG 95 282 DU 05 OCT 95 98 DU Jf — ' ^ts^ X , i . i . i . i . , i ■ i_^_ , i ■ . 2 4 6 8 10 12 14 16 18 20 OZONE PARTIAL PRESSURE (mPa) 2 4 6 8 10 12 14 16 18 20 OZONE PARTIAL PRESSURE (mPa) Fig. 4.2. Vertical profiles of ozone partial pressure in millipascals (mPa) at SPO during the ozone hole of 1994 and 1995. The lighter line represents the predepletion profile while the thicker line is the profile observed at the total ozone minimum. 75 NOAA was also involved in regular ozonesonde and water vapor measurements at McMurdo Station, Antarctica, from February to August 1994 during a winterover project designed to study the development of polar stratospheric clouds using balloonborne instruments. The University of Denver, University of Wyoming, and NOAA conducted balloon flights to measure ozone, water vapor, nitric acid, and particle concentration profiles during the austral summer, fall, and winter of 1994 prior to and during the development of polar stratospheric clouds and ozone depletion. An early sign of ozone depletion was observed in the June 1994 profile in the 12-20 km layer [Vomel et al., 1995a] (section 4.2.3., this report). CMDL continued measuring ozone profiles on a weekly basis at McMurdo from November 1994 to February 1995. This was done in order to complete the first full year of ozonesonde profiles from McMurdo (February 1994-February 1995). The University of Wyoming launched ozonesondes during the ozone hole period from August to November 1994. Weekly ozonesondes began at Tahiti and SMO in July 1995 as part of the Global Tropospheric Experiment Pacific Exploratory Mission in the Tropics (PEM-Tropics). The intensive, short-term ozonesonde projects were all part of the AEROCE II and AEROCE III and the North Atlantic Regional Experiment (NARE). Ozone profiles were measured on a nearly daily basis from several sites (Table 4.6) in the spring and summer of 1994 and 1995 to investigate the sources (anthropogenic and natural) of high ozone layers in the troposphere over the north Atlantic Ocean region. The 21 ozonesondes flown from the R/V Malcom Baldrige cruise in the Indian Ocean began near South Africa at ~30°S, 30°E and ended near Sri Lanka at ~7°N, 73°E. This was a preliminary study for the Indian Ocean Experiment (INDOEX) planned for January 1998 to study the chemical and radiative composition of the atmosphere over the Indian Ocean particularly in the region south of the Indian subcontinent. The Aerosol Characterization Experiment (ACE) R/V Discoverer cruise in the Pacific Ocean extended from ~31°N, 214°E to 45°S, 145°E. This set of measurements provided the first ozone profiles in a long cross section through the mid-Pacific. 4.1.5. Atmospheric Water Vapor Monthly water vapor profile measurements continued at Boulder. As was noted earlier [Oltmans and Hofmann, 1995; Ferguson and Rosson, 1992], water vapor in the stratosphere over Boulder has increased significantly. The updated trend information is summarized in Table 4.7. As was reported in the past, the largest trends are seen in the lowest part of the stratosphere over Boulder (16-20 km). This change of about 0.8% yr 2 is somewhat less than reported earlier. This is primarily because the seasonal minimum which occurs in winter and early spring was somewhat lower than in recent years (Figure 4.3). This may be associated with enhanced transport from the tropics during early 1995. Lower stratospheric ozone amounts were also less than normal, indicative of tropical transport. Above 20 km the increase is about 0.5% yr 2 , which is consistent with the expected increase resulting from increasing CH 4 concentrations in the atmosphere. 4.1.6. Atmospheric Transport CMDL supports various research efforts to verify sources and sinks of trace gases and aerosols. The CMDL isentropic transport model [Harris and Kahl, 1994] calculates trajectories at requested elevations, including those in the stratosphere. Trajectories may then be compared to data collected at the surface or data collected at elevation (sonde, aircraft, and lidar data). Variations in concentration may be linked to transport where applicable. Trajectories were used to describe seasonal flow patterns to MLO '[Harris and Kahl, 1990], SPO [Harris, 1992], and BRW [Harris and Kahl, 1994]. A similar study of SMO flow patterns is underway. Highlights of this study appear as a special project at the end of this section (4.2.4). These four studies summarize many years of trajectories for each observatory in order to understand the average flow patterns, their meteorological causes, and the range of yearly and seasonal variations. Knowledge of transport characteristics has led to a better understanding of seasonal patterns in MLO methane data [Harris et al., 1992] and SMO carbon dioxide data [Halter et al., 1988], among other constituents. TABLE 4.7. 1981-1995 Water Vapor Mixing Ratios Over Boulder, Colorado Level (km) Mean Standard Deviation Number of (ppmv) (ppmv) Observations Trend* (% yr" 1 ) 95% Confidence! Interval (% yr" 1 ) 10-12 12-14 14-16 16-18 18-20 20-22 22-24 24-26 60.46 12.23 4.68 3.90 3.87 4.08 4.24 4.34 40.27 6.97 1.04 .49 .35 .29 .30 .34 137 137 137 137 136 131 125 108 1.47 1.34 .61 .78* .80t .481: .51* .55 2.60 1.88 .87 .49 .35 .28 .29 .34 *The trends are computed for deseasonalized values. tThe 95% confidence interval is based on students t-distribution. iSignificant at 95% confidence level. 76 U3 CL O : 22-24 km Boulder, Colorado * • •« • •• . •* 5. "" en c s -.i.i.i.i.i.i, • 0.51 + 0.29 %/ycar 1,1,1.1,1,1,1,1, 31 82 83 84 85 87 88 90 91 92 93 94 95 96 16-18 km 90 91 92 93 94 95 96 Fig. 4.3. Layer average water vapor mixing in parts per million (ppmv) at Boulder, Colorado, for the 16-18 km and 22-24 km layers. The dashed line is the overall mean and the solid line is the linear trend fitted to the monthly anomalies. The trend and 95% confidence levels in percent per year are also shown. average relative standard deviation of 2-4% in the lower troposphere (0-5 km) and in the stratosphere from 15 km to burst altitude (-35 km). The poorest precision was in the mid- to upper troposphere, where very low concentrations of ozone approach the background levels of the ozonesonde. In this region the relative standard deviation was as high as 20%. Figure 4.4b shows the average ozonesonde profile from the August 30 flight, the lidar and microwave profiles, and a SAGE overpass ozone profile measurement. All of the profiles agreed very well above 15 km, except for the JPL lidar between 15 and 18 km. At the ozone peak, the ozonesonde profile is about 8-10% greater than the ground based instruments. The ozonesonde profiles measured during ML03 were decreased by a maximum of 6% at burst altitude due to an observed increase in response to ozone as the 1% potassium iodide solution evaporates during the flight and becomes more concentrated. Additional testing has shown that the sonde may be reading even higher than the 6% correction. This would reduce the ozonesonde profile further resulting in less than 5% differences between the ozonesondes and ground based instruments. 4.2.2. Ozone Vertical North Atlantic Profiles Over the Information about the transport model (methodology, description of plots, and formats of data files) is available on the Internet at http://www.cmdl.noaa.gov/traj. This home page also serves as the distribution site for "real- time" trajectories. These are trajectories calculated from data downloaded twice a day as it becomes available from National Centers for Environmental Prediction (NCEP) (previously National Meteorological Center). For various CMDL baseline and regional observing sites, trajectories are thus provided within a day of when measurements are actually made. This capability will be expanded in the future to include any site on the globe. The trajectory home page also includes pointers to several archives of trajectory data. 4.2. Special Projects 4.2.1. The Mauna Loa Ozone Profile Inter- comparison From August 14 through September 1, 1995, the CMDL Ozone Group measured daily ozone profiles during the Network for the Detection of Stratospheric Change (NDSC) Stratospheric Ozone Profile Intercomparison (ML03) held at Mauna Loa Observatory and Hilo, Hawaii. Participating groups in Hawaii included the JPL lidar, NASA Goddard lidar, NASA Langley Microwave, and NOAA umkehr and ozonesondes. All the remote sounding instruments were operating at MLO (3397 m). Seventeen electrochemical concentration cell (ECC) ozonesondes were launched from Hilo (11m) to coincide with the evening MLO observations. Six of the balloons launched were carrying a new "triple" ozonesonde platform. The "triple" flights showed very good precision that can be seen in the August 30, 1995, profiles (Figure 4.4a). These profiles were fairly typical of all the triple flights with an As part of AEROCE and NARE, several intensive ozone vertical profiling campaigns were carried out. During these campaigns, ozonesondes are launched on a near daily schedule for periods of approximately 1 month. The focus of these intensive measurements is to describe the ozone variations throughout the troposphere over the North Atlantic and to relate the processes identified as being responsible for surface ozone variations with changes throughout the troposphere [Oltmans and Levy, 1992; Moody et al., 1995]. The results, primarily from the 1993 and 1994 campaigns, have recently been prepared for publication [Oltmans et al., 1996]. During spring 1995, an intensive series of measurements was made at Bermuda. Over the month the soundings were carried out and several profiles were also obtained at the University of Rhode Island and at the University of Maryland. These soundings on the east coast of the United States were made in order to look at the ozone content of air masses as they moved from the United States to Bermuda. The profiles from May 6, 1995, at Rhode Island and Maryland (Figures 4.5a and b) and for May 7 at Bermuda (Figure 4.5c) illustrate how such a system can produce high ozone amounts in the midtroposphere over the North Atlantic. At the more northerly location (Rhode Island), the upper troposphere from 8-11 km has ozone concentrations over 125 ppb (Figure 4.5a) and large ozone amounts (-85 ppb) extend down to 6.5 km. At Maryland (Figure 4.5b), on the other hand, the layer of elevated ozone over 100 ppb is confined to a relatively thin layer at about 7 km. On May 6 at Bermuda (profile not shown) ozone throughout the troposphere is 50-70 ppb. Early on May 7 at Bermuda (Figure 4.5c) there is a peak of -120 ppb at about 6.5 km. The Bermuda trajectories for May 7 (Figure 4.5d) show that for the 0000 UT arrival time, air had passed over the northeastern United States about 12 hours earlier at an altitude of 8 km. The larger ozone amounts seen at 77 40 35 J, 30 w 5 25 H 3 20 15 10 5 ; a ) 30-Aii£ ;-95 •^^^su ; j ^**^> : : i \S^X^ c !\t | \ i , i ■ , Fig. 4.4. (a) Three vertical profiles of ozone concentration (10 12 cm- 1 ) measured by the August 30, 1995, triple ozonesonde flight, (b) The average of the triple ozonesonde profiles from (a) and the profiles of ozone concentration from the two MLO lidars and microwave ozone profilers and the coincident Stratospheric Aerosol and Gas Experiment II (SAGE II) satellite profile. Maryland and Rhode Island (1400 Z on May 6) are clearly part of the same system producing the large ozone peak over Bermuda seen at 0100 Z at about 6.5 km. Air travels rapidly from near the Arctic Circle and descends over 2.5 km in just 2 days before reaching Bermuda. This meteorological pattern with flow behind the upper air trough brings air from a region where significant transfer of air from the stratosphere into the troposphere is likely to take place [Merrill et al., 1996], The presence of these layers of larger ozone concentration aloft at Bermuda and other sites over the North Atlantic are invariably associated with transport from higher altitudes and latitudes [Oltmans et al., 1996], These layers are also very dry, which is another indication that the air was mixed down from the stratosphere. It is likely that this process is an important source of ozone in the troposphere [Oltmans etal., 1996]. During July 1995, intensive profiling campaigns were carried out at the Canary Islands, Azores, Bermuda, and Newfoundland. For each of these sites, ozone amounts near the surface are much smaller than are seen at the surface during the spring. In the middle and high troposphere, however, intrusions of large ozone amounts are common during the early summer and the peak values are larger than those seen in the spring [Oltmans et al., 1996]. The presence of these layers of large ozone concentration is strongly tied to flow characteristics and water vapor amounts that demonstrate the stratospheric origin of these layers in a manner very similar to what is seen in the spring. Transfer of ozone-rich air from the stratosphere into the troposphere during the summer is significant. 4.2.3. Water Vapor and Ozone Profiles at McMurdo, Antarctica The very cold temperatures of the Antarctic winter stratosphere lead to the formation of polar stratospheric clouds (PSCs). The formation of these clouds, particularly when temperatures reach the frost point of water (type II PSCs), leads to significant dehydration of the Antarctic stratosphere [Vomel et al., 1995b; Peterson and Rosson, 1994]. In order to more completely describe and better understand the process of dehydration within the Antarctic stratospheric vortex, a program of 19 frost-point soundings was carried out at McMurdo between February and October 1, 1994. Each frost-point sounding was accompanied by an ozone vertical profile as well. In addition, ozonesondes were flown between the water vapor profile measurement times on about a one-per-week schedule. Measurements of PSC particles and nitric acid in the stratosphere were made by groups from the University of Wyoming and Denver University, respectively. About the middle of June the coldest portions of the Antarctic stratospheric vortex reach the water vapor saturation temperature leading to rapid formation of ice crystals which fall with sufficient speed to rapidly dehydrate the stratosphere [Vomel et al., 1995b]. By late July continuing into October (Figure 4.6), much of the stratosphere in the vortex between 12 and 20 km remains highly dehydrated. During this period of sustained dehydration, there does not appear to be significant continued removal of water vapor, and also little moisture 78 15 E u Q P H H 10 a) o Rhode Island May 6, 1995 1355 UT 30 A Ozone V Air Temp. D Frostpoint 15 10 w Q 5 H H A Ozone V Air Temp. D Frostpoint Bermuda May 7, 1995 0100 UT 30 125 25 50 75 100 125 15 ? 10 fed Q 5 H H - «< 5 60N 30°N 0°N ~~i — v : ^ > ^ Bermuda swMay7, 1995 Solid Dashed 00 UT 12 UT 170°W 140°W 110°W 80°W 50*W JS X 25 50 75 100 125 n 1 1 1 — 12 3 4 Days from Bermuda Fig. 4.5. Vertical profiles of ozone mixing ratio (ppbv), temperature (°C), and frost-point temperature (°C) at (a) University of Rhode Island for May 6, 1995, at 1355 UT, (b) University of Maryland for May 6, 1995, at 2020 UT, and (c) Bermuda Naval Air Station for May 7, 1995, at 0100 UT. (d) The isentropic back trajectories for May 7 at 0000 UT (solid line) and 1200 UT (dashed line) arriving at 6.5 km at Bermuda. 79 2 4 6 10 12 14 16 18 20 30 ." T" iininiiiMiininiiuii|Mnniii|niiiiin|iiiiiiiii|iiiiiinijiiiiiMiijiiiiiiiii 28 '- 26 _ A f f y% 24 f jfc-**^p* j " ' "^ 22 *_ , if"" 20 (f^\ 18 s I-.--"- I IF 16 C ^ 3 14 'Sl§/ < 12 ^>* \fei— ^ 10 £ ~~^-r— JEr ysl'l r , ,.,_ 8 6 ■^ ' »~ -^^->.. - t ~.—~ ■M& a, fe» J M( Murdo station, wi nter 1994 13 June 1994 ™. 25 July 1994 4 7 — 9 August 1994 — 15 August 1994 2 - 13 September 1994 — 5 October 1994 iii ! 1 1 1 1 1 i j 1 1 1 ■ j 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ilMilliliiiiillltll Inn 1 100 a. 1000 2 3 4 5 6 7 8 Water Vapor Mixing Ratio [ppmv] 10 Fig. 4.6. Vertical profiles of water vapor mixing ratio at McMurdo, Antarctica, during the sustained dehydration period of the winter of 1994. The June 13, 1994, profile shows conditions before dehydration begins. 3 on iiiiiiiiii|iii n iii i |ii M iiii i |iiii i ii i i|iiiiiiiii |i iiiiiiii|iiii i iiii | iii ii iiii|i n iii n i|iiiiii i ii 25 20 15 10 Water Vapor, 13 June • Water Vapor, 19 June - Ozone, 13 June - Ozone, 19 June U Illllinulhu o E Q. o o TO ki LL _0> O E £r Q 280 - 275 270 - 265 - 260 A AOIdGC(NH) a OTTO (NH) o Old GC (SH) + OTTO (SH) A " A A i* A* 44 1 *" -frf A *aV|* A 41 oV * ' * O * A t A M ♦ + «, + + + o + J o* ° ' ° o + A A *■ A 4 4 * * "a « "4! *f *: a :^ 4 a ■ -o -5-+-*-*-* o o 1 ♦ : * 1 + + + + ' 1 1 1 ' 1 ' 94 94.5 95 Year 95.5 96 Fig. 5.2. Continuity of CFC-11 data from the old GC and automated flask GC (OTTO) during 1994-1995. Data are shown for sites in both hemispheres. portion of the inlet line. Although the inlet lines (Dekabon) and pumps (Air-Cadet, Cole-Palmer) contain plastic, they are kept clean by continuous flushing, 24 hours per day at 5-10 L min 1 . No noticeable difference was observed in the data as a result of making this change. Pumps and lines have been installed at NOAA sites, e.g., KUM, that do not support in situ GCs. In addition to the routine, weekly sampling of flask pairs at the CMDL observatories and cooperative sampling sites, NOAH scientists also analyzed air in flasks collected during two cruises in 1994 (Bromine Latitudinal Air/Sea Transect (BLAST I and BLAST II); section 5.4 and SF 6 section) to obtain "snapshots" of the interhemispheric gradient of a number of gases and to support measurements made by in situ GCs onboard. These measurements included over 25 gases and involved all of NOAH laboratory instrumentation. Another project (section 5.6) involved the flask program for the analysis of air sampled from South Pole firn (compressed snow). This provided NOAH scientists with a unique opportunity to observe the N 2 and halocarbon content of air dating back to the end of the 19th century. Although the air was collected into glass flasks with Teflon o-rings, which in the past have caused some problems in the analysis of halocarbons, contamination was minimal for most gases in this instance. The success of these measurements prompted NOAH scientists to pursue similar analyses from firn air collected at Vostok and Greenland. Because of the number of investigators requiring air from the SPO flasks, sharing was limited. Consequently, the samples were analyzed only with the OTTO and Low Electron Attachment Potential Species (LEAPS) GCs, which require less sample than the GC-MS systems. Finally, a number of changes were made in instrumentation, data acquisition, and data management for flask measurements that have improved the precision of some measurements, enhanced detection limits for others, and dramatically streamlined the processing of data. Today, data from samples run on OTTO and LEAPS can be 85 finalized and evaluated alongside all previous data within minutes following analysis. Measurements by EC-GC Improvements in Analysis. The precision of flask measurements by EC-GC has improved dramatically during 1994-1995. Modifications in sampling technique and sample introduction, full automation of CFC, N2O, and chlorocarbon measurements, and installation of 24-bit interfaces for analyses by OTTO and LEAPS combined to yield analytical and sampling precisions about 0.1 ppt or less for LEAPS gases and on the order of tenths of a ppt for gases measured on OTTO. The old Nelson Analytical, Inc. data acquisition and handling system on OTTO was replaced with entirely new hardware and software to allow more rapid and consistent processing of samples. The HP Model 210 computer was replaced with an IBM PC compatible 486, the 16-bit A/D converters were replaced with two HP 24-bit A/D boards for the PC, and the Rocky Mountain Basic software was replaced with the 1995 version of HP Chemstation software. Programs were written in Microsoft Visual Basic to consolidate the HP Chemstation output from each run of flasks, compute results, generate flags for erroneous or anomalous data, perform additional quality control tests, and load the results into a Microsoft Access data base. Currently, eight flasks can be run at once on OTTO, obtaining precise measurements of CFC-12, CFC-1 1, CFC- 113, CH3CCI3, CCI4, N 2 0, and SF 6 . Results and Trends. The years 1994 and 1995 heralded the downturn in total chlorine, equivalent chlorine, and effective equivalent chlorine in the earth's troposphere [Montzka el al., 1995b, 1996b]. Led by a marked drop in CH3CCI3, this suggested that the abundance of ozone- depleting halogen in the stratosphere could begin to decline in the near future. Other gases that began decreasing in abundance during this time include CFC-1 13, CCI4, and, to a lesser extent CFC-1 1 (Figure 5.3). CFC-12 continued to increase in the atmosphere, although not in sufficient quantity to offset the losses in organic chlorine represented by the other compounds (Figure 5.3). As expected, the atmospheric abundances of CFC alternative compounds (HCFCs and HFCs) have been increasing at reasonably fast rates, although these gases contain relatively little chlorine and have shorter lifetimes than the CFCs ([Montzka et al., 1993, 1994, 1996a, b]; section 5.1.5). SF 6 — An Important Tracer and Strong Greenhouse Gas On a per molecule basis, SFg is one of the strongest greenhouse gases known, about 25,000 times greater than CO2 [Albritton et al., 1995]. It is solely anthropogenic in origin and used primarily for the insulation of high-voltage electrical equipment. With its increasing use and very long 560 460 O J "o E S 360 c o o TO ■= 260 160 60 x Alert Pt. Barrow ■> Niwot Ridge a Mauna Loa D Am. Samoa \ Cape Grim •>*^^^^ x South Pole CFC-12 77 79 81 83 85 87 Year 89 91 93 95 Fig. 5.3. CFCs and chlorocarbons measured on the old GC and OTTO in ppt versus time since 1977. The transition from old GC data to OTTO data for CFCs -ll and -12 is shown by a vertical, dashed line at the beginning of 1994. Noticeable are the tighter measurements of OTTO and the lack of an offset between the instruments. Also shown in proportion are the recent growth rates of the major, Class I ozone-depleting, chlorinated compounds and their narrowing interhemispheric gradients. 