Climate Monitoring and 

Diagnostics Laboratory 

No. 23 

Summary Report 1994-1995 

w 

0 :J 0.5 

I-

~ 0 

w z-0.5 

en 

-1 

CO Growth Rate (ppm I yr) 

84 85 86 87 88 89 90 91 92 93 94 

YEAR 

Growth Rate (ppb I yr) -r-~~~..----r---'---r ~-

95 

84 85 86 87 88 89 90 91 92 93 94 95 

YEAR 

~TM08p"1~ 

1 

0.5 

0 

-0.5 

-1 

1 

0.5 

0 

-0.5 

-1 

~ 

A_. 

~ § National Oceanic and Atmospheric Administration 

..... i U.S. Department of Commerce 

~II' I Environmental Research Laboratories ~.. ~~ "'"117.fr;:NT Of c,<r 
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 1996 

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, YA 22161 

ii 
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: 

l . 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 

iii 
Eldon E. Ferguson, Climate Monitoring and Diagnostics Laboratory Director, 1990-1995. 

iv 
Contents 

Preface .... .................. .................................. .. ........... .. ...... ...... .,. . . . ......... ..... ...... .... ... . . . . ..... .. . . . . .... ... . . .. . . ... . . ... .. . . .. . .. . . . . 111 

CMDL Organization, 1995 ................................................ .................................. .......................... ............... .......... ix 

CMDL Staff, 1995 ................................. ..... .............. .. ................ .. ............................................................................ x 

CMDL Station Information ............................... .............. ........... ... . ................ .. .. .... ....... ....... ........ ........... ........... ..... xi 

I. Observatory, Meteorology, and Data Management Operations ...................................................................... . 

1.1. Maun a Loa Observatory ............................ ...................................................................... ....................... . 

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 C02 .................................................................. .... .............. 33 

2.2.5. The Airkit Sampler...................................................................................................................... 34 

2.2.6. Calibration of Measurements of Stable Isotopes of C02 ......... ...... ............ ......... ............. .... ........ 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&N20 ....... ..... ........................................................................ ......................... 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 

v 
3. Aerosols and Radiation................................................................................................. ................................... . 50 

3.I. Aerosol Monitoring ................... .......... .. .......... .......... .......................... ............. ...... ................................. 50 

3. I. I. Scientific Background ....... .. .. .. ................ ..... .. ..... ........... .... ........ .. .. ... .. .. .... ..... .. ..... ..... .. ... ... .. .... .. . 50 

3.I.2. Experimental Methods................................................................................................................. 50 

3.I.3. Annual Cycles............................................... .... ...... ....... .. ............................ ......... .. .................... . 5I 

3.I.4. Long-Term Trends................................................................................................................. ...... 53 

3.I.5. Results From I994-I995.............................................................................................................. 53 

3. I .6. Aircraft Observations................................................................................................................... 56 

3.1.7. Lidar Measurements at Mauna Loa............................................................................................. 59 

3.2. Solar and Thermal Atmospheric Radiation.............................................................................................. 60 

3.2. I. 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. I. Continuing Programs .. ............................................... .......... ............................. ...... ......... ....................... 69 

4. I. I. Total Ozone Observations .................................................................................................... ...... 69 

4. I .2. Umkehrs............................................ .. .................................................................... ..................... 70 

4. I .3. Surface and Tropospheric Ozone................................................................................................. 7 I 

4.I.4. Ozonesondes................................................................................................................................ 74 

4.I.5. Atmospheric Water Vapor............................................................................ ............................... 76 

4. I .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.I. Continuing Programs.............................................................................................................................. 84 

5. I. I. Introduction ......................................................................................... ........................................ 84 

5. I .2. Flask Samples............................................................................................................ .................. 84 

5.1.3. RITS Continuous Gas Chromatograph Systems.......................................................................... 87 

5.1.4. LEAPS......................................................................................................................................... 89 

5. I .5. Chlorofluorocarbon Alternative Measurements Program............................................................ 90 

5. I .6. Gravimetric Standards ................................................................................................................. 95 

5.2. Aircraft GC Project: SHOE/MAESA Mission......................................................................................... 96 

5.2.I. Overview..................................................................................................................................... 96 

5.2.2. Transport in the Lower Stratosphere............ .. ....... ..... ............. .................. ................... .... ... ........ 96 

5.2.3. Bromine Budget........................................................................................................................... 99 

5.3. LACE ..................................................................................................................... ... ........ ......... ........ .... IOI 

5.4. Ocean Project: BLAST Cruises............................................................................................................... IOI 

5.5. STEALTH Project: Automated Four-Channel Field Gas Chromatographs..... .... ............... ... ............ ...... I03 

5.5.I. 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 

6. Cooperative Programs .. ....... ................................ ................... ........................ ... ...... .... .......................... ........... 112 

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 ................... ................................. 117 

A Preliminary Comparison of 813C Measurements in C02 From Mace Head, Ireland 

A. Gaudry, P. Mon/ray, M. Trolier, C. Flehoc, P. Ciais, and S.G. Jennings............................ ... 119 

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. Lenka, J.F. Scarzello, and D. Taylor........ ........................................................................... 130 

Exposure Experiment, South Pole 

J.E. Mak, C.A.M. Brenninkmeijer, and J.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 

l.S. McDermid, E.W. Sirko, and T.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, D.M. Cunnold, P.J. Fraser, 

L.P. Steele, and P.G. Simonds........................... ...................................................................... 142 

The 13C/12C of Atmospheric Methane 

P. Quay, J. Stutsman, and D. Wilbur ............... ............. ............................................ ................... 144 

Aerosol Measurements on American Samoa 

D.L. Savoie and J.M. 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 

vii 
Director's Office 

David Hofmann, Director 

James T. Peterson, Deputy Director 

Sandra Howe, Administrative Officer 

Ann Thome, 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 Mcinnes, 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 

CMDL Staff, 1995 

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 Viimel, 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 Ramone!, 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 

x 

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 Mcinnes, 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: Barrow (BRW) Mauna Loa (MLO) 

Latitude: 71.323 19.539 

Longitude: 156.609 155.578 

Elevation: 8m 3397m 

Time Zone: GMT-9 GMT-10 

Office Hours: 8:00 am-5:00 pm 8:00 am-5:00 pm 

Telephone 

Office hours: (907) 852-6500 (808) 961-3788 

Fax: (907) 852-4622 (808) 961-3789 

Postal Address: Officer in Charge U.S. Dept. of Commerce 

NOAAIERUCMDL NOAA - Mauna Loa Observatory 

Pouch 8888 P.O. Box 275 

Barrow, AK 99723 Hilo, HI 96720 

Freight Address: Same as above U.S. Dept. of Commerce 

NOAA - Mauna Loa Observatory 

154 Waianuenue Ave. 

Hilo, HI 96720 

Name: Samoa(SMO) South Pole (SPO) 

Latitude: -14.232 -89.997 

Longitude: 170.563 -102.0 

Elevation: 77m 2841 m 

Time Zone: GMT-11 GMT+12 

Office Hours: 8:00 am-5:00 pm 8:00 am - 5:00 pm 

Telephone: 

Office hours: 011 (684) 622-7455 Relayed through CMDL Boulder 

After hours: 011 (684) 699-9953 

Fax: 011 (684) 699-4440 

Postal Address: U.S. Dept. of Commerce Officer in Charge 

NOAA - CMDL Samoa Observatory NOAA/CMDL Clean Air Facility S-257 

P.O. Box 2568 South Pole, Antarctica 

Pago Pago, American Samoa 96799 PSC 468 Box 402 

FPO AP 96598-5402 

Freight Address: Same as above Same as above 

xi 
xii 
1. Observatory, Meteorology, and Data Management Operations 

1.1. MAUNA LOA OBSERVATORY 

R. C. SCHNELL AND THE MLO STAFF 

1.1.1. OPERA TIO NS 

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 m2) 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 

m2 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 l S 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 measurements 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 (S02) 

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 administrative community included the NOAA Administrator; NOAA 

Deputy Under Secretary; NOAA Associate Under 

Secretary; Director, Sustainable Development and Intergovernmental 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 (C02) 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) C02 

analyzer and the Scripps Institution of Oceanography 

(SIO) Applied Physics IR C02 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 C02 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 C02 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 C02 analyzer and plot 

C02 concentrations in near-real time. The CCG has the 

capability of modifying the C02 measurement control 

software from Boulder. The venerable C02 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 C02 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 C02 

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 C02 concentration, 

TABLE 1.1. Summary of Measurement Programs at MLO in 1994-1995 

Gases 

C02 

co 

Program Instrument 

Siemens Ultramat-3 IR analyzert 

0.5-L glass flasks, through analyzer 

Trace Analytical RGA3 

reduction gas analyzer no. R5t 

2.5-L glass flasks, MAKS pump unit* 

3-L evacuated glass flasks+ 

Carle automated GC no. 6 (removed 11/95) 

HP6890GCt (began 11/95) 

AIRKIT pump unit, 2.5-L glass flasks+ (began 5/95) 

TECO model 435 pulsed-florescence analyzert 

(began 6/94) 

2 

Sampling Frequency 

Continuous 

I pair wk· 1 

Continuous 

1 pair wk· 1 

I pair wk· 1 

1 sample (24 minr 1 

Continuous 

I pair wk· 1 

Continuous 
TABLE 1.1. Summary of Measurement Programs at MLO in 1994-1995--Continued 

Gases - Continued 

Surface 0 3 

Total 0 3 

0 3 profiles 

Program 

N20, CFC-I I, CFC-12, CFC-113, 

CH3CCl3, CCl4 

N20, CFC-I I, CFC-12, CFC-113, 

CH3CCl3, CCl4, SF6, HCFC-22, 

HCFC-14lb, HCFC-142b, CH3Br, CH3CI, 

CHFl2· CHCl3, C2HCl3, C2Cl4, H-1301, 

H-1211, H-2402, HFC-134a 

CFC-I I, CFC-12, CFC-113, N20, 

CCl4, CH3CCl3 

N20 

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 (IR) radiation 

Turbidity 

Column water vapor 

Meteorology 

Air temperature 

Air temperature (30-70 KM) 

Temperature gradient 

Dewpoint temperature 

Relative humidity 

Pressure 

Instrument 

Dasibi ozone metert 

Dobson spectrophotometer no. 76t 

Dobson spectrophotometer no. 76t 

(automated Umkehr method) 

Balloonborne ECC sonde 

300-mL stainless steel flasks 

850-mL stainless steel flasks 

HP5890 automated GCt 

Shimadzu automated GCt 

Two-filter system 

Pollak CNC 

TSI CNCt 

Four-wavelength nephelometert: 450, 550, 

700, 850 nm three-wavelength nephelometer: 

450, 550, 700 nm 

Aethalometert 

Lidar: 694.3 nm, 532 nmt 

Eppley pyranometers with Q, 

OGI , and ROS filterst 

Eppley pyrheliometer with Q filtert 

Eppley pyrheliometer with RGS filtert 

Eppley pyrheliometer with Q, OGI, 

RG2, and RGS filterst 

Eppley/Kendall active cavity radiometert 

Eppley pyrgeometer with shading disk 

and Q filtert 

Yankee Environmental UVB pyranometer 

(280-320 nm)t 

Global downwelling IR pyrgeometert 

J-202 and J-314 sunphotometers with 

380-, 500-, 778-, 862 nm narrowband filters 

PMOD three-wavelength sunphotometert: 

380, 500, 778 nm; narrowband 

Two wavelength tracking sunphotometer: 

860, 940 nmt 

Aspirated thermistor, 2-, 9-, 37-m heightst 

Max.-min. thermometers, 2-m height 

Lidar 

Aspirated thermistors, 2-, 9-, 37-m heightst 

Dewpoint hygrometer, 2-m heightt 

TSL 2-m heightt 

Capacitance transducert 

Mercurial barometer 

3 

Sampling Frequency 

Continuous 

3 day- 1, weekdays 

2 day-I 

I wk- 1 

I sample wk- 1 

I sample wk- 1 

I sample h- 1 

I sample h-1 

Continuous integrated 

30-min samples 

I day- 1 

Continuous 

Continuous 

Continuous 

l profile wk- 1 

Continuous 

Continuous 

3 day-I 

I mo- 1 

Continuous 

Continuous 

Continuous 

3 day· 1, weekdays 

Continuous 

Continuous 

Continuous 

I day-I 

I profile wk- 1 

Continuous 

Continuous 

Continuous 

Continuous 

5 wk-I 

q 

i

j 

·

~

4 

J

1

n

a

g 

N

1

-

1

a

l

I

; 

:

0 

>

I

;

l

1

1

n 

a 

.

l

h 
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, S02, 

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 FfS2000. This 

resulted in an increase of eight voice and data lines split 

between MLO and Hilo at no increase in monthly expenses. 

8 

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 

9 

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 downfacing 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 

CH4. 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 AID, 

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 (C02), methane (CH4), 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. 

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 net'¥ork (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 CO, and the Dasibi. Plans call 

for replacing the CO, early in 1996. The CAMS system 

has had minimal problems during its entire IO-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. 

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- I I 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 1994-1995 

Gases 

C02 

Program 

C02, CH4, CO, and 13C/12C and 

180/160 of C02 

CH4 

Surface OJ 

Total OJ 

C02 

N20, CFC-I I, CFC-12, CFC-113, 

CHJCCIJ. CCl4 

Instrument 

Siemens Ultramat SE analyzer 

3-L glass flasks 

O.S-L glass flasks, through analyzer 

0.5-L glass flasks, P3 pump unit 

Carle automated GC 

Dasibi ozone meter 

Dobson spectrophotometer no. 91 

Siemens Ultramat SE analyzer 

300-mL stainless steel flasks 

IO 

Sampling Frequency 

Continuous 

I pair wk- 1 

I pair wk-1 

I pair wk-I 

1 sample (12 min)-1 

Continuous 

3 day-I 

Continuous 

I sample mo· I 
TABLE 1.4. Summary of Measurement Programs at BRW in 1994-1995-Continued 

Program 

Gases - Continued 

N20 , CFC-I I, CFC-12, CFC-113, 

CH3CCI3, CCI4, SF6, HCFC-22, 

HCFC-14lb, HCFC-142b, CH3Br, 

CH3CI, CH2CI2, CHCl3, C2HCI3, 

C2Cl4, H-1301, H-1211, H-2402, HFC-134a 

Instrument 

850-mL stainless steel flasks 

CFC-I I, CFC-12, CFC-113, N20 HP5890 automated GC 

CCl4. CH3CCI 3 

N20 

co 

Aerosols 

Condensation nuclei 

Optical properties 

Black carbon 

Solar Radiation 

Global irradiance 

Direct irradiance 

Albedo 

Terrestrial (IR) Radiation 

Upwelling and downwelling 

Meteorology 

Air temperature 

Dewpoint temperature 

Pressure 

Wind (speed and direction) 

Precipitation 

Cooperative Programs 

Total surface particulates (DOE) 

Precipitation gauge (USDA) 

Magnetic fields (USGS) 

Various trace gases (OGIST) 

C02, 13C, N20 (SIO) 

CH4 (Univ . of Calif., Irvine) 

Earthquake detection 

(Univ. of Alaska) 

13cH4 ( 13c/ 12C) (Univ. of Washington) 

14CO (Univ. of Washington) 

UV monitor (NSF) 

Magnetic fields (NA VSWC) 

Sound Source (DOE) 

Ice Buoys (NOS) 

0 2 in air (Univ. of Rhode Island) 

Magnetic micropulsations (Univ. of Tokyo) 

Aerosol chemistry (Univ. of Alaska) 

Shimadzu automated GC 

Trace Analytical GC 

Pollak CNC 

T.S.I. CNC 

Four-wavelength nephelometer 

Aethalometer 

Eppley pyranometers with Q and RG8 filters 

Tracking NIP 

Eppley pyrheliometer with Q, OGI 

RG2, and RG8 filters 

Eppley pyranometer 

Eppley pyrgeometers 

Thermistor, 2 levels 

Max.-min. thermometers 

Dewpoint hygrometer 

Capacitance transducer 

Mercurial barometer 

R.M. Young aerovane 

Rain gauge, tipping bucket 

High-volume sampler (I filter wk-I) 

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 

A150 aluminum cylinders filled to 2000 psi 

UV spectrometer 

3He sensors 

RASS 

Ice buoys 

3-L glass flasks 

Magnetometer and cassette recorder 

High-volume sampler 

11 

Sampling Frequency 

I sample mo· I 

I sample h-1 

I sample h-1 

I sample (6 min)-1 

I day·I 

Continuous 

Continuous 

Continuous 

Continuous 

Continuous 

Discrete 

Continuous 

Continuous 

Continuous 

I day-I 

Continuous 

Continuous 

Discrete 

Continuous 

Continuous 

I mo-I 

Continuous 

6 sets mo·l 

I set wk-I (3 flasks set· I) 

I pair wk-I 

I set (3 mo)-1 

Continuous, check 

site I wk-I 

I (2 wk)-1 

I (3 wk)- 1 

I scan per 0.5 hour 

Continuous 

I hr-1 

Continuous 

I pair (2 wk)-1 

Continuous 

3 wk-I 
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 0BSERV A TORY 

M. WINEY 

1.3.1. OPERATIONS 

The environmental engineer pos1t10n 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 

12 

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. 
TABLE 1.5. Summary of Measurement Programs at SMO in 1994-1995 

Program 

C02, CH4, CO, and 13C, ISO of C02 

Surface 0 3 

Total 0 3 

N20, CFC-I I, CFC-12, CFC-113, 

CH3CC13, CC14 

N20, CFC-I I, CFC-12, CFC-I 13, 

CH3CC13, CC14, SF6, HCFC-22, 

HCFC-14lb, HCFC-142b, CH3Br, CH3Cl, 

CH2Cl2, CHC13, C2HC13, C2CI4, H-1301, 

H-1211, H-2402, HFC-134a 

CFC-I I, CFC-12, CFC-113, N20, 

CC14, CH3CCl3 

N20 

Aerosols 

Condensation nuclei 

Solar Radiation 

Global irradiance 

Direct irradiance 

Diffuse irradiance 

Meteorology 

Air temperature 

Dewpoint temperature 

Pressure 

Wind (speed and direction) 

Precipitation 

Cooperative Programs 

C02, 13C, N20 (SIO) 

GAGE project: CFC- I I, CFC-12, 

N20, CH3CC13, CC14 (SIO) 

Various trace gases (OGIST) 

Bulk deposition (DOE) 

Total suspended particulates (DOE) 

Total suspended particulates (SEASPAN) 

CH4,(13C/12C ratio) (Univ. of Wash.) 

Light hydrocarbons (UCI) 

0 2 (URI) 

0 2 (SIO) 

SIO - Scripps Institution of Oceanography 

Instrument 

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 

S50-mL stainless steel flasks 

HP5S90 automated GC 

Shimadzu automated GC 

Pollak CNC 

TSI CNC 

Eppley pyranometers with Q and ROS filters 

Eppley pyrheliometer with Q filter 

Eppley pyrheliometer with Q, OG 1, 

RG2, and ROS filters 

Eppley pyrgeometer with shading disk and Q filter 

Thermistors (2) 

Polished mirror 

Capacitance transducer 

Mercurial barometer 

Bendix Aerovane 

Rain gauge, tipping bucket 

Rain gauge, plastic bulk 

5-L evacuated glass flasks 

HP5SSO 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 

OGIST - Oregon Graduate Institute of Science and Technology 

UCI - University of California, Irvine 

URI - University of Rhode Island 

13 

Sampling Frequency 

Continuous 

I pair wk-1 

I pair wk- 1 

1 pair wk- 1 

Continuous 

4 day-I 

1 sample wk- 1 

1 sample wk- 1 

I sample h-1 

1 sample h-1 

I day-I 

Continuous 

Continuous 

Continuous 

Discrete 

Continuous 

Continuous 

Continuous 

Continuous 

J wk-I 

Continuous 

Continuous 

1 day- 1 

1 set wk-I (3 flasks set-I) 

1 h-1 

1 set wk-I (3 flasks set-I) 

Continuous (I bucket mo-I) 

Continuous (I filter mo-I 

Continuous (I filter wk-I) 

Continuous (l filter wk-I) 

Biweekly 

3-4 flasks qtr-1 

2 pair mo-I 

2 sets mo- I (3 flasks set-I) 
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 Apri 1 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 

14 

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 (C02) was the only 

program still using CAMS for data acquisition. The C02 

CAMS unit has done a fine job but some day it too will be 

retired in favor of a more modern system. 

Cooperative Programs 

SID 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. 
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 (C02) 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 

15 

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 ystem was upgraded in January 1994 

wi th all new sensors and a new data acquisition system. 

Manual weaLher observations took place daily at midnight 

w1iversa l 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 C02, t3C/12C ratio, and 

N20. Twice per month, three evacuated glass flasks were 

exposed to ambient air. 

S/O. Three glass flasks were pressurized with ambient 

air on the first and fifteenth of each month for the longterm monitoring of 0 2 and N2· 

DOE. The Department of Energy (DOE)conducts longterm 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. 

CS/RO. CSIRO monitors the ratio 13C/12C in 

atmospheric C02 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 H20 2 in the air/snow interface. In 

the summer of 1994 CMDL began collecting surface snow 

and micropit snow samples once per week. 
TABLE 1.6. Summary of Measurement Programs at SPO in 1994-1995 

Program 

Surface 0 3 

Total 0 3 

Ozone profiles 

Water vapor 

N20, CFC-I I, CFC-12, CFC-113, 

CH3CCl 3, CCl 4 

N20, CFC-I I, CFC-12, CFC-113, 

CH3CCl3, CCl4, SF6, HCFC-22, 

HCFC-14lb, HCFC-142b, CH3Br, CH3CI, 

CH2Cl 2, CHCl3, C2HCl3, C2Cl4, H-1301, 

H-1211, H-2402, HFC-134a 

CFC-I I, CFC-12, CFC-113, N20, 

CH3CCl 3, CCl4 

Aerosols 

Condensation nuclei 

Optical properties 

Solar Radiation 

Global irradiance 

Direct irradiance 

Albedo 

Terrestrial (IR) Radiation 

Upwelling and downwelling 

Meteorology 

Air temperature 

Pressure 

Wind (speed and direction) 

Frost-point temperature 

Cooperative Programs 

C02, 13C, Np (SIO) 

Total surface particulates (DOE) 

Various trace gases (OGIST) 

lnterhemispheric 13C/14C (CSIRO) 

0 2, N2 (Scripps) 

H20 2 (Univ. of Arizona) 

Isotope production (SUNY) 

Instrument 

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 

Pollack CNC 

TS! CNC 

Four-wavelength nephelometer 

Eppley pyranometers with Q and RG8 filters 

Eppley pyranometer with Q filter 

Net radiometer 

Eppley pyrheliometer with Q, OG I, RG2, 

and RG8 filters 

Eppley pyrheliometers with Q and 

RG8 filters 

Eppley pyranometers with Q and RG8 filters 

filters, downward facing 

Eppley pyrgeometers 

Platinum resistor, 2- and 20-m heights 

Capacitance transducer 

Mercurial barometer 

Bendix Aerovane 

Hygrometer 

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 

16 

Sampling Frequency 

Continuous 

I pair twice mo-I 

I pair twice mo-I 

Continuous 

3 day-I 

I wk-I, summer, autumn, 

winter; I (3 day)-1, spring 

IO times yr-I 

I sample mo-I 

I sample mo-I 

I sample h-1 

2 day-I 

Continuous 

Continuous 

Continuous, summer 

Continuous, summer 

Continuous, summer 

2 day-I 

Continuous, summer 

Continuous, summer 

Continuous 

Continuous 

Continuous 

I time wk-I 

Continuous 

Continuous 

2 mo- I (3 flasks sample-I) 

Continuous 

(4 filters mo-I) 

I week-I (2 flasks set -1), 

summer only 

I or 2 flasks mo-I 

I mo-I (3 flasks set-I) 

I time wk-L 

NIA; checked once mo-I 
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 31, 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. l % for the 17-

year climatology period of 1977 through 1993 (Figure 1.3). 

Wind speeds that were greater than 10 ms-I 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·l in 1994 

(Table 1.8) was the second lowest average while the 5.0 ms-I 

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 .l°C in 1994 was 0.5°C 

colder than the 17-year average (Table 1.8). In 1995, the 

average of -l l.4°C was l.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~I 0 

ms·l) from predominately westerly and south-easterly 

TABLE 1.7. CMDL Meteorological Sensor Deployment December 31, 1995 

Sensor 

Primary anemometert 

Secondary anemometert 

Pressure transducer:j: 

Mercurial barometer 

Air temperature A§ 

Air temperature B §'I 

Air temperature C** 

Dewpoint temperature 

Rain gauge 

BRW 

Serial Elevation, 

No. m 

14584 10.5 

374199 9.5 

641 9.5 

2.2 

16.3 

2.0 

GOOOI 2.0 

-4 

MLO 

Serial Elevation, 

No. m 

13864 10.0 

13865 38.2 

374198 3398.4 

278 3398.4 

2.0 

37.4 

2.0 

G0004 2.0 

0.8 

tPropeller Anemometer, model no. 05105, R. M. Young Company, Traverse City, Michigan. 

SMO 

Serial Elevation, 

No. m 

15945 13.7 

374200 78.5 

961 78.5 

14.0 

12.8 

G0008 12.8 

-4 

Serial 

No. 

14583 

358960 

215 

G0007 

SPO 

Elevation, 

m 

10.0 

2841.0 

2841.0 

2.0 

22.0 

2.0 

2.0 

tPressure 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. 

'fThermometer, 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 
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 iil. units of percent.occurrence. Wtnd speed is displayed as a function of direction in three speed classes. 

BARROW /~ / ~~- -~=-·-... '· '......_. WIND ROSE 

1977-93 .-- .--~-- -r .. __ .. _ ... , . / _,,, ..... _ . .----"-·-1 .. ·-·-·-.... ........... "· '·-... 

,.-<.._ ,/ ,/ ~·-· · ·-.. ·--. ~ .... , '" > .... I ;x, ,, _,,.... ., ... , X. '\ 1 . . < /' .... ---]'"""-... _ . ..._ ,...,,... 

'- \ I .. = 1•'..... .... .... '-..... ~ ... ·· \ " / I / ,.?·.:.·v/ ,,,. ,.- ... --! ............ ' ... "··"-./'-... , \ " I ; i ,.· / ., / "" --- ·-~. ...... . ...- '. \ .\ \ \ 

/ / I I / ;<.......,. .. ..r- .-.-- -...........,)\, \ \ . \ \ 

I t.!f' I I ' i I ," ·, / I ' "\ '\ ' \ \ ., ... y · . \\ ~' 

. I i f J J I / .....,_....,. """"' ),.--\" \ I \ \ I I J ' I f ? - ~ ,' I l \ 1 

l!!fl,11/ i\\l'\l ,;~ +·-+-- .. 1-·l-··l-·f ! I '·--r .. + .... \....... j ... ~ ... 

, \ \ \ \ \ '\. .· ; ij 1 1 1 r 

\ \ \ \ \ \ ./' ,,_./ /' I I I I I i 

\ \\ \ . )('-........ "·· ....... j .. --" -c; .,x~ / / / ;' /; ! ' .. \ . ... I .-,,,,. I \ . ·. '-._ -~-r .. -·- ~~( . _,... ,i / I , \ ·\ \ .Y" " ....... ~~· ........ _ .. r _ --·~· .. . -·/X./ .. / I \ '· . , . '"' . ---1--·-"- / i> . )" .// ,X.. ........... '·· .,...,...r- .... _)<. t- 1-ND-SP_E_E_D..,.(M ~S'}~ °"·, ···-···--. ,_ .. _...- .. / // ":/ ...... .. .. . ......._ I _,,,....... .. ~ r --.5 ' ws ' 5 -. ...... ·-.. _$_ .. _ _.,·' _,,/ 17l'Ul22'2Z15 '" WS < 10 , ......_---..... _., _ _ , __ ............. ·• _.,. .:.-··'...- WIND FREQ 

-. ...._,J.. :It 

c:::=::J W'S • I 0 "·~." · ••. - -" 

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. 

18 

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;::-) 0 ms· I) 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 
TABLE 1.8. BRW 1994 and 1995 Monthly Climate Summary 

Jan. Feb. March April May June July 

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) 

ENE 

8.8 

17 

67 

1028.5 

1050 

ESE ENE 

7.2 5.9 

20 13 

95 73 

1026.5 1016.l 

1050 1036 

Minimum pressure* 1003 1003 995 

(hPa) 

Average air -23.0 -23.2 -28.1 

temperature ( 0

C) 

Maximum temperature* -14 -2 -II 

(•C) 

Minimum temperature* -35 -36 -40 

(•C) 

Average dewpoint -26.0 -2S.6 -30.9 

temperature (0C) 

Maximum dewpoint -16 -4 -13 

temperature (

0

C) 

Minimum dewpoint -38 -39 -43 

temperature (0

C) 

Precipitation (mm) 0 0 0 

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) 

ENE 

4.8 

13 

104 

1010.4 

1025 

E ENE 

5.1 S.4 

16 15 

50 112 

1025.5 1023.6 

1042 1040 

Minimum pressure* 986 1002 1002 

(hPa) 

Average air -24.3 -26.8 -27.4 

temperature (0

C) 

Maximum temperature* -4 -7 -3 

(•C) 

Minimum temperature* -44 -46 -44 

c·c> 

Average dewpoint -26.6 -29.4 -29.9 

temperature (

0

C) 

Maximum dewpoint -5 -8 -3 

temperature (

0

C) 

Minimum dewpoint -49 -50 -49 

temperature (

0

C) 

Precipitation (nun) 0 0 0 

1994 

ENE ENE W E 

4.2 6.1 4.0 4.3 

13 12 9 12 

72 64 270 90 

1020.1 1014.6 1011.3 1010.0 

1036 102S 1023 1024 

1006 998 1001 

-17.8 -7.7 -0.3 

-2 2 9 

-33 -18 -II 

-19.7 -9.1 -1.3 

-4 0 8 

-36 -19 -12 

0 2 

ENE ENE NE 

S.2 5.4 3.8 

13 13 9 

226 S8 2S8 

1014.9 1017.5 1012.7 

1024 1036 1028 

995 

3.6 

17 

-3 

2.5 

11 

-3 

IS 

1995 

E 

5.1 

12 

74 

1012.4 

1022 

997 I 003 1000 I 003 

-13.7 -4.5 1.2 2.8 

2 2 16 17 

-3S -11 -6 -2 

-IS.2 -4.9 -0.9 0.9 

0 0 0 11 

-37 -12 -7 -6 

0 IS 28 

Aug. Sept. Oct. 

ESE NE ENE 

5.0 5.6 4.3 

13 14 13 

231 264 71 

1009.2 1012.3 1009.5 

1030 1027 1022 

995 998 991 

5.5 -3.2 -13.0 

20 7 -3 

-3 -12 -31 

3.7 -5.0 -14.4 

15 7 -3 

-9 -13 -34 

48 3 0 

ENE ENE ENE 

4.3 5.7 6.6 

9 13 14 

246 72 64 

1011.2 1011.2 1013.3 

1025 1030 102S 

999 990 1001 

1.7 1.7 -7.2 

14 16 -1 

-3 -4 -27 

1.4 0.4 -8.9 

10 10 -2 

-5 -6 -28 

5 3 0 

Nov. Dec. Year 

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 IS 

-40 -48 -48 

0 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 

-IS.I -24.5 -11.4 

-2 -12 17 

-29 -35 -46 

-16.I -26.2 -12.8 

-2 -12 11 

-31 -37 -SO 

0 0 S3 

Instrument heights: wind, 10.S 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 
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. 

c:::::::::J WS • 10 --- ......... 

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 
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 

barometri c pressure for 1994 and 1995 (679.7 hPa and 

680.0 hPa rcspecli vely) were both lower Lh an the longterm average pressure of 6.80 ,5 hPa. July 1994 and March 

1995 each tied its record minimum pressure fo r those 

month s and April 1995 set a new record minimum for th e 

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 th at 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 percent age (61.2%) than the long-term 

average of 59.8%. The occurrence of winds in the 10 ms·l 

or greater class was 6.7 % in 1994 and 3.9% in 1995 while 

the ex pected occurrence based on the 17 -year record is 

4. 9%. The average wind speed fo r both 1994 and 1995, 4.8 

ms-1 (Table 1 .11 ) is close to norma l. The monthly average 

for May 1995 set a new minimum reco rd fer the mon tl1. 

The average ambient temperature for 1994 and 1995 was 

27.3°C and 27. 0°C res pecti vely , whi ch are both very close 

to th e I 7-year average of 27. l "C. Five new record hi ghs 

we re ·et in 1994 th at occurred during the month s of 

Febru ary through June with a new record low occurrin g 

durin g the month of June. In I 994, temperatures during 

rhe fi r t 7 months were above th e ir mo nthly mean a.nd rhe 

oth er 5 months were below th e ir res pective mo nthly 

means. The average ba rometric pressure fo r 1994 and 

1995 (Table 1.11) was 1.2 hPa and I. 9 hPa above the 17-

21 

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-1 cla (3 .5% in 1994 and 3.1 % in 1995) were 

observed as compa red 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 r r 1994 (679.7 hPa) and 1995 (679 .6 hPa) 

(Table 1.12) were both above the 17-year average of 679. l 

hPa. June 1994 ti ed its record high pressure for the month 

and July 1995 set a new record high pressure. 
TABLE 1.9. MLO 1994 Monthly Climate Summary 

Jan. Feb. March April May June July Aug. Sept. Oct. 

Prevailing wind SW SW SW 

direction 

Average wind 3.7 4.3 4.8 

speed (m s- 1

) 

Maximum wind 12 12 13 

speed* (m s- 1

) 

Direction of max. 248 241 129 

wind* (deg.) 