86 lifetime, SF^ is rapidly accumulating in the atmosphere at -7% yr 1 . In addition to its importance as a greenhouse gas, SF 6 is a nearly ideal tracer of atmospheric dynamics due to its well understood sources and long atmospheric lifetime of -3200 years [Ravishankara et a!., 1993]. CMDL scientists recently began monitoring atmospheric SF 6 in weekly flask samples from all baseline stations and many CCG network sites as high-resolution latitudinal profiles during the 1994 BLAST ocean cruises [Geller et ai, 1994] as in situ stratospheric measurements from the Airborne Chromatograph for Atmospheric Tracers (ACATS) field missions [Elkins et ai, 1996], and as in situ measurements at Alert, Harvard Forest, and North Carolina [Hurst et ai, 1995]. SF 6 was measured with ECD-GC as described in Elkins et ai [1996]. Even though ambient levels of SF 6 are only -3.5 ppt, it is possible to measure direct air injections (no sample preconcentration) to a precision of 1-3%. A suite of gravimetric SF 6 standards ranging from 3 to 108 ppt was developed in the NOAH Group. An intercalibration with the University of Heidelberg (Germany) showed CMDL measurements are less than 2% lower that the German calibration scale. The long-term trend of SF 6 is illustrated in Figure 5.4, which shows NOAA data together with the University of Heidelberg data. These different data sets, collected and analyzed by different techniques, show good agreement. A northern hemispheric trend was fit to the combined Izafia and NWR data, because data from these two midlatitude sites are close to the latitudinally weighted hemispheric mean. Likewise, in the southern hemisphere, data from Antarctica and Cape Grim well represent the true southern hemisphere mean, therefore the southern hemisphere trend was fit to the Neumayer and Cape Grim data from the University of Heidelberg, and the SPO and Cape grim data from NOAA data. A preliminary estimate for the global trend (the average of the northern and southern hemispheric trends) shows a quadratic increase described 4 a O Neumayer* . • South Pole D lzana# ? 3 5 ■ Niwot Ridge ■ ^j? X N Carolina arrfV)*^ T BLAST cruises ^Mptf *■■'"' jrf*- 3 ♦ Alert ♦ Barrow ^rfpU^'*'"'' o Pf^^ ;,j( $r*f. 9.- data points — runrung mean 10 20 30 40 50 60 60 50 -40 -30 -20 -10 10 20 30 40 50 60 till ■ 1 1 1 1 - 4 c) NOAH tlask data / Nov 1995| « Alert 3 8 d Pt Barrow « Cape Grim -j O Mauna Loa j 1 ' 3 6 V Niwot Ridge A Am Samoa Jf—- " * 1 X South Pole ^s^*~ - 3.4 sk North Carolina (in situ) -"""^ 1 3 2 \t~ 1 X - 1 1 1 1 i i l i - year Fig. 5.4. Temporal trends of SF 6 . CMDL data shown together with University of Heidelberg data [from Maiss et at., 1996, marked in the figure legend as #]. The Heidelberg data has been adjusted to the CMDL calibration scale and binned into monthly means. The curve fitting is described in the text. Fig. 5.5. Latitudinal profiles of atmospheric SF 6 (dry, ppt by mole fraction), (a) and (b) are in situ data from the marine boundary layer in 1994. (c) shows the monthly mean mixing ratios for November 1995 obtained from flask samples collected at seven sampling stations and from the in situ North Carolina data. Error bars represent ±1 standard deviation of the flask pair mixing ratios at each station. 87 is not received in a specified recurring period of time. This restarts data acquisition when station personnel are not present at night or on weekends and the system locks up. In June 1994 the hardware was installed at the Barrow Observatory, Alaska (BRW) in June and at MLO and Samoa Observatory, American Samoa (SMO) in August. At this same time a new function was added to the system software to decrease paper usage by the printer. A set of calibration gas and air chromatograms were printed only once a day prior to the arrival of the station personnel instead of continuous printouts. In August, system software was modified to include a menu-driven log for problems, failures, and changes to be easily documented. In the past such information was written on daily and weekly check lists and then typed into a database. Original data acquisition and control computers, HP Model 9816s of mid-1980 vintage, were replaced in 1995 by 486 PCs. The software port from HP Basic to TransEra HTBasic running in Microsoft Windows 3.1 required only minor changes. This software upgrade was installed in April at NWR, in May at MLO and SMO, and in June at BRW. An additional feature of the new computers is network access. Data downloading, software upgrading, and determining equipment status is now possible over the Internet. Alert A single-channel GC equipped with an ECD and based on the STEALTH GC design (section 5.5) was built in 1995 and installed at ALT as part of a cooperative research agreement between CMDL and AES. Continuous instrument operation began in late August 1995 with two samples of ambient air analyzed each hour for N 2 and SF 6 . These measurements augment the weekly flask samples taken at ALT since late 1987 and allowed detection of episodic pollution events. Of particular interest was the monitoring of polluted air that arrives at Alert from northern Asia and from the former Soviet Union. Data Analysis In response to observed depletion of stratospheric ozone, the 1987 Montreal Protocol on Substances That Deplete the Ozone Layer mandated a 50% reduction of chlorofluorocarbons and selected chlorinated solvent production over the next 10 years. In 1990 this was strengthened to a 100% phase out by the year 2000. An additional amendment in 1992 required a 75% reduction by 1994 and a complete ban by 1996. The chemical industry responded quickly with substitutes. Emissions have, therefore, generally been reduced in excess of expectations. The global average CFC-11 tropospheric mixing ratio reached a maximum of 272 ppt in 1993 (Figure 5.6). The growth rate has now started to decline at -1 ppt yr 1 . Recently the interhemispheric difference declined by half, indicative of a long lifetime and a mostly northern hemisphere source that is diminishing quickly. In situ measurements of CFC-11 and CFC-12 are described in Elkins et al. [1993], and the data were recently updated in Montzka et al. [1996b]. CFC-12 growth continues to slow down with the end of 1995 growth rate about 6 ppt yr-'. Because CFC-12's major use is in domestic, commercial, and industrial 290 280 Q. 270 a ^ 260 ■ o 240 230 ■ * * * * * * ■ * Pt. Barrow * Niwot Ridge □ Mauna Loa ▼ Am. Samoa o South Pole 1 1 1 1 " '" I |u iii | i i n i| ii n i| m i l l i'ii h i n 87 88 89 90 91 92 93 94 95 96 97 Year Fig. 5.6. Monthly average CFC-1 1 mixing ratios in ppt from the in situ GCs. refrigeration and air conditioning, release to the atmosphere is slower than foam blowing, propellant, and solvent applications. Assuming a constant deceleration of -1.66 ppt yr 2 , CFC-12 is estimated to peak in the atmosphere in mid- 1999 with a global-average tropospheric mixing ratio of 544 ppt (Figure 5.7 and 5.8). Southern hemispheric mixing ratios of methyl chloroform peaked in 1992 and northern hemisphere mixing ratios peaked a little more than a year earlier (Figure 5.9). The time lag is similar to the known interhemispheric mixing time. The large north to south gradient before 1993 is indicative of very strong northern hemisphere sources. The rapid decrease in mixing ratios during phaseout shows the chemical has a short lifetime estimated at about 5 years [Prinn et al., 1995]. The chlorinated solvent CC1 4 , was used as the primary source (feed stock) for the chemical synthesis of all the chlorofluorocarbons. With their ban, this role has * Pt. Barrow * Niwot Ridge □ Mauna Loa ▼ Am. Samoa o South Pole i j 1 1 1 1 1 j 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 87 88 89 90 91 92 93 94 95 96 97 Year Fig. 5.7. Monthly average CFC-12 mixing ratios in ppt from the in situ GCs. 88 -1 .66 ppt/yr/yr constant deceleration -i 1 1 1 1 1 1 1 1 , 1 1 r- 1986 1988 1990 1992 1994 1996 1998 2000 Year ^112 3iio 0) "D "J 1081 lo 106" t_ +-> 0) I- 104 c o ■S 102" (0 O 100 ■ I I ■ ■ ' ' ' I I ' I ■ 1 I 1 1 1 I I I I 1 I I ■ I I I ■ I I I I I I I I I I I * Pt. Barrow a Niwot Ridge □ Mauna Loa t Am. Samoa o South Pole ' " I i ' ""i i i i i' "" i i " 87 88 89 90 91 92 93 94 95 96 97 Year Fig. 5.8. A decrease in the global average growth rate of CFC- 12 is projected to become zero in mid- 1999. Fig. 5.10. Monthly average CC1 4 mixing ratios in ppt from the in situ GCs. diminished significantly. Atmospheric mixing ratios were observed to be slowly decreasing at approximately -0.75 ppt yr 1 since 1991 (Figure 5.10). One unusual feature is the north to south gradient was near constant during this same period. The methyl chloroform and carbon tetrachloride data were published in Montzka et al. [1996b]. The mixing ratios of both compounds are decreasing with time as a result of the Montreal Protocol. N 2 continued to increase in the troposphere (Figure 5.11). The average global growth rate for 1995 was 0.61 ppb yr 1 . 5.1.4. LEAPS Although precision of the Low Electron Attachment Potential Species (LEAPS) analyses was improved by an order of magnitude in 1992 with better chromatography (tenths to hundredths of a ppt; Swanson et al. [1993]; Thompson et al. [1994]), the system still operated with the old Nelson Analytical hardware and software. In 1994 this was replaced with a 24-bit A/D board and an IBM PC- compatible 386, and HP Chemstation software. New software was written for processing data and incorporating it into a Microsoft Access data base manager. As with data from OTTO, final LEAPS data are now available immediately following analysis. Halons have not been produced by industry since January 1, 1994, except for some small exceptions; however, the mixing ratios of the three major halons (H- 1211 or CBrClF 2 , H-1301 or CBrF 3 , and H-2402 or CBr 2 F 4 ) in the troposphere continued to rise (Figure 5.12), because a considerable amount of halon remains stored in fire suppression systems. The growth rates are, however, 1701 2 160 Q. IT 1501 O 140: O O 130" O 120 X 110: (U 1001 90 j ' ■ ■ ' ' ' ' ' '■ *r % a ro □ * Pt. Barrow a. Niwot Ridge a Mauna Loa ▼ Am. Samoa o South Pole 111 1 " 1 "i ' "" i "'"i i |n i i i| u n i| in 87 88 89 90 91 92 93 94 95 96 97 Year 314 312" q.310 3*308 306 ' ' ' ' I ..... I I ■■ ... I ..... 1 ... i.^ &** « Pt. Barrow * Niwot Ridge a Mauna Loa t Am. Samoa o South Pole OQ4 1 1 i i i i [ i i i i i | i i i i i | i i i i i | i i i i i | i i i i i | i i i i i | i i i i i | i i i i i | i i i i i 87 88 89 90 91 92 93 94 95 96 97 Year Fig. 5.9. Monthly average CH3CCI3 mixing ratios in ppt from the in situ GCs. Fig. 5.11. Monthly average N 2 mixing ratios in ppb from the in situ GCs. W « 1.5 o E * 1 Q 0.5 H1211 = -0.0087X 2 + 0.1494X + 2.9774 H1301 = -0.0148X 2 + 0.1361X + 2.1613 i * a - - - - n H2402 = 0.0004 x + 0.4661 ♦ H1211 □ H1301 a H2402 91 92 93 94 Year 95 96 Fig. 5.12. Growth of halons in the atmosphere since 1991. Growth rates are given for January 1, 1994, thus approximating today's increase of stratospheric bromine from halons. Pre- 1995 data for H-2402 are from the NOAA archive; all other measurements are from the flask network. considerably lower now than during the 1970s and 1980s [Butler et al., 1992]. 5.1.5. Chlorofluorocarbon Alternative Measurements Program Flask air analysis by GC-MS continued through 1994- 1995. Mixing ratios of selected CFCs, HCFCs, HFCs, chlorinated hydrocarbons, brominated hydrocarbons, and halon-1211 were determined from air collected in flasks at the seven remote flask sampling observatories (four CMDL stations and three cooperative flask sampling locations). Toward the end of 1995, flask samples were also collected at three additional sites: KUM, ITN, and HFM. During this period, analysis methods were developed on a second instrument for precise measurement of halocarbons such as HFCs at mixing ratios of -0.1 ppt and higher. This was accomplished by using larger volumes of air per injection than in the original GC-MS instrument (up to 1 L of air per injection versus -0.17 L in Montzka et al. [1993]). Detection of halocarbons in this second instrument is also performed with mass spectrometry. Larger flasks (2.4 L) were incorporated into the sampling network in early 1995 to allow for air analysis on this new instrument in addition to other instruments. With these changes and the development of the second GC-MS instrument, measurements of selected HFCs and additional HCFCs became possible in modern air starting in early 1995. Furthermore in 1995, enhanced sensitivity has allowed for the analysis of HFCs, HCFCs, and other halocarbons within archived air samples that were collected at NWR and other locations since 1987. HCFC-22 (CHCIF 2 ) Measurements The most abundant HCFC, HCFC-22, increased in the global troposphere at a rate of 4.5% yr 1 (mean exponential rate estimated from flask samples collected between 1992 and 1996; Table 5.2, Figure 5.13a, and Montzka et al., [1996b]). This rate represents a slower annual increase on a relative basis when compared to growth rates reported for time periods encompassing the 1980s and early 1990s [Montzka et al., 1993; Zander et al., 1994; Irion et al., 1994; Rinsland et al, 1996]. Informal exchange of flask air samples and standards in 1994-1995 with the National Center for Atmospheric Research (NCAR), the University of Bristol, England, and the Scripps Institution of Oceanography has suggested that consistent results (within 5%) can be obtained by chromatographic analysis of air even when different detectors are used (MS and O^-doped ECD). These results are also reasonably consistent with surface mixing ratios inferred from long-path absorption studies [Irion et al., 1994]. Emission estimates compiled by industry can be used to infer an atmospheric lifetime for HCFC-22. However, uncertainties associated with this exercise limit its usefulness for providing constraints to the global mean burden of the hydroxyl radical. With simple box-model calculations and emission estimates [AFEAS, 1995] (without adding additional emission to allow for unreported production), an atmospheric lifetime of 12 ± 2 years is estimated for HCFC-22 from CMDL data. This lifetime is consistent with 11.5 ± 0.7 years, which has been estimated for HCFC-22 based upon a comparison between measurements and model calculations of methyl chloroform [Prinn et al., 1995]. HCFC- 141b (CH 3 CCl 2 F) Measurements Rapid atmospheric growth continues to be observed throughout both tropospheric hemispheres for HCFC-141b (Table 5.2, Figure 5.13c, Montzka et al. [1996b]). Mixing TABLE 5.2. Annual Mean Growth Rate and Mean Tropospheric Burden (Mixing Ratio) for HCFCs and HFC-134a*, Mid-1994 and Mid-1995 Mid- 1994 Mid- 1995 Compound Growth Rate, pptyr 1 Mixing Ratio, ppt Growth Rate, pptyr 1 Mixing Ratio, ppt HCFC-22 HCFC- 142b HCFC- 141b HFC- 134a 5.3 1.2 1.4 ~0.7t 111.1 5.6 1.9 N.D4 5.6 II 1.9 1.2 116.6 6.8 3.5 1.6 Global mean growth rates and mixing ratios estimated from polynomial fits to data binned by monthly, bimonthly, odd month, and even month periods, and by station. HCFC-22 growth of 4.5% yr 1 is estimated from an exponential fit to global mean data between 1992 and 1996. *See Figure 5.13. Estimates reported here for HCFC- 142b were corrected for an error in Table 1 of Montzka et al. [1996b]. tEstimated from mean of two cruises in 1994. tNot determined. 90 140 T 130 120 110 100 90 80 1991 a) HCFC-22 1992 1993 1994 1995 1996 u.u c)HCFC-141b 7.5 • s 5.0 2.5 £$&°^ 'iti**^ 00 - — , , , , 1 1— , , r-^f £p& <,*%£ — 1— . A _^» 1991 1992 1993 1994 1995 1996 40 3.0 2.0 1 00 d)HFC-134a 1991 1992 1993 1994 1995 1996 Fig. 5.13. Atmospheric dry mole fractions (ppt) determined since 1992 for the most abundant substitutes for ozone-depleting substances. Each point represents a mean of two simultaneously filled flasks from one of seven stations: ALT, open circles; BRW, open triangles; NWR, open diamonds; MLO, open squares; SMO, filled triangles; CGO, filled squares; SPO, filled diamonds. These data were obtained from the original GC-MS instrument (see text). Solid lines represent fits to hemispheric monthly means. ratios have increased more than tenfold throughout the global troposphere since the beginning of 1993. Fairly good agreement was reported among different laboratories that have published measurements for this compound [Montzka et al, 1994; Schauffler et al, 1995; Oram et al, 1995]. Preliminary emissions have been estimated recently for HCFC-141b by industry (P. Midgley, Alternative Fluoro- carbon Environmental Acceptability Study (AFEAS), personal communication, 1996). At the beginning of 1993, the global tropospheric abundance estimated from the measurements was -2.0 times greater than the burden estimated from these emissions. By the end of 1994, this ratio had decreased to between 1.3 and 1.4. The exact cause for this discrepancy is currently unknown; however, the difference (but not its time dependence) could be reconciled if emissions are a larger fraction of production than currently assumed. Some of this difference could also be explained by larger vertical gradients within the troposphere than assumed in the simple box-model calculation. Whereas the atmospheric lifetime of HCFC-141b also influences ambient mixing ratios and affects the magnitude of the difference discussed here, mixing ratios are fairly insensitive to the lifetime chosen for HCFC-141b during the initial phase of use and emission. For example, if we were to consider a lifetime for HFC-141b of 20 years instead of the more accepted value of -10 years [WMO, 1995], the ratio calculated for the end of 1994 would be 1.2-1.3 instead of 1.3-1.4. Analysis of the CMDL air archive reveals fairly constant mixing ratios of 0.08 - 0.10 ppt for HCFC-141b from 1987 to 1990 (Figure 5.14). After 1990, the abundance increases to -0.6 ppt in 1993, which is consistent with mixing ratios determined for the northern hemisphere from the flask program at that time [Montzka et al., 1994]. These results are also similar to data reported by Oram et al. [1995] where fairly constant mixing ratios of 0.08 ± 0.01 ppt HCFC-141b were found in samples collected at Cape Grim between 1982 and 1991. A dramatic increase was observed at this southern hemispheric site in 1992 and 1993, or 1 to 2 years after that observed at NWR in the CMDL archive. 91 10 ■o o Q. E o o CL 0.01 ▲ * 1986 1988 1990 1992 1994 Sampling date 1996 Fig. 5.14. Atmospheric dry mole fractions for HCFC-142b (filled diamonds) and HCFC-141b (filled triangles) in archived air samples as determined on the newer GC-MS instrument. Analyses of archived air were performed in early 1995. With the exception of samples filled in mid- 1987, all samples were obtained from NWR or MLO. Samples collected in mid- 1987 were obtained shipboard in both hemispheres. Solid lines represent hemispheric (northern always higher than southern) and global monthly means for HCFC-142b and HCFC-14lb as determined from the data in Figures 5.13b and 5.13c. HCFC-142b (CH 3 CCIF 2 ) Measurements Rapid atmospheric growth was also observed for HCFC- 142b during 1994-1995 (Table 5.2; Figure 5.13b; Montzka et al. [1996b]). Published results from ground-based air samples disagree by -30%, with CMDL data [Montzka et al., 1994] being higher than mixing ratios reported from the UEA [Oram et al., 1995]. Accurate comparison with a few earlier measurements from NCAR [Pollock et al., 1992; Schauffler et al., 1993] is difficult because these earlier measurements were from air collected above 15 km in northern latitudes. However, from informal exchange of air samples and standards between CMDL and NCAR, and between CMDL and the University of Bristol, mixing ratios determined from these three independent laboratories are expected to span a range of approximately 10% (with CMDL results approximating the mean of the three laboratories: University of Bristol, NCAR, and CMDL). It is also noted that the mixing ratio reported for HCFC- 142b in Table 1 of Montzka et al. [1996b] is too high by approximately 6%. The revised growth estimate for 1995 is reduced by a larger percentage (Table 5.2). This error arose in determining the mixing ratio for HCFC-142b in an air sample used for reference in the analysis of flask samples in 1995. This correction does not affect mixing ratios reported or conclusions drawn in Montzka et al. [1994]. This error was corrected in public accessible data files (CMDL World Wide Web site) in July 1996. Emissions estimated by industry from production figures [AFEAS, 1995] underestimate the atmospheric burden of HCFC-142b [Montzka et al., 1994; Oram et al., 1995] regardless of which measurements are considered accurate. Oram et al. [1995] have suggested that a portion of this discrepancy arises from non-negligible emission of HCFC- 142b in the years before 1981, which is the first year for which industry emission estimates are available. Between 1992 and the end of 1995, mixing ratios deduced from these emissions appear to underestimate the atmospheric burden of HCFC-142b by a consistent factor of -1.9 (CMDL scale). Analysis of the CMDL NWR air archive in 1995 for HCFC-142b shows mixing ratios of between 0.9 and 1.0 ppt between 1987 and 1989 (Figure 5.14). This is approximately 1.3 times higher than reported by Oram et al, [1995] for this period at Cape Grim, and this dif- ference is consistent with calibration differences as discussed above. After 1989, enhanced growth was observed at NWR. The rate of accumulation is believed to have accelerated at Cape Grim approximately 1 year later [Oram et al., 1995]. HFC-134a (CH 2 FCF 3 ) Measurements Development of techniques for determining mixing ratios of halocarbons present in the atmosphere at ~1 ppt and higher were refined in 1995 on a second GC-MS instrument. This allowed for analysis of air samples for numerous HCFCs, HFCs, and other halocarbons. Archived samples were also analyzed to determine how the abundance of HFC-134a has changed over the past 10 years. Results from these analyses show that the abundance of HFC- 134a in the northern hemisphere has risen from -50 parts per quadrillion (ppq) in 1990 (the limit of detection for this instrument) to -2.5 ppt in mid- 1995 [Montzka et al., 1996a]. Analysis of flask samples filled onboard ship during cruises in 1987, early 1994, and late 1994 show similar atmospheric increases. The abundance of HFC-134a approximately doubled in the time elapsed between the two 1994 cruises in both hemispheres. Cruise flask samples were filled and stored prior to analysis in early 1995 under dramatically different pressures and humidities than the archived samples filled at NWR. The consistency observed between archived samples from NWR and cruise flask samples suggests that the amount of HFC- 134a has not been altered significantly during storage by container-related effects and that the measurements are likely representative of atmospheric abundances at the time of sampling. Routine measurements of HFC-134a in flask samples filled at the CMDL observatories and cooperative sampling locations began in early 1995 (Figure 5.13d; [Montzka et al., 1996a,b]). Mixing ratios for this HFC are increasing rapidly at all sampling locations. Although it is not possible to accurately estimate the growth rate from such a short data record, the increase observed between 1994 and 1996 is consistent with exponential growth at -100% yr 1 . In simultaneously-filled flasks, mixing ratios determined for HFC- 134a were not significantly different. The amount of HFC- 134a measured in flasks filled in parallel typically agreed to within 30 ppq and was <100 ppq for 95% of the flask pairs analyzed. Similarly, analysis precision (1 s.d.) for replicate injections of air from flasks collected after 1995 from the ground-based stations was typically <30 ppq (<2%) and was <100 ppq for 95% of the flasks analyzed. This consistency is expected for properly-filled flasks and for molecules not adversely affected by storage in flasks. Flasks received from ground-based stations after February 1, 1995, were analyzed an average of 23 days after sampling. Preliminary emissions for HFC- 134a have recently been estimated by industry (P. Midgley, personal communication, 1996). At the end of 1994, these 92 emissions overestimate the observed abundance of HFC- 134a by only -0.1 ppt (measured/calculated = -0.8-0.9). CMDL Instrument Comparison from Routine Flask Analyses Beginning in early 1995, large flasks (2.4 L) were filled and analyzed at the stations on both GC-MS instruments. For the compounds shown in Table 5.3, mixing ratios were assigned to air samples based upon independent calibration of reference air with CMDL gravimetric standards. Comparisons of results obtained from these independent instruments can provide further estimates of measurement uncertainty for halocarbons at these low mixing ratios, especially because different analytical conditions are used in the two instruments. The second instrument incorporates a different analytical column (DB-1 versus DB-5), trapping of compounds at different temperatures on a different substrate (a section of alumina PLOT column at -80°C versus a length of uncoated fused silica at -140 to -150°C), and a different valving arrangement. Different mass fragments were monitored during air analysis on the different instruments to determine HCFC-22 mixing ratios (Table 5.3). Because different ions would likely be influenced to different degrees by any coeluting compounds, consistent results obtained with different ions gives additional confidence that these measurements are not affected by such potential chromatographic problems. Good consistency is observed for measurements of HCFC-22, HCFC-142b, and HFC- 134a from the two different instruments. These results suggest that potential problems associated with sample analysis (such as coelution or instrument-specific problems) are not influencing the results that are obtained for these halocarbons on either instrument. A small, consistent offset is apparent for HCFC-141b. The cause of this offset is currently unknown. Variability observed between instruments for measurements of HFC- 134a is larger than for other compounds because measured mixing ratios in early 1995 were often near the detection limit on the older GC-MS instrument. Measurements of Additional Chlorinated Compounds with GC-MS Instrumentation Mixing ratios for numerous other compounds were determined from flasks during 1994-1995. Data for certain chlorinated hydrocarbons with atmospheric lifetimes of <1 year show dramatic seasonal cycles in both hemispheres (Figure 5.15). Minima for these compounds were observed TABLE 5.3. Results of Individual Flask Air Analysis on Two Different GC-MS Instruments* New Instrument to Old Instrument Ratio Mass to Ions Charge Ratio Monitored Compound Mean Standard Deviation New Instrument Old Instrument HCFC-141b HCFC-142b HCFC-22 HFC- 134a 0.96 0.99 1.00 1.00 0.04 0.03 0.03 0.13 81 65 67 83 81 65 51 83 *Comparison based on - instruments in 1995. 150 flasks analyzed on both shortly after midsummer in each hemisphere when loss rates were expected to be greater than at other times of the year. Atmospheric Trends for Chlorine and Bromine Contained in Long-Lived Halocarbons Chlorine and bromine catalyze reactions leading to the depletion of stratospheric ozone. Enhanced use of DU - 50 - 40 ■ 30 - 20 : a) CH2CI2 4 B 83 J °°8 8 « , «< r n Q ° u a> n Q° °»: » < B Y 10 - I , , , , I , , . . ! . . I ■ I 1991 20 T 15 - 10 5 1991 1992 1993 1994 1995 1996 b) CHCI3 1992 1993 1994 1995 1996 Fig. 5.15. Atmospheric dry mole fractions (ppt) for selected chlorinated compounds. Symbols are identical to those described in Figure 5.13. These data were obtained from flask air analyses on the original GC-MS instrument (see text). Mixing ratios reported are based on a preliminary calibration scale. 93 chlorine- and bromine-containing compounds by mankind has led to a steady increase in the abundance of chlorine and bromine in the atmosphere in recent time and to the depletion of stratospheric ozone [WMO, 1995]. Only bromine and chlorine-containing compounds that are relatively insoluble and have atmospheric lifetimes longer than a year can deliver significant amounts of halogen to the stratosphere. In 1994 the atmospheric abundance of CI contained in these types of halocarbons was approximately five times greater than the burden estimated in the absence of anthropogenic emissions. Similarly, anthropogenic emissions of bromine-containing compounds have resulted in an atmospheric bromine abundance that is approxi- mately twice that estimated for preindustrial times. Model studies suggest that the tropospheric abundance of CI will peak in the mid 1990s at 3.5-4.0 ppb if limits outlined in the most recent Copenhagen amendments to the Montreal Protocol are not exceeded. Not all nations have agreed to the restrictions set forth in the Protocol; in addition, evidence suggests that significant amounts of CFCs are currently produced illegally. Furthermore, developing countries are allowed a 10 year grace period on consumption restrictions under the Montreal Protocol. As a result, much uncertainty has remained regarding the timing and magnitude of peak halogen (CI and Br) loading of the atmosphere. In the NOAH Group, global tropospheric distributions and abundances are routinely determined for the most abundant, long-lived anthropogenic halocarbons. Mea- surements of the halogen burden in the troposphere can supply a reasonable estimate for the stratospheric halogen burden 3 to 5 years in the future [WMO, 1995]. Accordingly, the results provide estimates for the burden of ozone-depleting gases in the future stratosphere. By accounting for the number of CI atoms contained in the most abundant CFCs, HCFCs, chlorinated solvents, and halon-121 1, it is estimated that the tropospheric abundance of CI contained within these halocarbons peaked in early 1994 and is currently decreasing at a rate of 25 ppt yr 1 (Figure 5.16a; Table 5.4) [Montzka et al., 1996b]. The current decrease is a dramatic turnaround from reported increases of 110 ppt yr 1 in 1989 and 60 ppt yr 1 in 1992 [WMO, 1995]. Most of the current decline in tropospheric CI can be attributed to a decrease in the atmospheric abundance of CH3CCI3 (Figure 5.9) which has a relatively short atmospheric lifetime (-5 yr) [Prinn et al., 1995]. The abundance of the major CFCs and chlorinated solvents were all stable or decreasing in 1995 with the exception of CFC-12. The abundance of CFC-12 continued to increase in mid-1995 at a rate of -6 ppt yr 1 or approximately one- third the rate observed in the late 1980s (Figure 5.7 and 5.8). Increases in the abundance of HCFCs (HCFC-22, -142b, and -141b) accounted for growth in tropospheric chlorine of -11 ppt per year in 1995 [Montzka et al., 1996b]. After accounting for chlorine contributed from CH3CI, other chlorinated hydrocarbons (-700 ppt), and less abundant CFCs, it is estimated that the mean global chlorine loading of the troposphere peaked in 1994 at -3.7 ppb. Stratospheric ozone is destroyed through reactions of inorganic bromine and chlorine molecules. To estimate how the abundance of stratospheric inorganic halogen will change as a result of the observed trends for halocarbons in the troposphere, stratospheric degradation rates of halocarbons must be considered. Halogen release rates Q. 3150 T 3100 a) a> c o O 2900 &' 2850 1992.0 1993.0 1994.0 1995.0 1996.0 2550 2500 b) 2250 1992.0 1993.0 1994.0 1995.0 1996.0 3250 3000 ^ 1992.0 1993.0 1994.0 1995.0 Sampling Date 1996.0 Fig. 5.16. (a) The amount of total chlorine, (b) effective equivalent chlorine (EEC1) and (c) equivalent chlorine (ECI) contained within anthropogenic halocarbons: CFC-11, CFC-12, CFC-113, CH3CCI3, CCI4, HCFC-22, HCFC-142b, HCFC-141b, halon-121 1, and halon-1301. Data were binned by month and hemisphere (northern hemisphere, filled triangles; southern hemisphere, filled squares; global mean, plus symbols). Solid lines represent fits to monthly means. 94 TABLE 5.4. Mean Rate of Change Estimated for Mid-1995 From Measured Halocarbons (ppt yr 1 )* Compound Global NH SH Chlorine EEC1 EC1 -22 -30 -2(1 -23 -35 -16 -15 .22 - 8 *CFC-11, CFC-12, CFC-113, CH,CC1 3 , CC1 4 , halon 1211, halon 1301, HCFC-22, HCFC-14lb, HCFC-142b. vary over altitude and latitude in the stratosphere, as does the efficiency for bromine to catalyze the destruction of stratospheric ozone when compared to chlorine (the alpha factor). Whereas bromine is estimated to be about 40 times more efficient than chlorine for destroying stratospheric ozone in the polar vortex [WMO, 1995], it may be as much as 100 times more efficient in the lower, midlatitude stratosphere [Garcia and Solomon, 1994]. In the following, the future reactive halogen burden is estimated for the lower, midlatitudinal stratosphere (effective equivalent chlorine, EEC1) [Daniel et al., 1995] and for the springtime, polar stratosphere (equivalent chlorine, EC1) with halogen release rates and alpha factors appropriate for each region. The abundance of halons increased over this period so that by considering higher estimates for alpha, the decline in EEC1 or EC1 is underestimated. The current mix and abundance of halocarbons within the troposphere ultimately will release fewer halogen atoms to the lower, midlatitudinal stratosphere than in previous years. The mean global tropospheric burden of halogen that will become inorganic halogen in the stratosphere reached a maximum in early 1994 and was declining in mid-1995 at 21 ± 8 ppt EEC1 yr 1 . (Figure 5.16b; Table 5.4; Montzka et al. [1996b]). The actual rate of change for EEC1 in mid- 1995 may be somewhat lower if the atmospheric abundance of methyl bromide has increased since 1992. However, limits to production outlined in the Copenhagen Amendments and production figures from the major global producers for 1991 and 1992 suggest anthropogenic methyl bromide emissions may have stabilized in the early 1990s. It is unlikely that an increase in methyl bromide over this period would have been large enough to offset the decrease reported here for EEC1 [Montzka et al., 1996b]. For a mean transport time between the troposphere and lower, midlatitude stratosphere of 3-4 years [Hall and Plumb, 1994; Fahey et al, 1995; Boering et al., 1995], maximum levels of inorganic halogen are expected in the lower midlatitudinal stratosphere between 1997 and 1998. Modeling studies suggest that when stratospheric mixing ratios of reactive halogenated compounds begin declining, column-ozone abundance at midlatitudes will begin to recover [WMO, 1995]. However, because stratospheric ozone is influenced by other variables such as aerosol loading and temperature [Solomon et al., 1996], the exact timing will also depend on how these variables change over this period. To estimate the stratospheric abundance of ozone- depleting gases in the springtime polar vortex, equivalent chlorine (EC1) was calculated based upon CMDL tropospheric halocarbon measurements. The current mix and growth rates of these gases in the troposphere will result in lower EC1 in the polar stratosphere in the future. In mid-1995 equivalent chlorine was decreasing at 18 ± 7 ppt EC1 yr- ' (Figure 5.16c; Table 5.4; Montzka et al. [1996b]). It is unlikely that an increase in atmospheric methyl bromide in recent time would have been large enough to offset this decrease. Because transport of air from the lower troposphere to the polar stratosphere below -25 km occurs in 3-5 years [Prather and Watson, 1990; Pollock et al., 1992; WMO, 1995], or over a slightly longer period than to the lower, midlatitude stratosphere, levels of equivalent chlorine are expected to reach a maximum in the polar stratosphere between 1997-1999 and decline thereafter as long as current growth rates for halons and CFC-12 and the abundance of other CFCs and halocarbons continue to decline. Although the abundance of reactive halogen in the polar stratosphere above Antarctica will decline when air currently within the troposphere reaches this region, springtime, total-column ozone levels will not increase there immediately. Ozone was nearly completely destroyed in the lower stratosphere above the Antarctic continent in springtime for the past 8 years [WMO, 1995]. Total- column ozone abundance within this region is expected to begin recovering only when mixing ratios of reactive halogenated compounds drop below those present in the late 1980s [Prather and Watson, 1990; WMO, 1995]. 5.1.6. Gravimetric Standards One of the strengths of NOAH is the ability to generate unique standards for "hot-topic" molecules with ease. Almost all of the NOAH standards are produced by actually weighing the individual components in air or by gravimetry. With maximum dilutions of 1:20,000 and accuracy's of better than 0.2%, two or four dilutions are sometimes required to produce standards at the ppt level. Not only does NOAH produce standards for internal use, but some of the clients have included other international and national research institutions. Some of this work over the past 2 years is summarized below. Aluminum compressed gas cylinders are now being used with brass and stainless steel valves that have all-metal valve stems and seats. Materials such as KEL-F have a high absorption/desorption potential for gases such as l,l,2-trichloro-l,2,2-trifluoroethane (CFC-113). Five compressed gas cylinders containing pure reagent gases were analyzed for impurities using a CEC-103 mass spectrometer located at the National Institute of Standards and Technology (NIST) in Gaithersburg, Maryland. The results of the analyses indicated that the measured purity levels of the pure methane (CH 4 ), carbon monoxide (CO), carbon dioxide (CO2), hydrogen (H?), and nitrous oxide (N2O) gases are consistent with the stated purity as specified by the gas supplier. These pure mixtures are being used to prepare gravimetric standards for CCG (CH 4 , CO, C0 2 , and H 2 ) and for NOAH (N 2 0). A total of 26 gravimetrically prepared CH 4 in air standards now exist for use by CCG. The nominal mixing ratios of the gas mixtures range from 32 ppb to 20 ppm. The standards are currently being studied for stability. 95 A suite of gravimetrically prepared sulfur hexafluoride (SFg) in air standards were prepared for the first time this year. The standards were prepared with nominal mixing ratios ranging from 3 ppt to 1 10 ppt. A suite of hydrogen (H 2 ) in air standards were also gravimetrically prepared for the first time this year. The mixing ratios of these standards range from approximately 450 ppb to 600 ppb. HFC- 134a in air standards were prepared in 1995 and were intercompared with existing HFC- 134a standards prepared several years ago. The results confirm that the gas is stable over many years. Several nine-component standards containing various methyl halide compounds were gravimetrically prepared primarily for the ocean and flask programs. The standards contain methyl bromide (CH 3 Br), methyl chloride (CH3CI), methyl iodide (CH3I), dibromomethane (CH 2 Br 2 ), tribromomethane (CHBr^), chlorodibromo- methane (CHBr 2 Cl), bromochloromethane (CH 2 BrCl), chloroiodomethane (CH 2 IC1), and diiodomethane (CH 2 I 2 ). Nine two-component mixtures were initially prepared with mixing ratios at the ppb level. The pure liquids were handled under darkroom conditions with the use of a black-light source, because compounds with iodine are photochemically active and decompose quickly in sunlight and artificial light. Existing CH3CCI3 and CC1 4 primary standards at the ppb level were compared to standards recently prepared to determine the stability of these gases over a number of years and to resolve a difference in sensitivity between several suites of ppt level standards that were prepared from the ppb standards. The mixing ratios range from 120 ppb to 760 ppb for CH3CCI3 and from 190 ppb to 950 ppb for CCI4. The gases were analyzed using GC with a FID. The results of the analyses indicate that eight of nine CH3CCI3 standards and nine of nine CC1 4 standards are consistent to within ±2%. 5.2. Aircraft GC Project: Mission ASHOE/MAESA 5.2.1. Overview A new four-channel GC, Airborne Chromatograph for Trace Atmospheric Species (ACATS-IV), was deployed for the first time in 1994 as part of the year-long Airborne Southern Hemisphere Ozone Experiment/Measurements for Assessing the Effects of Stratospheric Aircraft (ASHOE/ MAESA) mission. ACATS-IV flew successfully on 24 flights spanning latitudes from 70°S to 60°N during four seasons. During ASHOE/MAESA, ACATS-IV was configured to measure ten different molecules. In addition to CFC-11, CFC-113, and CH 4 (compounds measured previously with a two-channel version of the instrument) ACATS-IV measured CH3CCI3, CC1 4 , CFC-12, H-1211, N 2 0, SF 6 , and H 2 . ACATS-IV provides an important set of tracer measurements for several different aspects of atmospheric research: (a) Dynamic and chemical models can be constrained by the wide range of these tracer's lifetimes (4.5-3200 years). (b) Halogens play an important role in stratospheric ozone destruction and ACATS-IV provides in situ stratospheric measurements of 80% of the chlorine containing species and the bromine containing compound, H-1211 which contains about 20% of the total organic tropospheric bromine, (c) Apart from tropical transport of water from the troposphere to the stratosphere, CH 4 oxidation is the largest source of stratospheric water, which has a large global warming potential. Simultaneous CH 4 , hydrogen, and water measurements completely constrain the stratospheric hydrogen budget, (d) The age of stratospheric air is an important input to atmospheric models. SF 6 is a purely anthropogenic compound with no known tropospheric sinks, a stratospheric lifetime of 3200 years, and an approximately linear tropospheric growth rate that makes it an excellent indicator of the age of stratospheric air. A complete instrument description can be found in a recent publication by Elkins et al. [1996]. The GC has been optimized for low ppt work and frequent sampling of 3-6 minutes by using an appropriate choice of separation columns, very sensitive ECDs, and 12-port gas sampling valves that permit heart-cutting the chromatogram (Figure 5.17). The measured tracers have a wide range of lifetimes that can be used to estimate a tropical-midlatitude exchange in the stratosphere as demonstrated in Volk et al. [1996]. The H-1211, SF 6 , CFC-11, and CFC-12 measurements from ASHOE/MAESA have also been incorporated into a calculation that indicates the oldest stratospheric air measured by ACATS-IV has 17 ± 3 ppt of bromine and that all of the bromine resides in inorganic form. 5.2.2. Transport in the Lower Stratosphere ACATS-IV observations in the lower tropical and midlatitude stratosphere during ASHOE/MAESA provide new information about mass exchange between the tropics and midlatitudes. Because of the profound impact of transport on the distribution of long-lived stratospheric constituents, the magnitude of such exchange is critical for prediction of ozone depletion by human activities. The sparse set of previous tropical in situ tracer data [Goidan et al., 1980; Murphy et al., 1993] and satellite observations of tracer and aerosol distributions [Trepte and Hitchman, 1992; Randel et al., 1993; Mote et al., 1996] have provided evidence for a subtropical "barrier" to horizontal exchange. These observations led to the suggestion that the stratosphere might be closer to a "tropical pipe" model [Plumb, 1996], in which tropical air ascends in isolation from midlatitude influence, than a "global diffuser" model [Plumb and Ko, 1992]. For the first time the ASHOE/MAESA campaign provided extensive tropical measurements of many tracers with local lifetimes ranging from less than 1 to 100 years. These data provide a powerful tool for quantifying the amount of transport across the subtropical barrier. A simple tropical tracer model was used to analyze ACATS data for CFC-11, CFC-12, CFC-113, CCI4, CH3CCI3, halon-1211, and CH 4 along with measurements of N 2 0, NO y , and O3 from three other instruments aboard the ER-2 [Podolske and Loewenstein, 1993; Fahey et al., 1989; Proffitt and McLaughlin, 1983]. The observations during ASHOE/MAESA span latitudes from 60°N to 70°S and altitudes up to 21 km. The model considers the vertical evolution of a tropical tracer, including loss and production resulting from