Averagestation 678.1 677.9 679.1 

pressure (hPa) 

Maximum pressure* 682 682 684 

(hPa) 

Minimum pressure* 675 673 672 

(hPa) 

Average air 4.0 3.7 4.7 

temperature (

0

C) 

Maximum temperature* 10 9 12 

(oC) 

Minimum temperature* 0 

(OC) 

Average dewpoint 

temperature (

0

C) 

Maximum dewpoint 

temperature (

0

C) 

Minimum dewpoint 

temperature (

0

C) 

Precipitation (mm) 

-16.7 

4 

-32 

38 

0 0 

-8.6 -14.3 

5 4 

-24 -30 

23 22 

Night 

SSE SSE SSE SSE SSE SSE SSE 

4.1 4.4 3.4 5.9 4.1 3.9 3.3 

12 13 10 16 14 13 9 

150 148 157 153 154 155 166 

679.6 680.2 680.4 680.6 680.9 680.0 679.6 

683 683 684 683 684 683 683 

676 678 678 677 678 677 676 

5.5 6.5 7.1 7.7 7.1 6.7 6.5 

11 12 15 13 13 11 10 

2 4 3 3 3 

-17.6 -13.5 -II.I -6.1 -3.7 -3.9 -12.1 

4 7 9 8 9 8 6 

-29 -30 -29 -24 -16 -18 -29 

0 0 13 4 7 0 

Day 

Nov. Dec. Year 

SSE SSE SSE 

5.4 6.5 4.5 

13 17 17 

158 143 143 

679.8 680.3 679.7 

682 684 684 

677 677 672 

4.8 6.0 5.9 

10 11 15 

2 0 

-9.0 -22.8 -11.7 

4 -3 9 

-29 -32 -32 

31 0 140 

Prevailing wind 

direction 

NW NNW NW NNW NNW NNW ESE NNW NNW NNW SE SE NNW 

Average wind 3.9 4.3 4.4 

speed (m s-1

) 

Maximum wind 12 12 15 

speed* (m s- 1

) 

Direction of max. 259 214 104 

wind* (deg.) 

Average station 678.1 677.9 679.1 

pressure (hPa) 

Maximum pressure* 682 683 684 

(hPa) 

Minimum pressure* 675 673 672 

(hPa) 

Average air 7.3 6.5 8.3 

temperature (°C) 

Maximum temperature* 12 13 16 

(OC) 

Minimum temperature* 0 0 

(oC) 

Average dewpoint 

temperature (

0

C) 

Maximum dewpoint 

temperature (

0

C) 

Minimum dewpoint 

temperature (

0

C) 

Precipitation (mm) 

-11.7 -5.7 

6 6 

-32 -24 

29 42 

0 

-8.9 

6 

-30 

38 

3.5 3.7 2.8 5.0 3.7 3.1 2.7 4.5 5.8 4.0 

13 13 8 15 13 11 10 13 16 16 

141 153 106 142 147 152 160 142 124 124 

679.7 680.3 680.6 680.8 681.0 679.9 679.6 679.7 680.3 679.8 

683 682 684 683 683 683 683 683 684 684 

677 678 678 677 678 677 676 677 677 672 

9.8 10.6 11.2 11.4 11.2 10.3 10.4 7.9 10.2 9.7 

15 15 17 16 15 15 15 14 16 17 

2 3 4 5 4 4 3 2 0 

-9.6 -6.1 -4.4 -1.6 -0.3 0.6 -5.9 -4.6 -18.4 -6.5 

8 8 9 9 9 10 8 7 2 10 

-28 -28 -27 -22 -18 -21 -26 -27 -31 -32 

0 0 10 19 56 58 12 34 0 298 

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. 

Prevailing wind 

direction 

SE WSW WSW 

Average wind 5.4 7.0 6.5 

speed (m s-1) 

Maximum wind 17 15 16 

speed* (m s-1

) 

Direction of max. 249 241 224 

wind* (deg.) 

Average station 680.0 677.4 678.7 

pressure (hPa) 

Maximum pressure* 683 681 684 

(hPa) 

Minimum pressure* 677 673 669 

(hPa) 

Average air 5.8 4.2 5.7 

temperature (°C} 

Maximum temperature* 11 11 13 

(OC) 

Minimum temperature* 

(OC) 

Average dewpoint 

temperature (

0

C} 

Maximum dewpoint 

temperature (0

C} 

Minimum dewpoint 

temperature (0 C} 

Precipitation (mm) 

-12.8 

5 

-30 

5 

-I -I 

-15.0 -15.0 

3 

-38 -30 

18 5 

SW SE SE 

Night 

SSE SE SSE SE 

6.1 4.5 4.4 3.8 3.9 3.5 4.3 

16 13 12 11 II II 15 

224 241 164 169 164 141 140 

678.4 680.2 681.1 680.6 680.3 680.9 680.1 

682 684 684 683 683 684 684 

672 677 678 678 678 678 677 

5.7 6.5 8.8 8.1 7.3 8.5 6.9 

II II 14 14 13 14 13 

0 2 5 2 2 3 

-12.5 -12.7 -15.9 -11.2 -13.I -15.2 -14.7 

5 8 7 8 7 7 6 

-32 -28 -25 -24 -27 -28 -29 

0 3 0 0 0 

Nov. Dec. Year 

SSE SSE SE 

3.8 4.4 4.8 

13 14 17 

152 160 249 

680.4 680.8 679.9 

684 684 684 

677 676 669 

5.6 5.5 6.6 

10 11 14 

2 -I 

-5.5 -12.3 -13.0 

6 6 8 

-24 -31 -38 

12 3 49 

Prevailing wind 

direction 

WSW WNW W NNW NNW NE 

Day 

NE NE NE NNW NNW NNW NNW 

Average wind 5.1 7.1 6.5 

speed (m s-1) 

Maximum wind 17 14 17 

speed* (m s-1

) 

Direction of max. 248 297 233 

wind* (deg.) 

Average station 680.0 677.5 678.8 

pressure (hPa) 

Maximum pressure* 683 682 684 

(hPa) 

Minimum pressure* 677 673 670 

(hPa) 

Average air 9.4 7.6 9.7 

temperature (

0

C} 

Maximum temperature* 16 15 17 

(OC) 

Minimum temperature* 

(DC) 

Average dewpoint 

temperature (

0

C} 

Maximum dewpoint 

temperature (°C) 

Minimum dewpoint 

temperature (

0

C} 

Precipitation (mm) 

-I 

-10.4 -10.9 -10.6 

5 4 6 

-30 -38 -30 

7 16 7 

6.5 4.7 3.8 3.6 3.5 3.1 3.8 3.0 3.4 4.5 

16 13 10 14 12 13 13 13 12 17 

233 251 144 148 155 125 147 155 234 248 

678.4 680.3 681.2 680.8 680.5 681.0 680.2 680.3 680.7 680.0 

682 684 683 684 683 684 683 684 685 685 

673 677 678 678 678 678 677 678 676 670 

9.7 10.6 13.0 11.7 11.2 12.2 10.5 8.9 9.0 10.3 

15 16 17 16 17 19 17 14 15 19 

2 3 7 5 4 5 2 2 2 -I 

-7.9 -4.7 -7.7 -2.8 -3.8 -5.8 -7.1 -2.2 -7.7 -6.8 

6 9 8 9 10 9 7 8 6 10 

-30 -26 -24 -22 -27 -26 -29 -23 -31 -38 

10 II 0 8 16 9 IO 25 19 140 

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. 

23 
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. 

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. 

24 

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 
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) 

Jan. 

SE 

3.8 

9 

310 

998.7 

1003 

Minimum pressure* 991 

(hPa) 

Average air 28.7 

temperature (

0

C) 

Maximum temperature* 35 

(OC) 

Minimum temperature* 23 

(OC) 

Average dewpoint 23 .2 

temperature (

0 C) 

Maximum dewpoint 26 

temperature ( 0

C) 

Minimum dewpoint 21 

temperature (

0C) 

Precipitation (mm) 215 

Prevailing wind 

direction 

Average wind 

speed (m s· 1

) 

Maximum wind 

speed* (m s· 1) 

Direction of max. 

wind* (deg.) 

Average station 

pressure (hPa) 

SSE 

5.9 

14 

322 

998 .7 

Maximum pressure* I 005 

(hPa) 

Minimum pressure* 992 

(hPa) 

Average air 27.2 

temperature (

0 C) 

Maximum temperature* 29 

(OC) 

Minimum temperature* 24 

(OC) 

Average dewpoint 23.9 

temperature (

0

C) 

Maximum dewpoint 26 

temperature ( 0

C) 

Minimum dewpoint 21 

temperature (0C) 

Precipitation (mm) 288 

TABLE 1.11. SMO 1994 and 1995 Monthly Climate Summary 

Feb. March April May June July 

NW SSE 

3.1 3.5 

8 14 

140 334 

999.3 999.5 

1003 1004 

996 992 

29.5 29.l 

37 36 

23 24 

23 .5 23.8 

2S 26 

22 22 

121 181 

SE ESE 

3.1 3.2 

10 8 

138 323 

1000.1 1000.6 

1004 1005 

995 996 

27 .7 27 .8 

30 29 

24 24 

24.4 24.6 

27 26 

21 22 

128 192 

NW 

3.7 

14 

315 

999.I 

1003 

994 

28.2 

36 

23 

23.6 

26 

20 

288 

SSE 

3.1 

10 

l18 

SE 

4.6 

12 

144 

SSE 

6.5 

13 

138 

1994 

SE 

5.5 

13 

146 

1001.0 1001.8 1001.2 

1005 1006 1004 

996 998 

27.7 26.9 

34 34 

21 23 

22.4 22.8 

25 25 

20 19 

283 84 

SSE SE 

3.4 6.6 

12 11 

156 153 

998 

26.3 

29 

23 

23 .0 

26 

18 

233 

1995 

SE 

6.1 

IS 

124 

1000.0 1001.0 1002.9 1002.5 

1003 I 004 I 007 I 006 

997 997 999 999 

27 .3 27.1 27 .2 26.8 

30 30 29 28 

23 23 24 24 

23.9 24.0 23 .4 23.5 

26 26 26 25 

20 22 20 21 

258 183 85 143 

Aug. Sept. Oct. 

SE SSE SE 

7.3 4.8 3.7 

15 11 12 

145 112 113 

1002.8 1002.7 1001.8 

1007 1007 1005 

997 999 998 

25.5 25.9 26.4 

27 28 29 

23 23 23 

21.7 22.8 24.0 

25 2S 26 

15 17 21 

200 65 299 

SE SE SSE 

6.1 6.9 5.7 

13 13 13 

164 130 130 

1002.9 1003.7 1001.8 

1007 1007 1006 

999 1000 998 

26.4 26.4 26.3 

30 29 28 

23 23 24 

23.3 22.7 22.9 

25 25 25 

20 17 20 

273 119 103 

Nov. Dec. Year 

SE SSE SE 

6.5 4.0 4.8 

14 11 15 

138 151 145 

1000.3 997 .8 1000.5 

1004 1003 1007 

994 992 991 

26.8 27.3 27.3 

29 30 37 

23 24 21 

23 .8 25 .0 23.3 

26 27 27 

20 23 IS 

201 332 2503 

SSE E SSE 

4.1 2.1 4.8 

12 6 15 

87 64 124 

1000.2 999.0 1001.2 

I 005 JOOS I 007 

995 995 992 

26.8 27 .6 27 .0 

29 30 30 

23 25 23 

26 27 27 

22 21 17 

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 
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. 

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. 

26 

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 hygrothermometer 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. 
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 6.2 6.0 5.8 6.6 5.7 4.3 3.4 5.4 

speed (m s· 1

) 

Maximum wind 11 10 12 10 13 14 12 12 13 10 9 7 14 

speed* (m s· 1

) 

Direction of max. 359 5 13 40 7 214 20 359 30 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 (

0

C} 

Maximum temperature* -23 -35 -37 -38 -35 -37 -45 -37 -31 -34 -27 -22 -22 

(oC) 

Minimum temperature* -37 -55 -64 -70 -74 -68 -72 -73 -74 -63 -47 -34 -74 

(OC) 

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. l -52.6 

temperature (

0

C} 

Maximum dewpoint -24 -42 -42 -42 -39 -41 -50 -41 -34 -38 -33 -26 -24 

temperature ( 0

C} 

Minimum dewpoint -52 -63 -71 -71 -71 -71 -71 -71 -71 -70 -56 -41 -71 

temperature (

0

C} 

Precipitation (mm) 0 0 0 0 0 0 0 0 0 0 0 0 0 

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 I 0 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 (

0

C} 

Maximum temperature* -24 -28 -40 -44 -37 -39 -34 -49 -50 -31 -27 -20 -20 

(oC) 

Minimum temperature* -38 -51 -66 -74 -76 -72 -68 -74 -77 -66 -49 -33 -77 

(OC} 

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 (

0

C} 

Maximum dewpoint -27 -32 -44 -49 -42 -43 -37 -54 -55 -35 -30 -23 -23 

temperature (

0

C} 

Minimum dew point -47 -60 -73 -81 -85 -79 -75 -81 -86 -73 -55 -37 -86 

temperature (

0

C} 

Precipitation (mm) 0 0 0 0 0 0 0 0 0 0 0 0 0 

Instrument heights: wind, 10.0 m; pressure, 2841 m (MSL); air temperature, 2.0 m; dewpoint temperature, 2.0 m. Wind and temperature 

instruments were on a tower JOO m grid east-southeast of the CAF until November 9, 1995, when the tower was moved to a location 183 m grid 

northeast of the CAF. 

*Maximum and minimum values are hourly averages. 

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 

10.0 

2841.0 

1.1 

10.0 

2841.0 

2.0 

Air temperature B 

Air temperature C 

Dewpoint temperature 

Non-aspirated temperature 

20.0 

1.6 

1.6 

1.4 

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. 

Station 

BRW 

MLO 

SMO 

SPO 

BRW 

MLO 

SMO 

SPO 

TABLE 1.14. CMDL Meteorological Operations 

Summary, 1994-1995 

Expected Number Percent Data Number of Missing 

of Data Points Capture Data Points 

1994 

3,006,720* 99.08% 27,678 

6,832,800 94.48% 377,222 

l,955,520t 99.27% 14,215 

3,985,920:1: 94.95% 201,128 

1995 

4,204,800 99.40% 25,115 

6,832,800 95.85% 283,394 

3,679,200 84.08% 585,716 

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. 

:j: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 

28 

occasions, the static buildup damaged electrical components, 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 l 981. 

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 .. 95-115, 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. 
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: C02, CH4, 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 fro_m 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 C02. Methane 

was added in 1983, CO in 1988, isotopic ratios of C02 (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 socalled 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 N20 

(a greenhouse gas) and SF6 were added to the suite of flask 

measurements, and other species are under investigation. 

29 

The development of a method to routinely measure the 

13C/12C ratio of CH4, 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 C02 and CO, calibrated 

reference gases are provided under the auspices of the 

World Meteorological Organization (WMO). At the 

"product" end, a common database for C02 has been 

assembled without significant calibration or methodological 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 CH4, 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 C02 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 C02 

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 C02 mixing ratios 

for the entire record through 1995 are plotted versus time 

for the four observatories in Figure 2.1. 

The C02 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 C02 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 C02 NDIR measurements, but the CH4 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 
TABLE 2.1. Provisional 1994 and 1995 Monthly Mean 

C02 Mixing Ratios From Continuous Analyzer Data 

(micromol/mol, abbreviated as ppm, relative to 

Month 

Jan. 

Feb. 

March 

April 

May 

June 

July 

August 

Sept. 

Oct. 

Nov. 

Dec. 

Year 

Jan. 

Feb. 

March 

April 

May 

June 

July 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

Year 

370 

360 

350 

340 

330 

dry air WMO X85 mole fraction scale) 

BRW 

361.83 

363.76 

365.04 

364.26 

364.07 

362.76 

354.37 

349.03 

350.41 

357.37 

360.80 

364.28 

359.83 

364.49 

366.13 

366.27 

366.60 

365.78 

364.01 

356.53 

351.49 

355.24 

357.90 

363.80 

366.94 

362.10 

--G- Borrow 

~Mouno Loo 

+ Samoa 

0 South Pole 

1975 1980 

MLO 

1994 

358.01 

358.82 

359.74 

361.13 

361.49 

360.60 

359.20 

357.23 

355.44 

355.89 

357.42 

358.74 

358.64 

1995 

359.74 

360.59 

361.59 

363.05 

363.56 

363.08 

361.57 

358.91 

357.94 

357.78 

359.21 

360.45 

360.62 

1985 

SMO 

357.00 

357.37 

357.10 

357.35 

356.76 

357.02 

357.60 

357.32 

357.33 

357.63 

358.16 

358.59 

357.44 

358.54 

359.30 

359.31 

359.03 

359.43 

359.28 

359.50 

359.31 

359.17 

359.47 

359.89 

360.15 

359.36 

1990 

SPO 

355.48 

355.45 

355.51 

355.63 

355.76 

356.04 

356.46 

357.14 

357.52 

357.56 

357.52 

357.40 

356.46 

357.22 

357.23 

357.40 

357.40 

357.63 

357.87 

358.35 

358.78 

359.10 

359.29 

359.39 

359.40 

358.26 

1995 

Fig. 2.1 . Preliminary selected monthly mean C02 mixing ratios 

expressed in micromol/mol at the four CMDL observatories 

30 

acqu1s1t1on and control systems will be installed at the 

remaining observatories during 1996. 

In addition to the new data system, the C02 NDIR 

analyzer was fitted with smaller optical cells, 60 mm in 

length compared with the original 180 mm length cells. 

The glass H20 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-I 

from 300 cc min· I. 

2.2.2. FLASK SAMPLE CARBON DIOXIDE 

MEASUREMENTS 

Measurements of the distribution and variations of 

atmospheric C02 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 C02 measurement 

program and is intended to study the North 

Atlantic/subarctic marine sink for C02. 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°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°1 I' 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 C02 growth rate determined from 

the air sampling network data is shown in Figure 2.3. The 

C02 growth rate declined from a high of =2.6 μmol 

(abbreviated ppm) per year in 1987 to a low of =0.6 ppm 

yr·l 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. 
90"N 

60"N 

30"N 

:g~ CHINA SEA MAUNA LOA l • CAPE KUMUKAHI 

)lJ GUAM 

.(}f.t~. •' " Q' 

o· 

30"5 PACIFIC OCEAN CRUISES • 

EASTER ISLAND 

60"5 -1---------

OBSERVATORY • 

COOP. NETWORK e 

TOWER A 

-- ALERT 90"N ZEPPELIN 

~ 

60"N 

30"N 

o· 

ASCENSION • ISLAND 

30°S 

CROZET • ~ 

60°5 

SYOWA 

AIRCRAFf + SOUTH POLE 

90°5 -+-----...--.---....--.-"----.--.......-- --.-- llllWIJry 1996 g o·5 

100°E 140°E 180° 140°W 1 oo·w 60°W 2o·w 20°E 60°E 100°E 

Fig. 2.2. Network of continuing measurements by the Carbon Cycle Group. 

A two-dimensional model was developed to use the flask 

C02 data, together with measurements of the 13C/12C ratio 

in C02 from the same air samples, to partition C02 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 C02 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 DIOXIDE REFERENCE GAS 

CALIBRATIONS 

The calibration of COi-in-air reference gas tanks 

continued in 1995; 407 tanks were calibrated using the 

NDIR analyzer. All COi-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 C02 

in a carrier (air) gas. The manometric apparatus itself is 

31 

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 C02 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 0.01 °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 C02, N10. and residual water 

vapor. Upon completion of the extraction, the C02 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 C02 (and N20) is thawed, 

the temperature and pressure are continuously measured 
TABLE 2.2. Provisional 1993-1995 Annual Mean 

C02 Mixing Ratios From Network Sites 

Code 

ALT 

ASC 

AZR 

BAL 

BME 

BMW 

BRW 

BSC 

CBA 

coo 

CHR 

CMO 

CRZ 

EiC 

GM! 

GOZ 

HBA 

HUN 

ICE 

IZO 

KEY 

KUM 

MBC 

MHT 

MID 

MLO 

NWR 

PSA 

QPC 

RPB 

SEY 

SHM 

SMO 

SPO 

STM 

SYO 

TAP 

TDF 

UTA 

UUM 

ZEP 

Station 

Alert, N.W.T., Canada 

Ascension Island 

Terceira Island, Azores 

Baltic Sea 

Bermuda {east coast) 

Bermuda (west coast) 

Barrow, Alaska 

Constanta, Romania 

Cold Bay, Alaska 

Cape Grim, Tasmania 

Christmas Island 

Cape Meares, Oregon 

Crozet Island 

Easter Island, Chile 

Guam, Mariana Islands 

Gozo Island, Malta 

Halley Bay, Antarctica 

Hegyhatsal, Hungary 

Vestmanaeyjar, Iceland 

Jzana Observatory, Tenerife 

Key Biscayne, Florida 

Cape Kumukahi, Hawaii 

Mould Bay, Canada 

Mace Head, Ireland 

Midway Island 

Mauna Loa, Hawaii 

Niwot Ridge, Colorado 

Palmer Station, Antarctica 

Qinghai Province, China 

Ragged Point, Barbados 

Mahe Island, Seychelles 

Shemya Island, Alaska 

American Samoa 

South Pole, Antarctica 

Ocean Station M 

Syowa Station, Antarctica 

Tae-ahn Peninsula, S. Korea 

Tierra de! Fuego, Argentina 

Wendover, Utah 

Ulaan Uul, Mongolia 

Ny-Alesund, Svalbard 

1993 

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.I 

357.3 

356.7 

356.0 

357.7 

355.6 

354.8 

357.5 

354.5 

360.4 

[] 

357.1 

C02 {ppm) 

1994 

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.I 

361.2 

[] 

361.2 

359.3 

359.2 

1995 

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.I 

366.6 

360.l 

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 C02 in the original air sample can be 

calculated with the virial equation of state, taking real gas 

compressibility into account, and correcting for the N20 

contribution. 

From December 1995 to February 1996, the C02 

concentrations of three cylinders with COrin-air mixtures 

were determined by the manometric calibration system. 

The results of the tests are presented in Table 2.5. For 

32 

TABLE 2.3. Provisional 1993-1995 Annual Mean C02 

Mixing Ratios from Pacific Ocean Cruises 

Latitude 

30"N 

25"N 

20"N 

15"N 

IO"N 

5"N 

Equator 

5'S 

JO'S 

!S'S 

20'S 

25'S 

30'S 

35'S 

1993 

357.7 

357.7 

357.1 

357.6 

357.8 

357.7 

357.5 

357.0 

356.7 

356.2 

355.8 

355.4 

355.4 

355.5 

C02 (ppm) 

1994 

359.4 

359.5 

359.6 

359.7 

359.2 

359.5 

359.1 

358.9 

358.3 

357.8 

358.1 

357.6 

356.9 

357.0 

1995 

360.8 

361.4 

361.0 

360.7 

361.1 

361.0 

360.6 

360.4 

360.2 

359.5 

359.0 

358.5 

358.4 

358.6 

TABLE 2.4. Provisional 1993-1995 Annual Mean C02 Mixing 

Ratios from South China Sea 

Latitude 

21'N 

18"N 

15"N 

J2"N 

9"N 

6"N 

3"N 

1993 

361.1 

360.2 

357.8 

359.9 

357.9 

357.9 

359.2 

C02 {ppm) 

1994 

360.4 

360.3 

360.2 

360.0 

359.9 

359.8 

359.8 

Fig. 2.3. Global C02 growth rate. 

1995 

362.0 

362.2 

362.3 

361.2 

362.3 

361.5 

361.1 
TABLE2.5. Results of Tests Using Manometric Calibration System 

Cylinder Manometric Standard Difference 

Date Serial No. C02 Average Deviation NDIR (ND IR-MANO) 

Dec. 6, 1995 71568 386.33 

Dec. 6, 1995 71568 386.30 

Dec. 8, 1995 71568 386.37 386.33 0,035 386.25 -0.08 

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 352.89 352.74 0.090 352.77 0.03 

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 315.08 314.99 0.063 315.05 0.06 

C02 concentrations in μmol/mol. 

comparison, the C02 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 μmol for a total of 20 measurements. The largest 

mean difference of measurements between the NDIR and 

the manometric system is 0.08 μmol for the three 

COz-in-air mixture cylinders. 

2.2.4. MEASUREMENTS OF STABLE lsOTOPES OF C02 

Since 1990, the Stab.le Isotope Laboratory at INSTAAR 

has been measuring lhe stable isotopic composition of C02 

from flask sample s from the CMDL global air sampling 

network . The natural ratio of t3C to 12C 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 aga inst 13C durin g photosynthetic uptake, 

therefore the 13C/12C ratio in plant carbon (and, by 

derivation, in soils and fossi l fu e ls) is depleted relative to 

the atmosphere, typically by about 20%0 (per mil, or parts 

per thousand)-which in turn leaves the atmosphere subtly 

enriched in nc. Observing such a nc signature allows 

exchanges of C02 with rh·e bi os phere to be discinguis hed 

from oceani c fluxes because the latter do not carry a 

signi licant isotopic signature [e.g., Keeling et al., 1995]. 

The ISQ compositi on of atmos pheric C02 ultimate ly 

derives fro m its equili bration with liqui d water, providing 

a link between the globa l carbon and hydrologic cyc les. 

Por example , C0 2 ex posed Lo 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 C02 " remembers" the 

18Q signature of the water reservoir it has most recently 

33 

visited, this tracer may prove to be useful in quantifying 

the gross annual uptake of C02 by photosynthesis and its 

release by respiration . 

INSTAAR currently measures ol3C (the normalized 

difference between the isotopic ratios of a sample and 

standard) and o•so in C02 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 C02 from about 750 

standard cm3 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 0.0330 and 0.06%0 are 

obtained for ol3C and o•so respectively. Small numerical 

corrections account for the presence of N20 trapped with 

C02 and for the presence of isotopi c species includi ng 17Q. 

The isotopic data are full y integrated into the Carbon 

Cycle Group's trace gas data base. 

A sample of the isotope data is gi ven in Figure 2.5, 

which shows time series of C02 mi xi ng ra tio, ljl 3C, and 

l)18Q from Barrow, Alaska, from 1990 through 1995 . 

There is a striking anticorrelation between the seasonal 

cycles of mixing ratio and ol3C, 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 o13C is to lighter values, reflecting 

the depletion in 13C of fossil fuel relative to the 

atmosphere. The seasonal cycle of l)ISQ lags behind C02 

and l)IJC, 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 C02 

between biosphere and atmosphere that are subject to 

efficient oxygen isotope exchange. 
60 (a) 

NOAA 

40 ~ - (/) 

2 

Ul cu 

20 f- -

0 

6000 

NOAA (b) 

(/) 4000 - - -"'-

(/) 

0 

G:: 2000 

0 

cu -

i -

100 

g 80 

[" 60 0 

a. 40 u 

0 

0 20 (.'.) 

0 

1990 1991 1992 1993 

Year 

Fig. 2.4. Statistics of the isotope measuring effort. The extent 

of the NOAA C02 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 ol3C and o•so. 

~ 

E 

Q_ 

Q_ 

'-" 

"' 0 

u 

~ 

i;-.1! 

'-" 

S? 

'<> 

~ 

i;-.1! 

'-" 

0 

:!! 

'<> 

380 

360 

340 

-7.0 

-8.0 

-9.0 

1.0 

-1.0 

-3.0 

Point Barrow 

0 Retained 

+ Non-bo_fkground 

1990 1991 1992 1993 1994 1995 

Year 

Fig. 2.5. Time series of C02 (upper panel), ol3C of C02 (middle 

panel), and o•so (lower panel) from Point Barrow, Alaska. 

34 

The INSTAAR isotope data were recently described in 

detail [Trolier el al., 1996]. The INSTAAR one time 

series, though beginning only in 1990, were used in 

concert with the longer one time series from Cape Grim, 

Australia, obtained by CSIRO, to identify a global 

flattening of the long-term o13C trend during 1988-1992 

[Francey et al., 1995a]. The decadal average trend 

observed during the 1980s, about 0.02530 yr-1, was 

apparently offset during these years by anomalously high 

uptake of C02 by the global biosphere. Similarly, the 

INSTAAR o13C 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 el al., 1995b]. Interpretive work using the 

o180 data is underway. In addition to these scientific 

analyses, the measurements are actively intercompared 

with other atmospheric monitoring laboratories measuring 

C02 isotopic composition [Francey et al., 1995b; Gaudry 

el al. , 1996]. 

INSTAAR recently obtained a more precise isotoperatio 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 180/160 in C02 (Figures 2.6 and 2.7). In 

samples collected at humid, tropical locations without 

drying, the 180/160 measurements are highly variable and 

consistently more depleted in 180 due to the exchange of 

oxygen atoms between C02 and H20 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. 7330 (1 cr) to 0.0930. 

2.2.6. CALIBRATION OF MEASUREMENTS OF 

STABLE ISOTOPES OF C02 

The INSTAAR stable isotope data are reported as 

isotopic composition relative to VPDB-C02 for both o13C 

and 01so. Calibration of this record has two distinct 

facets. The first relies on comparatively precise 

intercomparisons of samples of C02 extracted from air. 

Carbon dioxide from individual flask samples is always 
E 

'-

Q) 

a. 

4 

2 ._ 

-sh 

1993 1994 

YEARS 

+ AIRKIT 

+ MAKS 

1995 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 l)IBO signature of C02 

at equatorial latitudes from the CMDL network has been seen. 

compared with C02 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 C02 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 

0 ,-... 

.E 

-2 '-

Q) 

a. 

p - 4 

'O 

-6 

-8 

-10 

1993 1994 

YEAR 

+ AIRKIT 

+ MAKS 

1995 1996 

Fig. 2. 7. Oxygen-18 in flask samples from Cape Kumukahi, 

Hawaii. The comparison between Airkit and MAKS is very 

similar to Samoa. 

35 

TABLE 2.6. Comparison of Airkit to MAKS Sampler 

Airkit Minus MAKS 

Site Species No. Pairs Average Standard Deviation Units 

KUM C02 31 -0.07 0.40 ppm 

SMO C02 48 -0.04 0.18 ppm 

KUM CH4 33 0.19 1.99 ppb 

SMO CH4 53 0.42 2.35 ppb 

KUM co 28 -2.01 2.49 ppb 

SMO co 53 0.05 1.19 ppb 

KUM 1)13C 29 0.02 0.05 permil 

SMO 1)13C 47 0.02 0.14 permil 

KUM 1)180 7 0.67 0.82 perm ii 

SMO 1)180 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 l)IBO, where the 

retained MAKS pairs are considerably depleted in IBO at both KUM and 

SMO. 

working reference gas scales for 1)13C and 1)180. 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 o13C and 

o 180. 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 intercomparison 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 (1 cr) are shown 

where more than one determination is made in a month. 

Uncertainties clearly persist, particularly for the absolute 

assignment of the 1)180 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) 0.02U3o for o13C 

and 0 .0430 for 1)180. 

2.3. METHANE 

2.3.1. IN SITU METHANE MEASUREMENTS 

Quasi-continuous in situ measurements of atmospheric 

CH4 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 CH4 ~ole 

fractions (in nanomol/mol or IQ-9 mole/mole; abbreviated 

ppb) are plotted in Figure 2.9 for BRW (a) and MLO (b). 
- 7.4 

-7.6 

,---.... 

~ -7.8 

5? 

'Cl -8.0 

-8.2 

-8.4 

0.5 

,---.... -0.5 ~ 

'--" 

.? 