local photochemistry and entrainment of midlatitude air (due to isentropic mixing): 96 Data System Sample Loop Pressure Control Sample Loops: Molecules: Channel: SampU Sample In Loop Somp |, 0u1 Pre-Column Flow Controller =" ^ Fig 5.17. (a) Schematic of the ACATS-IV instrument showing pressure transducers (P), electron capture detectors (ECD), gas sampling valves (GSV), and the stream selection valve (SSV). Shaded areas are temperature-controlled zones where the temperatures for the GSV, SSV, and flow module are indicated. ECD and sample loop pressure controllers use a valve (MKS Instruments, Inc., Andover, Massachusetts) servo-controlled to a pressure gauge (Micro Gage, Inc., El Monte, California). The GC inlets for the calibration, carrier gases, and air sample have 10 |im screens to remove particles, (b) The first position of the 12-port GSV permits loading the sample loop, backflushing of the pre-column, and detection of the peaks of interest from the previous sample injection, (c) Turning the rotor of the 12- port GSV allows injection of the sample onto the columns and diversion of the column exhaust away from the ECD. "X r\ — d _ X _ -i/v, _ X X mid de V-r T YX (l) where % and Xmid are tne mean tropical and midlatitude mixing ratios; 9 is potential temperature used as vertical coordinate; Q = d6/dx is the net diabatic heating rate, equivalent to vertical ascent rate; P is the photochemical production rate; T is the lifetime for photochemical loss; y is the long-term growth rate; and T in is a time scale for import of midlatitude air, the quantity to be determined by this analysis. Tropical ascent rates (Q) were obtained from published calculations [Rosenlof, 1995; Eluszkiewicz et al., 1996]; chemical production and sinks for the species considered were calculated with a radiative transfer model [Minschwaner et al., 1993] and a photochemical model [Salawitch et al., 1994]; and long-term growth rates (y) were derived from CMDL network data. Midlatitude mixing ratios were constrained from observations between 35° and 55° in both hemispheres. Tropical air was identified as the region equatorward of the sharp meridional gradient in the NO y /03 ratio observed in the subtropics [Murphy et al., 1993]. A qualitative impression of the isolation of the tropical ascent region can be gained by comparison of vertical profiles of tracer mixing ratios observed in the tropics to profiles calculated assuming unmixed ascent (unmixed profiles), i.e., solutions to Eq. (1) with Tj n = °° (Figure 5.18). Observed profiles of the longer-lived species, N 2 and CFC-12, and also of CH 4 and NO y (not shown) deviate noticeably from unmixed profiles, indicating mixing with photochemically aged midlatitude air. However, for CFC- 113, CFC-11, and the shorter-lived species CH 3 CC1 3 , CCI4, and halon-1211 (not shown), observed profiles fall within the uncertainty range of values calculated for unmixed ascent because their vertical profiles are controlled primarily by photochemical loss that dominates loss by mixing for these shorter-lived species. Quantitative derivation of the rates of transport between the tropics and midlatitudes is best achieved by analyzing correlation diagrams of two species with disparate lifetimes [Voile et al., 1996]. Differences in the slopes of correlations observed at midlatitudes and in the tropics provide a direct measure of exchange between the two regions if horizontal mixing is fast compared to photochemistry for one of the two species (but not both). As an example, for a given mixing ratio of N 2 0, the shorter-lived species show lower abundances in the tropics than at midlatitudes because their loss processes are larger near -20 km (Figure 5.19), whereas N 2 is not destroyed until the air reaches higher altitudes. Because the abundance of N 2 in the tropics is sensitive to isentropic mixing, however (Figure 5.18), the tropical correlations do not match the correlations calculated assuming unmixed ascent. In order to derive the entrainment time (T in ) from the correlation diagrams in Figure 5.19, we consider Eq. (1) for the tropical mixing ratios of two tracers X and Y: dY ^ P y -(Ty'+y y )Y-T-'(Y-Y mid ) dX P x -(Tx'+y x )X-Tr„ 1 (X-X mid ) (2) 97 CFC-12(ppt) 300 400 500 CFC-11 (ppt) 100 200 a. 380 200 240 280 N 2 (ppb) 40 60 80 CFC-11 3 (ppt) Fig. 5.18. Vertical profiles of mixing ratios of several long-lived trace species in the tropics (light filled circles) and at midlatitudes (dark filled squares) [Volk et al., 1996]. For the midlatitudes the data was binned into 10K increments of potential temperature (0); the profiles shown represent the bin averages and the error bars represent the standard deviation within each bin. Calculated tropical profiles are shown for unmixed ascent (x in = «■) ( — ) from 8 = 380K (the mean tropical tropopause height) along with an uncertainty range induced by a 50% uncertainty in Q (---). Also indicated is the "effective lifetime" T ( = l/(x 1 +y)) at 6 - 440 K (-19 km altitude) for each of the species. Eq. (2), constrained by the mixing ratios for midlatitudes from observations and computed photochemical sources and sinks, is solved to calculate the tropical correlation Y(X) of two species; the entrainment time x, n is treated as a free (altitude-independent) parameter. For each pair of tracers displayed in Figure 5.18, the value of T in is determined giving best agreement between the calculated tropical correlations (Figure 5.19) and the observations. The same procedure was also applied to correlation diagrams of the longer-lived species, CH 4 , N 2 0, CFC-12, CFC-113, and NO y , versus O3, which is shorter-lived (with a photochemical production time of only -3.5 months at 19 km). Analysis of each correlation diagram yielded a mean for x m of 13.5 months, with an uncertainty of -20%. This seasonally and vertically-averaged entrainment time is longer than the time scale for isentropic mixing at midlatitudes of less than 3 months [Boering et al., 1995], confirming that mixing into the tropics is slow compared to mixing within midlatitudes. Because of the variability of the tropical correlations and the limited seasonal coverage, the data do not provide information on the dependence of Tj n with height. Entrainment of air into the tropics is not necessarily balanced by poleward detrainment from the tropics. In the annual mean, the net mass flux out of the tropics (detrainment minus entrainment) must be balanced by the mean mass divergence within the tropics (that can be determined from the mean ascent rate): Tin dz (pw) (3) where x out is a time scale for export of air whose inverse is the detrainment rate; p is the air density; z is altitude; and w is the mean vertical velocity. Detrainment rates computed from Eq. (3) for the estimate of Xj n (13.5 months) and ascent velocities averaged over 24 months, show that over much of the altitude range considered, more air is exported from the tropics than is imported (Figure 5.20a). The corresponding detrainment time (x out ) of less than ~6 months below 19 km and the morphology of decreasing detrainment with altitude is consistent with observations of the propagation of the seasonal cycles of CO2 and H 2 from the tropics to midlatitudes [Boering et al., 1995; McCormick et al., 1993] and with studies of aerosol dispersal from the tropics [Trepte and Hitchman, 1992]. As shown in Figure 5.20b, for an entrainment time of 13.5 months, -45% of air of extratropical origin accumulates in a tropical air parcel during its -8 month ascent from the tropopause to 21 km. The large uncertainty range in this result (Figure 5.20b) results from the uncertainty of the ascent velocity. This substantial entrainment of midlatitude air into the tropical ascent region of the lower stratosphere implies that a significant fraction of NO x (=NO + N0 2 ) and other effluents emitted 98 250 o -n O 200 - & T> Z 1b0 T3 a> 3 ra 100 0J 120 100 80 o o 60 40 220 240 260 280 N 2 (ppb) 300 Fig 5.19. Correlations of mixing ratios for the shorter-lived species versus N 2 in the tropics (dark filled circles) and at midlatitudes (light filled circles) [Volk et al., 1996], Mean midlatitude correlations used in the model (long dash) were obtained from quadratic fits to the correlations. Calculated tropical correlations are shown for the unmixed case (x jn = °») (short dash) and for a constant entrainment time x in that yielded the best agreement (in a least-squares sense) with the observed tropical correlations (long dash). Also indicated is the "effective lifetime" T (= l/(r'+g)) at = 440 K for each of the species. from supersonic aircraft at midlatitudes between 16 and 23 km will likely reach the middle and upper stratosphere where enhancements in NO x are expected to lead to reductions in ozone [Stolarski et al., 1996]. While estimating the effects of human activity on ozone remains a task for multi-dimensional models of atmo- spheric transport and chemistry, the determination of the rates of transport and the fraction of midlatitude air within the tropical ascent region constitutes important tests for the accuracy of such models. Most current 2-D models do not reproduce steep meridional tracer gradients in the sub- tropics such as observed in the NOy/03 ratio [Murphy et al., 1993], suggesting they generally overestimate the magnitude of mixing between the tropics and midlatitudes. Tests with a particular two-dimensional model show that greater reductions of midlatitude ozone are calculated, improving agreement with observed trends, if mixing para- meters are modified to simulate restricted exchange across the tropics [M.K.M. Ko, private communication, 1996]. Realistic representation of dynamical coupling between the tropical source and midlatitude sink regions of ozone may thus hold the key to understanding and reliably predicting the response of the stratospheric ozone layer to a variety of anthropogenic as well as natural perturbations. 480 460 440 420 400 380 ■J Fraction of Mid-latitude Air (%) 20 40 60 80 100 21 1 / \/^entrainment (1/t in ) x detrainment (1/t ou ,) -- t in = 16.2 months w = 1.5"nominal / t = 13.5 months, w nominal t ln = 11.3 months w = 0.5'nominal ?0 ■a x 19 3 01 ra OJ 18 c c ID 17 40 80 120 Transport rate (%/month) 16 Fig 5.20. (a) Entrainment rate into and detrainment rates out of the tropics versus potential temperature, expressed as % of air within a tropical air volume (at a fixed altitude) entrained/detrained per month [Volk et al., 1996]. Results are for T| n =13.5 months and ascent rates from Rosenlof [1995] (short dash) and Eluszkiewicz et al. [1996] (dotted). The disagreement between the detrainment rates based on these two studies reflects differences in the vertical profiles of the ascent rates, (b) Fraction of midlatitude air within the tropics versus potential temperature for nominal (long dash) and extreme (dotted) values of x, n and ascent rates w from Rosenlof [ 1995] as indicated. 5.2.3. Bromine Budget Concern over bromine's contributions to stratospheric polar ozone loss [McElroy et al.. 1986] and potential for midlatitude ozone destruction [Yung et al., 1980] has resulted in an international regulation of halons and methyl bromide. These bromine-containing compounds occur at much lower stratospheric mixing ratios than chlorine- containing compounds, but bromine is 40-100 times more efficient than chlorine at destroying ozone in the lower stratosphere [WMO. 1995]. In an effort to improve the understanding of brominated compounds in the strato- sphere, the first real-time, in situ stratospheric measurements of the purely anthropogenic compound, CBrClF 2 (H-1211) [Elkins et al.. 1996] were obtained. Measurements of H-1211 and nine additional tracers were obtained in 1994 at latitudes ranging from 70°S to 60°N and to altitudes of 20 km as part of the ASHOE/MAESA mission. The complete H-1211 data set for ASHOE/ MAES A is shown in Figure 5.21. These measurements were incorporated into a calculation of the total 1994 stratospheric bromine burden. The lower stratosphere was calculated to contain 17 ± 3 ppt of bromine in 1994 and that essentially all of the organic bromine had been converted to inorganic forms. The total stratospheric bromine burden was calculated by summing the bromine content in the tropospheric organic bromine species with lifetimes long enough to allow their transport to the stratosphere. This approach assumed that the only source of stratospheric bromine is at the earth's surface. The organic bromine species included in the model are CH 3 Br, H-1211, H-1301, CH 2 Br 2 , H- 2402, and CH 2 BrCl with November 1994 mixing ratios of 10.1, 3.3, 2.3," 1.1, 0.47, and 0.14 ppt respectively. The CMDL background site monitoring program provided a historical record of H- 121 1, H-1301, H-2402, and CH 2 Br 2 . The CH 3 Br data were collected on transects of the Atlantic and Pacific Oceans in 1994 by CMDL researchers 99 Q r l ' I' i | ' i i i | i i i i | i i i i | i i i i | i i i i i i i i i | i i i i | i i i i | i i i 1 i ii i ii i i i | i i i i | i n i 1 ii ~jm\ - W - 20 „p^ Q%^ ,#^ i * fl ?' ^^W^v^ _ 18 | f *x * z x « K o ° «j v txi o A — V; *X i t* A i - 1 16 R v * x tx! ^-^ D i 2 _ LJ O 1 i *k x i X X : o - 3 ^ i x *i - X < * ! X - 14 - o hi i * ! - X i* ~ _ * ; s ¥ * - X : _ x i * - 12 tx] : S - * ■ - Bin Ranges in ppt of H-1211: - O 0.0 - 0.4 □ 0.4 - 0.8 A 0.8 - 1.2 V 1.2 - 1.6 o 1.6-2.0 - 10 7 i 2.0-2.4 2.4-2.8 \A 2.8-3.2 X 3.2-3.6 Li i i i- 1 - 1 i - 1 i i i ljh i i i i i i i i i i i i i * 3.6-4.0 ' ' ' ' ' ' I'' i l i 7 -60 -40 -20 Latitude 20 40 60 Fig. 5.21. Latitudinal profile of halon-1211 as a function of pressure (mb). ACATS-IV measurements of halon-1211 in ppt during ASHOE/MAESA. [Lobert et ai, 1995]. The CH 2 BrCl data are from Whole Air Sampler (WAS) measurements taken by researchers at NCAR in early 1995. Taking the weighted sum of the mixing ratios of these species yields the following equation for the total bromine contained in these species as a function of time. age of the stratospheric air and thus, the total bromine present in the air being sampled. Photolysis of the organic bromine species produces inorganic bromine species with the majority of the inorganic bromine in reactive forms. The partitioning of stratospheric bromine was calculated using the equation Tropospheric [CBr y ](t) = [CH 3 Br] + [H-121 l]500 m, and vertical gradients approach zero. In studying regional emissions of trace gases, it is critical that the influences of local sources are minimized. At WITN, the boundary layer height during the night is typically <500 m. Hence, mixing ratio variability at 496 m during the nighttime is primarily driven by horizontal transport of polluted air to the site, and mixing ratios of long-lived species should reflect regional-scale emissions. Figure 5.31 shows the correlation of CH3CCI3 and C 2 C1 4 mixing ratios at 496 m between 2200-0900 EST during November 1995. An orthogonal distance regression through the data yields a slope of 0.62, which can be taken as the regional emission ratio of these two compounds. Using accurate (±5%) estimates of North American emissions of C 2 C1 4 [McCulloch and Midgely, 1996], CH3CCI3 emissions can be calculated. Using this methodology, emissions of halocompounds, especially those whose production and emissions are controlled by the Montreal Protocol, are monitored. 5.6. Measurement of Air From South Pole Firn As part of a cooperative venture with scientists from the University of Rhode Island, Pennsylvania State University, and CCG, NOAH analyzed the contents of flasks filled with firn air from the SPO in early 1995 [Battle et ah, 1996]. The sampling system was designed so that large quantities of air could be pulled from discrete depths in the firn down to the firn-ice transition depth of 122 m. Because it was possible to obtain large amounts of air, flasks could be flushed adequately and filled for nearly routine air analyses in Boulder and elsewhere. Air at the bottom of the firn had a C0 2 age of about 100 years [Battle et ai, 1996]. 105 285 ^280 Q. t- 275 J 270 O 265 . M X * Iffy ! XX K *** **x * * x* x* w M XX * * * ** **x ft 123 123 123 123 SK 123 123 123 123 123 123 fe 123 123 £? 150 Q. 3 140 ^120 X O 110 M X X X **x XX X x** **x m *xx *** "■Si ft ** X *** Sfe dip 123 123 123 123 123 123 123 ■fzf 123 123 123 123* 560 Q. Q.550 CM t- 540 o o 530 . x* <}j« -<* or SI ** "ti >S ^< 123 123 123^123 WD 123 x ** X * * *** , * , X * X Wl .* $, X t" x U "Si 'IT *** X* x« *"* X X 123 123 123 123 123 123 110 §1109 O O 107 106 x* * x*x *** (II) *** 123 123 123 123 123 123 123 123* 123 123 123 123 123 4.5 Q. Q.4.0 CO 3.5 3.0 * *x xx X X ** &} X X 1 ** X nil Sx*^ ** !fcft XX* XxX x*» M XX* X* *** * ** 1 X K it XX $f 123*123 123 123 123 123 123 123 123 123 123 123 123 t t m ui CD CD O P> ^ ?3 ^ in CT> 51 320 ^318 Q.316 S 3 14 O 312 c\j Z 310 **x *** W 1 <*><> x x I cb x X 308 ,123 123 123 123 123 123 123 123 123 123 123 123 123 Fig. 5.29. Monthly statistics of CFC-ll, CFC-12, CFC-113, methyl chloroform, carbon tetrachloride, nitrous oxide, and sulfur hexafluoride mixing ratios at the WITN tower. Crosses represent medians (horizontal bars) and interquartile range (vertical bars). Circles and asterisks are means and means ±1 standard deviation, respectively. The numbers across the bottom of each plot are the sampling level (1,2, and 3 refer to 5 1 , 1 23, and 496 m, respectively). N 2 in these samples analyzed by NOAH forms a bridge between ice-core data, which typically are much less precise owing to sample handling procedures and small samples, and real-time, present-day measurements (Figure 5.32). These results suggest that preindustrial levels of N 2 in the atmosphere had to be about 280 ppb and that N 2 was increasing steadily through the latter part of the 20th century. The growth rate of atmospheric N 2 from 1904 through 1958 was 0.06 ± 0.01% yr 1 (95% confidence level); thereafter, it has increased at a rate of 0.22 ± 0.02% yr 1 (95% C.L.). N 2 covaried well with C0 2 throughout the profile, although the smoothness of the fit could be attributable to subsurface diffusion of the gases. Nevertheless, the overall trend of N 2 as a function of C0 2 was 0.50 ± 0.03 ppb N 2 ppnv 1 C0 2 -' (95% confidence level, r 2 = 0.98). Surprisingly these flasks, which were sealed with Teflon o-rings, did not cause significant contamination of most halocarbons. Consequently, depth profiles were obtained of CFCs, chlorocarbons, and bromocarbons representing air as far back as the late 19th century. (Dates assigned to halocarbons will be older than C0 2 in the same bolus of air owing to their slower rates of diffusion.) As shown in Figure 5.33, which is a close-up of the lower portion of the CFC-ll profile, the sampling and analytical precisions are on the order of tenths of a ppt. Small amounts of contamination are suggested in that the lowest values were still 2 ppt (<1% of today's atmosphere) and that two pairs of flasks showed higher levels of CFC-ll in some of the deepest firn. This latter contamination was probably caused by stress on the pump near the firn-ice transition zone where less air was available to pull, thus increasing 106 3 * X }S Q. X * Q. 2 X X X ° X X 2 i -"-" ox x x o * x * -o 1 X X X * cc * -ir-"-** X * iL JL CD ir <> „< r <) x *"!*"" -__ * i! si o M¥4-f-JL*.-§- f ,-$ X "(kTp x XXX X X X X * X * x i * - - X 1! I 1 1 1 T * WITN Tower, 496 m 12 15 18 21 24 Hour of Day (Local Time) Fig. 5.30. Statistics of 51 m - 496 m mixing ratio gradients for N 2 0, CH3CCI3, and SF 6 , binned by hour, for November 1995. Crosses indicate means (horizontal bars) ± the 95% confidence interval (vertical bars). Circles represent medians, and asterisks indicate upper and lower quartiles. The left panel gives statistics of 51 m - 496 m gradients for the entire month. the probability of sucking in unrepresentative air. This feature showed up in all of the gases, further suggesting contamination with modern air. Nevertheless, this level of contamination is not representative of the rest of the profile. Thus, we were able to obtain precise, but probably accurate, measurements at sub-ppt levels throughout most of the profile. These results yield entire atmospheric histories for CFCs, halons, and other halocarbons of purely anthropogenic origin (Figures 5.33 through 5.37). They also showed atmospheric trends for gases of both natural and anthropogenic origin, such as CH^Br, during a time when the human population, its agricultural output, and its industrial activity increased dramatically. These data demonstrate that natural sources of CFCs and halons are minimal at best and most likely nonexistent. Models of 3 3 3 3 ~ 3 / 3 y = 0.62x +111 r = 0.861 10 15 20 C 2 CI 4 (ppt) Fig, 5.31. Correlation between CH3CCI3 and C 2 C1 4 mixing ratios at 496 m between 2200 and 0900 (EST) during November 1995. The slope of an orthogonal distance regression (0.62) is taken as the regional emission ratio of these two compounds. 315 305 o E is O E O CM 295 - 285 iJK sP * 4 A A *° □ A * A A A A -SH Flasks (CMDL) a Ant. Ice (Machida 1995) d SPO Firn (CMDL) 1 ' 275 - 265 1900 1920 1940 1960 1980 2000 Year (based on C02) Fig. 5.32. History of atmospheric N 2 over the past century, derived from antarctic ice-core measurements [Machida et a/., 1995], real-time air measurements in the southern hemisphere (NOAH), and analyses of South Pole firn air (NOAH). Firn air ages are determined from correlation of C0 2 in the samples with the atmospheric CO, history of Etheridge et al. [1996]. Diffusivities of N 2 and C0 2 are assumed to be identical and ice core data of Machida et al. [1995] have been lowered by 1 ppb to conform to the CMDL scale. 107 CFC-11 (pmol/mol) -105 -110 £ -115 Q. -120 -■ -125 10 20 30 40 50 —I 1 I 1-=— A South Piole Firn Air a Measured ■ Grav. Corrected -20 -40 E -60 Q. d) -80 O -140 Dry Mole Fraction (pmol/mol) 25 50 75 100 — ' A- 125 -100 -120 \f£& ♦% ♦♦:♦ aa SPO Firn Air &£A C A -♦ - A* A*- - ACCI4 ♦ CH3CCI3 Fig. 5.33. CFC-ll in the lower portion of the firn at the South Pole. The high degree of precision is shown in the actual measurements (triangles), where two flasks were collected at each depth and plotted separately. Only at 108 m depth are these symbols distinguishable and there only because two pairs of flasks from this depth in two separate holes were analyzed. Flasks at 120 and 1 22 m were subjected to some contamination with modern air during sampling, probably owing to stress on the pump as the firn layers began to turn to ice. Also shown here is the effect of the gravitational correction for settling of CFC-l l, which is a gas heavier than air. Again, the error is small. Fig. 5.35. Depth profiles of CCl 4 and CH 3 CCl, in South Pole firn. There is some evidence of contamination of a few ppt in the CH3CCI3 data, although mole fractions of this compound came very close to zero near the bottom of the profile. Mole fractions of CCI4 never fell below 10 ppt, suggesting either significant, specific contamination of this compound, a very early history of significant anthropogenic release, or a natural source. Dry Mole Fraction (pmol/mol) 100 200 300 400 500 600 -20 -40 E -60 Q. S - 80 -100 -140 u --•--■-- ■ ------- ■ -m ----- t ■ A I A , A ------- A |- - - - A - - - -fl- ------ - A SPO Firn Air f ■ ■ A A A A ■ CFC-11 aCFC-12 A w£ I i — i Dry Mole Fraction (pmol/mol) 2 4 6 8 10 -20 -40 D A ■ -60 + m a Q. * -80 B -100 CBA P A tn □ B £ IDA -120 -140 SPO Firn Air ♦ CH3Br DH1301 AH1211 r Fig. 5.34. Depth profiles of CFC -II and -12 in South Pole firn air. Mole fractions of both gases near the bottom of the firn are less than 1% of the present day values, suggesting that natural sources are minimal or non-existent. Fig. 5.36. Brominated gases in South Pole firn air. The anthropogenic halon mole fractions both drop to zero early in the profile. These gases were not introduced into the atmosphere in significant amounts until the 1970s. CH,Br is about 6.5 ppt in air nominally dating back to about 1880. 108 0.0 +■ -20 -40 SF6 (pmol/mol) 0.5 1.0 1.5 2.0 2.5 3.0 3.5 i A I A A - - - A I 1 I A - - - , - -A- . - - - - ' A . A- - i ---,--- - SPO Firn Air 1 6 A - - - -A A E. -60 Q, ■ i ;,.■ (Downsl(>pe Winds Qfttyj. 1 ' Fine SOIL (ng/m A 3) In ■■■■. _1hb.b-1b 2 9 9 12 16 18 23 26 X 2 • • 13 16 20 23 27 X 4 7 11 14 18 21 25 21 March April May 2 < a c I ' II M 5 u V c Ik B§B EHbm bBh «■_ 2 5 9 12 16 19 23 26 30 2 March ■ 9 13 16 20 23 27 30 4 7 11 14 18 21 25 28 April May TABLE 2. Comparison of Trace Elements From Potential Sources of Arsenic 1000* 1000* 1000* 1000* Se/S0 4 Cu/S0 4 Zn/S0 4 As/S0 4 Volcanoes: Kilauea, Nov. 21, 1992 1 9 0.39 0.37 0.32 Copper Smelters: Average Arizona "Smelter No. 5" 1.7 0.02 20.0 1.0 28.0 3.8 6.0 2.3 Mauna Loa (downslope) April 9, 1994 <0.08 0.9 3 8 2.4 Fig. 1. Aerosol concentrations at Mauna Loa Observatory, spring 1994. All concentrations are given in nanograms nr 3 . For details of the parameters, see Malm et al. [1994]. Note: All values have been normalized to sulfate. for very fine (D p <0.5 urn) particles was only a factor on the order of 3 (Table 3). If we use this small particle dilution factor to calculate the arsenic levels at Asian sources, the resulting arsenic concentrations are high, but not unprecedented. Thus, it is possible that other materials in the smallest size ranges (including many anthropogenic pollutants) could also be efficiently transported to MLO. The final topic involves experiments to be conducted during the spring of 1996 to test some of the hypotheses raised by the prior work. The experiment will take place during April and May of 1996 and include the following: (a) direct measurement of organic particles by carbon combustion from quartz filters and by GC/MS from quartz filters, (b) establishment of nitrate levels via direct collection of denuded nylon filters, (c) size/time resolved sampling of optically efficient aerosol (three sizes <2.5 pm), and (d) l4 carbon dating of organic aerosols. These measurements will be complemented by the IMPROVE Channel A sampler and the full suite of MLO observables, including carbon soot via aethelometer and isentropic trajectories every 12 hours from CMDL. Acknowledgments. This work would not have been possible without the capable support of the staff at MLO who have delivered samples biweekly with an efficiency that is among the very best in the entire 70-site network. We also wish to thank Joyce Harris for both her insights and her trajectories. if we use typical soil dilution factors to calculate the ambient levels of arsenic and other toxic species at the source regions in Asia, we find that the concentrations would need to be in the microgram nr 3 range over a wide area of the mainland during periods of strong venti- lation and dilution associated with the dust storms. In non dust-storm periods, one would then expect arsenic levels unprecedented in western experience, levels that would likely be lethal in a relatively few years. As a result, the second explanation is probably the dominant factor. For example, using data from dust storms that occurred during the spring of 1981, we found that the dilution factor TABLE 3. Comparison of Fine Soil Dust Transport Efficiencies from China (April 19, 1981) to MLO (May 12, 1981)* Beijing Mauna Loa Ratio D p <0.5 pm 0.5 E b O en O IS-*- -te. 4. 3.0- 2.0- 1.0- 0.0- * * '**£*-■ ^ B^K a ^fr^ m m •"m f^i w wj 'l k 1 Tm j wrtanwo- an*a -»*-***. "*#ex& a &&$&t*9d£tj H &&&& H I . M H' IUMKW 1 Ozone x N20 i — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — 1 — r 05/02 11/01 05/03 11/02 05/04 11/03 05/05 11/04 11/01 Fig. 1 . Total column amounts of ozone and N 2 over Mauna Loa Observatory. 117 LiJ CO O z I 9 8.5- 80 7 5 70 65 60 5 5' 5.0- 4.5- 4.0- 3.5- 3.0 I i i 11/01 x< X X X X & ~*x x X x X t — i — i — r 05/02 -i — i — i — i — i — i — i — r 05/03 -i — i — r 11/03 **? ^ 11/01 11/02 05/04 05/05 11/04 Fig. 2. Total column amount of HNOj over Mauna Loa Observatory. 2 5- LU O 0) « **»* ^** *£? *^* ^(^^ ***^***^* *^5? -i — i — I — I — r 05/02 -i — I — I — i — I — i — i — I — I — i — I — I — i — i — I — i — r 11/01 05/03 11/02 n — i — r 05/04 ~i — : — i — i — i — i — i — i — i — i — i — i — i — i — i — r 11/03 05/05 11/04 11/01 Fig. 3. Total column amount of F22 over Mauna Loa Observatory. Finally, we measured the 2n 2 Q-branch of CHF 2 C1 (F22) at 829.05 cm" 1 . Figure 3 shows the total columns measured for F22. Basically, we measured an increase of 20% yr 1 which slowed down between spring and summer of 1994. Both instruments operated at MLO for several months. This resulted in four to six same-day data comparisons. If we look at the average of the new-to- old ratio, we find approximately 1% difference for 3 and N 2 with the new instrument slightly higher, approximately 2% difference for the F22, and approximately 5% difference for the HNO3 with the old instrument running slightly higher. Overall, these results have been very encouraging. Acknowledgments. This research was partially supported by NASA under grants NSG 1432 and NAG2-351. The collection of the data was done with the support of CMDL. We are especially grateful to Bob Uchida for collecting most of this data very early each Wednesday morning. References David, S.J., S.A. Beaton, M.H. Anderberg, and F.J. Murcray, Determination of total ozone over Mauna Loa using very high resolution infrared solar spectra, Geophys. Res. Lett., 19, 2055-2058, 1993. David S.J., F.J. Murcray, A. Goldman, C.P. Rinsland, and D.G. Murcray, The effect of the Mt. Pinatubo aerosol on the HNOj column over Mauna Loa, Hawaii, Geophys. Res. Lett., 21, 1003-1006, 1994. 118 A Preliminary Comparison of 813C Measurements in CO2 From Mace Head, Ireland A. Gaudry and P. Monfray Centre des Faibles Radioactivites, LMCE. CEA L'orme des Merisiers, 91191 Gifsur Yvette, France M. TROLIER Institute of Arctic and Alpine Research, University of Colorado, Boulder 80309 C. Flehoc and P. Ciais LMCE, CEA L'orme des Merisiers, 91191 Gifsur Yvette, France S.G. Jennings Department of Physics, University College of Galway, Ireland Background The 13 C composition of atmospheric CO2 makes it possible to estimate biospheric fluxes of CO2, as plant photosynthesis discriminates against 13 C02, whereas isotopic fractionation during CO2 dissolution into the ocean is small. However, to infer the partitioning of anthropogenic CO2 between its oceanic and terrestrial sinks requires measurements of very high precision. Fluxes of CO2 that are readily measured via changes in the atmospheric CO2 mixing ratio have a smaller impact on 8 I3 C. For instance, adding 1 ppm (analytical precision is -0.1 ppm) of purely "biogenic" CO2 to the atmosphere changes the 8 13 C of that reservoir by only 0.05%c (analytical precision is ~0.02%c). The isotopic effect of adding 1 ppm of "oceanic" C0 2 is even smaller. Although the internal precision of mass spectrometers is about 0.01%c, systematic experimental errors may bias measurements of the 8 13 C of air samples [Francey et al., 1995]. Drift of the reference gases used to calibrate measurements can also introduce biases [Trolier, 1994]. Intercomparisons between different laboratories using independent calibration strategies and experimental protocols are crucial in order to assimilate their various data for use in models [Ciais et al., 1995]. One of the best ways to monitor the intercalibration of independent programs is to conduct parallel sampling of whole air on an ongoing basis and at a common site. In this paper we report a preliminary intercomparison of 8 13 C measurements of air samples independently collected at Mace Head Station (53.43°N; -9.90°W) in the North Atlantic by CMDL and by the Centre des Faibles Radioactivites at the Laboratoire de Modelisation du Climat et de L'Environnement (CFR-LMCE; France). The CMDL samples are measured for isotopic composition at the Institute of Arctic and Alpine Research (INSTAAR) at the University of Colorado. Mace Head is located in the vicinity of the North Atlantic oceanic sink of CO2 [Lefevre, 1996], but it is also reached by continental air, especially in winter. The seasonal cycle of 8 13 C at Mace Head has a fairly large amplitude (0.9%c), so 8 ,3 C values can be compared over a rather wide range, from about -8.3%o in winter to about -7.4%c in spring and summer. The results of this intercomparison are summarized and discussed below. Sampling and analytical techniques CFR-LMCE began continuous atmospheric C0 2 monitoring at Mace Head station in cooperation with the University College of Galway (Ireland) and International Science Consultants (United Kingdom) in July 1992. Meteorological data are also continuously recorded, enabling "background" sampling conditions to be distinguished from conditions that are influenced by local sources. Beginning in July 1993, flask samples (2-L glass flasks with Viton O-ring stopcocks, filled to 1 bar with air dried to a dewpoint of -55°C) have been measured for the 13 C composition of C0 2 . The usual sampling frequency is two pairs of flasks per month. During the period from May 31, 1993, to June 7, 1993, the sampling frequency was about one pair per day; 8 13 C data for these samples are not shown here. A different standard was used for the isotopic analysis which increases the uncertainty. CFR-LMCE has operated an isotope-ratio mass spectrometer (Finnigan MAT 252) since January 1993, collaborating with CSIRO (where a similar instrument is used) to characterize the effects of instrumental artifacts on 8 13 C measurements. The recognized effects include [Francey et al., 1995] memory effects (when a sample has a very different 8 13 C than the reference gas), size effects, which can affect linearity, and the "bleed correction," due to the fractionation that results from consumption of the reference gas. CFR recently made an accurate determi- nation of the N 2 interference. The CFR flask measure- ments are calibrated against one sample of carefully purified C0 2 , called SNAIL. SNAIL was calibrated against NBS-19, a carbonate provided by International Atomic Energy Agency (IAEA) [Hut, 1987] and two standard pure C0 2 gases, GS19 and GS20, provided by the University of Groningen, Netherlands. The 8 13 C of SNAIL standard was determined to -9.67 ± 0.04% c (relative to VPDB-C0 2 ). NOAA began sampling at Mace Head in June 1991; the flasks (2.5-L glass flasks with Teflon o-ring stopcocks) are sampled in pairs and analyzed for the mixing ratios of C0 2 , CH 4 , and CO by CMDL, and for 8 13 C and 8 18 of C0 2 by INSTAAR. At INSTAAR, C0 2 (with N 2 0) is extracted from about 750 bar-cm 3 of whole air cryogenically, then analyzed for isotopic composition using a VG Sira Series II isotope-ratio mass spectrometer. The raw data (ratios of ion currents at masses 45 and 46 to 119 mass 44) are corrected for the presence of N 2 and for the contribution of species containing 17 to the ion currents. The experimental technique and data analysis are described by Trolier el al. [1996]. The INSTAAR flask measurements are calibrated against a suite of whole-air reference gases, which in turn are calibrated against VPDB-C0 2 and VSMOW. The estimated precision of individual 5 13 C and 8 18 measurements are 0.03%o and 0.05%c respectively; the uncertainties in the absolute calibrations are ~0.02%c and ~0.1%c respectively. Intercomparison Figure 1 shows the time series of 8 13 C measurements from Mace Head from both groups. Overall, the agreement appears to be good with the data sets showing no large offset and comparable seasonal cycles. We have made three quantitative comparisons of the two data sets: (1) directly comparing flask samples obtained close in time by the two programs; (2) comparing CFR data to a smoothed curve representing the entire INSTAAR data set; and (3) comparing CFR data obtained during "background" atmospheric conditions to the same smoothed curve from the INSTAAR data set. Background conditions correspond to winds higher than 4 m s _1 in the wind sector within 200° and 300°. Because the two flask sampling programs are independent, their flasks are not necessarily filled close together in time. For example, there are only six instances between May 1993 and January 1995 for which flasks were obtained by both groups on the same day; in these cases, the flasks were sampled less than 1 hour apart. The average difference for these samples (CFR - INSTAAR) is -0.04 ± 0.09%c (the error estimate is the standard deviation, la, of the differences). In an attempt to compare the two records for flasks sampled on different days, a smooth curve [Thoning et al., 1989] was used to represent the INSTAAR record for days on which samples were not available. The smoothed curve is obtained by first fitting a curve consisting of the sum of a third-order polynomial trend and four-harmonics to the flask data; the residuals are then filtered in the time domain using a low-pass filter with a full width at half maximum of 100 days, and the smoothed residuals are added to the fitted curve. The smoothed curve was fitted to the INSTAAR data, and differences were calculated between the original flask data (for both INSTAAR and CFR) and the smoothed curve. These differences are shown in Figure 2. The mean difference between the CFR 8 13 C values and the INSTAAR smoothed curve is -0.05 ± 0.08%o for 26 samples. This analysis has been repeated using only INSTAAR data obtained under "background" conditions as defined by CFR; this eliminates -50% of the INSTAAR measurements. This comparison of background samples appears in Figure 3. In this case, the average difference is -0.03 ± 0.07%c for 18 samples. Each comparison suggests a slight offset between the calibration scales of the two groups, although in no case is the discrepancy greater than the error of the comparison. Conclusion A preliminary comparison between the time series of 8 13 C measurements at Mace Head, obtained by LMCE and MACE HEAD STATION 0.2 O O 0.15 ° ° O O • • 0.1 Q O ° ° ° °° 0.0S 11 oc§ O = I, I 7(, *° o 2, in Climate Monitoring and Diagnostics Laboratory, No. 23: Summary Report 1994, edited by J.T. Peterson and R.M. Rosson, NOAA Environmental Research Laboratories, Boulder, CO, pp. 106-110, 1995. Hut, G., Consultant's group meeting on stable isotope reference samples for geochemical and hydrological investigations, IAEA report, Vienna, September 1985, 1987. Lefevre, N., A first step towards a reference AP map for the North Atlantic ocean, IGBP-10, working paper 1 1, 1995. Thoning, K.W., P.P. Tans, and WD. Komhyr, Atmospheric carbon dioxide at Mauna Loa Observatory, 2: Analysis of the NOAA/GMCC data, 1974-1985, J. Geophys. Res., 94, 8549- 8565, 1989. Trolier, M., Calibrating the INSTAAR-NOAA/CMDL record of stable isotopic composition of atmospheric CO2, in Final Report on the IAEA Coordinated Research Program on Isotope Variations of Carbon Dioxide and Other Trace Gases in the Atmosphere, edited by K. Rozanski, IAEA, Vienna, Austria, 1994. Trolier, M., J.W.C. White, P.P Tans, K.A. Masarie, and PA. Gemery, Monitoring the isotopic composition of atmospheric CO2: Measurements from the NOAA global air sampling network, J. Geophys Res., in press, 1996. 121 Measurement of Short Period Magnetic Pulsations at Barrow: A Key Location in the STEP Polar Network Kanji Hayashi Department of Earth and Planetary Physics, The University of Tokyo, Bunkyo, Tokyo 113, Japan The main objective of the Solar Terrestrial Energy Program (STEP) polar network is to realize a high time- resolution global scale network to trap disturbances induced by the solar-terrestrial links that occur somehow like earthquakes. Solar cycle effects found in occurrences of a type of short period magnetic pulsations termed as Pel, is an unsolved and interesting target for long-term observation. Magnetic field measurements are obtained at BRW with a highly sensitive (- 3 pT @ 1Hz) induction magnetometer in operation almost continuously for more than 1 year when a new digital data logger was installed. The installation and the initial settings were carefully managed by the station operators. Data status: A significant amount of DC offset and its drift in the Y component were observed in warm seasons. It was a known problem of the instrument and was reported that it settled down in the cold season. We guess that connection points along the signal cable going to the Y sensor were probably wet. Electromotive force from the sensor is very low (less than 1 Mv) and is easily overcome by battery effects at wet contacts. It will be fixed in 1996 by checking the cable. Data release: Acquired data are primarily processed for our research but are provided for any other researchers on request and compressed data is in free access on the Internet via anonymous ftp at "hpgrl.grl.s.u-tokyo. ac.jp." The volume of high resolution data such as acquired at BRW is as much as 130 MB each month on a cassette tape. Whole-month data from about 20 sites (potentially 30 if all work well) is too much to place on the disk for free access, but will be placed on image files that contain frequency versus time display. 122 Total Nitrate and MSA Variation at Mauna Loa B. J. HUEBERT AND L. ZHUANG Department of Oceanography, University of Hawaii. Honolulu 96822 Introduction Much of the NO and NO2 emitted into the atmosphere is converted to nitric acid vapor or aerosol nitrate before being removed by dry or wet deposition. This conversion to nitrate is largely complete within a few days of the odd- nitrogen's emission so that in remote areas such as at the Mauna Loa Observatory, Hawaii (MLO), the total nitrate concentration (vapor plus aerosol) represents a fair estimate of the total odd-nitrogen concentration [Atlas et al., 1992]. With support from NSF, we have measured nitrate concentrations at MLO for several years to help identify the important sources of odd-nitrogen compounds in remote parts of the globe. We now measure total nitrate every night from the walkup tower in collaboration with the MLO staff. We have also begun measuring methanesulfonate (MSA) aerosol. Material and Methods We use a Teflon/nylon filter pack method for collecting atmospheric nitrate. Since August 1988, one filter has been exposed each night from 2000 to 0800 LST. Filters are returned to the University of Hawaii laboratory for extraction and analysis by ion chromatography. The data from August 1991 to July 1992 was, unfortunately, treated differently from the remainder. These samples were all analyzed as a batch during a brief period between the return of our analytical labora- tory from a field deployment in the Azores and its shipment to its new home at the University of Hawaii. Once it became apparent that this data looked very different from previous years, it was no longer possible to replicate the analytical conditions or the standards to resolve questions of its validity. Hence, that data is excluded from the figures in this report. Results and Discussion In 1993 we published a description of gradient measurements of nitric acid and aerosol nitrate at MLO [Lee et ah, 1993]. This work showed surface-active species, like nitric acid, often have large gradients near the surface at MLO, raising the potential for underestimating free tropospheric concentrations due to depletion of material upstream of samplers. The deposition velocity of nitric acid to the lava surface varied from 0.3 to 4 cm s 1 . During our intermittent MLO sampling prior to September 1988, we observed a sharp maximum in nitric acid and aerosol nitrate concentrations in the summer. The search for an explanation for this maximum continues to stimulate our science. The daily total nitrate values for 1995 are plotted in Figure 1. The lowest sustained concentrations are still evident in the winter with a mix of high-concentration events and cleaner periods in the spring and late summer. Figure 2 shows monthly averages of 2000 to 0800 LST total nitrate concentrations from September 1988 to December 1995. The 1993 data represent the lowest 400 100 200 Julian Day 300 Fig. 1. Nightly concentrations of total nitrate in 1995. 