'Cl -1.5 

desi-002 

of II ~~'Y'Q:tRD 

lucy-00 

~ des;-001 

eddo-001 

~~~#/ lucy-001 inor.- oa 

ethl- 00 

+ fred-001 

I 

+ f 0 

~es)~ des;-002 

__ ±£ lucy-001 

fred-001 • 

lucy-00 "' 

1990 1991 1992 1993 1994 1995 

Year 

Fig. 2.8. Calibration of the NOAA-CU data set. The upper 

panel shows calibrations for l)l3C, the lower for l)I8Q. 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 

CH4 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 H2 to 

the FID [Peterson and Rosson, 1993]. On December I, 

1995, a new analytical system was installed at MLO 

ushering in a new era of high precision in situ CH4 

measurements at MLO. Main components of the system 

are an HP 6890 GC with FID, an HP 35900E analog-todigital 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 N2 to improve sensitivity. Two columns 

are used to separate CH4 from air, and flame ionization is 

used for detection. Column head pressure and flow rates 

36 

a 

2000 ,---.... 

_() 

Q_ 

Q_ 

1900 .. :r: 

u 

1800 I~ 

b 

1800 ,---.... 

_() 

Q_ 

Q_ 

'---' 1750 .. :r: 

u 

1700 

1994 1995 

YEAR 

Fig. 2.9. Daily mean CH4 mixing ratios in J0-9 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 AID. Previously the AID was included in a 

stand-alone integrator. The new HP 35900E AID 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 CH4 

chromatography and GC system. This integration system is 

also paperless; about I-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 CH4 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 μV. Previously, peak height was used to 

calculate CH4 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 CH4 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 
4.5x106 

4.0 x 106 

Cf) 

~ 3.5x106 0 

u 

3.0x10 6 

H.~ 1740 ppb 

~ 

I ! 

2.5x106 ""--~----../ ~ l 

_ ____, 

0 20 40 60 80 100 120 140 160 180 200 

Time (seconds) 

Fig . 2. 10. Typical CH4 chromatogram from MLO obtained with 

the new analysis system. AJD sampling rate was I 0 Hz. On the 

y-axis. there are 105 counts mV·I. Signal-to-noise is -2000, 

based 011 a peak height of 16.8 mV and penk-ro-peak noise of 

- 8μV . The retention time for CH4 is 124.3 seconds, und the fullwidlh-at-half-max i 8 seconds. 

from the sample is ratioed to the average peak area of the 

bracketing standard gas injections. This ratio is then 

multipli ed by the assigned value for the standard gas 

cylinder. By only using rhe injections of standard gas, this 

calculation can be u ed to assess the instrument precision 

as described in the following paragraph. 

The preceding improvements have lead to an overall 

improvement in precision al MLO of a fac tor of 4. Typical 

rel ative precision is 0 .04 to 0 .07% (or < I ppb CH4 for 

ambient levels of about l 700 ppb). In Figure 2.11, relative 

differences between measurements of standard gas and the 

assigned value for the standa rd gas cyfrnder ("Relative 

0.10 

,-.... 

~ 0.05 

c 

0 

:~ u 

~ 0.00 . 0.. 

(j) 

.~ 

:§ 

~ -0.05 

- -- ---~-~-~ -- --- i-;- --~- --- -------i ;-

-0.10._..-'-~-'-._J, --'-~L....-'- ----"--'- L...._.___.___. 

0 2 4 6 8 10 12 14 1 6 18 20 22 24 

Hour 

Fig. 2.11. Relative measurement prec1S1on, 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 

Icr for each measurement of reference gas, was 0.03% (plotted as 

the dashed lln~s). This corresponds to a precision, in mole 

fraction, of ±0.6 ppb for each meas urement. 

37 

Precision") are plotted for a 24-hour period. The relative 

precision for this day (assessed as 1 cr) 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 CH4 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 CH4, C02. CO, and 

N20 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 S02 and 

3-5 km3 of ash into the upper troposphere and lower 

stratosphere, and CH4 and CO mixing ratios in the tropics 

immediately increased. The increased growth rates were 

short-lived as CH4 [Dlugokencky et al., 1994a] and CO 

[Novelli et al., 1994] growth rates showed dramatic 

decreases later during 1992 and 1993. 

In Figure 2. l 2a; CH4 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: 

4 

f(t) = a1 + a2 t + a3 t

2 + L [a2i+2 sin(2mt) + a2i+3 cos(2mt)]. ( 1) 

i=l 

Equation (I) is used to approximate (or model) the average 

trend and seasonal cycle for atmospheric CH4. 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., l 994b for details of the 

curve fitting process). Its derivative, the instantaneous 

CH4 growth rate, is shown in Figure 2. l 2b. The largest 

perturbation in CH4 growth rate observed in this time 

series was during late-1991 and early 1992. 

The CH4 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 CH4 is reaction with hydroxyl radical 

(2) 

In the clean marine troposphere, most OH formation is 

initiated through photolysis of 0 3 to give electronically 

excited oxygen atoms 

0 3 + hv (330 ~A.~ 290 nm)~ 0( 1D) + 0 2 . (3) 
TABLE2.7. Provisional 1994 and 1995 Annual Mean 

CH4 Mixing Ratios From the Air Sampling Network 

1994 1995 

Code Station CH4 (ppb) CH4 (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.I 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.I 1806.8 

ITN WITN, Grifton, N. Carolina 1817.1 1817.0 

IZO Izaiia Observatory, Tenerife 1754.0 1757.2 

KEY Key Biscayne, Aorida 1751.1 1765.1 

KUM Cape Kumukahi, Hawaii 1753.7 I756.8 

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.I 

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.I 1815.2 

Square brackets indicate insufficient data to calculate annual mean. 

Most 0(10) is quenched to ground state 0 atoms, but a 

small fraction reacts with water, 

O(ID) + H20 ~ 20H. (4) 

The photolysis rate coefficient for formation of 0(1 D), 

j03(0(1 D)), is a function of the actinic flux in the 

appropriate wavelength region, the ozone cross section, 

and the quantum yield (for O(ID) formation). Anything 

that affects the flux of radiation in the wavelength region 

330 ;;: /...;;: 290 nm, also affects the CH4 sink. 

The large increase in CH4 growth rate in 1991 is 

consistent with decreased actinic flux in the wavelength 

region 290-330 nm due to UV absorption by S02 and 

enhanced scattering by sulfate aerosols. In Figure 2.13, 

the change in j03(0(1 D)) calculated with a radiative 

transfer model is plotted. Initially, direct absorption of 

UV radiation by S02 lead to a 12% decrease in j03(0( 1D)). 

38 

,,..--.. 

.D 

0... 

0... 

.... 

1650 

0 1600 

15 ,,..--.. 

'--

>, 

........... 10 .D 

0... 

0... 

'-' 5 .. I 

u 

0 

84 85 86 87 88 89 90 91 92 93 94 

YEAR 

Fig. 2.12. (a) Zonally-averaged CH4 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 CH4 in the latitude zone 30-90°S. The curve is 

calculated as the derivative of the solid curve in (a). 

5 

0 ~ 

~ 

~ 

~ 

0 

~ -5 0 

~ 

..., 0 

<I 

-10 

-15 

' \ ·.· ,,., ....... ~· 

1991 

--S02 & Aerosol 

............ Aerosol Only 

1992 

YEAR 

Fig. 2.13. Relative change in j03(0(1D)) after the eruption of 

Mt. Pinatubo. The solid line includes the effects of direct 

absorption by S02 and scattering by sulfate aerosol; the dotted 

line includes aerosol only. The change is plotted relative to a 10-

year climatological background. 
This effect was relatively short-lived due to the short 

lifetime (-30 days) for S02. Later, UV scattering from 

sulfate aerosol produced by oxidation of the S02 

maintained lower than normal values for j for more than I 

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 CH4 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 CH4, 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 CH4 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 CH4 growth rate during late-1992 and 

1993 in the high northern latitudes. This is consistent with 

isotopic measurements of C02 that suggest that the 

biosphere was a larger than normal sink for fossil C02 

during 1992 and 1993 through either increased photosynthesis or decreased respiration [Ciais et al., l 995b], 

either of which could result from short-term variations in 

temperature or precipitation as a result of the eruption. 

2.3.3. MEASUREMENT OF 13C/12C OF METHANE 

Although many sources of CH4 have been identified, the 

uncertainty in individual source terms remains large. In 

order to explain trends in the CH4 growth rate, such as the 

period of almost no growth in 1992 and 1993 

[Dlugokencky et al., 1994a,b] a more precise understanding of the CH4 budget is needed. The global 

measurement of the stable carbon isotopes of CH4 (ol3C) 

afford an excellent means of furthering our understanding 

of the CH4 budget. The three primary processes that 

produce CH4 (bacterial fermentation, fossil fuel extraction, 

and biomass burning) all have different characteristic 

isotopic "signatures." Thus, global measurement of 1)13C 

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 1)13C. The 

technique employed is gas chromatography coupled with 

isotope-ratio mass spectrometry. Methane is 

chromatographically extracted from air, cryofocused, 

combusted to produce C02, 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 %0; therefore, the goal of a precision of 0.1 %0 is 

attainable even with such a small sample size. To date, our 

best precision for five replicate samples of air from Niwot 

Ridge is 0.16%0 (one standard deviation) (Figure 2.14). 

39 

,.-... 

Q) 

~ 

L 

Q) 

0... 

............. 

(/) 

0 

C) 

Qi 

c 

c 

c 

:J 

a::: 

0 

....... 

Q) 

> 

....... 

0 

Q) 

a::: 

u 

:'.! 

'O 

-4 

-6 

-8 

-10 

-12 

a 

-14 

c5 13C of Methane 

From Niwot Ridge 

0 0 

0 0 0 

- 0.16 Per Mille 

-16.__.__.__.__.__'--'--'--'--'--'--'--' 

0 2 4 6 

Sample Number 

Fig. 2.14. Reproducibility of repeated measurements of 13C 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 
[Novelli et al., 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 

450 

<00 

35'l 

a. 3·)-J 

~ Z5·: 

1;c 

D:· 

--~ ~--

Fig. 2.15. Preliminary in situ hourly average CO mixing ratios 

during 1994-1995 at (a) BRW and (b) MLO. 

40 

TABLE 2.8. Preliminary 1994 and 1995 Mean CO 

Mixing Ratios From Land Sites 

Annual Mean CO (ppb) 

Code Station 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.l 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 

GM! 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 [] 

!TN Grifton, N. Carolina 182.0 171.6 

IZO Izana, Tenerife 103.9 IOI.I 

KEY Biscayne, Aorida 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.I 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. 

samples of air to the corresponding hourly mean m1xmg 

ratio determined in situ. The results from the two 

sampling approaches agree well (r2 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 m1xmg 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 
240 

2w [ 

.. 

I )" ' .•, I • • 

; lllO I • '!." 

~ • ; c 

160 t ~.~ .. 0 

u 

140 

IW 

I 

100 

.. L- .. "'' 

\ 

.. 

) 

\ 

I 

\ 

". ·_~"" •. ~ 

I,. ·_ \, 

(a) I 

I 

• j 

& 

•1 

cf 

tl 

,v ·. 

. ' 94A IJ.I~ 948 9!i 952 9.54 956 958 96 

YEAR 

" YEAR 

9S2 4 9!i.6 958 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 H2 

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 H2 standards was 

prepared using gravimetric methods in collaboration with 

the NOAH Group. The H2 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 I 995, and, whenever possible, the 

1994 and 1995 annual mean values for these sites are 

41 

shown. Samples for CO were also collected on transPacific 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 199S 

N3S 119.3 123.3 

N30 12S.4 114.2 

N2S 108.6 [] 

N20 106.6 100.J 

NJS IOS.4 96.4 

NIO 89.6 83.S 

NOS 70.2 73.S 

000 66.I 66.3 

sos 6S.4 66.S 

SIO 63.3 61.9 

SIS S8.0 S8.I 

S20 S8.5 SS.8 

S25 55.6 54.9 

S30 S2.2 54.5 

S3S [] SS.I 

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 190.0 (] 

N18 147.3 [] 

NIS 147.3 172.0 

Nl2 138.S (] 

N9 142.8 130.9 

N6 145.9 126.0 

N3 145.3 126.4 

Approximately four samples per month were collected in each 

latitude bin. 
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 (C02), another combustion product, 

was also enhanced relative to mixing ratios observed at 

MHT. However, there are also times when the CO and 

C02 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 backtrajectories 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 AdministrationLangley 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 

42 

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 intercomparison of CO measurements made by 11 laboratories 

in 8 countries was organized. The round-robin intercomparison 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/N20 

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 N20 and SF6 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 N20 measurement program is to 

gain a better understanding of the budget of this 

compound. Both the natural and the anthropogenic sources 

of N20 are poorly quantified, and the effectiveness of in 

situ field measurements is limited due to the extremely 

heterogeneous nature of N20 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 N20 sources. The CCG 

network also includes regular ocean cruise sampling that 

will help us better understand the oceanic source of N20 

and the effect that El Nifio/QBO phenomenon has on this 

natural N20 source. More generally, the increased spatial 

coverage of the CCG network will improve our ability to 

use inverse modeling techniques to derive N20 sources and 

sinks on a more regional level, as has been done for C02 

[Tans, et al., 1989; 1990]. 

There are several motivations for the SF6 flask 

measurement program. (For more details on SF6 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 
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, SF6 is a nearly ideal tracer of 

atmospheric dynamics. To this end, the SF6 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 SF6 will aid in the ability to interpret the 

variations that are observed in the carbon gases and N20, 

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 SF6 levels that are on 

average z0.2 picomol/mol (abbreviated as ppt) higher than 

the marine sites (which are at z3 .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 N20 

using our standard glass flasks with Teflon a-rings filled 

with humidified air. After 1 year, a loss of "'1.0 ppb of 

N10 was measured most likely due to slow diffusion into 

the flasks' Teflon a-ring. Because the goal is to try to 

discern gradients about 1-3 ppb, this may rule out the use 

of NzO 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 SF6 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 C02, CH4, 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 

C02, CH4" 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 CH4). 

Observations of C02 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 C02 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 C02 near the ground is masked by a 

large diurnal cycle driven by photosynthesis and 

respiration [Bakwin et al., 1995]. The nighttime buildup 

of C02 near the ground due to respiration, is especially 

pronounced in summer and "fills in" the seasonal 

43 

345 

370 

e 

Q. 

..e :)60 

O' 

(.) 

350 

711192 111193 711193 111194 711194 111195 711195 111196 

Fig. 2.17. Daily mean C02 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 C02 . Observations well above the level of 

the nocturnal inversion, as can be obtained from tall 

towers, are necessary to quantify C02 mixing ratios typical 

of the whole planetary boundary layer (PBL). 

To determine the annual growth rate for C02 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-I, respectively. These 

growth rates are larger by about 0.3-0.6 ppm yr-I than 

those for the whole northern hemisphere in each year. The 

reason for this accumulation of C02 over the region, 

relative to the whole northern hemisphere, is not known. 

In October 1994 CCG began observations of CO, CH4, 

N20, 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 

N20 and halocompounds are discussed in Section 5.2.4 of 

this report. Figure 2.18 shows daily mean CH4 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 C02 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 C02 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 CH4 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, 
1935 

..-..1885 

D 

Q. 

~1835 

... i5 1765 

1735 

310 

250 ........ 

D 

Q. 

..e 190 

0 

u 130 

a 

70 " " 

1994 1995 1995 1995 1995 1995 1995 1996 1996 

Nov Jan Mar May Jul Sep Nov Jan Mar 

Fig. 2.18. Daily mean CH4 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]. 

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 km2, and the dominant forest types are mixed 

northern hardwoods (850 km2), aspen (750 km2), and 

lowlands and wetlands (600 km2). 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 

C02 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 CH4 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 C02 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 C02 data from 30, 76, and 396 m is displayed 

in Figure 2.19, and monthly statistics for CH4 and CO on 

the Wisconsin tower are presented in Figure 2.20. 

Figure 2.21 shows an example of C02, CH4, and CO 

mixing ratios, and C02 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., 

44 

0 "' 

u • 30 m 

350 • 76 m 

a 396 m 

340 

Oct: Nov Dec Jan Fib Mar Apr May Jun Jul Aug Sep Oct Nov Dec 

94 ~ ~ 95 95 95 95 95 95 95 95 95 95 95 95 

Fig. 2.19. Shaded regions indicate the inner 50% of daily 

average C02 mixing ratios for each month from 30, 76, and 396 

m on the Wisconsin tower. 

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 C02 and CH4 mixing ratios 

increase rapidly near the ground due to surface sources. 

Surface fluxes of C02 calculated from data obtained for 76 

and 396 m are generally in good agreement. The eddy 

fluxes show net uptake of C02 by the forest in the 

afternoon of up to around 0.4 ppm m s-1 or 7 kg (C) ha-I 

h-1. At night the forest releases C02 as is also indicated by 

the vertical profiles. In the future, plans are to measure 

C02 fluxes continuously and to be able to determine the 

annual net C02 balance of the forest. Some additional 

results from the flux measurements are presented by Davis 

et al. [ 1996]. 

1920 • ,..... 

..0 1890 • H· a. fr •• a. • • • •• +r .._, 1860 

++· I'* 1830 tt-+ #t .. t u .. + .. + .. + • • • • 1800 . • • • • • 2 3 6 2 3 6 2 3 6 2 3 6 2 3 6 2 3 6 

240 ••• •• ,..... • ..0 200 

#+ +-t--t- a. ••• .. a. 160 

tt+ 

•• 

++-+- '-' ••• • 

0 120 #4 #+ ••• u ••• ••• 80 • ••• 2 3 6 2 3 6 ~ 3• l' 2 3 6 2 3 6 2 3 6 

Jul Aug Sop Oct Nov Dec 

Monlh, 1995 

Fig. 2.20. Monthly statistics of CO and CH4 measurements at 

the Wisconsin tower. Circles and asterisks are means ±I 

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). 
410 

'E 390 Q. 

~ 

N 370 0 

u 350 

~ 

.. 

' . 

E 0.3 

E 

Q. 

~ 00 

)( 

" ;.: -0 3 

N 

0 

u 

140 

".C 120 a. 

~ 

0 100 

u 

80 

'.O 1910 

Q. 

~ 

• 1850 J: 

u 

1790 

0 6 12 18 24 30 36 42 48 

Local Time (hours) 

Fig. 2.21. nme series of mixing ratios and surface fluxes of 

C02 and mixing ratios of CO and CH4 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. 

Figures 2.22 and 2.23 show stat1st1cs for m1xmg ratio 

gradients between 30 m and 396 m, binned by hour of the 

day, for COz, CH4, and CO at the Wisconsin tower during 

August and December 1995, respectively. The gradients 

typically increase throughout the night as emissions 

accumulate in the shallow nocturnal PBL (below 396 m). 

In August the maximum mean gradients for C02 , CH4 .• and 

CO are 37 ppm, 95 ppb, and 18 ppb, respectively. If the 

nocturnal increase in CO in summer is attributed solely to 

fossil fuel combustion emissions with a CO/C02 of 0.02 

(mol/mol), then less than I ppm of the nocturnal 

accumulation of C02 can be attributed to fossil fuel 

combustion. The CO/C02 for emissions from the burning 

of forest biomass in North America is typically larger 

(0.15-0.25 [Hegg et al., 1990)). Hence, >95% of the C02 

that accumulates in the nocturnal stable layer in summer is 

biogenic (respiration). In December the maximum gradients 

for C02 and CH4 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 C02 and CH4 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. 

45 

- 50 • Ill 

E 

a. 

tt±t±tf. 

s 40 

-c: 

Q) 30 

'5 Ill 

~ 20 

(!) JlllllllllllllO+ •-t 

C\I 10 •• •• "t!i-111. 0 

(.) 0 t• 

:0- 150 •• 

a. 

s •• - t*ttttt 

c: 100 .~ 

"C 

~ Ill 

(!) 50 • 

111 • 111 111 111 11 • ot •Jiit ..,. -+- •+t I 0 0 •+ Ill (.) 

• JI( JI( • 

0 t· ·· 

40 

• :0- 30 • a. 

s 

- 20 c: • Q) 

'5 10 

~ "t 

(!) 0 

0 • JI( • 

(.) -10 • •• 

• 

3 6 9 12 15 18 21 24 

Hour of Day (Local Time) 

Fig. 2.22. Statistics of vertical gradients (30 m-396 m) for C02, 

CH4, 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 CH4 in the region 

surrounding the Wisconsin tower is biogenic (Figure 2.21 ). 

Future plans are to determine CH4 fluxes at the Wisconsin 

tower using measurements of C02 fluxes (by eddy 

correlation) and vertical profiles of C02 and CH4 . In 

contrast, our results for the North Carolina tower imply 

that the main regional CH4 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, 
'E • 4 llE a. llE llE llE 

& llE )II 

3 llE llE ll llE llE -c • 

ttt~~~t+ ~ ttE:~ Q) llE 

ii 2 

ell 

..... + CJ 

C\I 

0 0 

•••••••••• 0 () 0 llE 0 0! tf•o•• • 

• llE :0- 30 llE 

a. * • llE 

a. 

ttlttt+t~~· ·.··+tt+++ - 20 llE 

-

c 

Q) 

ii 10 * ell 

..... 

CJ 0 '<t llE llE llE llE llE llE llE llE 

llE llE llE llE 

I • • •• () -10 llE llE llE 

• 

:g: 40 • llE 

& 

ttWt~+tr "+th~~~ - llE c 

.Q:! 20 

"C 

ell + ..... 0 

CJ 0 

0 llE llE llE llE llE •• () • llE llE 

• • 

3 6 9 12 15 18 21 24 

Hour of Day (Local Time) 

Fig. 2.23. Statistics of vertical gradients (30 m-396 m) for C02, 

CH4, and CO, binned by hour, for December 1995. Symbols are 

the same as for Figure 2.22. 

profiles were scheduled on a weekly basis to investigate 

improved signal to noise from the increased data rate and 

to gain experience with the logistics of more frequent 

flights. Approximately 30 flights were made in 1995 

alone. An additional change was the use of a Cessna 

Model T2 I 0 aircraft beginning in June 1995 that increased 

the profile height to 7.9 km typical (9.1 km maximum). An 

example of a smoothed-curve fit to a profile altitude 

interval from the last 3 years of data is shown in Figure 

2.24. Although the plot shows a good seasonal cycle and 

trend, the irregularities in the fit and outliers in the data 

are a reminder of the difficulty in measuring continental air 

masses and the complexities of individual profiles. 

Also in 1995, collaboration began with the 

Aviaecocentre group in Moscow, Russia, to fly the CCG 

automated sampling system on a Russian Air Force twinturboprop AN-24. The project acquired six profiles 

between June and the end of the year at altitudes from 0.3 

to 6.1 km at a location about 100 km southeast of Moscow 

(54.9°N, 35.5°E). Meteorology and air mass back46 

1 

362 

,,. 

354 -

"' 

Jso ~--~

.,_, 9J .,, 94 "' '" 96 

YEAR 

Fig. 2.24. Carbon dioxide in samples obtained between 3-4 km 

above Carr, Colorado. 

trajectory data were also recorded. A typical profile from 

the Moscow site is shown in Figure 2.25. The Russian 

collaborators are working to develop a climatology for the 

site that can be correlated with the long-term carbon data. 

It is expected that this work will continue at least through 

August 1996. 

All of the sampling was performed with the automated 

sampling package developed by the Carbon Cycle Group. 

This package continues to evolve with experience and the 

testing of various components. A newer version of the 

package uses a more compact valve-actuator system so that 

each flask can be equipped with two valves and flushed 

more thoroughly and reliably than evacuated flasks. An 

internal Global Positioning System receiver was also 

included in the package for fully automatic operation. 

As part of this research and development effort, yearlong sample storage tests were performed on our 

"standard" 2.5-L glass flasks equipped with Teflon o-rings, 

to measure the trend of trace gas variability. Over a 12-

month period, the tests show a 0.4 ppm loss of C02, a 0.5 

ppb gain of CH4 (not significant), a 7.2 ppb gain of CO, a 

5. 7 ppb gain of H2 (not significant), and a 1.1 ppb loss of 

1 

1 

r '· 

0--~--~ " 0 ~----~ 

350 3 70 3QO 1700 1850 2000 80 215 350 

CO, (ppm) CH, (ppb) CO (ppb) 

Fig. 2.25. Vertical profiles of trace species over Yuchonov, 

Russia, near Moscow, on November 14, 1995. 
N20. These trends imply that the trace gas mixing ratio 

drift within the sample flask is easily less than the analysis 

limits if the samples are stored for a month or less, which 

is our normal operating procedure. 

2.8. DATA MANAGEMENT 

The long-term flask data management strategy adopted 

in 1992 (see Peterson and Rosson [ 1993] for a detailed 

description) maintains a sampling history for over 85,000 

ambient air samples and 23,000 special samples, and grows 

at a rate of - 7000 samples per year. Analysis and 

processing information is maintained for a suite of 

measurements that includes C02, CH4, CO, H2. SF6, NiO. 

and the stable isotopes of C02. The present database 

management strategy has several important features. While 

individual measurement projects retain a degree of 

independence, they are inextricably linked by way of the 

database, making multiple-species comparisons reliable 

and straightforward. Because the database employs UNIX 

text files as a storage format, database access does not 

require specialized software; files can be readily viewed 

using a variety of operating system commands and 

off-the-shelf software tools. Software written for the 

statistical and graphical analysis of flask measurement data 

can be species independent because the format is identical 

for different species, providing powerful tools to a greater 

number of flask programs. 

Database maintenance includes regular integrity checks 

designed to verify consistency throughout the database and 

to ensure the adequacy of security precautions. Although 

the current strategy is working well, it is anticipated that 

the approach will continue to evolve to meet the growing 

needs as both the sampling network expands and new 

projects are added. Recently, the need to log procedural 

changes or equipment modifications into a central 

repository was recognized so that complete histories of 

analytical systems or projects can be readily reconstructed. 

In response, software tools are being developed that will 

maintain a meta-database, e.g., a database containing 

information about the data, that will complement our 

existing strategy. 

2.9. DATA INTEGRATION 

Measurement records from the cooperative air sampling 

network are frequently used to constrain two- and threedimensional transport models that derive plausible 

source/sink scenarios of C02 [Tans et al., 1989; Ciais et 

al., l995a,b] and CH4 [Fung et al., 1991]. Interpretation 

of these scenarios is limited to large spatial scales and 

relatively short time scales due to the sparsity of sampling 

sites and the lack of temporal continuity among 

observations from different locations. In an attempt to 

reduce uncertainty in model-derived carbon budget 

scenarios due to the limitations of the observations, a 

procedure was developed that addresses these issues. Data 

extension [Masarie and Tans, 1995] attempts to extend the 

knowledge gained during a limited period of measurements 

beyond the period itself producing a record with no 

discontinuities. Extrapolated and interpolated values are 

derived using information about (l) the behavior of the 

record itself that can be described by its average seasonal 

47 

cycle and long-term trend, and (2) the average behavior of 

the record relative to other CMDL measurement records 

that are nearby in latitude. The result is a set of records 

containing measured data and extrapolated and 

interpolated values. To improve the spatial resolution of 

the observations, high precision C02 measurement records 

from many laboratories were extended and integrated with 

considerable effort to ensure compatibility with respect to 

methodology and calibration. 

During the past year, the Cooperative Atmospheric Data 

Integration Project for Carbon Dioxide was created with 

the ongoing aim of producing a globally-consistent C02 

database with unprecedented spatial resolution and 

temporal continuity. Flask and continuous data from the 

CMDL programs ·~omprise the bulk of the database, but 

measurement records contributed by other laboratories in 

Australia, Canada, China, France, Germany, Hungary, 

Italy, Japan, New Zealand, and the United States have 

enhanced the spatial and temporal coverage and have 

provided unique opportunities to compare overlapping 

independent records. This effort has resulted in the first 

release of GLOBALVIEW-C02, the most complete 

atmospheric C02 database yet available (Internet access by 

way of anonymous FTP to ftp.cmdl.noaa.gov, Path: 

ccg/co2/GLOBAL VIEW). 

With the framework of a global C02 database in place, 

ways to enhance the methods used to extend and integrate 

records from different laboratories are being explored. 

Data extension techniques will become more robust with 

the addition of updated and new measurements records. 

Data integration techniques will be enhanced by using 

information resulting from the comparisons of overlapping 

measurement records. Furthermore, frequent comparisons 

will improve the quality of the original data. Beginning in 

1991, for example, a subset of CMDL air samples collected 

at Cape Grim, Tasmania, was routed through the 

CSIRO/DAR Global Atmospheric Sampling Laboratory in 

Aspendale where they were analyzed for C02 and a host of 

other trace gas species [Peterson and Rosson, 1994 ]. This 

subset was then returned to Boulder where the same air 

was analyzed for a suite of trace gas species including 

C02• Results from this ongoing intercomparison will 

complement calibration and methodology considerations 

and further validate the integration of measurements from 

the two laboratories. Similar intercomparisons with other 

laboratories may be a necessary step to fully justify the 

merging of independent measurement programs. Data 

extension and integration techniques are now being applied 

to other trace gas species such as CH4, CO, and the stable 

isotopes of C02. It is anticipated that GLOBALVIEW-l 3C02 and GLOBALVIEW-CH4 will be available 

in the near future. 

2.10. THREE-DIMENSIONAL INVERSE MODELING 

In order to reconcile the contemporary budget of C02, 

and to understand by which processes this gas is absorbed 

by the ocean and/or by the terrestrial biosphere, it is of 

first importance to identify which regions are gaining or 

losing C02. In past years, several inverse calculations 

were performed to estimate the north/south gradient of net 

sources from the observed zonal mean concentrations 

[Tans et al., 1989; Enting et al., 1991; Ciais et al., 

1995a,b; Bousquet et al., 1996; Law et al., 1996]. The 

observational network has grown significantly in the last 
decade, and the present framework is designed to go 

beyond the interpretation of the north/south gradient. In 

the present work, the goal is to study the feasibility of a 

3-D inversion to assess the net fluxes over large regional 

scales. For this, about 25 continental and oceanic regions 

were defined. For each of them a forward simulation was 

made using a normalized source and the TM2 model 

[Heimann, 1995]. The linear combination of separate 

sources providing the best fit to the observations is 

calculated using the singular value decomposition 

technique. 

Before applying this method to real data, modeled data 

were defined from a forward simulation using a global flux 

distribution as realistic as possible [Ramonet, 1994]. 

Different subsets of these modeled data were used to 

recalculate the initial flux distribution over each postulated 

source. This methodology allows study of the influence of 

the surface and/or tropospheric network resolution and the 

contribution of new monitoring sites. The first results 

showed that the annual fluxes were resolved at ±0.2 GtC 

yr-I when a network of as few as 144 regularly spaced 

surface sites was used. The errors of the deduced fluxes 

strongly increase when the number of regularly spaced 

surface sites is reduced to 50. Using the same locations as 

the CMDL network, there are additional problems due to a 

lack of an observational site over large continental areas, 

especially over South America. Preliminary results show 

that the error for this region can be largely reduced by 

adding a surface site in Central Brazil. 

In the work described previously, the implicit 

assumption of perfectly simulated transport is made. It is 

known that simulation of the transport is one of the sources 

of uncertainty in inverse calculations [Rayner and Law, 

1995]. To take into account the error induced by the 

transport models, the NCAR Community Climate Model 

(CCM2) will be used to calculate the modeled data and the 

TM2 for the normalized sources. There will then be an 

estimate of how sensitive the results are to the transport 

calculations of different models. In the near future plans 

are to use the additional information provided by isotopic 

ratios l 3C02/l 2C02 and to apply the inverse method to the 

measurements smoothed in time. 

2.11. REFERENCES 

Bakwin, P.S., P.P. Tans, and P.C. Novelli, Carbon monoxide 

budget in the Northern Hemisphere, Geophys. Res. Lett., 21, 

433-436, 1994. 

Bakwin, P.S., P.P. Tans, C. Zhao, W. Ussler, III, and E. Quesnell, 

Measurements of carbon dioxide on a very tall tower, Tel/us, 

47B, 535-549, 1995. 

Bousquet, P., P. Ciais, P. Monfray, Y. Balkanski, M. Ramonet, 

and P.P. Tans, Influence of two different atmospheric transport 

models on inferring sources and sinks of atmospheric C02, 

Tel/us, in press, 1996. 

Ciais, P., P.P. Tans, J.W.C. White, M. Trolier, R.J. Francey, J.A. 

Berry, D.R. Randall, P.J. Sellers, J.G. Collatz, and D.S. 

Schimel, Partitioning of ocean and land uptake of C02 as 

inferred by 313C measurements from the NOAA CMDL global 

air sampling network, J. Geophys. Res., 100, 5051-5070, 

1995a. 

Ciais, P., P.P. Tans, M. Trolier, J.W.C. White, and R.J. Francey, 

A large northern hemisphere terrestrial C02 sink indicated by 

the 13C/12C ratio of atmospheric C02, Science, 269, 1098-

1102, 1995b. 

Davis, K.J., P.S. Bakwin, C. Zhao, W.M. Angevine, and D.F. 

Hurst, Monitoring regional forest-atmosphere exchanges of 

48 

carbon dioxide, in Proceedings of the 22nd Conference on 

Forest and Agricultural Meteorology, American 

Meteorological Society 76th Annual Meeting, January 1996, 

Atlanta, Georgia, pp. 302-305, 1996. 

Dlugokencky, E.J., L.P. Steele, P.M. Lang, and K.A. Masarie, 

Atmospheric methane at Mauna Loa and Barrow observatories: 

Presentation and analysis of in situ measurements, J. Geophys. 

Res., 100, 23,103-23,113, 1995. 

Dlugokencky, E.J., K.A. Masarie, P.M. Lang, P.P. Tans, L.P. 

Steele, and E.G. Nisbet, A dramatic decrease in the growth rate 

of atmospheric methane in the northern hemisphere during 

1992, Geophys. Res. Lett., 21, 45-48, I 994a. 

Dlugokencky, E.J., L.P. Steele, P.M. Lang, and K.A. Masarie, 

The growth rate and distribution of atmospheric methane, J. 

Geophys. Res., 99, 17021-43, 1994b. 

Dutton, E.G., and J.R. Christy, Solar radiative forcing at selected 

locations and evidence for global lower tropospheric cooling 

following the eruptions of El Chich6n and Pinatubo, Geophys. 

Res. Lett., 19, 2313-2316, 1992. 

Elkins, J.W., D.W. Fahey, J.M. Gilligan, G.S. Dutton, T.J. 

Baring, C.M. Volk, R.E. Dunn, R.C. Myers, S.A. Montzka, 

P.R. Wamsley, A.H. Hayden, J.H. Butler, T.M. Thompson, 

T.H. Swanson, E.J. Dlugokencky, P.C. Novelli, D.F. Hurst, 

J.M. Lober!, S.J. Cicora, R.J. McLaughlin, T.L. Thompson, 

R.H. Winkler, P.J. Fraser, L.P. Steele, M.P. Lucarelli, Airborne 

gas chromatograph for in situ measurements of long lived 

species in the upper troposphere and lower stratosphere, 

Geophys. Res. Lett., 23(4), 347-350, 1996. 

Enting, l.G., and J.V. Mansbridge, Latitudinal distribution of 

sources and sinks of C02: Results of an inversion study, 

Tel/us, 43(B), 156-170, 1991. 

Francey, R.J., P.P. Tans, C.E. Allison, l.G. Enting, J.W.C. White 

and M. Trolier, Changes in oceanic and terrestrial uptake since 

1982, Nature, 373, 326-330 (l 995a). 

Francey, R.J., C.E. Allison, L.P. Steele, R.L. Langenfelds, E.D. 

Welch, J.W.C. White, M. Trolier, P.P. Tans, and K.A. Masarie, 

Intercomparison of stable isotope measurements of C02, in 

Climate Monitoring and Diagnostics laboratory, No. 22: 

Summary Report 1994, edited by J.T. Peterson and R.M. 

Rosson, pp. 106-110, NOAA Environmental Research 

Laboratories, Boulder, CO, 1995. 

Fung, I., J. John, J. Lerner, E. Matthews, M. Prather, L.P. Steele, 

and P.J. Fraser, Three-dimensional model synthesis of the global 

methane cycle, J. Geophys. Res., 96, 13,033-13,065, 1991. 

Gaudry, A., M. Trolier, C. Flehoc, P. Ciais, S.G. Jennings and P. 

Monfray, A preliminary comparison of 313C measurements in 

C02 from Mace Head, Ireland, in Climate Monitoring and 

Diagnostics laboratory No. 24: Summary Report 1994-1995, 

edited by D. Hofmann, J.T. Peterson, and R.M. Rosson, this 

issue. 

Gemery, P.A., Investigation of the sources of deviation in oxygen 

isotope measurements made on atmospheric carbon dioxide, 

M.A. thesis, 157 pp., Univ. of Colorado, Boulder, CO, 1993. 

Hegg, D.A., L.F. Radke, P.V. Hobbs, R.A. Rasmussen, and P.J. 

Riggan, Emissions of some trace gases from biomass fires, J. 

Geophys. Res., 95, 5669-5675, 1990. 

Heimann, M., The global atmospheric tracer model TM2, 

Technical Report No. JO, 53 pp., edited by D. 

Klimarechenzentrum, Max-Planck-Institut fiir Meteorologie, 

Germany, 1995. 

Hogan, K.B. and R.C. Harriss, Comment on "A dramatic decrease 

in the growth rate of atmospheric methane in the northern 

hemisphere during 1992," by E.J. Dlugokencky et al., 

Geophys. Res. Lett., 21, 2445-2446, 1994. 

Keeling, C.D., T.P. Whorf, M. Wahlen, and J. van der Plicht, 

Interannual extremes in the rate of rise of atmospheric carbon 

dioxide since 1980, Nature, 375, 666-669 (1995). 

Lang, P.M., L.P. Steele, L.S. Waterman, R.C. Martin, K.A. 

Masarie, and E.J. Dlugokencky, NOAA/CMDL atmospheric 

methane data for the period 1983-1990 from shipboard flask 

sampling, NOAA Tech. Memo. ERL CMDL-4, 88 pp., 

Environmental Research Laboratories, Boulder, CO, 1992. 
Law, R.M., and I. Simmonds, The sensitivity of deduced C02 

sources and sinks lo variations in transport and imposed 

surface concentrations, Tellus, in press, 1996. 

Masarie, K.A., L.P. Steele, and P.M. Lang, A rule-based expert 

system for evaluating the quality of long-term in situ, gas 

chromatographic measurements of atmospheric methane, 

NOAA Tech. Memo. ERL CMDL-3, 37 pp., Environmental 

Research Laboratories, Boulder, CO, 1991 . 

Masarie, K.A., and P.P. Tans, Extension and integration of 

atmospheric carbon dioxide data into a globally consistent 

measurement record, J. Geophys. Res. 100, 11,593-11,610, 1995. 

Novelli, P.C., L.P. Steele, and J.W. Elkins, The development and 

evaluation of a gravimetric reference scale for measurements 

of atmospheric carbon monoxide, J. Geophys. Res., 96, 

13,109-13,121, 1991. 

Novelli, P.C., P. Steele, and P.P. Tans, Mixing ratios of carbon 

monoxide in the troposphere, J. Geophys. Res., 97, 20,731-

20, 750, I 992. 

Novelli, P.C., J.E. Collins, Jr., R.C. Myers, G.W. Sachse, and 

H.E. Scheel, Re-evaluation of the NOAA/CMDL carbon 

monoxide reference scale and comparisons to CO reference 

gases at NASA-Langley and the Fraunhofer Institute, J. 

Geophys. Res., 99, 12,833-12,839, 1994. 

Peterson, J.T., and R.M. Rosson, Climate Monitoring and 

Diagnostics laboratory, No. 21, Summary Report 1992, 

Environmental Research Laboratories, Boulder, CO, 131 pp., 

1993. 

Peterson, J.T., and R.M. Rosson, Climate Monitoring and 

Diagnostics laboratory, No. 22, Summary Report 1993, 

Environmental Research Laboratories, Boulder, CO, 152 pp., 

1994. 

Ramonet, M., Modelisation du transport atmospherique du 

dioxyde de carbone dans !'hemisphere sud, PhD. thesis, Univ. 

of Paris VII, 295 pp., 1994. 

49 

Rayner. P.J., and R.M . Law, A comparison of modelled responses 

to prescribed C02 sources, Tech. Paper No. 36. CSIRO/DAR 

Australia, 84 pp., 1995. 

Reichle, H.G., Jr., V .S. Connors, J .A. Holland, R.T. Sherrill, 

H.A. Wallio, J.C. Casas, E.P. Condon, B.B. Gormsen, and W. 

Seiler, The distribution of middle tropospheric carbon 

monoxide during early October 1994, J. Geophys. Res., 95, 

9845-9856, 1990. 

Seiler, W., H. Giehl, and H. Ellis, A method for the monitoring 

of background CO and the first results of continuous 

registrations on the Mauna Loa Observatory, WMO Spec. 

Environ. Rep.. JO, 31-39, World Meteorological 

Organization, Geneva, 1976. 

Tans, P.P., T.J. Conway, T. Nakazawa, Latitudinal distribution 

of the sources and sinks of atmospheric carbon dioxide 

derived from surface observations and an atmospheric 

transport model, J. Geophys. Res., 94(4). 5151-5172, 1989. 

Tans, P.P, I.Y. Fung, T. Takahashi, Observational constraints of 

the global atmospheric C02 budget, Science, 247, 1431-1438, 

1990. 

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., 94, 8549-

8576, 1989. 

Trolier, M .. J.W.C. White, P.P Tans, K.A. Masarie and P.A. 

Gemery, Monitoring the isotopic composition of atmospheric 

C02: Measurements from the NOAA global air sampling 

network, J. Geophys Res., in press, 1996. 

Weeks, I.A., I.E. Galbally, P.J. Fraser, and G. Matthews, 

Comparison of the carbon monoxide standards used at Cape 

Grim and Aspendale, in, Baseline Atmospheric Program 

1987, edited by B.W. Forgan and G.P. Ayers, pp. 21-25, 

Australian Government Department of Science and 

Technology, Canberra, Australia, 1989. 
3. Aerosols and Radiation 

3.1. AEROSOL MONITORING 

J. OGREN (EDITOR), S. ANTHONY, J. BARNES, 

M. BERGIN, W. HUANG, L. MCINNES, C. MYERS, 

P. SHERIDAN, S. THAXTON, AND J. WENDELL 

3.1.1. SCIENTIFIC BACKGROUND 

Aerosol particles affect the radiative balance of earth 

both "directly," by scattering and absorbing solar and 

terrestrial radiation, and "indirectly," through their action 

as cloud condensation nuclei (CCN) with subsequent 

effects on the microphysical and optical properties of 

clouds. Evaluation of the climate forcing by aerosols, 

defined here as the perturbation of the earth's radiation 

budget induced by the presence of airborne particles, 

requires knowledge of the spatial distribution of the 

particles, their optical and cloud-nucleating properties, and 

suitable models of radiative transfer and cloud physics. 

Obtaining a predictive relationship between the aerosol 

forcing and the physical and chemical sources of the 

particles additionally requires regional and global-scale 

chemical process, and physical transformation and 

transport models for calculating the spatial distributions of 

the major chemical species that control the optical and 

cloud-nucleating properties of the particles. Developing 

and validating these various models requires a diverse suite 

of in situ and remote observations of the aerosol particles 

on a wide range of spatial and temporal scales. 

Aerosol measurements began at the CMDL baseline 

observatories in the mid- l 970s as part of the Geophysical 

Monitoring for Climate Change (GMCC) program. The 

objective of these "baseline" measurements was to detect a 

response, or lack of response, of atmospheric aerosols to 

changing conditions on a global scale. Since the inception 

of the program, scientific understanding of the behavior of 

atmospheric aerosols has improved considerably. One 

lesson learned is that residence times of tropospheric 

aerosols are generally less than 1 week and that human 

activities primarily influence aerosols on regional/ 

continental scales rather than global scales. In response to 

this increased understanding and to more recent findings 

that anthropogenic aerosols create a significant 

perturbation in the earth's radiative balance on regional 

scales [Charlson et al., 1992; National Research Council, 

1996], CMDL expanded its aerosol research program to 

include regional aerosol monitoring stations. The goals of 

this regional-scale monitoring program are to characterize 

means, variabilities, and trends of climate-forcing 

properties of different types of aerosols, and to understand 

the factors that control these properties. 

A primary hypothesis to be tested by NOAA's aerosol 

research program is that the climate forcing by 

anthropogenic sulfate will change in response to future 

changes in sulfur emissions. The forcing is expected to 

decrease in and downwind of the United States as a result 

of emission controls mandated by the Clean Air Act, while 

continued economic development in China and other 

developing countries is expected to lead to an increased 

forcing in and downwind of those areas. Testing this 

hypothesis will require a coordinated research program 

50 

involving modeling, monitoring, process, and closure 

studies. This report describes the observations that CMDL 

is conducting towards this goal. 

CMDL's measurements provide ground truth for satellite 

measurements and global models, as well as key aerosol 

parameters for global-scale models (e.g., scattering 

efficiency of sulfate particles, hemispheric backscattering 

fraction). An important aspect of this strategy is that the 

chemical measurements are linked to the physical 

measurements through simultaneous, size-selective 

sampling, which allows the observed aerosol properties to 

be connected to the atmospheric cycles of specific 

chemical species. 

3.1.2. EXPERIMENTAL METHODS 

Extensive aerosol properties monitored by CMDL 

include the total particle number concentration (N101). 

aerosol optical depth (0), and components of the aerosol 

extinction coefficient at one or more wavelengths (total 

scattering CJsp• backwards hemispheric scattering CJbsp• and 

absorption CJ3 p). At the regional sites, size-resolved 

impactor and filter samples (submicrometer and 

supermicrometer size fractions) are obtained for 

gravimetric and chemical (ion chromatograph) analyses. 

All size-selective sampling, as well as the measurements of 

the components of the aerosol extinction coefficient at the 

regional stations, is performed at a low, controlled relative 

humidity (<40%) to eliminate confounding effects due to 

changes in ambient relative humidity. Data from the 

continuous sensors are screened to eliminate contamination 

from local pollution sources. At the regional stations, the 

screening algorithms use measured wind speed, direction, 

and total particle number concentration in real-time to 

prevent contamination of the chemical samples. 

Algorithms for the baseline stations use measured wind 

speed and direction to exclude data that are likely to have 

been locally contaminated. 

Prior to 1995, data from the baseline stations were 

manually edited to remove spikes from local 

contamination. For the 1995 baseline data an automatic 

editing algorithm was applied in addition to manual editing 

of local contamination spikes. For the baseline stations 

(Barrow (BRW), Mauna Loa (MLO), South Pole (SPO), 

and Samoa (SMO)), as well as Sable Island, data are 

automatically removed when the wind direction is from 

local sources of pollution (such as generators and 

buildings) as well as when the wind speed is less than a 

threshold value (0.5-1 ms-I). In addition, Maun a Loa data 

for upslope conditions (1800-1000 UTC) are excluded 

since the airmasses do not represent "background" free 

tropospheric air for this case. A summary of the data 

editing criteria is given in Table 3.1. 

Integrating nephelometers are used to determine the light 

scattering coefficient of the aerosol. These instruments 

operate by illuminating a fixed sample volume from the 

side and observing the amount of light that is scattered by 

particles and gas molecules in the direction of a 

photomultiplier tube. The instrument integrates over 

scattering angles of 7-170° . Depending on the station, 

measurements are performed at one, three, or four wave-
TABLE 3 .1. Data Editing Summary for NOAA 

Baseline and Regional Stations 

Station Editing 

South Pole a,b,c 

Samoa a,b,c 

Mauna Loa a,b,c,d 

Barrow a,b,c 

Sable Island a,b,c 

Niwot Ridge a 

Bondville a 

WD; Wind direction 

Clean Sector 

0° < WD < 110°, 330° < WD < 360° 

0° < WD < 165°, 285° < WD < 360° 

90° < WD < 270° 

0° < WD < 130° 

0° < WD < 35° , 85° < WD < 360° 

a-Manual removal of local contamination spikes 

b-Automatic removal of data not in clean sector 

c-Automatic removal of data for low wind speeds 

d-Removal of data for upslope wind conditions 

lengths in the visible and near-infrared. Newer 

instruments allow determination of the hemispheric 

backscattering coefficient by using a shutter to prevent 

illumination of the portion of the instrument that yields 

scattering angles less than 90°. A particle filter is inserted 

periodically into the sample stream to measure the light 

scattered by gas molecules, which is subtracted from the 

total scattered signal to determine the contribution from 

the particles alone. The instruments are calibrated by 

filling the sample volume with a gas of known scattering 

coefficient; carbon dioxide (C02) is used for high 

sensitivity instruments, while dichlorodifluoromethane 

(CFC-12) is used for the few single-wavelength, lower 

sensitivity instruments still in use. 

The aerosol light absorption coefficient is determined 

with a continuous light absorption photometer. This 

instrument continuously measures the amount of light 

transmitted through the filter. The rate of decrease of 

transmissivity, divided by the sample flow rate, is directly 

proportional to the light absorption coefficient of the 

particles. Newer instruments have been calibrated in terms 

of the difference of light extinction and scattering in a 

long-path extinction cell for laboratory test aerosols. 

Instruments at the baseline stations ("aethalometers") have 

been calibrated by the manufacturer in terms of the equivalent amount of black carbon, from which the light 

absorption coefficient is calculated assuming a mass absorption efficiency of the calibration aerosols of 10 m2 g- t. 

Particle number concentration is determined with a CN 

counter that exposes the particles to a high supersaturation 

of butanol vapor. This causes the particles to grow to a 

size where they can be detected optically and counted. The 

instruments in use have lower particle-size detection limits 

of l 0-20 nm diameter. 

Summaries of the extensive measurements obtained at 

each site are given in Tables 3.2 and 3.3. Table 3.4 lists 

the intensive aerosol properties that can be determined 

from the directly-measured extensive properties. These 

properties are used in chemical transport models to 

determine the radiative effects of the aerosol 

concentrations calcuated by the models. Inversely, these 

properties are used by algorithms for interpreting satellite 

remote-sensing data to determine aerosol amounts based on 

measurements of the radiative effects of the aerosol. 

Information and data from the aerosol group at CMDL 

are available on the Internet via FTP and World Wide Web 

servers. Recently processed data, file format specifications, documents summarizing data processing and flow, 

and clean processed data presented in hourly-averaged files 

for all years of station operation are available via 

anonymous FTP to ftp.cmdl.noaa .gov, directory "aerosol. " 

In addition to the above, the CMDL World Wide Web 

server at http://www.cmdl.noaa.gov supplies online plots 

of recently processed aerosol data and hypertext links to 

various related documents (including this one). 

3.1.3. ANNUAL CYCLES 

The annual cycles of selected extensive and intensive 

properties are illustrated in Figure 3.la-d. The data are 

presented in the form of box-whisker plots that summarize 

the distribution of values: the box ranges from the lower to 

upper quartiles, with a central bar at the median value, 

while the whiskers extend to the 5th and 95th percentiles. 

The statistics are based on hourly averages of each 

parameter for each month of the year, as well as for the 

entire year ("ANN"). 

In general, changes in long-range transport patterns 

dominate the annual cycles. For BRW, the highest values 

of a sp are observed during the spring because of the longrange transport of pollution from lower latitudes ("Arctic 

haze"). The BRW CN record shows a more variable 

semiannual cycle, with a maximum that usually coincides 

with the maximum in Osp and a secondary maximum in late 

summer or early fall. The secondary maximum in late 

summer is thought to be caused by local oceanic emissions 

of dimethyl sulfide (DMS) gas that are eventually 

converted to sulfate aerosol [Radke et al., 1990]. For 

MLO, the highest Osp values occur in the springtime, 

TABLE 3.2. CMDL Baseline Aerosol Monitoring Stations (Status as of January 1996) 

Baseline Tropical Free 

Category Baseline Arctic Troposphere Baseline Marine Baseline Antarctic 

Location Point Barrow Mauna Loa American Samoa South Pole 

Status Operational 1976 Operational 1974 Operational 1977 Operational 1974 

Sample RH Uncontrolled Uncontrolled Uncontrolled Uncontrolled 

Sample Size Fractions Uncontrolled Uncontrolled Uncontrolled Uncontrolled 

Optical measurements cr5p(41..), cr3P(ll..) cr,P(41..), a.pt..), cr.r< D .. ), li(61..) cr5p(41..) cr.P(41..) 

Microphysical measurements NlOl N101 N101 N101 

Chemical measurements none none none none 

51 
TABLE 3.3. CMDL Regional Aerosol Monitoring Sites (Status as of January 1996) 

Perturbed Perturbed 

Category Perturbed Marine Continental Continental Clean Continental Clean Marine 

Location Sable Island, Bondville, Illinois K'puszta, Niwot Ridge, Colorado Cheeka Peak, 

Nova Scotia Keszcemet, Hungary Washington 

Designator WSA BND KPO NWR CPO 

Latitude +43 .933 +40.053 +46.967 +40.036 +48.30 

Longitude +060.007 +088.372 -019.550 +105 .534 +124.62 

Elevation (m) 5 230 180 3020 480 

Responsible NOAA/CMDL NOAA/CMDL U. Veszprem, NOAA/CMDL U. Washington 

institute Hungary 

Collaborating Atmospheric University of NOAAICMDL U. Colorado, Boulder; NOAA/CMDL 

institute Environment Illinois; Illinois Colorado State U., 

Service, Canada, State Water Fort Collins 

NOAA/PMEL Survey 

Status Operational Operational Operational Site feasibility Operational, 

August 1992 July 1994 September 1994 measurements began May 1993 

November 1993 

Sample RH RH< 40% RH< 40% RH< 40% Uncontrolled RH< 40% 

Sample Size D <I μm D <I μm D <I μm Uncontrolled D <I μm 

Fractions L < D < 10 μm l<D<LOμm l<D<IOμm 

Optical a,P(3A.), a.p( I A.), a,p(IA.) a,p( I A.), a 0P( I A.), a,p(IA.) a,p(3A.), ahsp(3A), 

measurements absp(3A.), 1>(41..) 1>(41..) a.P(IA.) 

Microphysical N101 N101 NlOl N101> n(D) N1w n(D) 

measurements 

Chemical Major ions, mass Major ions, mass Major ions None Major ions, mass 

measurements 

TABLE 3.4. Intensive Aerosol Properties 

Derived From the CMDL Network 

Properties Description 

d The angstrom exponent, defined by the power-law <!sp oc )..-d. describes the wavelength-dependence of scattered light. In 

the figures below, d is calculated from measurements at 550 and 700 nm wavelength. Situations where the scattering is 

dominated by submicrometer particles typically have values around 2, while values close to 0 occur when the scattering 

is dominated by particles larger than a few microns in diameter. 

iii11 The aerosol single-scattering albedo, defined as <!spl(<!ur + cr,p). describes the relative contributions of scattering and 

absorption to the total light extinction. Purely scattering aerosols (e.g., sulfuric acid) have values of I, while very 

strong absorbers (e.g., elemental carbon) have values around 0.3. 

g, b Radiative transfer models commonly require one of two integral properties of the angular distribution of scattered light 

(phase function): the asymmetry factor g or the hemispheric backscatter fraction b. The asymmetry factor is the cosineweighted average of the phase function, ranging from a value of - I for entirely backscattered light to +I for entirely 

forward-scattered light. The hemispheric backscatter fraction b is IJhsrl<!sr· 

a 1 The mass scattering efficiency for species i, defined as the slope of the linear regression line relating IJsr and the mass 

concentration of the chemical species, is used in chemical transport models to evaluate the radiative effects of each 

chemical species prognosed by the model. This parameter has typical unites of m2 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 μm 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 O'sp 

levels observed in the late winter are due to the long-range 

52 

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]. 
2000 ,.--- -- -- --~19=1=6--: 995=--i 

BRW 

0 

llOO 

f~ 1977-1995 

600 

~ ~ ~ ~ ~ ~ ~ $ ~ ~ : ,..._ 

"' e 400 

~ 

200 

0 

llOO SPO 1974-1995 

- 600 - ,..._ :d "" - e 400 

e $ ~ ~- ~ 

~ 200 

it:i ... ... ~ ... Q 0 ANN JAN MAR MAY JUL SEP NOV 

Fig. 3.1 a. 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, O'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 

53 

5'10 ~--------- -~1994=--:1::995=-.J 

BNO 

6000 NWR 1994-1995 

c:~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ f ot......:... ~~~~~ ~~~~ ~~ 

WSA 1992-1995 

0 

JAN MAY JUL SEP NOV ANN 

Fig. 3.1 b. Annual cycles of CN concentration for regional 

stations at Bondville, Illinois (BND), Niwot Ridge, Colorado 

(NWR), and Sable Island, Nova Scotia (WSA). 

in 1990; 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], O'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 O'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, highsensitivity 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 (cr5p) and the 

angstrom exponent for the 550/700 nm wavelength pair from 

January I, 1994, to December 31, 1995. Significant day-today 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, 
l"-0 1974-1995 

;~~~~l~J~~ ~ 40 

~ ~ J ~ ~ ~ ~ ~ rl1 

o.__ ___ ___________ __, 

2.0 SPO 

11.01- I 1.5~1 

5~ ~ 

0.0 

200 BNO 1994-1995 

40 ~-------- -------. 

NWR 1994-1995 

-

100 

WSA 

ao~ 

::~ Or__ __~ ___________~ H d _ __, 

JAN MAR MAY .AJl SEP NOV ANN 

Fig. 3.1 c. Annual cycles of cr,P at 550 nm for baseline stations 

at BRW, MLO, SMO, and SPO and for regional stations at BND, 

NWR, and WSA. 

54 

4 BRW 1976-1995 

QI-

-Ir__ _ _ _____ _ _ ____ _ ___, 

i.o SM0 -- --19-n--1 99 , -., 

0.5 1-

1 ··~~ --0.!i -

-1 .0 i__ ___ ____ _______ __, 

1979-1996 

WSA 1992-1995 

1~~~~ 0.0 ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ JAN MAY SEP NOV 

Fig. 3.ld. Annual cycles of angstrom exponent (a, 5501700 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 
IOO BRW 

SPO 

I • \ I 'I\ 

·,,i 1' 

~ ,. I\ i ~ 

.i \ i ' I l • 

j ,~ . . 

f'. _; SEP 

; \ ........ '. ,.,·' 

i · 

I Nf:N 

-... -... - OL..~~~_:.__- '~-------~- -----~ .._~ ~~ ~~~ 

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). 

properties measured at Sable Island: the angstrom 

exponent (5501700 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 

N101 and Osp (550 nm, Dp < I μm) are below the lower 

quartile for the entire data set, "dirty" conditions in which 

N101 and Osp are above the upper quartile, and all "other" 

periods that do not meet the previously defined criteria (for 

example periods with low N101 and high Osp 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 sizesegregated 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, 

SS 

30 

BAW MAR 

20 ;'· .... . ~ ,,·, '· I '. JUN "' , ' \ /'. e , I · ..... / •11 ' .... . - . , 

' ,·-·- ·" ~ ·•· 

10 />H4 

0 ------------ ....... ' -

8 

MLO APR 

4 .., DEC 

e ....... 

/". ,. '. ,., ~ -·' \ \ 2 / v />H4 

.... _,,. __ ____ 0 

30 

SMO SEP 

20 MAY .., ' ·, e 

~ I ---- \ 

10 \"' />H4 

0 

0.8 

SPO SEP 

0.6 

~ 

.., NO'/ 

e o.4 ~ 

0.2 />H4 

------ \ 

- - , 

- 0.0 

1974 1979 1984 1990 1995 2000 

Fig. 3.2b. Long-term trends Osp at 550 nmfor baseline stations, 

showing months with the lowest and highest median values and 

annual averages. 

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 Osp for the submicrometer aerosol are consistently 

higher at Bondville than at Sable Island (Figure 3.1 b,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) demonstrates 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 
3 BAW ,, • 

I I 

I 

' , ' 

DEC 

SEP 

MAY 

MAY 

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. 

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 I μm aerodynamic diameter are sampled). Addi56 

1000 

7SO 

, 

.[ 500 

z 

0 

250 

0 

0 

• 

3 

'e 

~2 

• " 

r--~~~~~~~~~....-~---,-~~~~~~~~ 

I )1~ ~111lJ1 ~~ I 11/111 JI ~11 0 200 o400 600 Days since January 1. 1994 

Fig. 3.3a. Daily means of aerosol properties (CN concentration, 

<1sp• and a) for SPO for 1994, 1995. 

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 
2000 6000 

1500 •500 , 

A~J , l 1000 !_ 3000 

W~~~A~ z z 0 0 

500 1500 

0 0 

0 200 400 600 0 200 400 600 

16 

12 

200 400 

~~l 600 ~·J ~ '~ 4 L..-----~----' 

0 200 400 600 

1995. 0

0 200 400 600 

Days since Januaiy 1, 1994 

2000 

Fig. 3.3e. Daily means of aerosol properties for WSA for 1994, 1995. 

0 200 400 600 

• 48 ~-.----------i 

r 

o 

1~r11~~1l ~1l1 ~\111r'1rl\~~i,1l11 I~ N~ ~: ~~~~ ~ ~J ' 0 200 400 600 0 200 400 600 

Days since January 1, 1994 

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 
1.40-104----------------

,... 

! 1.00-103 

z 

0 

3.so-10

O'--

3 

------------------~ 