123 300 1988 1989 1990 1991 1992 1993 1994 1995 1996 Fig. 2. Monthly average total (aerosol plus vapor) nitrate versus time. (defendable) concentrations we have observed during our sampling at MLO. The concentration of total nitrate at MLO is to a large extent controlled by precipitation scavenging of soluble material during transport from the continents [Lee et al., 1994] so this interannual variability may be an indicator of changes in large-scale precipitation patterns. The apparently monotonic decrease in summertime total nitrate from 1988 through 1991 suggests that a cyclic process, such as the southern oscillation, may be reflected in this record. It is certainly reasonable that the transport of continental materials like mineral aerosol and fixed nitrogen (which can be limiting nutrients in certain parts of the Pacific) should be sensitive to changes in large-scale atmospheric circulation patterns. Clearly, we need to identify the climatological differences that cause this dramatic change in the annual cycle of nitrate from 1 year to the next since they may have impacts on phenomena as diverse as marine biological productivity and the earth's radiation budget. In February 1995 we began to analyze our filter samples for MSA, since MSA is an indicator of dimethylsulfide (DMS) oxidation [Huebert et al., 1996]. We are interested in the potential that DMS oxidation in the free troposphere may be responsible for much of the MSA (and some of the sulfate) found in ice cores. As Figure 3 shows, the annual cycle of MSA is both distinct and different from that of either nitrate or non-seasalt sulfate (NSS). The summer MSA minimum could be due to slower DMS transport, a change in the amount of MSA produced from DMS, or more rapid MSA removal. It is clear from the data that the MSA we see is not due to boundary-layer contamination of our samples since it is rarely accompanied by CI or Na, which are clear indicators of boundary-layer air in our samples. -160 120 200 CO 3 5 7 9 Month 11 T3 C CO CO C/> CD O) CO 1— CD > < o -«- MSA -*- N03 -±- NSS Fig. 3. Monthly average MSA, sulfate, and total nitrate for 1995. 124 Ongoing Research With the help of the MLO staff, we are continuing our nightly sampling from the tower. Although equipment failures and analytical problems unavoidably cause lapses in the data, a very interesting record is emerging. We intend to continue this total nitrate data record in the hopes of identifying those factors which control the form and the range of its annual cycle. References Atlas, E.L., B.A. Ridley, G. Hiibler, MA. Carroll, D.D. Montzka, B. Huebert, R.B. Norton, J. Walega, F. Grahek, and S. Schauffler, Partitioning and Budget of NO y Species During MLOPEX, J. Geophys. Res., 97, 10,449-10,462, 1992. Huebert, B.J., D.J. Wylie, L. Zhuang, and J. A. Heath, Production and loss of methanesulfonate and non-sea salt sulfate in the equatorial Pacific marine boundary layer, Geophys. Res. Lett., 23, 737-740, 1996. Lee, G., J.T. Merrill, and B.J. Huebert, Variation of Free Tropospheric Total Nitrate at Mauna Loa Observatory, Hawaii, J. Geophys. Res., 99, 12,821-12,831, 1994. Lee, G, L. Zhuang, B.J. Huebert, and T.P. Meyers, Concentration Gradients and Dry Deposition of Nitric Acid Vapor at Mauna Loa Observatory, Hawaii, J. Geophys. Res., 98, 12,661- 12,671, 1993. 125 Radionuclides in Surface Air at BRW, MLO, SMO, and SPO During 1994 and 1995 John Kada and Colin G. Sanderson Environmental Measurements Laboratory, U.S. Department of Energy, New York, 10014-3621 Introduction High volume air filter samples are routinely collected by CMDL personnel at BRW, MLO, SMO, and SPO for the Surface Air Sampling Program (SASP), a global network of aerosol sampling sites operated by the Environmental Measurements Laboratory. On a global scale the SASP network provides the capability to track atmospheric releases of artificial radionuclides due to nuclear weapons tests or nuclear accidents. At BRW this was most recently demonstrated by the detection of anthropogenic radionuclides released into the atmosphere by a chemical explosion and fire at the Tomsk-7 nuclear complex in Russia, 5000 km from BRW [Larsen et al, 1994]. The SASP network also produces data on temporal and spatial trends in the worldwide distribution of the natural radionuclides 7 Be and 210 Pb. The SASP data has proven to be a valuable check on the transport and aerosol scavenging components of global climate models [Rehfeld and Heimann, 1994] and provides the bulk of the data available for this purpose. Material and Methods Air samplers drawing -1700 m 3 of air per day through polypropylene air filters are in continuous operation at all four sites. Air filters are changed four times per month by local CMDL personnel and sent back to our laboratory on a monthly basis. Monthly composite samples are formed using half samples from each air filter, and these are analyzed for gamma emitting radionuclides using an n-type coaxial high-purity germanium (HPGe) detector. Under special circumstances, as discussed below for SMO samples collected in the autumn of 1995, monthly analyses are supplemented by individual filter sample analyses; subsamples representing about 15% of the active area of each filter are analyzed using a 1.5-cm diameter HPGe well detector. More detailed information on preparation and analysis of samples is available in reports containing data for the full SASP network [Larsen et. al., 1995]. Results In Table 1 monthly 2io Pb> 7 Be , 95z r , "37Cs, and '^Ce concentrations in surface air at BRW, MLO, SMO, and SPO during 1994 and 1995 are decay corrected to the midpoint of the sample collection month. Concentrations reported as "less than" values reflect the lower limits of detection for the individual nuclides, which we take to be three times the one sigma uncertainty in the background counts in the region of the gamma spectrum used to quantitate each nuclide. The gap in 7 Be and 210 Pb data for the SPO site in 1994 is due to the loss of samples TABLE 1. Average Surface Air Concentrations of Radionuclides 7 Be 2K)p b ^Zr >"Cs !44 Ce Date (mBq nr 3 ) (mBq nr 3 ) (uBq nr 3 ) (uBq m ? ) (uBq nr 3 ) BRW 1994 Jan. n.d. .74 ± .09 <87 <3 <10 Feb. 2.1 ±0.3 .83 ± .09 <9 <2 90% yield). The methodology takes advantage of gas-handling tech- niques previously developed by these authors. A known amount of CO carrier gas was mixed in with zero air and compressed into a suite of cylinders, some of which were placed 1 m above the surface at SPO. There they sit, exposed to incoming cosmic rays. After a certain length of time the cylinders are brought back to the isotope laboratory where the CO is extracted and measured for 14 C content at the Lawrence Livermore Center for Accelerator Mass Spectrometry. Monte Carlo simulations are currently being performed at LLNL to estimate any effects from the mass of the cylinders used as well as the ground effect. These simulations indicate that the effect from the cylinders is small. The experimental results are still being analyzed, and preliminary analyses show that the amounts of l4 C produced at the South Pole would be easily detectable for an exposure time of about 6 months. To our knowledge, this is the second time direct 14 C detection has been achieved and the first time a ground effect has been accounted for by direct measurement. This is an ongoing cooperative project. 131 Investigation of the Transfer Function Between Snow and Atmosphere Concentrations of Hydrogen Peroxide at South Pole Joseph R. McConnell and Roger C. Bales Department of Hydrology and Water Resources, University of Arizona, Tucson, 85721 Introduction A key to understanding past and future climate lies in understanding the oxidizing capacity of the atmosphere through time. Extensive efforts were made over the past few years to use photochemical models to estimate past and future atmospheric concentrations of hydroxyl radical, ozone, and hydrogen peroxide which are the primary oxidants in the atmosphere [Thompson et ai, 1995]. However, these model studies of past atmospheres lack sufficient data for validation. Ice cores provide temperatures and CH 4 concentrations, but two of the oxidants, hydroxyl radical and ozone, are not preserved in the ice, and the correspondence between atmospheric and ice core hydrogen peroxide is not well understood [Neftel et ai, 1995]. A glacial ice record of atmospheric formaldehyde, an intermediate species in the oxidation of CH 4 by hydroxyl radical attack, could also help to lead to a reconstruction of the local hydroxyl radical concentration in the paleo-atmosphere. As with hydrogen peroxide, however, the correspondence of atmospheric and ice-core formaldehyde concentration is not known. Therefore, if the formaldehyde and hydrogen peroxide records in the polar ice cores are to be useful for oxidant modeling of both past and future climates, the transfer functions that relate atmosphere to snow to ice concentrations must be well defined. Our research is an investigation of the atmospheric-ice transfer function for the reversibly deposited chemical species formaldehyde and hydrogen peroxide through laboratory, field, and computer modeling studies. Reversible implies that the species can be released from the snow and firn back to the atmosphere as conditions change and can be deposited back to the snow in response to further changes. The objective is to develop the capability to describe concentrations of formaldehyde and hydrogen peroxide in snow and ice, as functions of depth and time, given concentrations and conditions in the local atmosphere and properties of the snow and ice. This modeling capability will then be inverted and used to infer possible past atmospheric concentrations from observations of what is trapped in the ice, providing additional data constraints on tropospheric modeling. Procedures As part of our cooperative agreement with CMDL, we deployed a detector for measuring H 2 2 at the South Pole for a 3-week period in late November and early December 1994 and for a 2-week period in January 1996. Atmospheric measurements were made almost continuously during these time periods. When used for atmospheric analyses, our custom built H 2 2 detector makes atmospheric measurements at approximately 10-minute intervals using a glass coil scrubber to transfer the peroxide from the continuous stream of air to water and then a chemical fluorescence method to determine the concentration in the water [Bales et ai, 1995]. When making snow and firn analyses, the samples are melted and the peroxide measurement made directly. A number of surface snow and shallow snowpit samples were collected and analyzed. In 1994, systematically and stratigraphically placed firn samples were collected from a 2.2 m backlit snowpit and a 1.0 m snowpit, both located in the clean air sector. Four snowpits, located adjacent to the snow stake accumulation field near the South Pole, were excavated and sampled at 1 cm resolution in 1996. The CMDL winterover staff collect approximately 12 surface-snow samples each week throughout the year. This sampling started in December 1994 and continues currently. The samples collected prior to mid-January 1996 were returned to our laboratory in Tucson and were analyzed for H 2 2 and, on a subset of the samples for 6 18 0, and some ionic species. Results Average atmospheric H 2 2 concentrations for the 3- week period in spring 1994 were approximately 320 pptv and, as expected, no diel cycle was observed [Fuhrer et ai, 1996]. Occasional rapid changes in atmospheric H 2 2 were observed and a qualitative comparison with air parcel trajectories suggest a correlation of atmospheric H 2 2 concentration with a source area, although there is also a correlation with local meteorological conditions. This is the subject of ongoing atmospheric chemistry modeling [Thompson, 1995]. Concentrations in summer 1996 were lower at approximately 100 pptv. Construction at the new clean air facility at the South Pole may have degraded these measurements somewhat. Snowpit H 2 2 concentrations from a pit collected in January 1996 are shown in Figure 1. Note the very obvious annual cycles in H 2 2 . Along with the other three snowpits from 1995 [McConnell et ai, 1995], these data will be used to parameterize and validate a snowpack model that we have developed and applied at Summit, Greenland, to investigate the atmosphere to snow transfer process [McConnell, et ai, 1996a]. Some revisions to the model are required because snow accumulation at the South Pole is much more sporadic [McConnell, et ai, 1996b]. The H 2 2 concentrations in the surface snow samples are shown in Figure 2. Along with complimentary laboratory data [Conklin, et ai, 1992], these surface snow samples have been used to estimate the annual cycle in atmospheric H 2 2 concentration [McConnell et al., 1996c]. The results indicate that the surface snow provides a good proxy of the atmospheric H 2 2 concentration throughout the year at the South Pole. Evaluation of the surface snow data continues. 132 100 200 300 400 H 2 2 (ppbw) Fig. 1. Variations in hydrogen peroxide concentrations with depth at South Pole. relationship between atmospheric and snow/ice concentration for reversibly deposited species such as hydrogen peroxide and formaldehyde. Based on year-round surface snow samples collected for us by CMDL staff, we conclude that the surface snow is acting as an effective archive of the atmospheric loading of hydrogen peroxide during the year. Whether or not this archive is preserved and under what conditions is the focus of ongoing work. Photochemical modeling is underway to better understand the atmospheric concentration time series measured in 1994 and 1996, especially in the context of the annual cycle inferred from the surface snow. Physical and chemical modeling of the near-surface snow and firn continues as we investigate the atmosphere-surface snow relationship and the differences in the near-surface firn profiles at Summit, Greenland, and the South Pole. The cooperation of the NOAA personnel in collecting surface snow samples and making atmospheric measurements have proven invaluable in our research into the atmosphere-to- snow transfer process, both for H 2 2 and for reversibly deposited chemical species in general. 800 94.50 95.00 95.50 Year since 1900 96.00 Fig. 2. Estimated atmospheric concentration of hydrogen peroxide at South Pole from a physically based inversion of surface snow concentrations. Conclusion A record of the oxidizing capacity of the atmosphere would improve our understanding of interactions between atmosphere and climate. This information could be used to better verify and parameterize global and local atmospheric circulation and photochemical models and so aid in predicting the impact of anthropogenic increases in greenhouse gases. However, a required step in reconstructing the oxidizing capacity of the atmosphere from polar ice cores is to fully understand the transfer References Bales, R.C., M.V. Losleben, JR. McConnell, K. Fuhrer, and A. Neftel, H 2 2 in snow, air, and open pore space in firn at Summit, Greenland, Geophys. Res. Lett., 22(10), 1261-1264, 1995. Conklin, M.H., A. Sigg, A. Neftel, and R.C. Bales, Atmosphere- snow transfer function for hydrogen peroxide: microphysical considerations, J. Geophys. Res., 98(D10), 18,367-18,376, 1992. Fuhrer, K., M. Hutterli, and J.R. McConnell, Overview of the recent field experiments for the study of the air-snow transfer of H 2 2 and HCHO, in Chemical Exchange Between the Atmosphere and Polar Snow, edited by E. Wolff and R. Bales, NATA ASI Series I, 675 pp.. Springer- Verlag, 1996. McConnell, J.R., M. Conklin, and R. Bales, Hydrogen peroxide trends in South Pole firn, poster paper presented at the NATA ARW: Process of Chemical Exchange Between the Atmosphere and Polar Snow, II Ciocco, Italy, 1995. McConnell, JR., R.C. Bales, JR. Winterle, H. Kuhr.s, and C.R. Stearns, A lumped parameter model for the atmosphere-to- snow transfer function for hydrogen peroxide, J. Geophys. Res., in press, 1996a. McConnell, J.R., R.C. Bales, D.R. Davis, Recent intra-annual snow accumulation at South Pole: Implications for ice core interpretation, J. Geophys. Res., in press, 1996b. McConnell, JR., A.M. Thompson, and R.C. Bales, Surface snow as a proxy for atmospheric hydrogen peroxide at South Pole, EOS. Trans. AGU, 5156, 1996c. Neftel, A., R.C. Bales, and D.J. Jacob, Hydrogen peroxide and formaldehyde in polar snow and their relation to atmospheric chemistry, in Ice Core Studies of Global Biogeochemical Cycles, edited by R. Delmas, NATO ASI Series I, Vol. 30, pp. 249-264, 1995. Thompson, A.M., Photochemical modeling of chemical cycles: issues related to the interpretation of ice core data, in Ice Core Studies of Global Biogeochemical Cycles, edited by R. Delmas, NATO ASI Series I, Vol. 30, pp. 265-297, 1995. 133 NDSC Stratospheric Ozone-Temperature-Aerosol Lidar I. Stuart McDermid, Eric W. Sirko, and T. Daniel Walsh Jet Propulsion Laboratory, California Institute of Technology. Table Mountain Facility, Wrightwood. California 92397-0367 Introduction The Jet Propulsion Laboratory (JPL) lidar system, which measures stratospheric profiles of ozone, temperature, and aerosols for the Network for the Detection of Stratospheric Change (NDSC), was installed at the Mauna Loa Observatory, Hawaii (MLO) in July 1993. Since then it has been making regular nighttime measurements of these parameters, averaging more than 100 nights per year. The incidence of cirrus clouds and high winds at the observatory are the primary limiting factors on the number of measurements obtained. A brief description of the original lidar system was given in CMDL Summary Report No. 22. Some modifications have been carried out since the initial installation to increase the altitude range over which the profiles can be measured. The impetus for these changes was the increased need to obtain ozone measurements in the upper troposphere in addition to the stratospheric measurements. To enable the increased altitude range of these measurements, the field-of-view of the telescope was increased so that the laser and telescope would overlap at lower altitudes. These changes were carried out just prior to the Stratospheric Ozone Profile Intercomparison (ML03) NDSC intercomparison campaign (see below) and it turned out the increased field-of-view caused a saturation in the receiver at low altitudes resulting in incorrect measurements in this region. Following ML03, the detectors in the receiver were changed to correct this problem, and since the beginning of 1996 high-quality ozone profiles are routinely obtained over the altitude range from ~13-km to >55-km. Temperature profiles, from the combined Rayleigh and Raman returns, typically cover the altitude range from just below the tropopause to about the mesopause, ~15-km to >80-km. Enhanced strato- spheric aerosols from the eruption of Mt. Pinatubo are no longer observable in our lidar observations and the level of aerosols in the Junge layer of the lower stratosphere only just exceeds our detection limit indicating that this region has returned, at least, to the pre-Pinatubo levels. Since we were not operating at MLO prior to the Mt. Pinatubo eruption, we cannot comment on the suggestion that the aerosol loading is even lower than before except to say that the aerosol levels we are currently observing are very low. Results During the winter of 1994-1995 the CMDL Dobson spectrophotometer indicated very low ozone column content dipping below 200 Dobson Units (DU) for the first time in the measurement record. The lidar profiles are routinely integrated to obtain stratospheric column amounts and these can be compared with the Dobson results. Also the profiles can be studied to determine where the losses are actually occurring. Changes in the integrated lidar profile for both daily measurements and for monthly mean column amounts agreed very well with the Dobson data. Compared to the winters of 1993-1994 and 1995-1996 the period of low ozone in 1994-1995 extended from about September through June. Inspection of the ozone profiles showed the maximum ozone reduction occurred at approximately 30-km altitude and extended from roughly 25-km to 35-km. ML03 During August 1995 a formal NDSC intercomparison of ozone profiling instruments was carried out at MLO and refereed by a National Aeronautic and Space Administration-Goddard Space Flight Center (NASA- GSFC) scientist. The participating instruments included the JPL lidar, the Millitech-NASA/LaRC microwave radiometer, the NASA/GSFC mobile lidar, and CMDL electrochemical concentration cell (ECC) balloon sondes (launched from Hilo). Additionally, satellite data from the Stratospheric Aerosol and Gas Experiment (SAGE) II and the Upper Atmosphere Research Satellite (UARS) MLS were provided for intercomparison. The results from the campaign are still being evaluated and will be published sometime in the near future. Here, we just consider the preliminary conclusions for the JPL lidar. From 20-km to the maximum altitudes reported (i.e., up to 60-km) the JPL lidar results agreed very well with the consensus profile in this region. However, below 20-km the JPL lidar profile showed a positive deviation from the correct profile, increasing as the altitude decreased. As indicated earlier, this was determined to be caused by a saturation effect caused by increasing the field-of-view of the telescope. Following the campaign, this problem was thoroughly investigated and a new, different design, photomultiplier tube was installed in all of the receiver channels. The correct operation of the modified system was then verified in several informal intercomparisons with the GSFC lidar and the Millitech-NASA/LaRC microwave radiometer over the period up to the end of 1995. We are now confident that the ozone results from the JPL lidar are accurate over the range from ~13-km to >55-km. An evaluation of the performance of the temperature measurement capabilities of the lidars is also underway and will compare the results obtained by JPL, GSFC, CMDL lidar systems, and the CMDL balloon sondes during ML03. Acknowledgments. The work described here was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under an agreement with the National Aeronautics and Space Administration. We are grateful to the staff at MLO for continuing support of this program. 