~~~ 200 

ISO 

'e 

~ 100 

t 

0 

0 200 .00 600 

OL-_______ _:_.:.:..._;__ ______ :....;.::'"-'--"-' 

0 200 600 

Fig. 3.3g. Daily means of aerosol properties for BND 1994, 1995. 

3 

I 2~ $ : 

-

j 1~ 

0 

WSAclean WSA~ WSA dirty 

1.0 

I o.a 

¢ $ ! 0.6~ 

~ ~ 04~ u. 0.2 ~ 

-

-

-

0.0 

WSAclean WSAother WSAdirty BND 

0.3 

~ !!! 0.2 u. $ i 0.1 

$ 

cZ 

0.0 

WSA clean WSAoll>er WSAdirty 

Fig. 3.4. Aerosol intensive properties (;i, 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. 

58 

c 3 y • 2.81x - 0.30 12 , ... 0.783 

)( n M 1021 CD 

~ u '. 2' 

< 0 

0.0 0.2 0.4 0.6 0.8 1.0 

Fine/Total Scattering Ratio 

Fig. 3.5. Linear regression of ;i versus the fraction of 

submicrometer scattering for WSA. 

3.6 shows the vertical profiles measured over Colorado of 

a, ii>0 , b, and O'sp (denoted by Bsp 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 &0 , b, and a throughout the lower troposphere. 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 parameters 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 O'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 (ii>o, b, a) are 

relatively constant in spite of large changes in the primary 

measured variables. 

1000......----,..---~--------,..-----. 

8000 

1000 

0.0 

• 

0.5 1.0 

• 

• I . 

1.5 

• 

• 

• 

2.0 

--llingl• lalller albedo -+- bac:Motal lalller 

-+-Mgstrom e~ • Bap (1E-S kn) 

2.5 

Fig. 3 .6. Vertical profile of aerosol properties over Colorado, 

June 6, 1995. 
5000 

i 4000 

i:. 

1000 • "'· 

0.0 0.5 1.0 1.5 2.0 2.5 

-+-single scatter albedo -+- backllotal scatter 

-+-Angstrom exponent • Bsp (1 E-4 hn) 

Fig. 3.7. Vertical profile of aerosol properties over the 

southeastern United States July 1, 1995. 

Finally, Figure 3.9 shows the latitudinal variability that 

was observed in the boundary layer over the midwestern U.S. (Tennessee-Indiana), where the values of &0 

and b are identical to the boundary layer values shown in 

Figure 3.8. Slightly more variability is seen in the singlescattering 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 

al ways below 0.13 except for the one vertical profile over 

Colorado. Although it is difficult to draw general 

conclusions from a I-month study, the results suggest that 

ground-based measurements of the light scattering and 

absorption coefficients of submicrometer, continental 

--· • I • I I 

o.ol-.....J~~....t.=-=:::o::::!;;::::::::;::::::::;:~::::;:!::::i~~~i==1::::~·..._........J 

-105 -100 

--single scatter albedo 

-+-Angstrom exporoet"( 

-95 -90 

longitude -+- backllolal scatter 

__._ Bsp ( 1 E-4 /m) 

Fig. 3.8. East-west transect, Colorado to Tennessee, June 19, 

1995. Open symbols denote free tropospheric measurements. 

59 

2.5 

2.0 

• ...-. ~ 

1.5 

1.0 

0.5 

0.0 

35 36 37 38 39 

latitude 

-+-single scatter albedo -+- backllo\al scatter 

-+- AngstrOm e)(f onenl __.,,_ Bsp (1E-4 hn) 

Fig. 3.9. North-south transect, midwest United States July 10, 

1995. 

particles can be used to derive values of the singlescattering 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 (JABS) 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 JABS 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 JABS data in 

the fall of 1994 may be observed in Figure 3.11 at 532 nm 

and 694 nm. The 532-nm data are from the new Nd:Y AG 

0.1 - - - --------- - - - ---

'C' 

~ 0.01 · · ·· · · · · · · · · ···· ··· · ·· · · · ··· · ·--·- · ·-·· ····- -· -······ 

I 0.001 

&! 

§ 

i»0.0001 

c( 

~ -· ·· · .. .. .. ·- . "lltw. ·- 1 N,.,....... 

I El Chchon Ruiz N~lra Pil1f\lbo 

[~ ; \ / K<111 I 

1E-05~......,. ....... .__~~~· ...... -.__~ AA~~*.-'-' ___.94 

80 82 84 86 88 90 92 

Year 

96 

Fig. 3.10. Integrated aerosol backscatter for 1980-1995 at 694 

nm (ruby lidar) from 15.8 to 33 km. 
0.00035 .------------.---------;::== =-i 

~0.00030 . . :::::.. 

Qj 0.00025 .. 

~ l;l 0.00020 ~ 

0 &l 0.00015 

g 0.00010 

e 

~ 0.00005 

· 532 nm 

·· · ··· · · 694 nm --

0.00000 --;--;--+-+--+--+--;--;=;r-+-+-+-+-+--+-+--+-+--+-->--+--<-+-

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. Preliminary 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. DUTION (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 

60 

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 satellitebased 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 measurements, 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. 
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 μm to 

2.8 μm 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 Dutton 

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 wa~i:r vapor. Previous studies [Bodhain~ 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 Chich6n in 

1982, Mt. Pinatubo in 1991, and an annual oscillation 

caused primarily by the springtime transport_ of AsiJln ___ aer<~sol 

over the -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 

61 

03r--r-...--.-~~-.-~~--.--.---,~.--.--.,..--...-.-....,....-,--~~ 

02 

0 1 .I\, /\ 03 1--+-+-~-+--:--+--+-~-t--t--t~t-'--'-+-+-~-+-~',....:....;--1 

0 2 ML0(19DEGN) 

01 

03 P'"""'~.i...=-=~;__,__~~~+.::.:ic::::;.!:1oo>:.::~;.,...___.:~"""',;;,_"--I 

0 2 

0 1 

0 . 2 SPO (90 DEG.SI 

0 1 

0 0 ..r-- __.--J--. 

77 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 

0.95 ' • • " • 

0.94 : 1"!<><•11CllJ.!nll!;!i•L i-~t---- ---- ---t0.93 /Y!f'fli. ";,-NP-~~\· _'.:! : .'·; ,. ·I 0.92 .. ~i flil1t • Fuego l: · ' : ' ' 1'\t."I '. . .. 0.91 ~ • . "!I SI. Helens+ : 

5 0.90 Aguno.+ ! NyamurnG'lra ' 

~ 0.89 . 1 ~ El CNc~o ; 

-~ 0.88 ~ : j i 

~ 0.87 : 1 i e 0.86 • 1 : 

~ o.85 ' , I . [ 0.84 ; Monthly Averages and i a. 

< 0.83 

0.82 

0.81 

0.80 

0.79 

: Smoolhed Curve 

i ! Jan 1958-May1996 

i 

i: 

0.78 .......__..__. _ _._._,___,_____.__._..._. ~ ........ " ..._ ~_,__~___.__.__.__, 

~WUM~~~TIMHHW~UU~%~M%~ 

Year 

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. 
several recent publications [Nemesure et al., 1994; Cess et 

al., 1995; Dutton and Cox, 1995; Garrett and Prata, 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 km2, 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, Photosynthetically Active Radiation (PAR), and improved solar 

tracking capability. Data from Kwajalein have been 

submitted to the BSRN data archive. 

Bermuda 

Observations of down welling 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 

62 

references were taken to the World Radiation Center in 

Davos, Switzerland, for participation in the WMOsponsored 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 Atmospheric 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 
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-I, 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 multichannel 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 PMODOl sunphotometer, two dualchannel 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 concentration, 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]. 

63 

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 DH I 0 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 PEL 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 A. < 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 μW 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 μW cm-2 have been 

measured at MLO. 

For the following analyses, UV spectroradiometer data 

for 45° solar zenith angles were chosen for clear mornings 
'I 

Ii 

~ 

" u 

c: 

~ 

10 

0. 1 

0.01 

0.001 

' ' ' 

' ' ' 

' 18 July 1w.i(DOY197) ' 

9:15:+1 HST ' 

SZA•s• 

Dobson ozon1 2S 1 OU 

Rtttievtd ozone 2S( DU 

Erythl"11 17.5 ~ cm·' 

--rcnal lrredi•l'ln 

Eryth•me 

enactive Action SpKtrum 

(Oimansionless) 

--- 00001 ~~ ~-~-~-~-~-~-~-~-~~ 

~ ~ = ~ ~ wavelength - ~ (nm) ~ m - ~ ~ 

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 I for A. < 298 nm. The erythema for this scan is 

17 .5 μW cm-2. 

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 I-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 UY spectroradiometer 

data using the method of Stamnes et al. [ 1991], which uses 

the irradiance ratio 1340/1305 to 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 = 

-dln(I)/dln(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 

64 

I 'l j 8 S' 260 : Q, 

-e. ·. ~ 250 

car(' 19 

~ E 'E 18 i ~ 17 

UJ ~ 18 

m1: 22 28 

-;i 28 

20 

rt 18 

~ 

~ 5.0 

~ • . 5 

•• "O •. o s 

200 210 220 230 2.0 250 260 

Day of Year 1995 

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 134!/1305 as described by Stamnes et al. [1991]. 

Error bars shown are 2-0' 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-cr 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 UY spectroradiometer has operated 

properly at MLO and is producing excellent data within 

expected calibration limits. The CMDL program plans to 
8 MLO Speclroradiometer 

45° Solar Zenith Angle 

1-nm Averages 

l__1_~J_____J_~_L_~L:::=!l::==3!=~ ....___,!r---_J 

290 295 300 305 310 315 320 325 330 335 340 345 

Wavelenglh {nm) 

Fig. 3.16. Radiative amplification factor {RAF) as a function of 

wavelength. Note that the erythema RAF is l.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 

opm.a! ::.omponents 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 spectroradiometer 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. 

65 

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 de! 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 de! 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 Chich6n (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 Chich6n. 

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 Chich6n and Mt. Pinatubo might be 

responsible for observed (MSU) and predicted [Hansen et 
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 

i 

~ i ... . 

i 

I 

i i ~ 

i I 

l 

~ 

~ 

" 

~ g 

~ If 

I 10 

• • 1 

~ • • • 

g ' 2 

1 

• 

Fig. 3.17. Daily average surface irradiance (W m·2) observations 

and sky cover (cloudiness in tenths of total sky), for Barrow, 

Alaska, 1994. 

66 

(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; 
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.K.B., 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, Tel/us, 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. 241-

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, D.P. 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 Chich6n 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 Chich6n 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, J.O., 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. 

67 

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 JO-day isentropic flow 

patterns for Barrow, Alaska: 1985-1992, J. Geophys. Res., 

99(DI 2), 25,845-25,855, l 994. 

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, W.D. Komhyr, R.D. Evans, B.J. 

Johnson, D.M. 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. Climatol., 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. 

///um., 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, D.C., 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, J.R. Key, R.F. Kokaly, and D.A. 

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. 
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-11, NOAA 

68 

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, C.D. 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. 
4. Ozone and Water Vapor 

S. 0LTMANS (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 Oione 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 μ 

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 Izafia 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 34 NOAA 

Wallops Is., Virginia July 1, 1967-present 38 NOAA; NASA 

SMO Dec. 19, 197 5-present 42 NOAA 

Tallahassee, Florida May 2, 1964-Nov. 30, 1989; 58 NOAA; Florida State University 

Nov. I, 1992-present 

Boulder, Colorado Sept. 1, 1966-present 61 NOAA 

Fairbanks, Alaska March 6, 1984-present 63 NOAA; University of Alaska 

Lauder, New Zealand Jan. 29, 1987-present 72 NOAA; DSIR 

MLO Jan. 2, 1964-present 76 NOAA 

Nashville, Tennessee Jan. 2, 1963-present 79 NOAA 

Perth, Australia July 30, 1984-present 81 NOAA; Australian Bureau Meteorology 

SPO Nov . 17, 1961-present 82 NOAA 

Haute Provence, France Sept. 2, 1983-present 85 NOAA; CNRS 

Huancayo, Peru Feb. 14, 1964-Dec. 31, 1992 87 NOAA; !GP 

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 

Bismarck, North Dakota 

Caribou, Maine 

Wallops Is., Virginia 

SMO 

Tallahassee, Florida 

Boulder, Colorado 

UAF-GI, Alaska 

Lauder, New Zealand 

MLO 

Nashville, Tennessee 

Perth, Australia 

SPO 

Haute Provence, France 

Huancayo, Peru 

BRW 

Fresno, California 

Bismarck, North Dakota 

Caribou, Maine 

Wallops Is., Virginia 

SMO 

Tallahassee, Florida 

Boulder, Colorado 

UAF-GI, Alaska 

Lauder, New Zealand 

MLO 

Nashville, Tennessee 

Perth, Australia 

SPO 

Haute Provence, France 

Huancayo, Peru 

BRW 

Handford, California 

Jan. Feb. March April 

361 

340 

320 

241 

289 

321 

277 

244 

367 

382 

343 

242 

291 

331 

[371) 

267 

256 

321 323 

266 262 

266 253 

326 373 

Station closed 

314 324 

334 

349 

307 

242 

267 

296 

277 

217 

321 

272 

287 

293 

358 

382 

344 

243 

282 

290 

[349) 

267 

223 

323 

257 

270 

319 

Station closed 

372 

390 

347 

244 

306 

333 

420 

262 

339 

265 

[245) 

314 

457 

325 

341 

357 

316 

243 

284 

304 

365 

282 

254 

339 

268 

[231) 

333 

[354] 407 

293 292 315 

351 

377 

325 

237 

308 

341 

408 

265 

328 

257 

[231] 

382 

445 

332 

347 

372 

325 

244 

288 

328 

367 

273 

268 

328 

276 

(256] 

340 

386 

316 

May 

1994 

327 

369 

355 

237 

338 

315 

380 

289 

279 

334 

269 

(277) 

352 

379 

333 

1995 

347 

348 

316 

243 

302 

325 

341 

280 

280 

334 

268 

[255] 

340 

339 

338 

June 

322 

338 

327 

241 

321 

295 

347 

315 

271 

322 

291 

[231] 

332 

346 

303 

321 

323 

323 

247 

313 

299 

326 

302 

274 

322 

282 

(245) 

331 

345 

330 

July 

319 

324 

309 

240 

322 

299 

312 

337 

268 

313 

294 

(239) 

320 

310 

305 

311 

320 

312 

245 

302 

281 

300 

335 

262 

313 

295 

[246] 

322 

304 

298 

Aug. Sept. 

302 

324 

302 

244 

299 

280 

278 

361 

265 

304 

300 

[226) 

305 

293 

292 

282 

304 

297 

250 

308 

276 

302 

336 

262 

304 

292 

[223) 

329 

300 

292 

286 

316 

292 

244 

277 

370 

258 

296 

309 

311 

286 

302 

288 

259 

294 

284 

268 

361 

261 

296 

312 

304 

269 

286 

Oct. 

294 

299 

281 

248 

274 

360 

256 

277 

317 

132 

295 

269 

290 

267 

262 

266 

270 

326 

348 

255 

277 

311 

120 

277 

[260) 

272 

Nov. 

286 

293 

255 

251 

241 

265 

341 

238 

252 

307 

269 

273 

275 

292 

311 

299 

251 

277 

276 

328 

254 

252 

306 

192 

283 

264 

Dec. 

300 

304 

270 

242 

269 

276 

302 

220 

276 

278 

316 

293 

280 

297 

325 

284 

251 

263 

275 

287 

239 

276 

273 

257 

303 

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 

70 

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 
TABLE 4.3. Dobson Ozone Spectrophotometers Calibrated in 1994-1995 

Instrument Calibration 

Station Number Date 

1994 

Lisbon, Spain DOI3 Aug. 2, 1990 

Oslo, Norway D056 Aug. 21, 1986 

Potsdam, Germany D064 Aug. 2, 1990 

Huancayo, Peru D087 May 15, 1985 

Natal, Brazil D093 May 20, 1986 

Buenos Aires, Argentina D097 July 15, 1992 

El Arenosillo, Spain Dl20 Aug. 9, 1990 

Ushuaia, Argentina Dl31 None 

Tallahassee, Florida D058 Sept. 9, 1991 

Boulder, Colorado D061 Aug. 27, 1992 

MLO D076 June 13, 1993 

SPO D080 May 26, 1988 

BRW D091 May 26, 1989 

Fresno, California D094 June 26, 1989 

Mexico D.F Mexico D098 August 1978 

1995 

RA VI Spare 15 None 

Vindeln, Sweden 30 May 10, 1990 

United Kingdom 32 May 1995 

Uccle, Belgium 40 Aug. I, 1990 

United Kingdom, Standard 41 Aug. 2, 1990 

Sestola, Italy 48 Nov. 12, 1980 

Bordeaux, France 49 July I 0, 1990 

Reykjavik, Iceland 50 Aug. 2, 1990 

Arosa, Switzerland 62 Aug. 7, 1992 

Belsk, Poland 84 Aug. 2, 1990 

!'Obs. Haute Provence, France 85* July 10, 1990 

Denmark 92* Aug. 2, 1990 

Arosa, Switzerland 101 Aug. 2, 1990 

Hohenpeissenberg, Germany 104 Aug. 2, 1990 

Moscow, Russia 107 Aug. 5, 1990 

Budapest, Hungary 110 Aug. 2, 1990 

Tsukuba, Japan, Standard 116* June 29, 1992 

Bucharest, Romania 121 Aug. 5, 1990 

Bismarck, North Dakota D033 Oct. I, 1993 

Caribou, Maine D034 Sept., 9, 1991 

Wallops Island, Virginia D038 Sept. 16, 1991 

Nashville, Tennessee D079 Aug. 14, 1991 

Comodoro Rivadavia, Dl33 New Dobson 

Argentina 

Montevideo, Uruguay 0134 New Dobson 

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. 

71 

Calibration Standard 

Correction (%) Number Place 

+0.7% 65 lzaiia Observatory 

+0.5% 65 Izaiia Observatory 

+0.6% 65 Izaiia Observatory 

+0.9% 65 Izafia Observatory 

+2.9% 65 Izaiia Observatory 

+0.1% 65 Izaiia Observatory 

+1.3% 65 lzafia Observatory 

NIA 65 Izaiia Observatory 

-.3 83 Boulder 

0.0% 65 Boulder 

NIA 83 Boulder 

0.5% 83 Boulder 

0.0% 83 Boulder 

1.0% 83 Boulder 

-0.3% 83 Boulder 

NIA 65 LKO Arosa 

+0.7% 65 LKO Arosa 

NIA 65 LKO Arosa 

+2.0% 65 LKO Arosa 

+1.2% 65 LKO Arosa 

+2.4% 65 LKO Arosa 

+0.3% 65 LKO Arosa 

+1.1% 65 LKO Arosa 

+1.7% 65 LKO Arosa 

+0.2% 65 LKO Arosa 

+0.7% 65 LKO Arosa 

+1.0% 65 LKO Arosa 

+2. 1% 65 LKO Arosa 

+1.6% 65 LKO Arosa 

+1.4% 65 LKO Arosa 

+0.5% 65 LKO Arosa 

+0.6% 65 LKO Arosa 

Not consistent 65 LKO Arosa 

+1.5 83 Boulder 

+0.3 83 Boulder 

+1.0 83 Bou Ide 

+0.6 83 Boulder 

NIA 83 Boulder 

NIA 83 Boulder 

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 
TABLE 4.4. Annual and Seasonal Trends January 1979-December 1993 

Annual Dec.-Feb. March-May June-Aug. Sept.-Nov . 

Station Latitude 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 

Bismarck, North Dakota 46.8°N -3 .30 0.63 -3.25 

Boulder, Colorado 40.0°N -3 .85 0.61 -3 .97 

Wallops Is., Virginia 37 .9°N -3 .67 0.68 -4.79 

Nashville, Tennessee 36.3°N -3.09 0.70 -4.08 

Fresno, California* 36.8°N -3.81 1.37 -3 .18 

MLO 19 .5°N -0.53 0.77 -1.55 

SMO 14.3°S -1.66 0.66 -1.48 

Average over first five stations -3.58 -4.19 

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 

1.73 

1.43 

1.23 

1.33 

1.25 

2.00 

1.15 

0.96 

,-., 

;> 

,Q 

Q. 

Q. 

'-' 

.:? 

~ 

i::z:: 

eJI 

';:( = 

~ 4' 

0 = 

N 

0 

-5.64 1.12 -3.34 0.79 -1.52 1.16 

-5.69 I.OJ -2.00 0.93 -1.62 0.95 

-6.50 1.22 -2.68 0.75 -1.51 0.98 

-4.77 1.28 -2.66 0.78 -2.10 1.18 

-4.62 1.35 -2.03 0.92 - 1.23 1.22 

-3.84 3.00 -3.52 1.71 -4.74 1.31 

-0.51 1.44 -0.20 0.94 0.08 0.74 

-2.13 0.80 -1.42 1.09 -1.61 0.85 

-5.45 -2.54 -1.60 

lf'l 

,., Barrow, Alaska 70°N 0 

,., ffi ffi ffi 8l 8l Ell ffi EB lf'l 

N Ell Ell 

ffi Ell 

0 

N 

0.18 ± 0.24 %/year II m lf'l 

76 78 80 82 81 86 88 90 92 91 96 

0 

lf'l 

Mauna Loa 19°N lf'l EB 

EB ffi l;jJ 0 

.,. ·W·· .. -... ---· EB ·m-ffi- ·-"· "G)·-· ... 

Ell ,., 

lf'l EB EB 

0.35 ± 0.22 %/year 3397 m 0 

,., 76 78 80 82 81 86 88 90 92 91 96 

lf'l 

N 

American Samoa 14°S 0 

N 

lf'l 

--e.;-fil-~ t±l tB 61 al EB al lB Cfl ffi 111 e @ ~ ....... 

0 

lf'l 

lf'l 

,., 

76 78 80 

South Pole 

. EB 

-0.26 ± 0.38 %/year 82 m 

82 81 86 88 90 92 91 96 

90°S 

g --- .. ---m .. ~ .. ~ .. i.r! .. ~.=et w m EB .... m.e-.. ---.----.. ... EF.r -· .. • 

EB EB ffiEB9ffi Ell lf'l 

N 

0 

N 

-0. 70 ± 0.20 %/year 2835 m 

76 78 80 82 81 86 88 90 92 91 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. 

At SMO this decrease is not significant but at SPO a large 

and significant decline is evident. This is most apparent 

after 1986. This decline at SPO was discussed in the 1993 

Summary Report [Peterson and Rosson , 1994). 

The monthly ozone means for each of the four CMDL 

baseline sites for the period of observation are given in 

Table 4.5. For MLO the means are for the hours 0000-

0800 LST, which falls within the time of downslope flow 

at the observatory. 

TABLE 4.5 . Monthly Mean Surface Ozone Mixing Ratios (ppbv) 

Year 

1973 

1974 

1975 

1976 

1977 

1978 

1979 

1980 

1981 

1982 

1983 

1984 

1985 

1986 

1987 

1988 

1989 

1990 

1991 

1992 

1993 

1994 

1995 

1973 

1974 

1975 

1976 

1977 

1978 

1979 

1980 

1981 

1982 

1983 

1984 

1985 

1986 

1987 

1988 

1989 

1990 

1991 

1992 

1993 

1994 

1995 

Jan. 

28.7 

27.4 

29.2 

31.3 

32.l 

33.9 

33.5 

30.5 

31.6 

27.9 

26.8 

31.8 

35.5 

31.l 

36.4 

30.2 

32.3 

31.6 

29.l 

26.l 

31.4 

33.0 

34.5 

31.4 

37 .3 

36.1 

39 .5 

41.0 

43.5 

35 .l 

46.8 

40.4 

43.2 

39.9 

38.4 

44.8 

40.7 

37.8 

45 .3 

40.2 

42.2 

43.3 

34.4 

Feb. 

27.4 

29.9 

31.2 

32.9 

32.2 

31.l 

33 .6 

27.9 

31.1 

34.2 

19.9 

28 .7 

28.0 

27.2 

30.9 

36.8 

29.0 

30.2 

27.8 

26.5 

29.7 

28.5 

42.8 

38.9 

41.6 

35.8 

39 .2 

36.6 

42.1 

42 .2 

40.7 

53.6 

40.5 

41.6 

40.0 

40.5 

43.3 

37.4 

38.3 

41.8 

42.8 

41.3 

37 .5 

42.0 

March 

22.3 

32.7 

24.4 

20.8 

31.0 

22.6 

24.5 

24.5 

22.5 

25 .9 

21.5 

20.5 

22.0 

22.7 

32.9 

27 .l 

16.8 

27 .4 

14.7 

21.7 

18.0 

51.8 

47.5 

36.7 

48.5 

45.0 

48.5 

45 .0 

52. l 

48.8 

59 .l 

48 .4 

52.4 

43 .2 

50.0 

50.3 

40.6 

49 .6 

48.4 

53 .8 

50.0 

48 .5 

51.1 

April 

15 .8 

22.5 

9.7 

9.7 

21.7 

19 .7 

19.6 

23 .8 

12.2 

21.6 

6.8 

13 .9 

15.0 

23 .8 

24.6 

19.5 

14.3 

15 .5 

17.5 

10.9 

18 .8 

51.8 

51.7 

41.2 

41.6 

49.2 

50.3 

53 .8 

61.1 

52.5 

63.4 

50.7 

46.4 

53 .1 

48.4 

52.0 

56.9 

61.0 

63 .3 

57 .9 

50.5 

May 

15 .6 

23.3 

23.4 

11.3 

20.2 

22.0 

25.l 

18.l 

26.9 

15.3 

21.4 

16.4 

20.2 

17.4 

24.0 

22.2 

20.2 

24.6 

29.4 

16.9 

20.6 

11.3 

22.4 

49.6 

48.7 

39.3 

46.4 

37.2 

48.5 

47.1 

60.8 

54.3 

56.7 

47.1 

48.4 

47.2 

47.5 

45.9 

55.0 

55 .5 

46.9 

55.2 

48 .7 

52.l 

June 

BRW 

19.3 

22.0 

23.7 

24.l 

24.5 

24.l 

22.5 

24.7 

26.l 

27. l 

20.4 

25.5 

28 .0 

24.7 

30.9 

26.2 

24.3 

23.6 

25.4 

I 9.4 

22.4 

25 .6 

27 .6 

MLO 

40.8 

47.3 

35 .6 

41.5 

31.8 

43 .7 

42.0 

38.6 

39 .3 

47 .6 

46.8 

43 .9 

45.4 

32.3 

35 .8 

43 .3 

41.5 

49 .5 

50.6 

35.4 

44.6 

73 

July 

15 .1 

17 .7 

19.7 

18 .6 

21.l 

21.4 

18 .9 

20.3 

19.8 

24.5 

23 .6 

21.9 

21.2 

20.4 

23 .3 

21.7 

19.9 

21.1 

24.4 

18.3 

16.3 

21.5 

20.5 

38 .0 

43.3 

32.2 

29.2 

33 .5 

36.7 

35.8 

39 . I 

31.6 

44.4 

37 .8 

40.3 

31.3 

41.2 

37. I 

36.7 

39.2 

38.8 

38 .0 

30 .1 

34.6 

Aug. 

18 .8 

18 .1 

19.2 

18.l 

20.8 

22.3 

18 .5 

19 .l 

23 .2 

23 .3 

22.4 

22.1 

25 .0 

21.6 

25.6 

23 .8 

21.0 

25.5 

31.6 

18 .8 

19 .1 

19.4 

21.3 

31.5 

43 .7 

30.0 

28 .9 

29.2 

29.4 

38.6 

37 .0 

30.2 

32.2 

33 .8 

36.9 

38 .7 

36.3 

33.5 

38.5 

35.3 

33 . l 

30.6 

30.6 

29 .8 

45.8 

Sept. 

23 .3 

26.1 

23 .0 

20.3 

22.4 

23.6 

21.1 

27.9 

26.2 

29 .7 

28.2 

24.3 

28 .8 

25 .0 

31.1 

26.9 

31.4 

32.5 

28.3 

23.9 

24.1 

29 .6 

25.4 

31.2 

34.l 

25.6 

31.9 

37.4 

27.4 

35.9 

32.4 

31.0 

36.9 

31.4 

24.3 

31.9 

34.2 

38.6 

30.5 

31.5 

26.3 

26.6 

33 .5 

42.1 

Oct. 

30.8 

31.6 

30.3 

31.6 

25.6 

32.8 

33 .2 

25.6 

31.3 

34.6 

33.5 

35.7 

31.4 

30.3 

32.5 

31.6 

34.8 

33.1 

27 .5 

27.2 

29.l 

31.7 

35 .l 

36.5 

31.9 

31.5 

30.9 

28.8 

31.0 

36.8 

37.8 

32.9 

38.6 

31.0 

33 .2 

38.1 

34.4 

30.0 

24.8 

38. 1 

33 .9 

24.9 

35 .3 

41.4 

36.7 

Nov . 

30.2 

32.8 

28 .3 

30.7 

33.6 

29 .6 

32.2 

34.3 

34.6 

36.2 

30.8 

38.3 

33 .0 

34.6 

38.8 

34.2 

35.0 

34.3 

29 .8 

28.6 

30.3 

34.7 

32.2 

33.4 

29.6 

29 .6 

39.3 

39 .0 

27 .7 

38.2 

38.4 

38.3 

36.7 

34.3 

31.8 

36.2 

30.2 

40.5 

29.5 

35.0 

28 .8 

32.6 

29.2 

42.7 

40.5 

30.7 

Dec . 

34.8 

30.9 

26.3 

29.1 

28.0 

30.3 

29 .3 

30.0 

30.9 

34.5 

33.0 

32.2 

33.4 

31.4 

36.4 

31.4 

35.8 

32.4 

27 .3 

26.0 

31.8 

31.4 

28.0 

36.0 

31.9 

37.5 

33.2 

33.6 

4 1.6 

34.5 

39 .9 

45.7 

40.2 

37.6 

38. 1 

41.6 

33.4 

36. 1 

40. 7 

39.6 

33.3 

32.2 

38.3 

45.5 

35.5 
TABLE 4.5. Monthly Mean Surface Ozone Mixing Ratios (ppbv) - Continued 

Year 

1976 

1977 

1978 

1979 

1980 

1981 

1982 

1983 

1984 

1985 

1986 

1987 

1988 

1989 

1990 

1991 

1992 

1993 

1994 

1974 

1975 

1976 

1977 

1978 

1979 

1980 

1981 

1982 

1983 

1984 

1985 

1986 

1987 

1988 

1989 

1990 

1991 

1992 

1993 

1994 

1995 

Jan. 

9.9 

11.0 

10.2 

10.5 

9.8 

9.4 

8.2 

8.9 

7.4 

10.3 

8.4 

8.1 

7.4 

9.3 

11.4 

6.7 

12.2 

9.4 

8.9 

24.6 

26.2 

23 .5 

27.4 

25 .1 

24.9 

21.3 

21.3 

20.5 

22.7 

18.3 

20.0 

18.9 

22.9 

20.2 

23 .8 

18.0 

23.4 

25.0 

25 .3 

Feb. 

9.1 

8.6 

9.2 

8.3 

7 .9 

9.4 

9 .1 

6 .3 

7 .1 

10.0 

8.6 

6.4 

8.4 

8.0 

I I.I 

8.7 

9 .6 

8.3 

25 .7 

21.3 

22.0 

24.3 

22.2 

22.5 

19.6 

21.5 

20.5 

20.1 

19.3 

20.1 

17 .8 

21.5 

19 .7 

20.2 

19.9 

17.9 

20.I 

19 .7 

18.0 

March 

8.8 

8.8 

9 .2 

8.1 

8.5 

9.5 

6.7 

9.4 

8.0 

7.3 

8.4 

6.5 

8.1 

9.0 

11.3 

6.6 

12.l 

9.1 

9.4 

24.9 

21.9 

21.5 

23 .6 

22.3 

20.l 

24.0 

21.2 

21.3 

22.0 

21.9 

19.3 

23.7 

18.7 

23.1 

18.9 

16.9 

17 .5 

21.1 

18.0 

April 

8.3 

9.2 

8.4 

12.5 

11.6 

9.3 

7.3 

11.5 

5.7 

11.2 

7 .2 

13 .6 

9.9 

12.I 

10.8 

7.9 

6.9 

29.4 

25.2 

26.7 

29.6 

26.9 

24.6 

31.5 

27 .3 

29.0 

24.4 

27. 1 

23 .5 

27.4 

25.4 

24.5 

23 .8 

22.4 

23.I 

24.4 

19 .8 

May 

11.2 

12.2 

13.6 

15.I 

15.I 

14.0 

14.0 

11.2 

17.3 

11.8 

16.3 

11.8 

10.6 

16.7 

13 .8 

I 1.7 

12.7 

35 .7 

29.4 

31.5 

33.l 

29 .3 

29.0 

33 .6 

30.6 

34.2 

30.5 

34.4 

28.0 

31.0 

35.3 

27 .6 

26.8 

29 .7 

26.4 

27 .7 

24.0 

June 

SMO 

13.5 

20.7 

15 .9 

17.2 

19.3 

17.0 

16.9 

18.3 

18.4 

17.1 

14.0 

20.l 

13.9 

19.6 

16.1 

14.4 

18 .5 

18.0 

SPO 

34.9 

31.7 

33.I 

33.1 

34.7 

33 .3 

32.5 

35 .5 

33.1 

36.1 

36.6 

36.3 

30.9 

34.1 

35.4 

31.2 

30.9 

33 .5 

29.7 

33. I 

28.3 

July 

17 .6 

19 .9 

22.8 

18.6 

16.8 

20.0 

16.7 

19 .8 

18 .7 

20.2 

20.3 

20.7 

21.6 

21.5 

20.0 

20.9 

15 .2 

18 . J 

35 .3 

34.4 

34.2 

34.8 

37.9 

35.0 

35.3 

36.4 

34.3 

37 .5 

36.7 

38 .7 

29.7 

34.0 

36.2 

32.3 

31.8 

34.9 

30.7 

34.J 

34.5 

Aug. 

21.7 

20.7 

15.9 

19.7 

21.8 

16.4 

16.J 

20.8 

17 .6 

17.7 

21.3 

24.8 

17.1 

20.I 

19.3 

20.0 

I 3.7 

22.5 

34.4 

33.6 

36.0 

34.3 

34.5 

34.4 

37 .7 

34.9 

32.7 

36.1 

34.4 

38.2 

33.0 

36.0 

30.l 

34.1 

34.4 

30.3 

33.5 

33.0 

Sept. 

17 .9 

15 .9 

17 .7 

19.3 

17 .7 

15 . I 

20.2 

13.0 

14.5 

17.1 

14.5 

17.1 

18 .3 

19.4 

13.4 

23.2 

12.2 

13.6 

35 . 1 

26.6 

33. I 

33.5 

33 .I 

33 .0 

37 .8 

33 . I 

33.4 

35 .9 

32.3 

36.9 

33.9 

35 .5 

28.8 

27.7 

28 .5 

29 .I 

31.6 

21.8 

Oct. 

15.2 

16.7 

18 .6 

18.8 

15 .3 

13.5 

15 .3 

17 .2 

14.0 

16.6 

20.2 

15 .8 

16.I 

12.7 

15 . 1 

13 .9 

IO.I 

36.2 

25.2 

29.9 

31.8 

34.4 

29.I 

37.6 

28 .5 

30.6 

31.5 

28.3 

33 .0 

31.1 

24.2 

27.0 

27 .2 

25 .8 

27.5 

27.3 

26.3 

Nov. 

12.4 

15.2 

13.9 

13.8 

11.4 

10.9 

17.0 

13.0 

14.7 

14.9 

12.9 

JO.I 

13.3 

18.8 

13.2 

12.2 

13 .0 

13.7 

33 .9 

25.8 

26.7 

33.0 

26.8 

35.3 

27.7 

27.8 

34.0 

26.7 

29.4 

24.4 

29.5 

28.6 

27.4 

22.8 

26.7 

29.7 

29.3 

29.2 

Dec. 

13 .2 

15 .0 

13.3 

14.8 

9.7 

11.8 

12.2 

8.5 

10.7 

12 .7 

11.9 

9.1 

13 .8 

13 .2 

15.4 

9.9 

8.0 

28.7 

31.6 

24.9 

30.8 

31.3 

25 .J 

23 .2 

29.5 

24.5 

25 .6 

28.2 

24.8 

25.4 

26.0 

25 .3 

23.4 

23.7 

22.1 

29 .3 

22.9 

26.8 

26.4 

Monthly means are computed from daily (24-hr) averages. 

4.1.4. 0ZONESONDES 

Table 4.6 summarizes the I 994-1995 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 

74 

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 el al., 1996]. 
TABLE 4.6. Summary of 1994-1995 Ozonesonde Projects 

Ozonesonde 1994 1995 

Sites Totals Dates Totals Dates Project 

Station (weekly) 

Boulder 52 Full year 52 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. 25 6 Jan. I-Feb. 12 NSF and NOAA 

Tahiti 24 July 31-Dec. 29 PEM-Tropics 

SMO 16 Aug. I-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 June 27-July 21 Southern Oxidant Study 

Ship Cruises 

Indian Ocean 21 Feb. 12-April 14 NSF R/V Malcom Baldrige 

Pacific Ocean 17 Oct.17-Dec. II ACE R/V Discoverer 

Totals 278 418 

PEM-Tropics - Pacific Exploratory Mission in the Tropics (a global tropospheric experiment). 

35 

30 

~ 25 

r;i;l 

~ 20 

E::: 

~ 15 

10 

5 

0 

SOUTH POLE STATION 1994 

-02 SEP 94 282 DU 

-OS OCT 94 102 DU 

t f I 0 ' I 

---:- - - -- - : ----- ~ -- --- ~- -- ---:- -----:----- 1 I I I I I 

0 I I I 4 

• • ' • j 

I I I I 

. . ' . . . ' 

. ___ ,,1 _____ _ ... _ ___ _ ... __ ---

i : : 

. ' . • I • ' I 

. . -:---- -:-----:· -. --·:-- -- -:-----:-----:-. ----:-- - --:----- : : : : : : : : 

: : : : : : : 

: : : ; i : I 1 : --- -----:· ----:----- :--·---·: ·· ---~ ---··:----;-···:·· --- ' p t I I I 

I I I I I 

I 0 I I 

: : : : 

0 2 4 6 8 1 0 12 14 16 18 20 

OZONE PARTIAL PRESSURE (mPa) 

35 

30 

25 

20 

15 

10 

5 

0 

SOUTH POLE STATION 1995 

-22 AUG 95 282 DU 

98 DU 

: • • t l . : ,. -- _T ___ --f----· r-----; ----r--· T-· · -· . . . . . . 

. . ' I < I I 

I I I . I 

- - r -- - -· ' • • ••• ..,, • • -- - -,- - - • - -

' . ' ' . . . 

' . . . . . . . . . . . . . . . . • I t 0 I 

----~. ------:·- --- --:- . --- . ---~ ---- :-- -- -~- -----:----- -

: : : ' ' : : : I I ~ ~ : j 

t I I I 

-- - ;. ·-··- -- ---:-- ---:------~----- ~ ---- .; . ----~- -----:-- - : : : : : : I : 

: l : : : ' 

0 2 4 6 8 1 0 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., 

l 995a] (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 RIV 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 CH4 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 Mean Standard Deviation 

(km) (ppmv) (ppmv) 

10-12 60.46 40.27 

12-14 12.23 6.97 

14-16 4.68 l.04 

16-18 3.90 .49 

18-20 3.87 .35 

20-22 4.08 .29 

22-24 4.24 .30 

24-26 4.34 .34 

*The trends are computed for deseasonalized values. 

tThe 95% confidence interval is based on students t-distribution. 

:j:Significant at 95% confidence level. 

Number of Trend* 95% Confidencet 

Observations (% yr-1) Interval (% yr-1) 

137 l.47 2.60 

137 l.34 1.88 

137 .61 .87 

137 .78:j: .49 

136 .80:j: .35 

131 .48:j: .28 

125 .51:j: .29 

108 .55 .34 

76 
22-24 km Boulder, Colorado 

• ... ~ . • ! .. -- -~-- ~ , ·. -·· ___ , ,,. .. ... . ... \ . . ... .. 

0.51 t 0.29 %1yur 

81 82 83 81 85 B6 67 BB B9 90 91 92 93 91 95 96 

16-18 km 

': 

~ ~ ~ ,e , ,g •• e I •• "I 

~ ~ "Q"" t:. ~~:._i.~~~~~~__: , .. , • ~ ~- ,~ · nrno~ .;.· ...

-~-·.... ~~~ ~ •• ~ , ,,;::-:::: ,. ......'t~· ... __ -:::~--= .:. w 1 c.ll .\. • • •• • • ...· •• • • • • • • •• 

.: .·· . : . . :• . .. ~ n ;. •• .. 0.78 t. 0.49 '/./yar 

81 82 83 B'I 85 B6 87 88 89 90 91 92 93 9'1 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. 

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 "realtime" 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 I, l 99S, the CMDL 

Ozone Group measured daily ozoJ1e profiles during the 

Network for the Detection of Stratospheric Change 

(NDSC) Stratospheric Ozone Profil e lntcrcompari on 

(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 (11 m) 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, J 99S, profiles (Figure 4.4a). These 

profiles were fairly typical of all the triple flights with an 

77 

average relative standard deviation of 2-4% in the lower 

troposphere (0-S km) and in the stratosphere from l S km to 

burst altitude (-3S 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 ozoneson.de 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 IS km except for 1he JPL 

lidar between IS and 18 km. At the ozone peak , the 

ozonesonde profile is about 8-10% greater than the ground 

based instruments. The ozonesonde profile 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 

S% differences between the ozonesondes and ground based 

instruments. 

4.2.2. OZONE VERTICAL PROFILES OVER THE 

NORTH ATLANTIC 

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 I 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., 199S]. The results, primarily from the 1993 

and 1994 campaigns, have recently been prepared for 

publication [Oltmans et al., 1996]. 