134 Antarctic UV Spectroradiometer Monitoring Program: Contrasts in UV Irradiance at the South Pole and Barrow, Alaska T. Mestechkina, C. R. Booth, J. R. Tusson IV, and J. C. Ehramjian Biospherical Instruments Inc. San Diego. California 921 10-2621 Introduction The Antarctic Ultraviolet Spectroradiometer Monitoring Network was established by the U.S. National Science Foundation (NSF) in 1988 in response to predictions of increased ultraviolet (UV) radiation in the polar regions. The network consists of several automated, high-resolution spectroradiometers: five are placed in strategic locations in Antarctica and the Arctic, one is established in San Diego to collect data and serve as a training and testing facility (Table 1 ), and a portable system is used for instrument intercomparisons [Seckmeyer, et ai, 1995]. The network makes measurements of UV spectral irradiance and provides a variety of biological dosage calculations of UV exposure. Biospherical Instruments Inc., under contract to Antarctica Support Associates (ASA), directed by NSF, is responsible for operating and maintaining the network and distributing data to the scientific community. The spectroradiometers used in the system are Biospherical Instruments, Inc. Model SUV- 100. Each instrument contains an irradiance diffuser, a double holographic grating mono- chromator, a photomultiplier tube (PMT), and calibration lamps. A vacuum-formed Teflon diffuser serves as an all-weather irradiance collector, and it is heated by the system to deter ice and snow accumulation. Tungsten-halogen and mercury vapor calibration lamps are used for automatic internal calibrations of both responsivity and wavelength that occur two to four times daily. All instrument functions, calibration activities, and data acquisitions are computer controlled. Further details on the spectroradiometers can be found in Booth et al., 1996. The South Pole and Barrow, Alaska, installations of the network are in locations that also have CMDL installations. Therefore, the balance of this report will focus on these two sites. The South Pole site is located away from the influence of mountains in a region of almost constant albedo. Cloud cover is relatively infrequent and it is generally thin when it does occur. The very small hourly change in the solar zenith angle at the South Pole supports examination of changes in total column ozone (as estimated by UV irradiance) at hourly resolution [Booth and Madronich, 1993]. For example, in Figure la, a TABLE 1. Installation Sites Site Latitude Longitude Established Location South Pole 90.00°S 0° Feb. 1988 Clear Air Building McMurdo 77.51°S 166.40°E March 1988 Arrival Heights Palmer 64.46°S 64.03°W May 1988 Clean Air Building Ushuaia, Argentina 54.49°S 68.19°W Nov. 1988 CADIC* Barrow, Alaska 71.18°N 156.47°W Dec. 1990 UIC-NARLt San Diego, California 32.45°N 117. 1PW Oct. 1992 Biospherical Instruments, Inc. *CADIC: Centro Austral de Investigaciones Cientificas, Argentina tUkpeagvik Inupiat Corporation-National Arctic Research Laboratory 298.507 - 303.03 ran Integrated Spectral Irradiance UV-A (320 - 400 nm) Irradiance Barrow, Alaska South Pole Fig. 1. Noontime integrated spectral irradiance at Barrow, Alaska, and at South Pole from January 1993 through December 1995. Panel a (left) shows the integrated irradiance around 300 nm (293.507-303.03 nm) and is contrasted with panel b (right) which illustrates the UV-A irradiance (320-400 nm). The higher irradiance values at Barrow are due to the higher sun elevation. Normally, irradiance at Barrow peaks in June, while irradiance at the South Pole peaks in December. 135 substantial decrease is seen in irradiance around the 300 nm in late November 1993. Meanwhile, Total Ozone Maping Spectrometer (TOMS) Nimbus-7 data report a substantial increase in the 300 nm irradiance between November 15 and November 20, 1993. Barrow, Alaska, contrasts with the South Pole in that it is located where a significant change in surface albedo occurs due to both the springtime snowmelt [Dutton and Endres, 1991] and changes in sea-ice coverage. Also, Barrow experiences significant changes in incident irradiance due to Arctic storms. The contrast in irradiances between Barrow and the South Pole is seen in Figure lb, which depicts the integrated noontime irradiances over the UV-A spectrum (320-400 nm) from January 1993 through December 1995. The integral of spectral irradiance from 298.507 to 303.03 nm is one of the most sensitive to changes in total ozone (and solar angle). A strong correlation between the ozone concentration and UV irradiance is illustrated by the Barrow 1995 example in Figure 2. Figure 3 emphasizes that in 1994 high UV levels at South Pole were observed comparatively early in the season (at the end of October) with an early termination of influence of the "ozone hole." Table 2 lists the maximum UV-B irradiances (290-320 nm) recorded at each site in 1990-1995. The maximum irradiance reported in San Diego happened to be elevated by cloud coverage (days of partial cloud coverage are sometimes observed to have higher irradiances than completely clear days due to reflections off of cloud surfaces). The Antarctic site measurements are enhanced by high albedo due to snow and ice coverage. During the Palmer maximum, ice coverage was heavy, increasing surface albedo. Summary 298.507 • 303.03 nnm Inlegrtaed Spectral Irradiance ■Historical Minima & Maxima Figure 3. Integrated 298.507-303.03 nm spectral irradiance at South Pole. The thin lines represent historical (1991-1993) minimum and maximum observations, while 1994 data are expressed as diamonds. TABLE 2. UV-B (290-320 nm) maxima (uW/cm2) Solar Zenith Site Maxima Date Angle Palmer 382.7 Dec. 2, 1990 44.0° San Diego 361.6 May 20, 1993 15.5° Ushuaia 350.5 Decemer 3, 1990 35.9 McMurdo 226.5 December 1, 1992 56.1° Barrow 199.5 June 1, 1992 49.6 South Pole 129.4 December 3, 1992 67.8° High spectral resolution scanning UV spectro- radiometers have been established at six sites and are successfully providing multiyear data sets. Resulting data were used to test radiative transfer models [Lubin and Frederick, 1992; Smith et al., 1992], investigate radiation amplification [Booth and Madronich, 1993; Madronich, • 298.507 - 303.03 nm Integrated Spectral Irradiance , 300 ^TOVS Ozone 18-May 29-May 1995 Figure 2. Comparison of the 298.507 - 303.03 nm integrated spectral irradiance and TOVS total ozone measurements made at Barrow during austral spring 1995. Note that the right axis are inverted to make the effect of decreasing ozone on increasing irradiance readily apparent. 1994], derive ozone concentrations [Stamnes et al., 1992], examine the biological impact of enhanced UV [Cullen et al., 1992; Anderson et al., 1993; Benavides et al., 1993; Holm-Hansen et al., 1993] and explore geographical differences in the UV [Booth et al., 1995; Diaz et al, 1994; McKenzie et al., 1994; Seckmeyer et al., 1995]. Data, referenced to both beginning- and end-of-season calibration constants are distributed on CD-ROM and are available to any interested researcher. For more information, please contact: Biospherical Instruments Inc., 5340 Riley Street, San Diego, CA 92110-2621 (Fax: (619) 686-1887, Internet: uvgroup@biospherical.com, www: http://www.biospherical.com). Acknowledgments. This research and monitoring activity was funded by contract SCK-M 189 1.4-02 from Antarctic Support Associates under the direction of Polly Penhale at the National Science Foundation, Office of Polar Programs. B. Mendonca of CMDL assisted in providing operators and support for the installations at Barrow. R. McPeters of NASA/GSFC provided TOMS Total Ozone data for comparison purposes. A TOMS update CD-ROM is available from the National Space Science Data Center (NSSDC), Goddard Space Flight Center. Barrow operators include D. Norton (Arctic Sivumnun Ilisagvik College), D. Endres and M. Gaylord (CMDL). The Ukpeagvik Inupiat Corporation of Barrow provided installation assistance. Operators at Palmer, the South Pole, and McMurdo were provided by ASA. 136 References Anderson, S., J. Hoffman, G. Wild, I. Bosch, and D. Karentz, Cytogenetic, cellular, and developmental responses in antarctic sea urchins (Sterechinus neumayeri) following laboratory ultraviolet-B and ambient solar radiation exposures, Ant. J. U. S.. 1993 Review, 28(5), 115-116, 1993. Benavides, H., L. Prado, S. Diaz, and J.I. Carreto. An exceptional bloom of Alexandrium catenella in the Beagle Channel, Argentina, Proceedings of the 6th International Conference on Toxic Marine Phytoplankton; Nantes, October 18-22, 1993. Booth, C.R., T.B. Lucas, T. Mestechkina, J. Shmidt, and J. Tusson, High resolution UV spectral irradiance monitoring program - contrasts in UV exposure in Antarctica and the Americas, Ant. J. U. S., in press, 1996a. Booth, C.R., T.B. Lucas, T. Mestechkina, JR. Tusson IV, J. P. Schmidt, D.A. Neuschuler, and J.H. Morrow, NSF Polar Programs UV Spectroradiometer Network 1994-1995 Operations Report, 182 pp., Biospherical Instruments Inc., San Diego, CA, 1996b. Booth, C.R., and S. Madronich, Radiation amplification factors: Improved formulation accounts for large increases in ultraviolet radiation associated with Antarctic ozone depletion, in Antarctic Research Series, edited by C.S. Weiler and PA. Penhale, 62, pp. 39-42, 1993. Cullen, J.C., P.J. Neale, and M.P. Lesser, Biological weighting function for the inhibition of phytoplankton photosynthesis by ultraviolet radiation, Science, 258, 646-650, 1992. Diaz, S.B., Frederick, I. Smolskaia, W. Esposito, T.B. Lucas, and C.R. Booth, Ultraviolet solar radiation in the high latitudes of South America, Photochem. Photobio., 60(4), 356-362, 1994. Dutton, E.G., and D.J. Endres, Date of snowmelt at Barrow, Alaska, U.S.A., Arctic Alpine Res., 23(1), 115-119, 1991. Holm-Hansen, O., D. Lubin, and E.W. Helbling, Ultraviolet radiation and its effects on organisms in aquatic environments, in Environmental UR Photobiology, edited by A.R. Young et al; pp. 379-425, Plenum Press, New York, 1993. Lubin, D., and J.E. Frederick, Observations of ozone and cloud properties from NSF ultraviolet monitor measurements at Palmer Station, Antarctica, Ant. J. U. S., 1989 Review, 25(5), 241-242, 1992. Madronich, S. Increases in biologically damaging UV-B radiation due to stratospheric ozone reductions: A brief review. Arch. Hydrobiol. Beih: Ergebn. Limnol., 43, 17-30, 1994. McKenzie, R.L., M. Blumthaler, C.R. Booth, SB. Diaz, J.E. Frederick, T. Ito, S. Madronich, and G. Seckmeyer, Surface Ultraviolet Radiation, in Scientific Assessment of Ozone Depletion: 1994, World Meteorological Organization Global Ozone Research Monitoring Project, 37, pp. 9.1-9.22, WMO, Geneva, Switzerland, 1994. Seckmeyer, G., B. Mayer, G. Bernard, R.L. McKenzie, P.V. Johnston, M. Kotkamp, C.R. Booth, T.B. Lucas, T. Mestechkina, C.R. Roy, HP. Gies, and D. Tomlinson. Geographical differences in the UV measured by intercompared spectroradiometers, Geophys. Res. Lett., 22(14), 1889-1892, 1995. Smith, R.C., Z. Wan, and K.S. Baker, Ozone depletion in Antarctica: Modeling its effect under clear-sky conditions, J. of Geophys. Res., 97, 7383-7397, 1992. Stamnes, K., Z. Jin, J. Slusser, C.R. Booth, and T.B. Lucas, Several-fold enhancement of biologically effective ultraviolet radiation levels at McMurdo Station, Antarctica, during the 1990 ozone hole, Geophys. Res. Lett., 19, 1013-1017. 1992. 137 Gamma Radionuclide Deposition at SMO During Recent French Nuclear Weapons Testing on South Pacific Atolls M. MONETTI Environmental Measurements Laboratory, U.S. Department of Energy, New York 10014-481 1 Introduction The Environmental Measurements Laboratory (EML) has maintained a global network of deposition sampling sites for nearly 40 years. Through CMDL support, American Samoa (SMO) and Mauna Loa (MLO) have been a part of this network for many years. This network was initiated to investigate the transport and fate of radioactivity produced from atmospheric testing of nuclear weapons. Strontium- 90 was the radionuclide of primary interest due to the relatively high quantity released and its physical and chemical properties that made it a concern to human health. The global distribution and inventories of 90 Sr through 1990 have been determined in this program [Monetti, 1996]. Now that the period of atmospheric weapons testing appears to be past, EML has modified this program to meet new objectives. The most significant program change is that gamma spectrometric techniques are being used to measure the activity of several gamma- emitting radionuclides instead of the radiochemical procedure previously used to make a single 90 Sr measurement. Gamma radionuclides of particular interest include both anthropogenic ( 137 Cs, 95 Zr, and l44 Ce) and natural isotopes ( 7 Be and 210 Pb). This technique will allow EML to continue to monitor for atmospheric releases of fission products. In addition, the development of a database on 7 Be and 210 Pb deposition is valued by colleagues who can use this data to verify global circulation models. EML no longer has the resources to make these measurements in all of the samples collected from the 78 stations in the global network. As a result, samples from certain locations are analyzed and others are being archived for future interests. Whenever there is an indication of activities that can potentially release fission products into the atmosphere, EML will use the network samples to identify if a release has occurred and determine the extent and magnitude if a release is confirmed. Following announcements of France's intentions to perform a series of underground tests at the Mururoa and Fangataufa Atolls, EML conducted a special study to monitor the atmosphere in the South Pacific Ocean for radioactivity that may be released during the testing. This study involved the use of the SMO sampling station as described below. Materials and Methods The first sample from SMO was collected in a 23-L polyethylene bucket that was exposed from September 1 through September 20, 1995. This sample was eluted through an ion-exchange column at EML. All other samples were weekly collections of bulk precipitation from September 20, 1995 until February 14, 1996, using EML's ion-exchange fallout collector [EML, 1996]. Any sample collected within 2 weeks following a French detonation was processed for analysis individually. Samples collected during intermediate periods were composited by annual quarter and then processed. Processing of the samples involved homogenizing the surface paper pulp and ion- exchange resin and sealing the sample in a 90-cm 3 aluminum can. The samples were then counted on a gamma spectrometer equipped with an n-type coaxial high-purity germanium detector, and the activities of the radionuclides of interest were determined by computer analysis of the spectral data. These spectra were also visually checked for the presence of any other anthro- pogenic gamma radionuclides. In all, twenty samples from SMO were analyzed. Results Radionuclide deposition data from SMO obtained in this study is presented in Table 1. The results are shown in units of becquerels per square meter (Bq nv 2 ). A counting error is reported whenever a radionuclide was detected. The lower limit of detection (equivalent to three times the statistical variation of the background activity for each radionuclide) was used to calculate maximal deposition values for 210 Pb, l37 Cs, 144 Ce and 95 Zr when their activity was not detected. In addition, precipi- tation data in centimeters is provided for most sampling intervals. Discussion The results presented in Table 1 indicate that the primary source of gamma activity in deposition from September of 1995 through February of 1996 was from natural radionuclides. In all but two of the samples the anthropogenic component of gamma activity was below the detection limit. The ,37 Cs activity detected in two samples is only slightly higher than the detection limit. Cesium- 137 has a long half-life (30 years) and it is ubiquitous because of past nuclear weapons testing. Since no other anthropogenic radionuclide was detected in the samples, it is unlikely that there was a "fresh" release of anthro- pogenic radioactivity from the underground French test or any other source. Deposition data from other sampling sites used for this study revealed similar observations (unpublished data). Therefore, the presence of 137 Cs in these two samples was probably due to resuspension of previously deposited material. Of the natural radio- nuclides, 7 Be was detected in most of the samples, but 210 Pb was only detected in seven of the twenty samples. Beryllium-7 is a cosmogenic radionuclide produced in the earth's upper atmosphere, while 210 Pb is a daughter in the primordial 238 U decay series and its atmospheric presence follows the release of 222 Rn from the earth's surface. The deposition of 7 Be and 2,0 Pb ranged from undetectable to 271.8 and <0.7 to 8.8 Bq nv 2 respectively. The 7 Be deposition appears to be related to both the amount of precipitation and duration of the collection period. The 138 TABLE 1. Gamma Radionuclide Deposition at SMO from September 1995 Through February 1996 Collection Date Precipitation 7 Be (cm) (Bq m 2 ) Error 2 ">Pb Error 2l,) Pb Error ' 44 Ce y,; Zr (%) (Bq nv 2 ) (%) (Bq nv 2 ) (%) (Bq nv 2 ) (Bq m 3rd Quarter 1995 66.0 271.8 6 8.8 2S < 0.6 Sept. 1-20, 1995 18.1 90.8 9 < 1.5 < 1.0 Oct. 4-11, 1995 4.3 88.5 8 < 1.5 < 1.0 Oct. 11-18, 1995 S 14.9 16 < 1.3 <0.8 Oct. 18-25, 1995 8.4 ND < 1.7 < 1.0 Oct. 25-Nov. 3, 1995 1.0 21.4 10 5.9 40 <0.7 Nov. 3- 8, 1995 8.0 22.4 14 < 2.0 < 1.6 Nov. 8-15, 1995 13.1 27.7 4 < 1.0 0.9 Nov. 15-22, 1995 3.1 21.4 11 < 0.7 < 0.4 Nov. 22-29, 1995 13.2 45.1 9 < 1.1 0.7 Nov. 29-Dec. 6, 1995 2.2 33.7 13 < 1.3 <0.8 Dec. 6-15, 1995 1.1 20.1 14 3.4 36 <0.9 Dec. 15-20, 1995 0.0 ND 2.8 37 < 0.8 Dec. 20-29, 1995 2.7 54.6 8 < 1.6 < 1.2 Dec. 29-Jan. 3, 1996 2.7 30.0 14 8.5 38 < 1.2 Jan. 3-10, 1996 8.1 46.5 7 4.7 45 <0.6 Jan. 10-24, 1996 18.6 48.7 7 3.6 38 < 10 Jan. 24-31, 1996 0.9 10.1 22 < 1.5 < 1.1 Jan. 31-Feb. 7, 1996 NA 24.1 16 < 1.2 <0.8 Feb. 7-14, 1996 NA 27.2 13 < 1.2 <0.7 14 <0.7 < 1.1 < 1.1 < 1.0 < 1.2 < 0.9 < 2.0 <0.8 < 0.5 <0.9 <0.9 < 1.0 <0.9 < 1.5 < 1.4 <0.8 < 1.3 < 1.4 <0.9 < 0.8 < 2.7 < 2.9 < 2.2 < 2.9 < 2.0 < 4.8 < 1.6 < 1.2 < 1.9 < 2.0 < 2.4 < 2.1 < 3.4 < 3.0 < 1.8 < 2.9 < 3.3 < 2.0 < 2.1 ND - Not detected NA - Data not available 210 Pb data is subject to large counting errors (from 25 to 45%) as a result of the low deposition rate and high detector background counts at low energies. The con- centration of 210 Pb in the surface atmosphere at SMO has been shown to be relatively low [Larsen et al., 1995] presumably as a result of the oceanic influence. It is more difficult to identify if a similar correlation exists between the 210 Pb deposition and precipitation because of the large number of nondetects. Real 210 Pb deposition values occurred during periods of lesser precipitation which may suggest that there is a higher 222 Rn flux during these periods. Further measurements and comparisons with atmospheric concentrations of 2l0 Pb may reveal if this interpretation is valid. In the future, EML will analyze deposition samples collected at SMO and MLO to address this observation. Acknowledgment. The special assistance provided by Mark Winey at SMO was invaluable to this study. The continued sampling efforts by the CMDL staff at SMO and MLO are greatly appreciated by EML. References EML, EML Procedures Manual, 28th Edition, HASL-300, Vol. 1, pp 2.3-1 to 2.3-6, U.S. Department of Energy, Environmental Measurements Laboratory, New York, 1996. Larsen , R.J., C.G. Sanderson and J. Kada, EML Surface Air Sampling Program, 1990-1993 Data, EML-572, 247 pp., U.S. Department of Energy, Environmental Measurements Laboratory, New York, 1995. Monetti, M.A., Worldwide Deposition of Strontium-90 through 1990, EML-579, 56 pp.. Environmental Measurements Laboratory, New York, 1996. 