During spring l 99S, 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, l 99S, at Rhode Island 

and Maryland (Figures 4.Sa and b) and for May 7 at 

Bermuda (Figure 4.Sc) 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 12S ppb (Figure 4.Sa) and large ozone 

amounts (-8S ppb) extend down to 6.S km. At Maryland 

(Figure 4.Sb), 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 SO-70 ppb. Early on 

May 7 at Bermuda (Figure 4.Sc) there is a peak of -120 

ppb at about 6.S km. 

The Bermuda trajectories for May 7 (Figure 4.Sd) 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 
35 

40 

---------:-----

40 

a) 30-Aug-95 

. . . . ---f----------:-- -------- ----------:----------

30-Aug-95 b) 35 . . . . ' --,. - ------ -- ,-- -- - ---· -r · ·--- -- - - - -· ·~- ' . . . . 

. ' . ' i 30 30 

' . 

~ 

§ 25 25 

E-4 I 

r:= 

~ 20 

. ' . . ' 

. -·- ·-·-- ···-· 1···--·····r- ···-··-·· . . . . . ' . . . 20 I 

. . =.:;~~r------ --r --------1-·--------

. . . . . . . . 15 t 0 I I 

--- ---..:- --- --t --------:- ------· -{-------- --:-- ------- - . . . 15 ---NOAA Ozonesonde 

10 ' . -- -· -. ~- ---- ·- ---:----------~-- ---- -· -: .. ·-· ·-- -.L. --- . -· -- 10 ---JPL LIDAR 

j I I 0 

I I I I 

0 I I I -----------NASA LIDAR ~ I I I 

. . 5 I I I I 

- -- -~ -- -- -- --!-- --------!---- --- -~-- ----- -- . . 5 a LARC MICROWAVE 

. . ' . X SAGE 

0 0 

0 1 2 3 4 5 6 0 1 2 3 4 5 6 

Fig. 4.4. (a) Three vertical profiles of ozone concentration (1012 cm-3) 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 

et al., 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. 

78 

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 
-90 -60 -30 0 30 

15 

Rhode Island 

a) May 6, 1995 

1355 UT 

-10 ] 

-

~ 

~ 

~ 

f-' 

~ 

~ 

~ 

< 5 

!!. Ozone 

v Air Temp. 

D Frostpoint 

0 

0 25 50 75 100 125 

-90 -60 -30 0 30 

15 

Bermuda 

c) May 7, 1995 

-

e 10 

..:.:: 

-

~ 

~ 

~ 

~ ~ 

~ 

~ 

< 5 

!!. Ozone 

v Air Temp. 

D 

0 

Frostpoint 

0 25 50 

----......... 1 

4·~< 

30°N ···· ······ · .......... ,·.--.... -.......... _J"-.. __ 

0°N 

Solid 00 UT 

Dashed 12 UT 

OlOOUT 

75 100 

170°w 140°w llO°w so°w 

~= 1 .. ~·" . ' ~' ' .... ._, -

I= 

0 1 2 3 4 5 

Days from Bermuda 

125 

50°w 

I 

6 

Fig. 4.5. Vertical profiles of ozone mixing ratio (ppbv), temperature (

0 C), and frost-point temperature (

0

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 
28 

26 

24 

22 -

20 

IB 

e 

.=. 16 

-cl " 

~ 14 

< 12 

10 

8 

6 

4 

McMurdo station, winter 1994 

13 June 1994 

25 July 1994 

9 August 1994 

15 August 1994 

13 September 1994 

5 October 1994 

'";' 

0.. 

.=. 

.. 

.. 

" "' 

.. "' 

.. 100 0.. 

.. 

" E 

"' 0 

.. 

a. 

0.. 

<( 

0WJ..ulllllllliillllllJU!W.U.Wl.W.lllW.llW.W.WJJ.W.UWWU.W.WJJ.W.LW.tWU.LWJ.;WIW 1000 

0 2 3 4 5 6 7 8 

Waler Vapor Mixing Ratio [ppmv] 

9 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. 

is added from outside the vortex. By the time the sun 

reappears over Antarctica, the air in the entire stratospheric 

vortex is highly processed and ozone depletion can take 

place over a broad geographical scale and through a 

significant depth. 

Early in the dehydration process (June 19), an ozone 

profile was observed with significant depletion between 12 

and 20 km (Figure 4. 7). This depleted ozone layer 

corresponds very closely to the region where significant 

dehydration was first detected at McMurdo. Since it is 

dark over the Antarctic continent at this time, sufficient 

sunlight to allow ozone depletion can only be attained if 

the air parcel moves to a higher latitude after it is 

dehydrated and the air is significantly processed. The 

trajectory analysis [Vomel et al., 1995a] shows that indeed 

the dehydrated and ozone-depleted parcel passes through 

the coldest temperatures over the continent and 

subsequently moves to a sunlit region near 50°S latitude. 

Furthermore, this analysis shows that significant ozone 

depletion can take place on a relatively short time scale. 

An analysis of the time when the observed air masses could 

have formed type II PSCs (ice particles) for the first time, 

limits the time scale for the observed ozone destruction to 

about 4 days [Vomel et al., 1995a]. 

80 

0 2 4 

30 

25 

20 

10 

5 

0 1 2 

6 8 10 12 14 16 18 20 

.... :,,.,_... 

·:..~.: -:.:;: .. : . : _ _ • • • " • w 

Water Vapor, 13 June 

Water Vapor, 19 June 

Ozone, 13 June 

Ozone, 19 June 

3 4 5 6 7 8 9 10 

Fig. 4.7. Vertical profiles of ozone partial pressure (mPa) and 

ozone mixing ratio (ppmv) at McMurdo on June 13 and June 19, 

1994. The June 19 case shows significant ozone depletion and 

dehydration between 11 and 24 km compared to the unperturbed 

June 13 profiles. 

4.2.4. FLOW PATTERNS FOR SMO DESCRIBED 

WITH CLUSTERED TRAJECTORIES 

Ten years of isentropic trajectories (1986-1995) were 

calculated for SMO (14.25°S, 170.56°W) and were 

summarized for various time frames using cluster analysis. 

Ten-day back isentropic trajectories were produced twice 

per day at 0000 and 1200 GMT arrival times. Trajectories 

were calculated to arrive at approximately 500 mas!, an 

elevation close to that of the observatory (77 m) and 

representative of the boundary layer. Input to the transport 

model consists of gridded meteorological data from the 

European Centre for Medium Range Weather Forecasts. 

An earlier study by Halter et al. [ 1988] identified three 

distinct source regions contributing their signals to 

atmospheric measurements made at SMO, in particular 

those of carbon dioxide. Figures 4.8-4.10 show 

trajectories depicting transport from these three regions. 

Figure 4.8 shows trajectories arriving at SMO in the trade 

wind regime. At most, 1 km of descent is seen in this type 

of trajectory. Ten days back from SMO air parcels are in 

the remote southeastern Pacific, never reaching the South 

American continent. The second transport type is 

illustrated in Figure 4.9, which shows flow from southern 
20° N 

o' 

20° s 

40° s 

60°S I----~--~---.----.----.----.--~ 

1::2011 E 140° E urn• E rno• w 100· w 140• w u~o· w 1001 w 

f:~,r'.~·= n :I: 0 ,1 2 3 ~ 5 6 7 B 9 10 

DAYS FROM SMO 

Fig. 4.8. Ten-day back isentropic trajectories arriving at SMO at 

500 m on August 7, 1989, showing an example of trade wind type 

transport. The numbers along the trajectories give days back 

from SMO. 

20° N 

o' 

20' s 

40° s 

80° s !------~-------------- i 120° E 140' E 1eo • E loo' w 1ao' w 140' w t20 1 w 100° w 

~m =:=~ 

i~~ :to I 2 3 4 5 6 7 6 

DAYS FROM SMO 

I 

10 

Fig. 4.9. Ten-day back isentropic trajectories arriving at SMO at 

500 m on June 30, 1990, showing an example of transport from 

midlatitudes. The numbers along the trajectories give days back 

from SMO. 

midlatitudes to SMO. This trajectory type may descend 

3 km or more as it curves anticyclonically en route to 

SMO. Note that as air parcels descend in elevation, wind 

speeds decrease significantly. For this transport type, 

approach to SMO is often from the southeast. The third 

81 

20° N · 

o' 

20° s 

40° s \J 

so's I----~---.----.----.----.-----.---~ 

ieo• E 1401 E H:1o• E ieo0 w 1eo'!' w 140• w 120' w 100' v. 

i:~~ :t O 1 2 3 4 5 6 7 B 9 10 

DAYS FROM SMO 

Fig. 4.10. Ten-day back isentropic trajectories arriving at SMO 

at 500 m on February I, 1987, showing an example of transport 

from the northern hemisphere. The numbers along the 

trajectories give days back from SMO. 

least frequent transport type brings air from the northern 

hemisphere to the observatory. Figure 4.10 shows 

trajectories with origins well beyond the equator. Halter et 

al. [ 1988] found that carbon dioxide transported to SMO 

in this manner was in phase with that measured at 

Kumakahi, Hawaii, although the amplitude of the signal 

was reduced. To quantify the frequency of SMO transport 

types, the complete set of trajectories was summarized 

using cluster analysis. 

Cluster analysis is a multivariate statistical technique 

used here to group trajectories by shape and length. Each 

group or so-called cluster is represented by an average 

trajectory called the cluster mean. Figure 4.1 I shows six 

cluster means derived for the entire IO-year period. Each 

cluster mean is marked with plus signs indicating the I-day 

upwind intervals. At 10 days upwind, the cluster means 

are labeled with two numbers; the top number gives the 

percentage of trajectories that occurs in the cluster, and the 

bottom number identifies the cluster. The cluster 

identifiers (1-6) are used to distinguish one transport type 

from the other; the numbers themselves have no inherent 

significance and are not related from one clustering to the 

next. 

Figure 4.11 gives a quantitative estimate of the 

frequency of each transport type. For example, the rapid 

transport from southern midlatitudes is represented by 

cluster 2 and cluster 3, with 2% and 7% frequency of 

occurrence, respectively. These two clusters differ in the 

average length of trajectory contained in the cluster, but 

both bring air parcels to SMO from elevations of 3 km or 

more. As a result of subsidence on approach to the 

observatory, wind speeds decrease significantly compared 

with their initial magnitudes several days earlier. A third 

cluster with transport from the south, cluster 4, exhibits 

much lower wind speeds, but shares the characteristics of 
Fig. 4.11. Atmospheric flow patterns for SMO depicted by 

cluster-mean back trajectories arriving at 500 m as! for 1986-

1995. Plus signs indicate I-day upwind intervals. At 10 days 

upwind the cluster means are labeled with two numbers; the top 

number gives the percentage of trajectories that occurs in the 

cluster and the bottom number identifies the cluster. 

10-day average ongm south of 30°S and anticyclonic 

curvature on approach to SMO from the southeast. This 

cluster, comprising 18% of trajectories, has a mixed 

character because it contains some trajectories with 

tropical origins. 

Clusters 1, 5, and 6 in Figure 4.11 contain trajectories 

that correspond to the easterly trade wind transport type. 

Cluster 5 trajectories have a northerly component on 

approach to SMO and occur 15% of the time. Cluster 6 

trajectories approach from the due east 32% of the time. 

Cluster 1 trajectories have lower wind speeds, a southerly 

component, and occur 26% of the time. 

Transport from the northern hemisphere occurs in 

cluster 5. This cluster also contains trajectories that do not 

cross the meteorological equator. To estimate the 

frequency of transport of true northern hemisphere air, the 

number of trajectories that had 10-day origins north of 5°N 

were counted. Trajectories of this transport type have 

frequency of 2-3% per year. They occur most often in 

February and March at about 10% frequency, but can also 

occur in December, January, and April though usually at 

lower frequency. The occurrence of transport from the 

northern hemisphere is quite variable from year to year 

with frequency in the two most likely months (February 

and March) ranging from 0 to 25%. Trajectories were also 

clustered by month in order to learn more about the 

seasonality of flow patterns at SMO. Figures 4. I 2a 

(January) and 4. I 2b (July) represent yearly extremes in 

flow patterns. The marked differences between these plots 

show a strong seasonality in SMO transport. Summer 

months are characterized by minimal flow from southern 

midlatitudes, a northerly component in some of the trade 

wind trajectories, and a cluster with trajectories 

approaching SMO from the northwest (for example, cluster 

2, Figure 4. l 2a). Winter months are characterized by both 

easterly trades and strong flow from the south. In fact this 

"winter" pattern is present from May through November, 

with July having the highest frequency of strong southerly 

flow. Trade winds are evident during every month. 

In terms of 10-day origins, air transported to SMO is 

predominantly from remote tropical-marine regions. The 

82 

501 N .... 

(a) \ 

'401 s . 

?O's;---"- ~~ , 

~ ~E ~E ~E ~E ~E ~W 

50° N .... (b) \ 

20°N -

10' s . 

10' s .,....__....,..__ ~ '• 1so0' w 120°' w ~ ~E ~E ~E ~E ~E ~W 

Fig. 4.12. Atmopsheric flow patterns at SMO for 1986-1995 

depicted by cluster-mean back trajectories arriving at 500 m asl 

for (a) January and (b) July. Symbols are as in Figure 4.11. 

frequency of such origins is about 50% in winter to 80% in 

summer. The remaining trajectories are from more 

southerly latitudes usually from elevations of 3 km or 

higher. Northern hemispheric air is transported to SMO at 

a rate of 2-3% per year, exclusively during the summer and 

fall months. 

4.3. REFERENCES 

Deshler, T., B.J. Johnson, D.J. Hofmann, and B. Nardi, 

Correlations between ozone loss and volcanic aerosol at 

altitudes below 14 km over McMurdo Station, Antarctica, 

Geophys. Res. Lett., submitted, 1996. 

Ferguson, E.E., and R. Rosson (Eds.), Climate Monitoring and 

Diagnostics Laboratory, No. 20, Summary Report 1991, 131 

pp., NOAA Environmental Research Laboratories, Boulder, 

CO, 1992. 

Halter, B.C., J.M. Harris, and T.J. Conway, Component signals in 

the record of atmospheric carbon dioxide concentration at 

American Samoa, J. Geophys. Res., 93(012), 15,914-15,918, 

1988. 

Harris, J.M., An analysis of 5-day midtropospheric flow patterns 

for the South Pole: 1985-1989, Tel/us, 44B, 409-421, 1992. 

Harris, J.M., and J.D. Kahl, A descriptive atmospheric transport 

climatology for the Mauna Loa Observatory, using clustered 

trajectories, J. Geophys. Res., 95(09), 13,651-13,667, 1990. 

Harris, J.M., and J.D.W. Kahl, An analysis of 10-day isentropic 

flow patterns for Barrow, Alaska: 1985-1992, J. Geophys. 

Res., 99(012), 25,845-25,855, 1994. 
Harris, J.M., P.P. Tans, E.J. Dlugokencky, K.A. Masarie, P.M. 

Lang, S. Whittlestone, and L.P. Steele, Variations in 

atmospheric methane at Mauna Loa Observatory related to 

long-range transport, J. Geophys. Res., 97(D5), 6003-6010, 

1992. 

Hofmann, DJ., and SJ. Oltmans, Anomalous Antarctic ozone 

during 1992: Evidence for Pinatubo volcanic aerosol effects, 

J. Geophys. Res., 98(DIO), 18,555-18,561, 1993. 

Hofmann, DJ., SJ. Oltmans, J.A. Lathrop, J.M. Harris, and H. 

Vomel, Record low ozone at the South Pole in the spring of 

1993, J. Geophys. Res., 21 (6), 421-424, 1994. 

Komhyr, W.D., Dobson Data Re-Evaluation Handbook, Section II: 

Re-evaluation of instrument constants, WMO Report No. 29, pp. 

Il-1-11-82, edited by R.D. Hudson and W.G. Planet, World 

Meteorological Organization, Geneva, Switzerland, 1993. 

Komhyr, W.D., R.D. Grass, and R.K. Leonard, Dobson 

spectrophotometer 83 : A standard for total ozone measurements, 1962-1987, J. Geophys. Res.. 94(D7), 1847-9861 , 

1989. 

Komhyr, W.D., R.D. Grass, R.D. Evans, R.K. Leonard, D.M . 

Quincy, D.J. Hofmann, and G.L. Koenig, Unprecedented 1993 

ozone decrease over the United States from Dobson 

spectrophotometer observations, Geophys. Res. Lett., 21(3), 

201-204, 1994. 

Merrill, J.T., J.L. Moody, S.J. Oltmans, and H. Levy II, 

Meteorological analysis of tropospheric ozone profiles at 

Bermuda, J. Geophys. Res., in press, 1996. 

Moody, J.L., S.J. Oltmans, H. Levy II, and J.T. Merrill, A 

chemical transport climatology of tropospheric ozone: 

Bermuda 1988-1991 , J. Geophys. Res., 100, 7179-7194, 1995. 

Oltmans, S.J., and D.J. Hofmann, Increase in lower-stratospheric 

watervapor at a midlatitude Northern Hemisphere site from 

1981-1994, Nature, 374, 146- 149, 1995. 

Oltmans, S.J., and H. Levy II, Diurnal, synoptic and seasonal 

variability of surface ozone over the western North Atlantic, 

Nature. 358, 392-394, 1992. 

83 

Oltmans, S.J., J.A. Lathrop, A.S. LeFohn, H. Levy II, H.E. 

Scheel, W.A. Matthews, and I. Galbally, Recent changes in 

tropospheric ozone from ozonesonde and surface ozone 

measurements, IUGG XX/ General Assembly, B235, 1995 . 

Oltmans, S.J., H. Levy II, J. M. Harris, J.T. Merrill, J.L. Moody, 

J.A. Lathrop, W. Cuevas, M. Trainer, M.S. O'Neill, J.M. 

Prospero, H. Vomel, and B.J. Johnson, Summer and spring 

ozone profiles over the North Atlantic from Ozonesonde 

Measurements, J. Geophys. Res., in press, 1996. 

Peterson, J., and R. Rosson (Eds.), Climate Monitoring and 

Diagnostics Laboratory, No . 21. Summary Report 1992, 131 

pp., NOAA Environmental Research Laboratories, Boulder, 

co. 1993. 

Peterson, J., and R. Rosson (Eds.), Climate Monitoring and 

Diagnostics Laboratory, No. 22, Summary Report 1993, 152 

pp., NOAA Environmental Research Laboratories, Boulder, 

co. 1994. 

Staehelin, J., J. Thuclium, R. Buehler, A. Volz-Thomas, and W. 

Graber, Trends in surface ozone concentrations at Arosa, 

Switzerland, Atmos. Environ., 28, 75-87, 1994. 

Tarasick, D.W., D.I. Wardle, J.B. Kerr, J.J. Bellefleur, and J. 

Davies, Tropospheric ozone trends over Canada: 1980-1993, 

Geophys. Res. Lett., 22, 409-412, 1995. 

Volz, A., and D. Kley, Evaluation of the Montsouris series of 

ozone measurements made in the nineteenth century, Nature , 

332, 240-242, 1988. 

Vomel, H., DJ. Hofmann, SJ. Oltmans, and J.M. Harris, 

Evidence for midwinter chemical ozone destruction over 

Antarctica, Geophys. Res. Lett., 22(17 ), 2381-2384, I 995a. 

Vomel, H., SJ. Oltmans, D.J. Hofmann, T. Deshler, and J.M. 

Rosen , The evolution of the dehydration in the Antarctic 

vortex, J. Geophys. Res., 100. 13,919- 13,926. 1995b. 

World Meteorological Organization (WMO), Report of the 

International Ozone Trends Panel 1988, Global Ozone 

Research and Monitoring Project Report No. 18, WMO, 

Geneva, Switzerland, 194 pp., 1988. 
5. Nitrous Oxide and Halocompounds 

J.W. ELKINS (EDITOR), J.H. BUTLER, T.M. THOMPSON, S.A. MONTZKA, R.C. MYERS, J.M. LOBERT, S.A. YVON, 

P.R. WAMSLEY, F.L. MOORE, J.M. GILLIGAN, D.F. HURST (WITH CCG), A.D. CLARKE, T.H. SWANSON, 

C.M. VOLK, L. T. LOCK, L.S. GELLER (WITH CCG), G.S. DUTTON, R.M. DUNN, 

M.F. DICORLETO, T.J. BARING, AND A.H. HAYDEN 

5.1. CONTINUING PROGRAMS 

5.1.1. INTRODUCTION 

The Nitrous Oxide and Halocarbons Group was formed 

in 1986. In April 1995, the name was changed to Nitrous 

Oxide and Halocompounds Group (NOAH) to reflect the 

fact that noncarbon containing, halogenated gases such as 

sulfur hexafluoride (SF6) are now an integral part of our 

program. The general mission of the group is to quantify 

the distributions as well as the magnitudes of the sources 

and sinks for atmospheric nitrous oxide (N20) and 

halocarbons that include the chlorofluorocarbons (CFCs), 

chlorinated solvents (CCI4, CH3CC13, etc.), hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons (HFCs), 

methyl halides (CH3Br, CH3Cl, CH3I), halons, and 

numerous other important ozone-depleting and greenhouse 

gases. Two chromatographic techniques, electron capture 

detector-gas chromatography (EC-GC) and gas 

chromatograph-mass spectrometer (GC-MS), are used 

primarily to detect these trace atmospheric species. NOAH 

samples air from ground-based stations, towers, ocean 

vessels, aircraft, and balloons to accomplish its mission. 

Achieving these goals requires the production and 

maintenance of reliable gas calibration standards that are 

supplied to laboratories throughout the world. 

New sites for both the flask and in situ programs were 

added over the past 2 years. The location of these sites in 

the CMDL N20 and Halocompounds Network are shown in 

Figure 5.1. In cooperation with the Carbon Cycle Group 

(CCG), two tower sites (WITN Tower, North Carolina 

(ITN) and WLEF Tower, Wisconsin (LEF)) were added to 

the in situ program to ascertain source strengths of gases 

Fig. 5.1. Geographical locations of old and new stations in the 

NOAH flask (gray circles) and in situ (pluses) networks. 

84 

near urban and forested areas. With a similar purpose, an 

in situ gas chromatograph (GC) system was started at 

Harvard Forest (HFM) in collaboration with Harvard 

University scientists. At Alert, Northwest Territories, 

Canada (ALT) and in cooperation with the Canadian 

Atmospheric Environment Services (AES) program, an in 

situ GC for measuring N20 and SF6 also was installed and 

operated in 1995. Monthly, and in some cases weekly, 

flask samples were collected at these new in situ sites. 

Another site within CMDL, Cape Kumakahi, Hawaii 

(KUM), was added to obtain flask measurements of air 

from the remote, tropical, northern hemispheric marine 

boundary layer. Combined with MLO, this should allow us 

to estimate vertical gradients of trace atmospheric 

halocarbons, particularly those that react readily with 

sunlight or tropospheric OH . Table 5 .1 summarizes the 

geographic location and type of operations of eleven flask 

and nine in situ sampling sites. 

5.1.2. FLASK SAMPLES 

Overview 

NOAH' s flask sampling and measurement program 

underwent a number of changes and improvements in 1994 

and 1995. Most significant of these was the retirement of 

the "old" flask GC, a Hewlett-Packard (HP) Model 57 IOA 

GC-ECD, at the end of 1995 used for the measurement of 

CFC-12 (CCI2F2), CFC-I I (CCl3F), and N20 since 

inception of the old GMCC halocarbon monitoring 

program in 1973. This instrument, which operated in an 

almost entirely manual mode and for which data reduction 

was a cumbersome process, was replaced by the NOAH 

automated flask GC (OTTO). The OTTO GC, which began 

operation in 1992, analyzes samples for seven gases. A 

detailed comparison of mixing ratios of CFC- I I, CFC-12, 

and N20 from all stations between the old HP 571 OA and 

OTTO GCs shows that the new OTTO GC gives better 

precision and close agreement with the older GC (Figure 

5.2). The Whitey 300 mL-flasks were also removed from 

the sampling network. Over the past 10 years, the flask 

network was augmented with increasingly large flasks 

(0.85 L and 2.4 L) to accommodate the increased number 

of measurements and larger amounts of air required. The 

last Whitey flasks were filled at the end of 1995 at all 

stations except at the South Pole Observatory, Antarctica 

(SPO), which will not be able to return them until its 

reopening in the fall of 1996. Originally selected for 

sampling of stable CFCs and N20, the Whitey flasks, with 

their smaller volume and coarser internal surfaces, were 

also increasingly problematic for some of the more reactive 

gases such as methyl chloroform (CH3CCl 3), carbon 

tetrachloride (CCl4), and methyl bromide (CH3Br) that 

were added to the suite of measurements over time . All 

flasks in the network are now 0.85-L Biospherics or 2.4-L 

Max Planck Institute (MPI) electropolished, stainless steel 

containers with Nupro metal-bellows (SS-4H) valves. 
TABLE 5.1. Geographic and Network Information on NOAH Network Sites (In Order of Highest Latitude) 

Code Station 

ALT Alert, North West Territories. Canada* 

BRW Pt. Barrow, Alaska 

LEF WLEF tower, Wisconsint 

HFM Harvard Forest, Massachusetts* 

NWR Niwot Ridge, Colorado§ 

!TN WITN tower, North Carolinat 

MLO Mauna Loa, Hawaii 

KUM Cape Kumukahi, Hawaii 

SMO Tuluila, American Samoa 

CGO Cape Grim, Tasmania, Australia•• 

SPO South Pole, Antarctica 

Cooperative sites (F =flasks, I= in situ) with: 

*AES, in situ GC: Only N20 and SF6 

Latitude 

82.45°N 

71 .32°N 

45 .95°N 

42.54°N 

40.04°N 

35.37°N 

19.54°N 

19.52°N 

14.23°S 

40.4J 0 S 

89.98°S 

Elevations LST-GMT 

Longitude (m) (hr) Type 

62.52°W 210 -4 F,I 

136.60°W JI -9 F,I 

90.28°W 470 -6 F,I 

72.18°W 340 -5 F,I 

105.54°W 3013 -7 F,I 

77.39°W 9 -5 F,I 

155.58°W 3397 -10 F,I 

154.82°W 3 -JO F 

170.56°W 77 -11 F,I 

144.64°E 94 +10 F 

102.00°E 2841 +12 F,I 

tcco. Flasks will be added to WLEF in 1996. The ACATS-11 instrument ran as an in situ GC at WLEF for 1995. 

*Harvard University 

§University of Colorado 

••commonwealth Scientific and Industrial Research Organization (CSIRO) and Bureau of Meteorology, Australia 

Flasks are now filled to 376-505 kPa (40-60 psig) at all 

sites. Although this typically has not been a problem at 

sea level where the KNF Neuberger, Inc. pumps (Model 

UN05SV1) are rated to deliver 410 kPa (45 psi), samples 

collected at higher altitudes (SPO, Mauna Loa 

Observatory, Hawaii (MLO), Niwot Ridge, Colorado 

(NWR)) could only reach pressures around 273 kPa (25 

psig), which today are barely enough gas for CMDL 

measurements. To accommodate this change, the inlets 

were reconfigured to the automated, in situ GCs to allow 

the Neuberger pumps to draw air from the pressurized 

285 6 

........ 

0 

~ 280 

0 

E 

.s 

§ 275 

~ ca 

it 

GI 270 

0 

::::E 

~ 

c 265 

.. 6 .. 

+ 

6.0ldGC(NH) 

&OTTO(NH) 

o Old GC(SH) 

+OTTO (SH) 

+ 

.. 

260 -l-~-'- ~-'-~---+~ '-- -+-~--'-~---j 

94 94.S 95 

Year 

95.S 96 

Fig. 5.2. Continuity of CFC-I I data from the old GC and 

automated flask GC (OTTO) during 1994-1995. Data are shown 

for sites in both hemispheres. 

85 

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-I. 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 SF6 

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 

N20 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 
finalized and evaluated alongside all previous data within 

minutes following analysis. 

Measurements by EC-GC 

Improvements in Analysis. The prec1s1on of flask 

measurements by EC-GC has improved dramatically during 

1994-1995. Modifications in sampling technique and 

sample introduction, full automation of CFC, N20, and 

chlorocarbon measurements, and installation of 24-bit 

interfaces for analyses by OTIO 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 OTIO. 

The old Nelson Analytical, Inc. data acquisition and 

handling system on OTIO 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 AID 

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-11, CFC113, CH3CC1 3, CC14, N20, and SF6. 

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 et al., 1995b, 1996b]. Led by a marked drop in 

CH3CCl3, this suggested that the abundance of ozonedepleting halogen in the stratosphere could begin to 

decline in the near future. Other gases that began 

decreasing in abundance during this time include CFC-113, 

CC14, and, to a lesser extent CFC-11 (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 ~n Important Tracer and Strong Greenhouse Gas 

On a per molecule basis, SF6 is one of the strongest 

greenhouse gases known, about 25,000 times greater than 

C02 [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 - - - - - - - - - - - - - - - - - - - - - - - - - -

-

0 

.€ 

0 

E 

c.. 

-c 

0 

:u 

l!! 

LL 

CD 

0 

::::!E 

~ 

c 

460 

360 

260 

160 

xAlert 

o Pt. Barrow 

,,. Niwot Ridge -

AMaunaloa 

cAm. Samoa 

xCape Grim 

CFC-12 

CFC-11 

_ Autoflask GC _ 

Data Begin 

__ Cl:l3C_Cl3_ 

CCl4 

CFC-113 

I 

I l - -

I 

I 

I 

I l - - __., 

I 

60 +-~~~+--~L-----1~~~-+~_._~_,_~_._~_._~_._~_,_~_._~...._~_,__~,__ ..____...__~ 

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 -11 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, SF6 is rapidly accumulating in the atmos phere at 

-7% yr- 1. In addition to its importance as a greenh ouse 

gas, SF6 is a nearly ideal tracer of atmospheri c dynamics 

due to its well understood sources and long atmospheric 

lifetime of -3200 years [Ravishankara et al., 1993]. 

CMDL scientists recently began monitoring atmospheric 

SF6 in weekly flask samples from all baseline stations and 

many CCG network si tes as hi gh-resolution latitudinal 

profiles during the 1994 BLAST ocean cruises [Geller et 

al., 1994) as in situ strato spheric measurements fro m the 

Airborne Chromatograph for Atmospheric Tracers 

(ACATS) field missions [Elkins et al., 1996], and as in situ 

measurements at Alert, Harvard Forest, and North Carolina 

[Hurst et al., 1995). SF6 was measured with ECD-GC as 

described in Elkins et al. (1996]. Even though ambient 

levels of SF6 are onJy -3. 5 ppt, it is possible 10 measu re 

d.irect air injections (no sample preconcentration) Lo a 

prncision of 1-3%. A suite of gravimetri c SF6 standard 

ranging from 3 to 108 ppt was developed in th e NOAH 

Gro up. An intercalibration with the Uni versity of 

Heidelberg (Germany) showed CMDL measurements are 

less than 2% lower that the German calibration scale. 

The long-term trend of SF6 is illustrated in Figure 5.4, 

which shows NOAA data together with the University of 

Heidelberg data. These different data sets, coll ected and 

analyzed by different techniques, show good agreement. A 

northern hemispheri c trend was fit lo the combined Izafia 

and NWR data, becau e 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 

3 5 

3 0 

a 

~ 

2 5 

2 0 

1 5 

o Neumayer# 

• South Polo 

0 lzana# 

• Niwot Ridge 

llE N Carolina ,. BtASf crul"!'S 

• Alo rt 

. Barrow 

H Niwot Ridge 

A Mauna Loa 

t988 t990 1992 1994 t996 

year 

Fig. 5.4. Temporal trends of SF6. CMDL dota s hown together 

with Uni ve rsity of Hei delberg data [from M a i.r.r t i (I/., 1996, 

marked in thi: fi gure legend as #]. The Hei.delberg da to has been 

adju sted lo the CMDL calib rati on cale and binned into monthly 

means. The curve fill ing is described in the text. 

87 

0.23 ppt yr·l (6.86% yr·l). This trend, which is derived 

from the combined data sets, shows no significant 

difference from the trend derived from the University of 

Heidelberg data alone [Maiss et al., 1996]. Figure 5.5 

shows the high resolution latitudinal profiles of SF6 

collected over both the Pacific and Atlantic oceans on the 

BLAST cruises of 1994. Figure 5.5c also shows a mean 

latitudinal profile of SF6 for November 1995 obtained from 

the flask sampling network . These pro files should not be 

taken as representative of an overa ll global distribution of 

SF6 since they can vary seasonally. 

5.1.3. RITS CONTINUOUS GAS CHROMATOGRAPH 

SYSTEMS 

Operations Update 

A new watchdog timer turns the power off, then resets 

the computer, printer, and Nelson A to D boxes if a signal 

1987 <year <1996). This yields a late 1995 growth rate of 

by: y = 3.43 - 0.2352 x + 0.00487x2 (for x =(year - 1996); 

< O a) BLAST 11 E. Pac~ic Tranooct 

Jan JFob t994 

3, 5 

-60 -50 -40 -30 ·20 ·10 

< 0 b ) BLAST II I Atlantic l'ran;oct 

OctJNov t994 

3 ,5 

3 0 

2 s 

-60 -SO -40 ·30 ·20 ·10 

4 0 le) NOAH llask data I Nov 19951 

• Alert 

3 8 "- Pt Barrow 

• Cape Grim 

0 Mall'\a Loa 

.. Niwot Ridge 

"' /Vn, Samoa ~ 3 6 

• Souttl Pole 

.. North Cl!Oll lru 

On situ) ~ 

~ 

3. 

l .2 

·BO -60 .. 0 -20 

latitude 

. 

.:: 

I • d.lla_ points I - rurnng IM:i.tl 

I 0 20 30 '40 50 60 

~ data points 

- "61ni~mean 

10 20 JO .. 0 50 60 

20 40 60 80 

Fig. S.S. Latitudinal profiles of atmospheric SF6 (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 ±I standard deviation of the flask pair 

mixing ratios at each station. 
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 98 l 6s of mid-1980 vintage, were replaced in I 995 

by 486 PCs. The software port from HP Basic to TransEra 

HTBasic running in Microsoft Windows 3. I 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 N20 and 

SF6. 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 sol vent 

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. [ l 996b]. 

CFC-12 growth continues to slow down with the end of 

1995 growth rate about 6 ppt yr-1. Because CFC-12's 

major use is in domestic , commercial, and industrial 

88 

290 

280 

-

C..210 

c. 

-;::: 260 I 

0 

~ 250 

240 

ca 

a 

a 

0 

"Pt. Barrow 

.a. Nlwot Ridge 

o Mauna Loa 

"'Am.Samoa 

o South Pole 

230+...-........................................................................................ ~~ ......... ......1-

87 88 89 90 91 92 93 94 95 96 97 

Year 

Fig. 5.6. Monthly average CFC-I I 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 yr2, 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 

530 

Z-510 

c. 

c. -490 

N 

,.... 

0 470 

LL 

0 450 

430 

"Pt. Barrow 

.a. Niwot Ridge 

o Mauna Loa 

"'Am.Samoa 

o South Pole 

410;..-r.....,., ......... ..,...,.., ......... ,.....,...,r'TTT",..,..,.,..,,.......,.,.....,.., ......... ,.....,...,..,..,..,..,..,..,.,..,,.......,~ 

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. 
-... 25 

~ c. 20 c. 

-41 

- 15 cu 

a: -1.66 ppllyr/yr 

constant 

.c 10 deceleration 

i 

0 

... -. CJ 5 .... ,., 

N ...... ,.... ··. I 0 0 

LL 

0 -5 

1986 1988 1990 1992 1994 1996 1998 2000 

Year 

Fig. 5.8. A decrease in the global average growth rate of CFC12 is projected to become zero in mid-1999. 

diminished significantly. Atmospheric mixing ratios were 

observed to be slowly decreasing at approximately -0. 75 

ppt yr-I 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. [ l 996b]. The mixing 

ratios of both compounds are decreasing with time as a 

result of the Montreal Protocol. 

N20 continued to increase in the troposphere (Figure 

5 .11 ). The average global growth rate for 1995 was 0.61 

ppb yr-I. 

5.1.4. LEAPS 

Although precision of the Low Electron Attachment 

Potential Species (LEAPS) analyses was improved by an 

-'Q.160 

c. 

'E150 

... -s 140 

0 130 

:c 

0 120 

~110 

~ -100 

•Pt. Barrow 

& Nlwot Ridge 

o Mauna Loa 

""Am.Samoa 

o South Pole 

90.._..,..,.,..,.......,.....,., ........ ,.,..... ........ ......,......,., ........ ,......,..,.,.,..,.,.,...,.,.,.,.,......,.,..,........,.r 

87 88 89 90 91 92 93 94 95 96 97 

Year 

Fig. 5.9. Monthly average CH3CCl3 mixing ratios in ppt from 

the in situ GCs. 

89 

_ 112 

-

c. •Pt. Barrow 

E; 110 & Niwot Ridge 

41 o Mauna Loa 

"Cl ""Am.Samoa 

'C: 108 .2 

.c ~~· .. ~ 106 

-

... ~/ f(fl~ \,, .. 4': 41 

.... 

-e 

c 

0 

104 

102 

~~ 

""~' cu 

0 

100 

87 88 89 90 91 92 93 94 95 96 97 

Year 

Fig. 5.10. Monthly average CCl4 mixing ratios in ppt from the 

in situ GCs. 

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 AID board and an IBM PCcompatible 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 ra.tios of the three major halons (H1211 or CBrCIF2. H-1301 or CBrF3, and H-2402 or 

CBr2F4) 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, 

312 

-'[ 310 

c. 

-

Q.308 z 

306 

0 

•Pt. Barrow 

& Niwot Ridge 

o Mauna Loa 

""Am. Samoa 

o South Pole 

304 ................................. ~~ ........................................... ~ ........................................ 

87 88 89 90 91 92 93 94 95 96 97 

Year 

Fig. 5.11 . Monthly average N20 mixing ratios in ppb from the 

in situ GCs. 
3.5 

...... 

0 

:§ 

0 

E 

a. 2.5 ....... 

c 

0 

LI. 

~ GI 1.5 

0 

:iii 

- a_ J_ - Cl 

H1211 = O.OOB7x2 + ~.1494x + 2.9'774 

~ 

c 

1 - - - . . -. - - - - -' - - - - - ,- - -

H1301 = -p.014Bx2 + ~.1361x + 2.1~13 

0.5 • - - .i: - - it - - -,- -

' ' H2402 = ().0004x + 0.4661 

91 92 93 

Year 

, - L -

94 

·-· 

• H1211 

ci H1301 

t;. H2402 

! t••··-

95 96 

Fig. 5.12. Growth of halons in the atmosphere since 1991. 

Growth rates are given for January l, 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 199 5, 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. l ppt and 

higher. This was accomplished by using larger volumes of 

air per injection than in the original GC-MS instrument (up 

to l 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. 

90 

HCFC-22 (CHCIF2) Measurements 

The most abundant HCFC, HCFC-22, increased in the 

global troposphere at a rate of 4.5% yr-I (mean exponential 

rate estimated from flask samples collected between 1992 

and 1996; Table 5.2, Figure 5. l 3a, 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 Oz-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 em1ss10n 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-14lb (CH3CCl2F) Measurements 

Rapid atmospheric growth continues to be observed 

throughout both tropospheric hemispheres for HCFC-141 b 

(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- l 34a*, Mid-1994 and Mid-1995 

Mid-1994 Mid-1995 

Growth Mixing Growth Mixing 

Rate, Ratio, Rate, Ratio, 

Compound pptyrl ppt ppt yr- 1 ppt 

HCFC-22 5.3 111.l 5.6 116.6 

HCFC-142b 1.2 5.6 1.1 6.8 

HCFC-14Jb 1.4 1.9 1.9 3.5 

HFC-134a -0.7t N.D.:j: 1.2 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-l 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 I of Montzka et al. [1996b]. 

tEstimated from mean of two cruises in 1994. 

:j:Not determined. 
140 10.0 

a) HCFC-22 

c) HCFC-141b 

130 

7.5 

120 

110 5.0 

100 

2.5 

90 

80 0.0 

1991 1992 1993 1994 1995 1996 1991 1992 1993 1994 1995 1996 

10.0 

b) HCFC-142b 

4.0 

d) HFC-134a .. 7.5 3.0 

5.0 2.0 

2.5 1.0 

.. 

. 0.0 0.0 

1991 1992 1993 1994 1995 1996 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; Schauffier et al., 1995; Oram et al., 1995]. 

Preliminary emissions have been estimated recently for 

HCFC-141b by industry (P. Midgley, Alternative Fluorocarbon 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 

91 

influences ambient mixing ratios and affects the magnitude 

of the difference discussed here, mixing ratios are fairly 

insensitive to the lifetime chosen for HCFC-14lb during 

the initial phase of use and emission. For example, if we 

were to consider a lifetime for HFC-141 b of 20 years 

instead of the more accepted value of -IO 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-141 b 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 ± 

0.0 I ppt HCFC-141 b 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 I to 2 years after that observed at NWR in the 

CMDL archive. 
10 

~ 

• • ~~ !!i/' "'O 

c: • ::J --io •• P' 0 

a. .. E 

0 

(.) .. ...... 0.1 . .. a. .... '•'- .& .... a. .. 

0.01 +----+-----+-----+------+--......--+--. 

1986 1988 1990 1992 1994 1996 

Sampling date 

Fig. 5.14. Atmospheric dry mole fractions for HCFC-142b 

(filled diamonds) and HCFC-141 b (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 (CH3CClF2) Measurements 

Rapid atmospheric growth was also observed for HCFC142b 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 HCFCl 42b in Table 1 of Montzka et al. [ l 996b] 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 HCFC142b in the years before 1981, which is the first year for 

which industry emission estimates are available. Between 

92 

1992 and the end of 1995, m1xmg 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 difference 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 (CH2FCF3) Measurements 

Development of techniques for determining m1xmg 

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- l 34a has changed over the past 10 

years. Results from these analyses show that the 

abundance of HFC- l 34a 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 mid1995 [Montzka et al., 1996a]. Analysis of flask samples 

filled on board 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- l 34a 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., l 996a,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·l. 

In simultaneously-filled flasks, mixing ratios determined 

for HFC- J 34a were not significantly different. The amount 

of HFC- l 34a 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-l 34a have recently been 

estimated by industry (P. Midgley, personal 

communication, 1996). At the end of 1994, these 
em1ss10ns overestimate the observed abundance of HFC134a 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- I 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-141 b. The cause of this offset 

is currently unknown . Variability observed between 

instruments for measurements of HFC- l 34a 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 

<l 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 

Standard 

Compound Mean Deviation 

HCFC-14lb 0.96 

HCFC-142b 0.99 

HCFC-22 1.00 

HFC- l 34a 1.00 

0.04 

0.03 

0.03 

0. 13 

Mass to Charge Ratio 

Ions Monitored 

New 

Instrument 

81 

65 

67 

83 

Old 

Instrument 

81 

65 

51 

83 

*Comparison based 

instruments in 1995. 

on -150 flasks analyzed on both 

93 

shortly after midsummer in each hemisphere when Joss 

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 

60 

50 a) CH2Cl2 

40 

30 

20 

10 

•• Ill 

·~· j ogf Q. 0 Cll. :I: .t: efJ A> o. fl' • l r:P • !* e o.n.a e " • p lg • ,, ~ 

l • ' s'!I.' ••·:"ti ,·~·l!' · °' ~rioGJt>.r • •°'oo . •ll 

~ I\, 8 B.., •.Jt 0 : ! D oO . o , O (ID 

a o 8~ B 'lfi q;' °' o g O g BD ~ o 

..... 1 .... : ........... ~Mi;."' • ·...-:,.----. • I 

+--~~ -+-~~~-+-~~~-1--~~~-~~~~-1 

1991 1992 1993 1994 1995 1996 

20 

b) CHCl3 

15 

10 

5 

0 +-~~~-+-~~~-+-~~- 1-~~-t ~~~-1 

1991 1992 1993 1994 1995 

12 . 

10 c) C2Cl4 

8 

6 

4 

2 

1992 1993 

•. 

.~ 

e • • 

. .. J 0 : 

1994 1995 

1996 

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. 
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 Cl 

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 approximately twice that estimated for preindustrial times. 

Model studies suggest that the tropospheric abundance 

of Cl 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 (Cl 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. Measurements 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 Cl atoms contained in 

the most abundant CFCs, HCFCs, chlorinated solvents, and 

halon-1211, it is estimated that the tropospheric abundance 

of Cl 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 

Cl can be attributed to a decrease in the atmospheric 

abundance of CH3CC13 (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 onethird the rate observed in the late 1980s (Figure 5.7 and 

5.8). Increases in the abundance of HCFCs (HCFC-22, 

-142b, and -14lb) 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 

94 

-i5.. 

.3: 

(/) 

c:: 

0 

-e 

~ 0 

Iii 

:::c 

E 

.g 

Q) 

c:: 

·;:: 

..Q 

~ 

(.) 

Q) 

c:: 

·;:: 

..Q 

~ 

(.) 

'E 

Q) 

3150 

1 

a) 

3100 - •••••. -• .!.!·'-;;·~ •• ~ /"' . . ··~ .. :. 3050 •• • .......... ""-

•• ·:i·-!: 

3000 

2950 _,... ... • ~· .•········•···· i . ......... p .,... . •• 

.. ·- 2900 -...... 

2850 l--r--.-.-.-----t--T -r-r-+-.----r--.-~ 1992.0 1993.0 1994.0 1995.0 1996.0 

2550 

2500 

b) 

..... . . . . ?.:·-·:··.· 

2450 ----,,· . 

. ··~ ............. ........ .. ··~ 

~ ~2400 !I•• •••••• ._,..· · - -·;;-.. •• .._!.!.~ ow 

~ 

u 

2350 

; . .... ~(·· .,.. ..... ·'' . ffi 2300 •./" 

2250 I .... ~.~~. ~ . .-...1 ~. ~·~·--+-I ~~. --+-I · -;I 1992.0 1993.0 1994.0 1995.0 1996.0 

3200 ••• _ •. .,,,..,-· •• • • ---:.... . 

3250 t c) .... -·~.:· ~ / • . ;:·.....t. •.. .• 

'i:: 0 • . ·-··· . ....... 

ca. 

B _3150 i· +t 

-.~~ .3:3100 + + •••••• :J -~·······ii •••·····~~ Jr 3050 _., ••••• 

,.· •' ·"

·· .. 3000 -+ ~~~~~~~-+-~~~-+-~~---.----; 

1992.0 1993.0 1994.0 1995.0 1996.0 

Sampling Date 

Fig. 5.16. (a) The amount of total chlorine, (b) effective 

equivalent chlorine (EECI) and (c) equivalent chlorine (ECI) 

contained within anthropogenic halocarbons: CFC-I I, CFC-12, 

CFC-113, CH3CCl3, CCl4, HCFC-22, HCFC-142b, HCFC-141b, 

halon-1211, and halon-130 I. 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. 
TABLE 5.4. Mean Rate of Change Estimated for 

Mid-1995 From Measured Halocarbons (ppt yr·l )* 

Compound 

Chlorine 

EECI 

ECI 

Global 

-22 

-23 

-15 

NH SH 

-30 -20 

-35 -16 

-22 - 8 

*CFC-11, CFC-12, CFC-113, CH3CCl 3, CCl4• 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, EECl) [Daniel et al., 1995) 

and for the springtime, polar stratosphere (equivalent 

chlorine, ECl) 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 EEC! or EC! 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 EEC! yr-1. (Figure 

5.16b; Table 5.4; Montzka et al. [1996b]). 

The actual rate of change for EEC! 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 EEC! [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; Roering 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 ozonedepleting gases in the springtime polar vortex, equivalent 

chlorine (ECI) was calculated based upon CMDL 

95 

tropospheric halocarbon measurements. The current mix 

and growth rates of these gases in the troposphere will 

result in lower EC! in the polar stratosphere in the future. 

In mid-1995 equivalent chlorine was decreasing at 18 ± 7 

ppt EC! yr-1 (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]. Totalcolumn 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 l :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 

I, l ,2-trichloro-1,2,2-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 (CH4), carbon monoxide (CO), 

carbon dioxide (C02), hydrogen (H2), and nitrous oxide 

(N20) 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 (CH4 , 

CO, C02 , and H2 ) and for NOAH (N20). 

A total of 26 gravimetrically prepared CH4 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. 
A suite of gravimetrically prepared sulfur hexafluoride 

(SF6) in air standards were prepared for the first time this 

year. The standards were prepared with nominal mixing 

ratios ranging from 3 ppt to 110 ppt. 

A suite of hydrogen (H2) 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- l 34a in air standards were prepared in 1995 and 

were i ntercompared with existing HFC- l 34a 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 (CH3Br), methyl chloride 

(CH3CI), methyl iodide (CH31), dibromomethane 

(CH2Br2), tribromomethane (CHBr3), chlorodibromomethane (CHBr2CI), bromochloromethane (CH2BrCI), 

chloroiodomethane (CH2ICI), and diiodomethane (CH212). 

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 CH3CCl3 and CCl4 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 CH3CCl3 and from 190 ppb to 950 ppb 

for CC14. 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 CCl4 standards are 

consistent to within ±2%. 

5.2. AIRCRAFT GC PROJECT: ASHOE/MAESA 

MISSION 

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-I I, CFC-113, and CH4 (compounds measured 

previously with a two-channel version of the instrument) 

ACATS-IV measured CH3CCl3, CC14, CFC-12, H-1211, 

N20, SF6, and H2. 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 

96 

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, CH4 oxidation is the largest source of 

stratospheric water, which has a large global warming 

potential. Simultaneous CH4, hydrogen, and water 

measurements completely constrain the stratospheric 

hydrogen budget. (d) The age of stratospheric air is an 

important input to atmospheric models. SF6 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, SF6, CFC-II, 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 [Goldan 

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 I 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- I I, 

CFC-12, CFC-113, CCl4, CH3CCl 3, halon-1211, and CH4 

along with measurements of N20, NOy, and 03 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): 
Exhaust 

Sample Loop 

Pressure Control 

Sample Loops: 

Molecules: 

Channel: 4 

a 

~ 

:ll 1 L P-5 Cerrier Gas ~ 

l 

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, 

Mas~achusetts) servo-controlled to a pressure gauge (Micro Gage, Inc., El Monte, California). The GC inlet~ for th~ calibration, carrier 

gases, and air sample have 10 μm screens to remove particles. (b) The first position of the 12-~o~t o.sv permits loading the sample loop, 

backflushing of the pre-column, and detection of the peaks of interest from the previous sample inJecllon. (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. 

ax Q = P _ x -1X _ x - x mid 

d() T 'f;n (I) 

where x and Xmid are the mean tropical and midlatitude 

mixing ratios; 0 is potential temperature used as vertical 

coordinate; Q = d0/dt 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;n 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., 

I 996]; 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 N0/03 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. (I) with t;n = 00 (Figure 

5.18). Observed profiles of the longer-lived species, N10 

and CFC-12, and also of CH4 and NOy (not shown) deviate 

noticeably from unmixed profiles, indicating mixing with 

97 

photochemically aged midlatitude air. However, for CFC-

] 13, CFC-I I, and the shorter-lived species CH3CCl 3, 

CCl4, and halon- I 211 (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 [Volk 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 N20, 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 N20 is not destroyed 

until the air reaches higher altitudes. Because the 

abundance of N20 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;n) from the 

correlation diagrams in Figure 5.19, we consider Eq. (I) 

for the tropical mixing ratios of two tracers X and Y: 

Py-(-ry- 1 +yy)Y-Tin1(Y-Ymid) 

Px -(-r;1 + Y x)X- "l"in1(X- Xmid) 

(2) 
CFC-12 (ppt) CFC-11 (ppt) 

300 400 500 100 200 

520 

IT440K = 63 yrs I I T440K = 23 yrs I IT440K = 18 yrs [ IT440K = 3.9 yrs I 

- 500 ~ 

-0 480 

Cl.) 

..... 

:J 

- 460 n:s 

..... 

Cl.) 

c.. 440 • 6 

E 

Cl.) 

I- 420 

cu 

:;::: 

c: 400 

Cl.) 

-0 

D.. 380 

360 

200 240 280 40 60 80 

N20 (ppb) CFC-113 (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 !OK 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 ('t· = ~) (-) from 0 = 380K (the mean tropical tropopause height) along with an uncertainty 

range induced by a 50% uncertainty in Q 'C---). Also indicated is the "effective lifetime" T (=l/(t- 1+y)) at 0 = 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 't;n is treated as 

a free (altitude-independent) parameter. For each pair of 

tracers displayed in Figure 5.18, the value of 't;n 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, CH4, N20, CFC-12, 

CFC-113, and NOy, versus 0 3, 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 't;n 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 [Roering 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 

't;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): 

98 

P P a ---=--(pw) 

't'out 't';n dz (3) 

where 'tout 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 't;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 ('tout) 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 

C02 and H20 from the tropics to midlatitudes [Roering 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 NOx (=NO + N02) and other effluents emitted 
z;-

D. 100 .e, 

o" ao 

o.., 

::c 60 

0 

4.0 

z;-

D. 3.0 

.e, 

.... 

.... 2.0 ('II 

.... 

± 1.0 

220 

.. ~· dr ~7-1 

240 260 280 300 

N20 (ppb) 

250 0 

~ 200 :: 

1soi .e 

Fig 5.19. Correlations of mixing ratios for the shorter-lived 

species versus N20 in the tropics (dark filled circles) and at 

midlatitudes (light filled circles) [Volk et al., I 996]. 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 ('t; 0= ~) 

(short dash) and for a constant entrainment time 't; 0 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/(i:-l+g)) at 0 = 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 NOx 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 atmospheric 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 subtropics such as observed in the NOyf03 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 parameters 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. 

99 

Fraction of Mid-latitude Air(%) 

0 20 40 60 80 100 rtr"..,.-r-T~r---r----r~-r-i~""""T-r---rT~.--r.------.2 1 

g 480 

© 

E 460 :i 

~ 

G; 440 Cl. 

E 

.. 420 Iiii 

~ 400 .. 

0 

c.. 380 

0 

A 

entrainmenl (11-rin) 

\ 

\ detrainment (1'10 u1

l \ 

'----I .... 

40 80 120 

Transport rate (%/month) 

B .. 

"C 

20 "S! 

i:i 

19 3· 

~ 

18 a:: 

2" 

Cl. 

11> 

---- : 11.3 months 17 ">? w = o.s•naminal .! 

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., I 996]. Results are for 

't; 0 =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 't;0 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 chlorinecontaining 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 stratosphere, the first real-time, in situ stratospheric 

measurements of the purely anthropogenic compound, 

CBrClF2 (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 

m1ss10n. The complete H-1211 data set for ASHOE/ 

MAESA 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 CH3Br, H-1211, H-1301, CH2Br2, H2402, and CH2BrCI 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-1211, H-1301, H-2402, and CH2Br2. 

The CH3Br data were collected on transects of the Atlantic 

and Pacific Oceans in 1994 by CMDL researchers 
20 

18 

rx 

-~ ~ 

-----··--<>" ! .\ •, ~~ 6

'J : ,,,A A ~ ~ \,a I !>l ~ ~ <JI,<'/ : Pl1r ~ .;. ' QI = -~ : : 

f 

~ <> _ ~ 

<> <> l x'.,;s5±.._ : M ! I 

-X ~~-- --- rx---·-·-······ r ·· ···;;· ......... 1- -------- .. ---- x j ~ • Aj X' ; ~ 0 A i . llj x : 

; f>t[ l 

'<J oo--:-or·--- ________ , _____ ---· .x. x. 

x I 

i l>l : '-' ~ ·---· !<l ---1>4> ---- -·----·~· .. ·····---··---

~* x i 

x_ 

14 ... --·-j--··---···----o ---·------·-----· __ ,,_ -- ... x 

I xi 

x 

I 

.! 

: 

; 

I 

I 

~ <> ! 

x * ! I ! 

x ! 

,,,_____ 1 - * I i 

i· ., I 

x i I 

1'E -----·-·---·····----·-··-- --+--··-·---- ~. ·-·. -; 

! ~ 

12 i 

·---·r-·-

j 

Bin Ranges in ppt of H-1211: ! 

D 0.4 - 0.8 !:-:,, 0.8 - 1.2 'V 1.2 - 1.6 <> 1.6 - 2.0 

2.4 - 2.8 [XI 2.8 - 3.2 z 3.2- 3.6 * 3.6 - 4.0 

10 

-60 -40 -20 0 20 40 60 

Latitude 

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 al., 1995]. The CH2BrCI 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. 

Tropospheric [CBr yl<t) = 

[CH3Br] + [H-121 l](t) + 

[H-1301](t) + 2[CH2Br2] + (4) 

2[H-2402](t) + [CH2BrCI] = 

8.64 + (0.2863t) + (-0.0235 t2) 

where t is time in years measured from 1994. The 

tropospheric burden of these species provides an upper 

limit on the concurrent stratospheric bromine burden. 

ACATS-IV ASHOE/MAESA measurements of the sulfur 

hexafluoride (SF6) mixing ratios are used to determine the 

100 

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 

Total Bromine = Organic Bromine + 

Inorganic Bromine (5) 

where Total Br is determined as outlined previously. The 

only organic bromine species that ACATS-IV measured is 

H-1211, but from whole air sampler measurements from 

NCAR (Schauffler, private communication, 1996) and the 

University of California, Irvine (Blake, private 

communication, 1996), correlations were compiled of the 

unmeasured species with measured CFCs. These 

correlations are shown in Figure 5.22. These correlations 

permit an estimate of total organic bromine (Figure 5.23). 
1.0 

0.5 

0.0 1--1-""""""'CJ..-'-L....L.-'-L....L.-'-L....L.-'-L....L.-'-1-.1,. ........ 1..,1-...L...j 

1.0 

0.5 

0.0 1--1..-;e;;i.....&.....L...1....L.....L...JL...L-l-.................... ....&.....L...1 ............... '--1 

1.0 

0.5 

0.0 l-J-.J...JU....J.....J,.....-W-4-.L....1.i~~Q..,:!;...J...~....1...J,.-1.-1 

1.0 

0.5 

0.0 ....... -=:; ............... ..L..J....L.....L...JL...L-1-..................... _._ ........ ..,..._ ......... '--I 

1.0 

0.5 

0.0 L....L--1...J.....L-L...Lil.JlllilljlO;~-= ............... ........,,-L...L...1L...L-I-..... 

0.0 0.2 0.4 0.6 0.8 1.0 1.2 

Norm. CFC-11 

1.0 

0.5 

0.0 L....L....1.o::t::::l:...L...L...1..-'-L....L.-'-L....L.-'-L....L.-'-L....L.-'-L....L....L..I 

0.0 0.2 0.4 0.6 0.8 1.0 1.2 

Norm. CFC-12 

Fig. 5.22. Correlations of bromine-containing species with CFC11. The longest-lived species, H-1301, is correlated with CFC-12. 

Each data set was normalized individually and then the complete 

data set for each species was fit with a function of the form [X0 ] = 

[CFC0 ]0ldJ, where the subscript, n, represents a normalized 

quantity. The longest lived species, H-1301, is correlated with 

CFC-12. ACATS-IV data are shown by circles. NCAR data are 

denoted by triangles and UC-Irvine data are shown by squares. 

101 

The oldest air sampled by ACATS-IV during ASHOE/ 

MAES A indicated that all of the stratospheric bromine was 

in inorganic forms. 

5.3. LACE 

A new project titled Lightweight Airborne 

Chromatograph Experiment (LACE) is a 2-channel GC 

designed to measure CFC-I I, CFC-113, and SF6. It was 

built to fly on a balloon and take data from altitudes up to 

32 km. This will complement the lower altitude NASA 

ER-2 data, help solidify understanding of atmospheric 

dynamics, and provide a comparison for midlatitude and 

tropics chemistry. NOAH scientists used the ACATS-IV 

instrument as a starting point; however, several key 

differences have been introduced. The balloon's fast 

decent of 2.5 m s-1 imposes a faster data sample rate of I 

minute to acquire reasonable coverage of data every 150 m. 

Sample rates for the ACATS-IV instrument are currently 3 

and 6 minutes with the exception of one recent flight 

where the new I-minute chromatography (Figure 5.24) was 

successfully flown. Because of the higher altitude, clean 

air samples must be loaded from an ambient pressure of 

only I 0 mb compared to an ambient pressure of 50 mb or 

higher for the ACATS instrument. Finally, in contrast to 

the ER-2's Q-bay, which is pressurized to a minimum of 

300 mb and houses the ACATS instrument, the balloon 

platform required a self-pressurized, lighter-weight 

instrument that uses less power. 

Problems solved in building this GC for a balloon 

platform were similar to those that will occur when placing 

an instrument in a remotely piloted aircraft (RP A) like 

Perseus. When an operational RP A becomes available, 

LACE can be easily modified for flight on this type of 

platform. 

5.4. OCEAN PROJECT: BLAST CRUISES 

In 1994 the NOAH Group participated in two research 

cruises for the Bromine Latitudinal Air/Sea Transect 

(BLAST) project. The first cruise extended through the 

East Pacific between Seattle, Washington, and Punta 

Arenas, Chile, from January 26 to February 17, 1994; the 

second cruise was conducted between October 18 and 

November 21, 1994, heading through the Atlantic Ocean 

from Bremerhaven, Germany, to Punta Arenas, Chile 

(Figure 5.25). The main objective of these cruises was to 

gather data to ascertain the presence or absence of a 

potential oceanic source for methyl bromide (CH3Br). 

Methyl bromide contributes about 50% to tropospheric 

organic bromine and, hence, has received considerable 

attention, particularly because its budget is currently not 

well understood [Butler, 1995, 1996; Butler and 

Rodriguez, 1996]. Frequently collected CH3Br data from 

the two expeditions constitute the largest data set for 

oceanic CH3Br to date and the first solid estimate of 

oceanic emission, production, and chemical degradation of 

the compound. It is concluded from these studies that the 

ocean is not a net source of CH3Br but rather a net sink 

[lobe rt et al., 1995, 1996; Butler et al., 1995]. Although 

CH3Br is both produced and consumed everywhere in the 

surface ocean [Butler, 1994], the rate of consumption 

exceeds that of production in most waters sampled. 

Exceptions were coastal and coastally-influenced waters, 
.· ,/ 

i Br Total ./ 

' t .... I , i : / 

20 "···,::·.- .... ::::::::::·········!·· .... ;,,; ... .,;"'o; '' '' '' '"'',,f ''''"''''-·"''"'"'"''''''''""1 ... ~ .. , .. ,,"" .. ;, .. ,,,,. ........... -f ·- ~ .... ,,~ .. ·"' "" '~r:: ~~7l:::: · 

......... j············...... . i·: 

15 .-.. 

.... 

c. 

c. ..._, 

Q.I 

... = s 

0 

.... 10 ~ 

5 .. ~1 -·~ ·-~-~~.---~· -··· ;'•. 

i · ........ ..... . 

·· .. 

····················· ·· ... 

·· .. o.._ ....... ::;..i... ....... .._"""''-L.. ....... ~.._ ...................... __......_ ..................... __..._.._ ............... ___.~--------~ ...... -------~---

o 50 100 150 

CFC-11 (ppt) 

200 250 300 

Fig. 5.23. Calculated results for the total stratospheric bromine, Br,0 ,.1• (open triangles), and its partitioning into total organic CBry 

(open circles), and inorganic, Bry (open diamonds), components. The dashed lines represent standard deviation windows. 

which were typically supersaturated, and areas of open 

ocean upwelling, where CH3Br saturation anomalies were 

close to zero. About 80% of the oceans are undersaturated 

in CH3Br, representing a net annual sink of 8-22 Gg yr-I. 

CH3Br data from the second cruise further supported 

NOAH conclusions from the first expedition. The latter 

results give greater strength to the global extrapolations of 

the first data set. Data from the two cruises are 

summarized in Table 5.5 and Figure 5.26. 

The best estimate of the partial lifetime of atmospheric 

CH3Br with respect to oceanic losses is 2.7 (2.4-6.5) years. 

This range was derived from a 40-year, global data set of 

sea surface temperatures and wind speeds [Yvon and 

Butler, 1996] (Figure 5.27). Data from the two 

expeditions suggested a shorter lifetime of CH3Br of about 

2.4 years. The difference between the two estimates is 

due to higher than average wind speeds encountered during 

the cruises. The estimated atmospheric lifetime, based 

upon combined atmospheric, soil, and oceanic losses, is 

now 0.8 years compared to earlier estimates of 

1.8-2.1 years when the ocean was considered an 

insignificant sink, the soil sink [Shorter et al., 1995] was 

unknown, and tropospheric OH concentrations were 

underestimated by 15% [Prinn et al., 1995]. The oceanic 

sink correspondingly lowers ozone depletion potential 

estimates for CH3Br by about one-third from earlier 

estimates. 

102 

TABLE 5.5. Results for Atmospheric and Oceanic 

CH3Br From BLAST I and BLAST II Cruises 

Global mean (ppt) 

NH mean (ppt) 

SH mean (ppt) 

Variability (ppt) 

ITCZ ( 0 N) 

!HD (ppt) 

NH/SH ratio 

SA (%) 

P (Gg yr- 1) 

L (Gg yr· I 

Net Flux (Gg yr-I) 

Combined 

BLAST I BLAST II Estimate 

9.8 

11.2 

8.6 

0.6 

4. 1 

2.65 

1.31 

-15.7 

175 

-188 

-13.0 

10.4 

11.7 

9.4 

1.2 

6.4 

2.31 

1.25 

-19.7 

248 

-267 

-18.7 

10.l 

11.5 

9.0 

2.48 

l.28 

-18.4 

214 

-229 

-14.8 

Measured global, northern hemispheric, and southern hemispheric means (NH and SH) and the observed interhemispheric 

tropical convergence zone (ITCZ), which was used to determine 

the hemispheric ratios. The net saturation anomaly (SA), the 

hemispheric ratios, and the interhemispheric difference (IHD) 

were calculated from the measurements. Finally, estimates of the 

oceanic production (P), oceanic loss (L), and the net oceanic flux 

of CH3Br were added. The net satura-tion anomaly is the percent 

departure of CH3Br in the surface ocean from equilibrium with 

the atmosphere. Negative numbers indicate fluxes from the 

atmosphere to the ocean. Variability is the residual standard 

deviation of a loess fit through all atmospheric measurements. 
25 

" 

~ 20 x 

15 

10 

40 

" 0 30 

)( 

20 

300 

::: 250 

-;; 

" 200 ~ 

& 150 

0. 

.e 

100 

~ u 50 

0 

0 

I ACATS CH·3. I 

F·11 

I-min_ 

~ ~ 00 00 100 1~ 1~ 1~ 

sec. 

Linear Regr'e5$ion Results: 

y = (0.3 ± 2.2) + (1.000 ± 0 009) x 

•'= o.994302 - · 95~ confidence on regression 

' . ~ Fllghl: 951031 . 

.; -••• --•• ......-oo••~•••" i ...... ~ .............. l ........ _ ······~·· ·· 

0 50 100 150 200 250 

CFC· I I (ppt)(channel I) 

300 

Fig. 5.24. Simultaneous I- and 3-minute chromatograms and a 

correlation plot of the I-minute CFC-11 versus the 3-minute 

CFC-11 data for this flight. 

Fig. 5.25. Cruise tracks of both ocean missions. The cruises 

covered a diverse mixture of coastal waters, upwelling regions, 

large open ocean areas, and coastally influenced areas in the East 

Pacific and Atlantic oceans. 