139 Early Morning UV-B During the 1994-1995 Record Low Ozone at Mauna Loa Patrick J. Neale, David L. Correll, Vernon R. Goodrich, and Douglass R. Hayes, Jr. Smithsonian Environmental Research Center, Edgewater, Maryland 21037 Introduction The Smithsonian Environmental Research Center (SERC) has been monitoring surface spectral ultraviolet-B (UV-B) irradiance at Mauna Loa (MLO) since fall 1984. The instrument is similar to a radiometer in operation in Edgewater, Maryland [Correll et al., 1992]. The instrument measures UV-B irradiance in a series of eight, 5-nm band pass channels (290-325 nm) and records 1- minute averages. Operation is continuous except for an annual break of about 1 month when the instrument is returned to Maryland for calibration. Our primary objective is to monitor long-term changes in incident solar UV-B irradiance. Records of absolute calibration of the MLO instrument are under review, as are data from intercomparisons of the Edgewater and MLO instruments at Edgewater. We expect the results from these tests will be the subject of a future report. While absolute irradiance is presently not available, ratios of signal intensity between instrument channels provide information on relative changes in the solar UV-B spectrum. There are several ways such data may be useful. Previously, we used the data to estimate atmospheric optical depth in the UV-B at MLO [Neale et al., 1994]. Recently, there was evidence of a record low total column ozone at MLO during the winter of 1994-1995 [Hofmann et al., 1996]. In this latter report, we presented UV irradiance measured in the 295-nm, 300-nm and 305-nm channels, relative to the 325-nm channel for clear days when the secant of the solar zenith angle was equal to 1.5 (about 48°). Here we present additional UV data for the winter of 1994-1995 as well as other ancillary information concerning instrument operation during this period. Results and Discussion The instrument was calibrated at SERC and sent to MLO in July 1994 and remained in operation until April 1995. In June 1994, transmission spectra were measured for all eight interference filters in the instrument. The center wavelengths (wavelength midpoint between the upper and lower wavelengths at which transmission is 50% of maximum) calculated from these spectra for the 295-, 300-, 305- and 325-nm channels were 294.9, 300.4, 304.6 and 324.8 nm. After return of the instrument to SERC in April 1995, filter transmission spectra were again measured and these channels had center wavelengths of 295.1, 300.7, 304.9, and 325.4 nm. Apart from the 325-nm channel (0.6 nm shift), the shift in filter center wavelength was 0.3 nm or less. Figure 1 shows measurements of 295-, 300- and 305-nm irradiance during the winter of 1994-1995 on clear sky mornings when the secant of solar zenith angle (sec 6 S ) was equal to 2.5 (about 66°), i.e., between 0814 and 0857 LST in October and December, respectively. These are given as ratios of the irradiance in each channel to the 260 220- Nov 1994 | Dec 1994 | Jan. 1995 i 1 5.00 10'" 0.011 0.010 — 300nm/325nm 180 ■0.035 g a " CH3CCL3 pptv 1 1 1 I 1 1 1 I 1 1 i N 2 ppbv '■■■'■■ 1 ' ' 1 — ■ ■ ■ i 1 1 CCI 4 pptv. add 1 09 CFC11 pptv. add 260 200 400 CFC12 add 460 j 1 1 1 1 1 1 1 i_i 200 400 10 RADON mBq m -3 Signal to data logger ^u Photomultiplier ZnS screen 2000L delay chamber Air flow diffuser Exhaust" r) 625 mesh wire screen n W Internal flow A T loop blower 40 m air inlet External flow loop blower Fig. 1. Dependence of trace gas concentrations on radon concentration in the baseline wind sector at MLO. Fig. 2. MLO. Schematic diagram of the ANSTO radon detector at 151 [1996a] for MLO. Table 1 gives the basic specifications. As with most high sensitivity radon detectors, this design uses the two-filter principle. The first filter removes all radon decay products from the inlet air. This air moves steadily through the delay chamber and while there, a portion of the radon decays. The second filter, in this case a wire screen, collects as many of the decay products as possible. These decay products in turn decay, and the alpha radiation is detected by the zinc sulfide screen and photomultiplier. Two key features of the new design are use of a wire screen for the second filter and separation of the external flow which changes the air sample from the internal flow which acts to draw radon decay products produced inside the chamber onto the screen. It is possible to use a wire screen as the second filter because the decay products form ion clusters about 1 nm in diameter which diffuse so rapidly that they are trapped very easily. In this detector 70% of the decay products are collected on the screen even though the flow rate is 800 L mirr 1 . The high flow rate is necessary to minimize loss of decay products through the walls of the chamber and to allow measurement of the first decay product, Po-218, whose half life is only 3 minutes. The major benefit of using the wire screen is a reduction in power compared to that required by a conventional filter. Only 20 W are needed, compared to about 500 W for the filter. This translates to a reduction in power costs over a year from $440 to $18 at 10 cents per kW hour. As with the use of a wire screen, the second design feature, separation of the sampling from the collection flows, results in economies in design. An 800-L min 1 flow would need 100 mm air lines and a large inlet filter. It is desirable to include a delay of about 4 minutes to allow any thoron gas in the inlet to decay. At 800 L min _i this would need a capacity of at least 3200 L. Since the only requirement of the external flow is to achieve an average residence time of air in the chamber of 20 minutes, 100 L min -1 is sufficient, and 20 mm air lines are adequate. It can be seen from Figure 2 that the only moving parts are the blowers. There are no components that require regular maintenance or that are sensitive to temperatures over the range -10 to 40°C. Only a few components would need to be adapted for arctic use. TABLE 1. Specifications of the ANSTO Radon Detector at MLO Item Specification Sensitivity: Limit of detection: Time response. Routine maintenance: Power consumption: 0.5 c s" 1 per Bq nr 3 20 mBq nr 3 (30% counting error in 1 hour count) 45 minutes to 50% after step in radon concentration Minimal 40 W Data Acquisition Because of the simplicity of the detector and its insensitivity to environmental conditions, passive data logging is all that is required. A few parameters should be monitored, such as supply volts and flow rates. Since installation in February 1996, data are averaged over 30- minute intervals by a data logger. A computer downloads data automatically at preset intervals. At the time of preparation of this paper, it was not possible to operate a DOS-based download program from the pseudo-DOS accessible from Microsoft windows. The serial port was unreliable. As a result, data transfer to the computer network has to be done manually. It is hoped this incompatibility will be solved so that preliminary data can be viewed on the Internet in close to real time. Parameters needed for data quality assessment are included in the data set permitting largely automatic data editing and prompt review for general release. Conclusion Radon has been established as a useful tracer for tagging air recently in contact with land. In the case of air from Asia, it is the only species transported without loss by wash- out or chemical change which can indicate such contact. New instrumentation at MLO is inherently robust and simple to operate. Up-to-date preliminary data are available and a path established which should see processed data on the CMDL computer system within a few months of acquisition. Acknowledgment. This work has been made possible by the active participation of the staff of MLO. References Harris, J.M., P.P., Tans, E.J., Dlugokencky, K.A. Masarie, P.M. Lang, L.P. Steele, and S. Whittlestone, Variations in methane at Mauna Loa Observatory related to long range transport, J. Geophys Res., 97(D5), 6003-6010, 1992. Kritz M. A., The China Clipper — fast advective transport of radon-rich air from the Asian boundary layer to the upper troposphere near California, Tellus, 42B, 46-61, 1990. Schery, S.D., and S. Whittlestone, Evidence of high deposition of ultrafine particles at Mauna Loa Observatory, Atmos. Environ., 29(22), 3319-3324, 1995 Schery, S.D., R. Wang, K. Eak, and S. Whittlestone, New models for radon progeny near the earth's surface, J. Radiat. Prot. Dosim.. 45, 343-347, 1992 Whittlestone, S., E. Robinson, and S. Ryan, Radon at the Mauna Loa Observatory: Transport from distant continents, Atmos. Environ., 26A(2), 251-260, 1992. Whittlestone S., W. Zahorowski, and P. Wasiolek, High sensitivity two filter radon/thoron detectors deploying a wire or nylon screen as the second filter, ANSTO E718, 1994 Whittlestone, S., S.D. Schery, and Y. Li, Thoron and radon fluxes from the island of Hawaii, J. Geophys Res., 101(D9), 14,787- 14,794, 1996a. Whittlestone, S., S. D. Schery, and Y. Li, Pb-212 as a tracer for local influence on air samples at Mauna Loa Observatory, Hawaii, J. Geophys Res., in press, 1996b. 152 A Comparison of CO2 and 13/12C Seasonal Amplitudes in the Northern Hemisphere T. P. Whorf, CD. Keeling, and M. Wahlen Scripps Institution of Oceanography, La Jolla, California 92093-0220 Introduction To better understand the sources and sinks of atmospheric carbon dioxide, the Scripps Institution of Oceanography (SIO) continues to maintain cooperative programs of C0 2 measurements with CMDL at Mauna Loa Observatory, Hawaii (MLO, 20°N), Point Barrow, Alaska (BRW, 71°N), Cape Kumukahi (KUM, 20°N), Samoa (14°S), and the South Pole (SPO), where air samples have been collected in 5-L glass flasks on a weekly to twice monthly basis, the latter at SPO. In addition, SIO continues to record atmospheric C0 2 concentrations on a continuous basis at Mauna Loa using a non-dispersive infrared (NDIR) gas analyzer installed on site in 1958. Studies of the MLO record in the last few years include a report on changes in the rate of rise of CO2 and its relationship with global temperatures [Keeling et al., 1995]. More recently, seasonal cycle studies of data from MLO and BRW, augmented by data from Alert, N.W.T (ALT, 82°N), have been published [Keeling et al., 1996] that have yielded evidence of climate induced CO2 changes in the form of possible changes in the growth of plants on a very large spatial scale. The Alert measurements have been collected under a cooperative program between SIO and the Atmospheric Environment Service of Canada. The SIO carbon dioxide program also continues to monitor C0 2 concentrations at Christmas Island (2°N), Baring Head, New Zealand (41 °S), Raoul Island, Kermadec Islands (29°S), and La Jolla, California (LJO, 33°N), the last of which started in 1969 and now includes both continuous and flask measurements. Since 1978 the I3 C/ 12 C isotopic ratio of atmospheric C0 2 has been determined from the same 5-L flask samples of C0 2 that have been measured for C0 2 concentration. In the early years isotopic ratio was measured at MLO, SPO, and LJO and by the mid-1980s at a total of ten sites. Measurements before 1992 were determined using a VG Micromass 903 and a VG SIRA 9 mass spectrometer at the Groningen Isotopic Physics Laboratory in the Netherlands [Keeling et al., 1989]. Samples since then have been analyzed using a VG PRISM Series II mass spectrometer at SIO. Changes in the amplitude of the seasonal cycle in C0 2 concentration at MLO were first observed and reported in the early 1980s [Bacastow et al., 1985]. A more recent analysis of seasonal cycle variations observed at MLO has shown an increase in amplitude of 20% since the mid- 1960s, an earlier drawdown of C0 2 in the late spring and early summer by up to a week since the late 1970s, and a correlation between amplitude changes there and tempera- tures averaged over the northern hemisphere [Keeling et al., 1996]. Here we discuss seasonal changes in the 13 C/ 12 C isotopic ratio of atmospheric C0 2 and how they compare with changes in amplitude of CO2 concentration. Data and Analysis Measurements of 13 C/ 12 C used in this study come from the same 5-L flask samples that have all been analyzed for CO2 concentration with an NDIR analyzer of the same design as that installed at MLO. Concentrations were calibrated with our standard suite of reference gases and expressed in the X93 mole fraction scale. Air samples were rejected if pairs did not agree within 0.40 ppm of the lowest flask average (0.60 ppm at Point Barrow), if they were single analyses, or if found to be outliers having a residual greater than three sigma from our smooth curve fit. This fit, described in Keeling et al. [1989], uses four harmonics to describe the seasonal variations plus a cubic spline [Reinsch, 1967] to describe the interannual variations. A linearly-increasing gain factor was incorporated into the fitting routine when it became apparent that there were significant increases in the seasonal amplitude. This same fitting procedure has been applied to the isotopic measurements. Isotopic data are obtained from samples of C0 2 extracted cryogenically which have passed the above 0.40 or 0.60 ppm cutoff criterion. Data for MLO and BRW are shown in Figure 1 as monthly averages and expressed as the reduced isotopic ratio, 13 8, of atmospheric C0 2 [Keeling et al., 1989, p. 170]. Similar data have been obtained at the other SIO site locations. In 16 years of MLO 13 8 isotopic data, over 700 daily samples have been analyzed amounting to approximately 44 per year, while at BRW in 14 years, some 500 daily samples have been analyzed yielding about 36 per year. Since 1992 when samples were first analyzed at SIO, gas standards have also been run daily in order to track any changes in the spectrometer output and thereby correct for them. These standards were recently calibrated against NBS19 (in 1996), to finalize calibrations begun in 1994. Along with this set of recent calibrations, a correction of +0.095 per mil was applied to all data analyzed at Groningen and previously published [Keeling et al., 1989; 1995]. This correction term is based on extensive duplicated measurements of these daily gas standards on the mass spectrometers at the Netherlands and at SIO. Results Figures 2-4 show relative seasonal amplitudes computed annually by least-square fitting the annual function g(l + At m ) multiplied by the four harmonics derived in the overall fit to the data of each year independently. In this expression, g denotes the annual relative amplitude, t m the midpoint time of the record, and A, a constant gain factor for the record being fit expressed in percent change in amplitude per year. The harmonic function is thus phase locked to the fit of the overall data set. Amplitudes are 153 -7.4 - -7.2 YEAR Figure 1. Time trend of the reduced isotopic ratio, l3 5, of atmospheric C0 2 in per mil difference from the international carbonate standard, PDB, for Point Barrow (BRW) and Mauna Loa (MLO). The data are shown as monthly averages and the curve by a four-harmonic fit with spline, as described. expressed relative to the mean annual cycle arbitrarily set at the midpoint in time of the fit [Bacastow et al., 1985]. For purposes of intercomparison between stations or different time periods, the gain factor has been afterwards adjusted to a common date (see below). Figures 2 and 3 show comparisons of seasonal amplitudes for C0 2 and 13 5 for our northern hemisphere sites, (ALT, BRW, LJO, MLO, and KUM) in which the C0 2 station data have been fit over the same time periods as there exists data for 13 8, typically beginning around 1980 except for ALT data, which begins later. This is so that the relative amplitudes for the two quantities are referenced to the same times to give an optimal comparison. Though the daily averages used in the isotopic fits are not identically the same as those used in the C0 2 fits, they number approximately 90% of the number for C0 2 , except at La Jolla where it is about 60%. In addition, the figures showing BRW, LJO, and MLO flasks have C0 2 data extending back in time to before the beginning of the isotopic data. In these cases, fits to these longer records have yielded earlier C0 2 relative amplitudes which have subsequently been adjusted so as to be referenced to the same time as in the shorter fit and then 1.25 1.20 W 1. 15 Q D §1.10 Cl a <1.05 w > Pl.00 £ .95 .90 .85 I 1.20 1.15 SEASONAL AMPLITUDE AT STATION ALERT ; ' I > i | i I i i | I i I i 1 i i i i 1 i i 1 1 1 1 1 1 1 | i I I 1 : • C02 9 (a) i - o C13 I] - '-- ;. i z L. if V i 1 : , o ' \ -—-f-y- I : ' ? ~: 7 o i / - - 6 - 1 i i i 1 f i i > 1 i i i 1 1 1 1 1 1 1 1 1 i i 1 i i i i 1 , , , ,i 65 70 75 90 80 85 YEAR SEASONAL AMPLITUDE AT POINT BARROW 95 W 1.10 Q §1.05 a. <1.00 H .95 3 S .90 .85 ,80 I 1.15 1.10 ■ I 1 1 1 1 1 1 1 ] 1 1 i | I I I I | I I I I i i i i i i i i i t ; ~ • C02 (b) : : o C13 z r v /■ \ -_ ; ....O „.-l V^-i \ - . : * .. .q-r • . 7 A f\J "'• f *A a z - i i i i 1 i i i i 1 i i i i i i i i i i i i i 1 i i i i 1 i i i 1 65 70 75 90 80 85 YEAR SEASONAL AMPLITUDE AT LA JOLLA PIER 95 W1.05 Q §1.00 (X 5 .95 P .90 S .85 .80 .75 1 1 1 1 | 1 1 1 1 i i i i 1 i « ' i i i I | i i i i | i i : i ~ o C02 9 A ( c)1 - I O C13 I - t\ ?V >/v i * - J \ • e 1 o 1 J 13 - \ In 1 4 I "- I 1 1/ \\l i i 1 i .. 1 .... 1 ... .- 6S 70 75 80 85 YEAR 90 95 Figure 2. Comparisons of relative seasonal amplitudes for C0 2 concentration and n 6 at the three most northerly stations (a) Alert (ALT), (b) Point Barrow (BRW) and (c) La Jolla (LJO), each referred to the midpoint of its isotopic record (open circles). The large solid circles for LJO are continuous data. 154 S 1 D Si a. Pi to a: 1.25 1.20 , 15 .10 05 00 95 90 65 70 75 80 85 90 95 YEAR SEASONAL AMPLITUDE AT CAPE KUMUKAHI .85 1 i i i 1 i i i i 1 i i i 1 i i i i 1 i i i 1 1 ' i i 1 i i i i - 9 - '- . C02 - (b) '- o C13 :; : ; j '* - 7 A ~ i i i 1 i i i i 1 i I . i i i i i i i 65 70 75 80 85 90 95 YEAR Figure 3. Comparisons of relative seasonal amplitudes for C0 2 concentration and 13 5 at (a) Mauna Loa (MLO), flask data, and (b) Cape Kumukahi (KUM), each referred to the midpoint of its isotopic record (open circles). The large amplitude at KUM in 1984 is partly due to a strong shift in trend following the 1983 El Nino. included in these figures. Increasing amplitudes are more apparent in these longer records. Gain factors calculated for the longer records shown at these three sites and referenced to 1970 near the start of these fits are BRW: 1.03 ± 0.16% yr 1 , LJO: 1.21 ± 0.17% yr 1 , and MLO flasks: 0.82 ± 0.15% yr 1 . The slightly larger fluctuations before and including 1981 for LJO and MLO flasks are attributed to there being significantly fewer annual data than in the latter part of each of these records. As an exception, the LJO record includes continuous CO2 data in 1973-1975 (three large symbols) based on 5-hour averages of steady data subsequently converted to weekly data, so that these years are of significantly higher quality than other early years containing sparse flask data. The fluctuations in l3 8 seasonal amplitudes occurring over several year periods show a strong tendency to follow the C0 2 fluctuations during the same times, especially at BRW and LJO. A significant part of semi-decadal to ,85 .80 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 ' ' ' 1 1 1 i 1 1 _Li 1 1 1 I I 1 1 1 1 I 1 1 1 1 I 1 1 1 1 65 70 75 80 85 90 95 YEAR Figure 4. Comparison of seasonal amplitudes of C0 2 concentration for MLO (continuous data) and KUM, referred in this figure to the midpoint of the 1958-1995 Mauna Loa data. KUM amplitudes are adjusted to have the same mean as MLO amplitudes for the first 10 years of the KUM record (1979-1988). decadal changes in seasonal amplitude are likely due to large scale temperature changes [Keeling et al., 1996] while other fluctuations may be a result of the effect of interannual variations connected with El Nino events. Slightly larger isotopic swings in the annual amplitudes at LJO may be partly attributable to the fewer isotopic data at this site. Comparisons of the absolute seasonal amplitudes of ,3 8 with CO2 concentration for our northern hemisphere sites show a rate of change in ' 3 8 with respect to C0 2 of close to 0.05 per mil per ppm, as would be expected by a predominantly terrestrial component in C0 2 . An interesting but unexplained observation is that multi-year seasonal changes at ALT in both 13 S and C0 2 seem to be out of phase with changes at BRW by a couple of years, particularly near 1992. Comparison of seasonal changes in 13 8 and C0 2 concentration do not seem to follow each other as closely at MLO as at BRW and LJO. This may stem from part of the seasonal cycle in C0 2 concentration being produced by oceanic processes that influence it without significantly affecting the amplitude of l3 S. A difference in the trends of the seasonal amplitudes in concentration and 13 8 is also apparent at MLO as evidenced by the differing gain factors 13 8andC0 2 . Gain factors for C0 2 concentration and 13 8, compared over the same time intervals and referred to 1970, are expressed as annual rates of change in Table 1. Annual rates referred to 1980 would be about 8-10% smaller than if referred to 1970. No significant change in the seasonal cycle of ' 3 8 is apparent in the MLO flask record since 1980, whereas the increase in seasonal amplitude of C0 2 concentration over the same period exceeds the standard error by more than a factor of two. An additional observation of seasonal amplitude changes in C0 2 between MLO (continuous data) and KUM (Figure 4) where respective gain factors over the same period are shown in Table 1, shows no increase in seasonal amplitude at KUM since 1979. Also, no significant increase in amplitude is evident in the isotopic data. Since KUM, 155 TABLE. 1 . Annual Rate of Increase in the Seasonal Amplitude of Atmospheric C0 2 and 13 5 at Various Locations Approx. Location Latitude Type Rate of Inclusive Years Increase* of Observations (in percent) Alert 82°N C0 2 138 Point Barrow 71°N C0 2 C0 2 '38 La Jolla Mauna Loa (flasks) 33°N C0 2 C0 2 138 20°N C0 2 co 2 •38 1985-1995 1985-1995 1974-1995 1982-1995 1982-1995 1970-1995 1978-1995 1978-1995 1.21 ±0.36 2.48 + 0.63 1.03 ±0.16 1.10 ± 0.29 0.58 ±0.35 1.21 ±0.17 1.16 ± 0.33 0.65 ±0.42 1968-1995 0.82 ±0.15 1980-1995 0.61 ±0.25 1980-1995 -0.16 ±0.37 Mauna Loa (continuous) 20°N C0 2 co 2 Kumukahi 20°N C0 2 "8 1958-1995 1979-1995 1979-1995 1979-1995 0.62 ±0.04 0.34 ±0.12 -0.43 ± 0.23 0.11 ±0.41 *With reference to January 1 January 1, 1980. 1970, except for Alert referred to situated close to sea level, supplies principally oceanic air and MLO, at 3400 m, supplies air from aloft which is better mixed, some of this difference might stem from the sampling of different sources, MLO perhaps getting a greater percentage of air which has been influenced by passage over land. Finally, there is a hint that whatever may be causing any divergence between the trend in seasonal amplitudes of l3 8 and C0 2 concentration at MLO may also be occurring at BRW and LJO as shown by lower gain factors for l3 8 over the same intervals (Table 1). These changes, however, are not significant since the isotopic records are not yet long enough to draw any firm conclusions. Concluding Remarks The SIO '3C/ 12 C isotopic data have recently received final calibrations and have been analyzed to look for similarities and significant divergences in seasonal amplitude from the C0 2 concentration data. At several northerly sites including BRW and LJO, isotopic changes in seasonal amplitude appear to track the C0 2 amplitude changes quite well over periods of several years, suggesting that a dominant component in the seasonal signal of C0 2 is terrestrial plant activity. At other sites such as MLO in Hawaii, differences between trends in 13 8 and C0 2 concentration suggest an oceanic component. At this time, when subtle changes are just becoming apparent in concurrent concentration and 13 C/ 12 C records of atmospheric C0 2 , we hope to be able to continue these measurements, as in the case of concentration data in the early 1980s when an increase in seasonal amplitude first became apparent in our longest records. Acknowledgments. This work was supported by Grant ATM91-21986 of the National Science Foundation, Grant DE-FG03-95ER62075 of the U.S. Department of Energy and Grant NAGW-2987 of the U.S. National Aeronautics and Space Administration. In addition, through Contract 50RANR100090, NOAA provided for the cost of maintaining our primary standard reference gases used to maintain accuracy in our measurements of atmospheric C0 2 . 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