103 

Concentrations of CFC-12, CH3Br, and CH3CI in water 

column samples collected during BLAST II were higher 

within the mixed layer than at depth. Considering that 

oceanic CFC-12 originates from the atmosphere, this 

suggests that both CH3Br and CH3Cl have sources 

associated with the atmosphere or surface waters. 

Departures of CH3Br and CH3Cl concentrations from those 

of CFC-12 may result from chemical or biological in situ 

production or degradation of these gases. 

Potential artifacts associated with sampling and analysis 

of CH3Br and other compounds were investigated. These 

studies revealed significant problems associated with the 

measurement of CH3Br from air stored in stainless steel 

flasks that have historically been used for measuring 

CH3Br in the atmosphere. From a comparison between 

measurements made shipboard and from air stored in 

flasks, and from the reanalysis of air in flasks over time, it 

has been determined that CH3Br in stainless steel flasks 

can be unstable and may increase or decrease with time. 

In addition, results for CH3Br determined by GC-ECD can 

be compromised by some GC configurations [Montzka et 

al., l 995a; Lobert et al., 1996). 

Besides CH3Br, a suite of CFCs and methyl halides was 

measured during the cruises, and data for oceanic methyl 

chloride (CH3CI), methyl iodide (CH3I), dibromomethane 

(CH2Br2), and bromoform (CHBr3) are currently being 

finalized for publication. 

5.5. STEALTH PROJECT: AUTOMATED 

FOUR-CHANNEL FIELD GAS CHROMATOGRAPHS 

5.5.1. OVERVIEW 

The STEALTH GC was installed at ALT, HFM, ITN, 

and LEF with different custom configurations for each 

client. The four-channel STEAL TH GC will replace the 

old HP5920 GCs at the Radiatively Important Trace 

Species (RITS) stations (BRW, NWR, MLO, SMO, and 

SPO) and is currently being constructed and laboratory 

tested. 

The data acquisition software and operating system of 

the STEALTH GC computer is being upgraded. NOAH is 

currently cooperating with personnel at Harvard University 

in the development of new data acquisition software for the 

PC-based UNIX operating system, QNX. QNX is a 

multitasking and multi-user operating system that will 

facilitate data acquisition, data retrieval, data archival, and 

real-time display. The airborne GC, ACATS-IV, is 

currently being configured to test the QNX data acquisition 

software. In 1996, NOAH scientists will implement the 

software on an ACATS-IV deployment and on the new 

STEALTH station GCs. 

The STEALTH GC is an ECD/GC system based on 

technology developed on ACATS-IV and LACE. The first 

channel encompasses a Shimadzu mini-2E ECD and a 

Porapak Q packed column (Figure 5.28). This channel 

allows for the measurement of N10 and SF6. Channel two 

of the instrument uses a Valeo ECD along with a Unibeads 

2S packed column. This configuration is capable of 

measuring N20, CFC-12, H-1211, CFC-I I, and CFC-113 . 

The third channel also uses a Valeo ECD and an OV-10 I 

packed column and is used to measure CFC-I I, CFC-113, 

CHCl3, CH3CC13, CCl4, and C2Cl4 (perchloro-
20 

E: 

.So 15 

c 

.S? 

u 

~ GI 10 

Ci 

~ 

5 

-55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 

i 

! 

20 

15 

5 

Latitude 

-55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 40 45 50 55 

Latitude 

50% 

-50% L.Ll.LJ.JL.ll.J..U..J..U...U...LU..LJ.J..W..LLI.J...W...U..L.ll.LU.J.J..JL.ll.LU..LJ.J...U..LLI.J..L.1.J...l.JL.ll.LU.J..J.J..LJ..LLI..LLI..LL.l.J..LJ..LJ...L.LJU-L.J...LJ...L.LJl..l....L.Ll...L.J...J...JL..l..LL..U...l..LI 

-55 -50 -45 -40 -35 -30 -25 -20 -15 -10 -5 0 5 10 15 20 25 30 35 4-0 45 50 55 

Latitude 

Fig, 5.26 Atmospheric CH3Br, its partial pressure in the surface water, and the net saturation anomalies for both cruises. 

ethylene, PCE). All of the aforementioned channels have 

been proven in other similar instruments that have been 

constructed and deployed to various sites. 

Channel four, however, has just recently been developed 

and uses quite a different setup than the other three 

channels. This channel also uses a Valeo ECD, but 

incorporates a GS Q capillary column rather than a packed 

column. This channel also uses a Neslab cryocooler which 

allows for the preconcentration trapping of the three trace 

gasses, HCFC-22, CH3CI, and CH3Br being measured. 

With the current configuration of this channel, one is 

capable of measurements of better than I% for HCFC-22, 

0.5% for CH3CI, and 2% for CH 3Br. Figure 5.28d is a 

chromatogram of the newly developed fourth channel. 

104 

5.5.2. TOWER GC AT WITN IN COOPERATION 

WITH CCG 

The GC and instruments that monitor C02 and 222Rn are 

housed in a building adjacent to a tall tower (WITN) in 

rural North Carolina. Diaphragm pumps located in the 

building continuously draw air from 51, 123, and 496 m 

above ground through I cm i.d. Dekabon tubing affixed to 

the tower. Detailed descriptions of sample handling and 

drying, and initial results of C02 measurements at WITN 

were published [Bakwin et al., 1995]. GC analyses of air 

from each sampling level and of two calibrated whole-air 

standards are performed hourly. Standards are stored at 

high pressure in "Aculife"-treated aluminum cylinders. 
60N 

40N 

ON 

20S 

40S 

60S 

BOS L;.1_.._._......._ ......... .....__._._....._.._._......._...L...J._,_,_._._,_.._.__._.__._,_-'--'--'--''--'---L.J 

180W 120W sow OE 60E 120E 1BOE 

kocean,i (10-5 Y"1) 

0 2 3 4 5 6 7 8 9 1o+ 

Fig. 5.27. Map of the global distribution of the rate constant 

(kocean, 1) for the irreversible uptake of atmospheric methyl 

bromide (CH3Br) by the ocean (kocean, I = l/-C0 cean, 1; global 'C0 = 

2.7 years). This rate constant is computed with data from 

COADS for each cell on a 2° x 2° grid. Note that higher loss 

rates are found in the northern hemisphere in regions containing 

both high wind speeds and warm SST's. 

(a) (b) 

MOO ~ 

-· 

3000 "- __ ,.._-___ -I 

500 1000 1500 

... ' IJ ' 

12 

" 

IO 

: J 

(c) 400 8UO 1200 ll'IOU 

Timirt .. 1 

(d) 1000 llOO l .(IKI 

TJmet•l 

Fig. 5.28. Chromatograms of all four channels of the STEALTH 

GC that will replace the old RITS HP5890 GCs. 

105 

Chromatographic and housekeeping data are logged by a 

486SX PC and archived on 1.2 Gb optical disks that are 

sent to the NOAH laboratory each week for analysis. 

Instruments and gas supplies are maintained by a 

technician who visits the site weekly . 

Monthly statistics of m1xmg ratios for several 

halocompounds and N20 at the WITN tower are presented 

in Figure 5.29. Statistics for each sampling height (51, 

123, and 496 m) are denoted by 1, 2, and 3, respectively, 

along the bottom of each plot . For each month, the mean 

(circle) and standard deviation (distance between circle 

and asterisk) of the mixing ratios of each species generally 

decrease with increasing sample height. Variability in 

trace gas mixing ratios within the continental boundary 

layer is determined by sources, sinks, boundary layer 

dynamics, and horizontal transport. Since each species 

plotted in Figure 5.29 has solely ground-based sources, it 

is expected that mixing ratios and variability should be 

greatest near the ground. This effect is inflated at night by 

the accumulation of emissions from local, ground-based 

sources in the shallow nocturnal stable layer. 

Figure 5.30 gives statistics for the 51-496 m mixing 

ratio gradients, binned by hour of day, of N20, CH3CC13, 

and SF6 for November 1995. Significant vertical gradients 

of N20 and CH3CC13 were observed at night, indicating 

these compounds were emitted by local, ground-based 

sources. In contrast, the insignificant accumulation of SF6 

in the nocturnal stable layer suggests an absence of local, 

ground-based sources. During the late morning and 

afternoon, convection rapidly mixes air from the ground to 

>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 CH3CCl3 and C2Cl 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 C2Cl 4 [McCulloch and Midgely, 1996]. 

CH3CC13 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 el al., 

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 C02 age of about I 00 years [Battle el al., 1996). 
285 

15:200 

a. 

- 275 ..... 

";- 270 (.) 

u. 

(.) 265 

560 

-

a 

.g,550 

N 

..... 540 

c.) 

t5 530 

~ 87 

§: 86 

-('I) 85 

..... 84 

c.) 

• 

~-----· .. .,/'- .- ~~!!~~i!i~ . .. • 123 123 123 123 123 123 123 

• 

123 123 123 ~ 123 123 

• 

• . .. . . 

123 

~ 123 ~~~~~ii 123 123 123 123 123 

.... .. ,di!, ..... 

~ ~+ j1f rt!~~+!~ ~~t~~~~ u. 83 .. (.) DT._ .-. 

82 1~ 123 123 123 123 123 123 123 123 123 123 123 123 

4.5 

--a. 

.g,4.0 

U.'° 

en 3.5 

.,/'- .. • 

_.;#;~'~ S-v_.-.-... 123 123 123 123 123 123 

Ii) Ii) Ii) Ii) Ii) Ii) 

~ ~ ~ ~ ~ ~ ... 

~150 

a 

.9:140 

_M 130 

(.) 

~120 

:I: 

(.) 110 

110 ~ 

§: 109 

-.:: 108 

(.) 

(.) 107 

123 123 123 123 123 123 123 

100 123123123123123123123 

320 

..-.318 

.g_ 316 

-9:314 

0 312 N 

z 310 

308 

• 

;f ~~~Ei 1~ 123 123 123 123 1Y 

• 

Fig. 5.29. Monthly statistics of CFC-I I, 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 ±I standard deviation, respectively. The numbers across the bottom of each plot are the 

sampling level (I, 2, and 3 refer to 51, 123, and 496 m, respectively). 

N20 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 

N20 in the atmosphere had to be about 280 ppb and that 

N20 was increasing steadily through the latter part of the 

20th century. The growth rate of atmospheric N20 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.). N20 covaried well with C02 throughout 

the profile, although the smoothness of the fit could be 

attributable to subsurface diffusion of the gases. 

Nevertheless, the overall trend of N20 as a function of 

C02 was 0.50 ± 0.03 ppb N10 ppm-I C02-I (95% 

confidence level, r2 = 0.98). 

106 

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 C02 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-11 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 (<l % of today's atmosphere) and that two pairs 

of flasks showed higher levels of CFC-11 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 
3 

-..c 

a. 

..3: 2 

-c::: 

Q) 

'6 

~ 

{!) 

0 

C\J 

0 

z -1 

a a 

..3: 

a 

a. 

- 0.4 

"E 

Q) 

'6 

~ 0.2 

{!) 

LL<O 

CJ) 0.0 

• • 

• • • • • 

• •• • JI( 

JI( 

.;. 

0 

JI( 

3 6 9 12 15 18 21 24 

Hour of Day (Local Time) 

Fig. 5.30. Statistics of 51 m - 496 m mixing ratio gradients for 

N20, CH3CCI 3, and SF6, 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 CH3Br, 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 

107 

124 

122 

-

0.. 

..3: 120 

C') 

t5 

(.) 

C') 118 

I 

(.) 

116 

114 

WITN Tower, 496 m 

3 

3 

3 

3 

3 

10 

3 

3 

3 

3 3 

3 

3 

3 3 

y = 0.62x + 111 

r = 0.861 

15 20 

Fig, 5.3 I. Correlation between CH3CCl 3 and C2Cl 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 - - -- - - - - - , 

.-.. -/ 

0 - BP ._ :§ 295 - - - - - ia:i ' 

0 .. ' tic 

E .. .._.. c .. ' .. •Cl "' Cl 

0 285 - - -.. - - - N 

z .. .. ti Cl .. 

.. Cl .. ' 

.. 275 -,_ - ·SH Flasks (CMDL) 

& Ant. Ice (Machida 1995) 

c SPO Firn (CMDL) 

265-'-~~-'-~~-L~~~'--~~-'-~---

1900 1920 1940 1960 1980 2000 

Year (based on C02) 

Fig. 5.32. History of atmospheric N20 over the past century, 

derived from antarctic ice-core measurements [Machida et al., 

I 995), 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 C02 in the samples with 

the atmospheric C02 history of Etheridge et al. [ 1996). 

Diffusivities of N20 and C02 are assumed to be identical and ice 

core data of Machida et al. (1995) have been lowered by I ppb to 

conform to the CMDL scale. 
CFC-11 (pmol/mol) 

0 10 20 30 40 50 

-105 l 

• 

South ~ole Flrn Air 

-110 !. • 6 ·-

., A •6 

g ,•6 mA 

= ·- -115 

c. 

GI • 

0 • 

.. -120 .... - 16 Measured 1-

• •Grav. Corrected 

• 

-125 

Fig. 5.33. CFC-I I 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 122 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-I I, 

which is a gas heavier than air. Again, the error is small. 

Dry Mole Fraction (pmol/mol) 

0 100 200 300 400 500 600 

0 

• ' "' 

-20 . - • A 

•• A 

-40 -. - - ..ti -

• . A 

E' -60 -· -· . - A -- - - ...... SPO FirnAir .c • A -

c. • A 

Cll -80 - - ~ .. 0 "" • A 

• A • CFC-11 

-100 - . - 6 . A CFC-12 , 

-120 . -

-140 _,_ __ L___ _ __,.__ _ __. __ _._ __ _._ _ ___, 

Fig. 5.34. Depth profiles of CFC -11 and -12 in South Pole firn 

air. Mole fractions of both gases near the bottom of the firn are 

less than I% of the present day values, suggesting that natural 

sources are minimal or non-existent. 

108 

0 

0 

-20 

-40 

E' -60 ...... 

.c 

-

c. 

Cll -80 - 0 

-100 

-120 

-140 

Dry Mole Fraction (pmol/mol) 

25 50 75 100 125 

6 • 

SPO'Firn Air ' ·- • 6 

-4 '• -

A• 

· M 'r 

._. :-6-

., • A 

, . b 

,. 

'• 6 , A 

• • r /!r 

·~ , AA • •• 'A At/!i-6 ' 

.!\ ~A" - • - -

•A 

.- ACCl4 

•CH3CCl3 

Fig. 5.35. Depth profiles of CC14 and CH3CCI 3 in South Pole 

firn. There is some evidence of contamination of a few ppt in the 

CH3CCl 3 data, although mole fractions of this compound came 

very close to zero near the bottom of the profile. Mole fractions 

of CCl4 never fell below I 0 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) 

0 2 4 6 8 10 

a 6 • 

-20 -- - ID- -A .. _ 

a · .a. SPO ~irn Air • 

-40 

a 6 . • --E -60 Cil -6- -.• - ...... 

.c 8& -

c. 1Il6 ' 

•CH3Br • ~ GI -80 - a H1301 0 ca .. at. .a. H1211 • IB .. -100 -·· -

.i~ -120 - -- ,_ - -

-140 

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. CH3Br is about 6.5 ppt in 

air nominally dating back to about 1880. 
SF6 {pmol/mol) 

0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 

6 

-20 • • - 6-

6 

-40 . ,. -· · f>. -,-

'E 6 

-60 · ·A ....... ' .c SPG> Firn Air 'A -

a. ' 6 

Cll -80 

c ~ ' 6 

6 ' 

-100 . •6· 

l/ A I 

-120 A : .-

-140 

Fig. 5.37. SF6 in South Pole firn air. Because of its small 

analytical peak on the GC, the detection limit for SF6 in real air 

is around a few tenths of a ppt. Like the halons, this gas was not 

introduced into the atmosphere until the 1970s [Maiss et al., 

1996]. 

anthropogenic CFC emissions are supported by these 

findings, confirming the predominance of anthropogenic 

activity in the atmospheric budget of refractory, organic 

chlorine. The data for CFCs and the longer-lived organic 

chlorocarbons ultimately will be useful in dating oceanic 

water masses and isolated ground waters, providing 

atmospheric data where none existed before. Atmospheric 

CH3Br in the southern hemisphere appears to have been 

about 25% lower at the turn of the century than it is today 

(Figure 5.36). 

5.7. REFERENCES 

AFEAS (Alternative Fluorocarbon Environmental Acceptability 

Study), Production, Sales and Atmospheric Release of 

Fluorocarbons Through J 993, S & PS, Inc., Washington, D.C., 

1995. 

Albritton, D.L., R.G. Derwent, LS.A. Isaken, M. Lal, D.J. 

Wuebbles, Trace gas radiative forcing indices, in Climate 

Change J 994: Radiative Forcing of Climate Change and An 

Evaluation of the IPCC IS92 Emission Scenarios, edited by 

J.T. Houghton, L.G.M. Filho, J. Bruce, H. Lee, B.A. Callander, 

E. Hailes, N. Harris, and K. Maskell, 339 pp., Cambridge 

University Press, Cambridge, UK, 1995. 

Bakwin, P.S., P.P Tans, C. Zhao, W. Ussler, III, and E. Quesnell, 

Measurements of carbon dioxide on a very tall tower, Tellus, 

47B, 535-549, 1995. 

Battle, M., M. Bender, T. Sowers, P. Tans, J. Butler, J. Elkins, J. 

Ellis, T. Conway, N. Zhang, P. Lang, and A. Clarke, Histories 

of atmospheric gases from the firn at South Pole. Nature, in 

press, 1996. 

Boering, K.A., E.J. Hintsa, S.C. Wofsy, J.G. Anderson, B.C. 

Daube, A.E. Dessler, M. Loewenstein, M.P. McCormick, J.R. 

Podolske, E.M. Weinstock, and G.K. Yue, Measurements of 

stratospheric carbon dioxide and water vapor at northern 

midlati tu des: Implications for troposphere-to-stratosphere 

transport, Geophys. Res. Lei/., 22, 2737-2740, 1995. 

Butler, J.H., The potential role of the ocean in regulating 

atmospheric CH3Br, Geophys. Res. Lei/., 21, 185-189, 1994. 

Butler, J.H., Methyl bromide under scrutiny. Nature, 376, 469-

470, 1995. 

Butler, J .H., Scientific uncertainties in the budget of atmospheric 

methyl bromide, Atmos. Environ., 30(7), i-iii, 1996. 

Butler, J.H., and J. Rodriguez, Methyl bromide in the 

atmosphere, in The Methyl Bromide Issue, edited by N. Price, 

London, Wiley and Sons, Ltd., in press, 1996 . 

Butler, J.H., J.W. Elkins, B.D. Hall, S.O. Cummings, and S.A. 

Montzka, A decrease in the growth rates of atmospheric halon 

concentrations, Nature, 359, 403-405, 1992. 

Butler, J.H., Lobert J.M., S.A. Yvon, and L.S. Geller, The 

distribution and cycling of halogenated trace gases between 

the atmosphere and ocean, in The Expedition Antarktis Xll of 

RV "Polars/em" in 1994195. Reports of Legs ANT Xl/11 and 2, 

edited by G. Kattner and K. Fuetterer, Alfred Wegener 

Institute for Polar and Marine Research, Bremerhaven, 1995. 

Daniel, J.S., S. Solomon, and D.L. Albritton, On the evaluation 

of halocarbon radiative forcing and global warming potentials, 

J. Geophys. Res., 100, 1271-1285, 1995. 

Elkins, J.W., T.M. Thompson, T.H. Swanson, J.H. Butler, B.D. 

Hall, S.O. Cummings, D.A. Fisher, and A.G. Raffo, Decrease 

in the growth rates of atmospheric chlorofluorocarbons 11 and 

12, Nature, 364, 780-783. 1993. 

Elkins, J.W., D.W. Fahey, J.M. Gilligan, G.S. Dutton, T.J. 

Baring, C.M. Volk, R.E. Dunn, R.C. Myers, S.A. Montzka, 

P.R. Wamsley, A.H. Hayden, J.H. Butler, T.M Thompson, T.H. 

Swanson, E.J. Dlugokencky, P.C. Novelli, D.F. Hurst, J.M. 

Lobert, S.J. Cicora, R.J. McLaughlin, T.L. Thompson, R.H. 

Winkler, P.J. Fraser, L.P. Steele, M.P. Lucarelli, Airborne gas 

chromatograph for in situ measurements of long lived species 

in the upper troposphere and lower stratosphere, Geophys. Res. 

Lett, 23(4), 347-350, 1996. 

Eluszkiewicz, J., D. Crisp, R. Zurek, L. Elson, E. Fishbein, L. 

FroidevauK, J. Waters, R.G. Grainger, A. Lambert, R. 

Harwood, and G. Peckham, Residual circulation in the 

stratosphere and lower mesosphere as diagnosed from 

microwave limb soun<ler data, J. Atmos. Sci., 53, 217-240, 

1996. 

109 

Etheridge, D.M., L.P. Steele, R.L. Langenfelds, R.J. Francey, 

J.M. Barnola, and V.I. Morgan, Natural and anthropogenic 

changes in atmospheric C02 over the last 1000 years from air 

in Antarctic ice and firn. J. Geophys. Res., IOI (D2), 4115-

4128, 1996. 

Fahey, D.W., J.W. Elkins, S.A. Montzka, R.C. Myers, G.S. 

Dutton, C.M. Volk, Mean age of the air mass: In situ 

measurements of stratospheric sulfur hexafluoride in 1994, 

EOS, 76, p. 130, 1995. 

Fahey, D.W., D.M. Murphy, K.K. Kelly, M.K.W. Ko, M.H. 

Proffitt, C.S. Eubank, D.W. Ferry, M. Loewenstein, and K.R. 

Chan, Measurements of nitric oxide and total reactive nitrogen 

in the Antarctic stratosphere: Observations and chemical 

implications, J. Geophys. Res., 94, 16,665-16,681, 1989. 

Garcia, R.R., and S. Solomon, A New numerical model of the 

middle atmosphere 2. Ozone and related species, J. Geophys. 

Res., 99, 12,937-12,951, 1994. 

Geller, L., J. Lobert, J. Butler, R. Myers, J. Elkins, Latitudinal 

distribution of sulfur heKafluoride in and over the Atlantic and 

E. Pacific Oceans, EOS, 76, p. 17, 1994. 

Goldan, P.D., W.C. Kuster, D.L. Albritton, and A.L. 

Schmeltekopf, Stratospheric CFCl3, CF2Cl2. and N20 height 

profile measurements at several latitudes, J. Geophys. Res., 85, 

413-423, 1980. 

Hurst, D., L. Geller, P. Novelli, P. Bakwin, R. Myers, J. Elkins, 

Observations of sulfur heKafluoride from a very tall tower in 

the southeastern United States, EOS, 76, p. 70, 1995. 

Hall, T. M., and R. A. Plumb, Age as a diagnostic of 

stratospheric transport, J. Geophys. Res., 99, 1059-1070, 1994. 

Irion, F.W., M. Brown, G.C. Toon, M.R. Gunson, Increase in 

atmospheric CHF2CI (HCFC-22) over Southern California 

from 1985 to 1990, Geophys. Res. Lei/., 21, 1723-1726, 1994. 
Lobert, J.M., J.H. Butler, S.A. Montzka, L.S . Geller, R.C. 

Myers, and J.W. Elkins, A net sink for atmospheric methyl 

bromide in the East Pacific Ocean. Science, 267, I 002-1005, 

1995 . . 

Lobert, J. M., J. H. Butler, L. S. Geller, S. A. Yvon, S. A. 

Montzka, R. C. Myers, A. D. Clarke, J. W. Elkins, BLAST 94: 

Bromine Latitudinal Air Sea Transect 1994. Report on Oceanic 

Measurements of Methyl Bromide and Other Compounds, 

NOAA Tech. Memo. ERL CMDL-10, 39 pp., NOAA 

Environmental Research Laboratories, Boulder, CO, 1996. 

Machida, T., T. Nakazawa, Y. Fujii, S. Aoki, and 0 . Watanabe, 

Increase in the atmospheric nitrous oxide concentration during 

the last 250 years, Geophys. Res. Lett., 22(21), 2921-2924, 

1995. 

Maiss, M., L.P. Steele, R.J. Francey, P.J. Fraser, R.L. 

Langenfelds, N. B.A. Trivett, and I. Levin, Sulfur 

hexafluoride--a powerful new atmospheric trace, Atmos. 

Environ., 30, 1621-1629, 1996. 

McCormick, M.P., E.W. Chiou, L.R. McMaster, W.P. Chu, J.C. 

Larsen, D. Rind, and S. Oltmans, Annual variations of water 

vapor in the stratosphere and upper troposphere observed by 

the Stratospheric Aerosol and Gas Experiment II, J. Geophys. 

Res., 98, 4867-4874, 1993. 

McCulloch, A., and P. Midgely, The production and global 

distribution of emissions of trichloroethene, tetrachloroethene, 

and dichloromethane over the period 1988- 1992, Atmos. Env., 

30, 601-608, 1996. 

McElroy, M. B., R. J. Salawitch, S. C. Wofsy and J. A. Logan, 

Reductions of antarctic ozone due to synergistic interactions of 

chlorine and bromine, Nature, 321 , 759-762, 1986. 

Minschwaner, K., R.J. Salawitch, and M.B. McElroy, Absorption 

of solar radiation by 02: Implications for 03 and lifetimes of 

N20, CFCl3, and CF2Cl2. J. Geophys. Res., 98, 10,543-

10,561, 1993. 

Montzka, S.A., R.C. Myers, J.H. Butler, J.W. Elkins, and S.0. 

Cummings, Global tropospheric distribution and calibration 

scale of HCFC-22, Geophys. Res. Lett. , 20, 703-706, 1993. 

Montzka, S.A., R.C. Myers, J.H. Butler, and J.W. Elkins, Early 

trends in the global tropospheric distribution of 

hydrofluorocarbon-141b and -142b, Geophys. Res. Lett., 21 , 

2483-2486, 1994. 

Montzka, S.A., J.H. Butler, J.W. Elkins, S. Yvon, A. Clarke, J. 

Lober!, and L. Lock, Difficulties associated with measuring 

atmospheric levels of methyl bromide and other methyl 

halides, EOS, 76, SI60, 1995a. 

Montzka, S.A., R.C. Myers, J.M. Butler, T.M. Thompson, J.W. 

Elkins, L.T. Lock, A.D. Clarke, T.H. Swanson, Changing 

trends in the global tropospheric abundance of CFCs, HCFC, 

HFCs, and chlorine in recent time, EOS, 76, F98, I 995b. 

Montzka, S.A., R.C. Myers, J.H. Butler, J.W. Elkins, L.T. Lock, 

A.D. Clarke, A.H. Goldstein, Observations of HFC-134a in the 

remote troposphere, Geophys. Res. Lett., 23, 169-172, I 996a. 

Montzka, S.A., J.H. Butler, R.C. Myers, T.M. Thompson, T.H. 

Swanson, S.D. Clarke, L.T. Lock, J.W. Elkins, Decline in the 

tropospheric abundance of halogen from halocarbons, Science, 

272, 1318-1322, I 996b. 

Mote, P.W., K.H. Rosenlof, M.E. Mcintyre, E.S. Carr, J.S. 

Kinnersley, H.C. Pumphrey, R.S. Harwood, J.R. Holton, J.M. 

Russell III, J.W. Waters, J.C. Gille, and K.K. Kelly, An 

atmospheric tape recorder: The imprint of tropical tropopause 

temperatures on stratospheric water vapor, J. Geophys. Res., 

101, 3989-4006, 1996. 

Murphy, D.M., S.W. Fahey, M.H. Proffitt, S.C. Liu, K.R. Chan, 

C.S. Eubank, S.R. Kawa, and K.K. Kelly, Reactive nitrogen 

and its correlation with ozone in the lower stratosphere and 

upper troposphere, J. Geophys. Res., 98, 8751-8773, 1993. 

Oram, D.E. , C.E. Reeves, S.A. Penkett, and P.J. Fraser, 

Measurements of HCFC-142b and HCFC-141b in the Cape 

Grim air archive: 1978-1993, Geophys. Res. Lett., 22, 2741-

2744, 1995. 

Peterson, J.T., and R.M. Rosson (Eds.), Climate Monitoring and 

Diagnostics Laboratory, No. 21, Summary Report 1992, 131 

110 

pp., NOAA Environmental Research Laboratories, Boulder, 

co. 1993. 

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. 

Plumb, R.A., A "tropical pipe" model of stratospheric transport, 

J. Geophys. Res., IOI, 3957-3972, 1996. 

Plumb, R.A., and M.K.W. Ko, Interrelationships between mixing 

ratios of long-lived stratospheric constituents, J. Geophys. 

Res., 97, I0,145-10, 156, 1992. 

Podolske, J., and M. Loewenstein, Airborne tunable diode laser 

spectrometer for trace-gas measurement in the lower 

stratosphere, Appl. Opt., 32, 5324-5333, 1993. 

Pollock, W.H., L.E. Heidt, R.A. Lueb, J.F. Vedder, M.J. Mills, S. 

Solomon, On the age of stratospheric air and ozone depletion 

potentials in polar regions, J. Geophys. Res., 97, 12,993-

12,999, 1992. 

Prather, M.J., and R.T. Watson, Stratospheric ozone depletion 

and future levels of atmospheric chlorine and bromine, Nature , 

344, 729-734, 1990. 

Prinn, R.G., R.F. Weiss, B.R. Miller, J. Huang, F.N. Alyea, D.M. 

Cunnold, P.J. Fraser, D.E. Hartley, and P.G. Simmonds, 

Atmospheric trends and lifetime of CH3CCl3 and global OH 

concentrations, Science, 269, 187-192, 1995. 

Proffitt, M.H., and J. McLaughlin, Fast-response dual-beam UV 

absorption ozone photometer suitable for use on stratospheric 

balloons, Rev. Sci. Jnstrum., 54, 1719-1728, 1983. 

Randel, W.J., J.C. Gille, A.E. Roche, J.B. Kumer, J.L. 

Mergenthaler, J.W. Waters, E.F. Fishbein, and W.A. Lahoz, 

Stratospheric transport from the tropics to middle latitudes by 

planetary-wave mixing, Nature, 365, 533-535, 1993. 

Ravishankara, A. R., S. Solomon, A.A. Turnipseed, R.F. Warren, 

Atmospheric lifetimes of long-lived halogenated species, 

Science, 259, 194-199, 1993. 

Rinsland, C. P., E. Mahieu, R. Zander, M. R. Gunson, R. J. 

Salawitch, A. Y. Chang, A. Goldman, M. C. Abrams, M. M. 

Abbas, M. J. Newchurch, and F. W. Irion, Trends of OCS, 

HCN, SF6, and CHCIF2 (HCFC-22) in the lower stratosphere 

from 1985 and 1994 atmospheric trace molecule spectroscopy 

experiment measurements near 30°N latitude, Geophys. Res. 

Lett., in press, 1996. 

Rosenlof, K.H., Seasonal cycle of the residual mean meridional 

circulation in the stratosphere, J. Geophys. Res., I 00, 5173-

5191, 1995. 

Salawitch, R.J., S.C. Wofsy, P.O. Wennberg, R.C. Cohen, J.G. 

Anderson, D.W. Fahey, R.S. Gao, E.R. Keim, E.L. 

Woodbridge, R.M. Stimpfle, J.P. Koplow, D.W. Kohn, C.R. 

Webster, R.D. May, L. Pfister, E.W. Gottlieb, H.A. Michelsen, 

G.K. Yue, M.J. Prather, J.C. Wilson, C.A. Brock, H.H. 

Jonsson, J.E. Dye, D. Baumgardner, M.H. Proffitt, M. 

Loewenstein, J.R. Podolske, J.W. Elkins, G.S. Dutton, E.J. 

Hintsa, A.E. Dessler, E.M. Weinstock, K.K. Kelly, K.A. 

Boering, B.C. Daube, K.R. Chan, and S.W. Bowen, The 

diurnal variation of hydrogen, nitrogen , and chlorine radicals: 

Implications for the heterogeneous production of HN02, 

Geophys. Res. Lett., 21, 2251-2554, 1994. 

Schauffler S.M., L.E. Heidt, W.H. Pollock, T.M. Gilpin, J.F. 

Vedder, S. Solomon, R.A. Lueb, and E.L. Atlas, Measurements 

of halogenated organic compounds near the tropical 

tropopause, Geophys. Res. Lett. , 22, 2567-2570, 1993. 

Schauffler S.M., W.H. Pollock, E.L. Atlas, L.E. Heidt, and J.S. 

Daniel, Atmospheric distributions of HCFC 141 b, Geophys. 

Res. Lett., 22, 819-822, 1995. 

Shorter, J.H., C.E. Kolb, P.M. Crill, R.A. Kerwin, R.W. Talbot, 

M.E. Hines, and R.C. Harriss, Rapid degradation of 

atmospheric methyl bromide in soils. Nature, 377, 717-719, 

1995. 

Solomon S., R. W. Portmann, R. R. Garcia, L. W. Thomason, 

L.R. Poole, and M. P. McCormick, The role of aerosol 

variations in anthropogenic ozone depletion at northern 

rnidlatitudes, J. Geophys. Res., IOI , 6713-6727, 1996. 
Stolarski, R.S .. S.L. Baughcum, W.H. Brune, A.R. Douglass, 

D.W. Fahey, R.R. Friedl, S.C. Liu, R.A. Plumb, L.R. Poole, 

H.L. Wesoky, D.R. Worsnop, 1995 Scientific Assessment of 

the Atmospheric Effects of Stratospheric Aircraft, NASA Ref 

Pub. 1381, 1996. 

Swanson, T.H., J.W. Elkins, J.H. Butler, S.A. Montzka, R.C. 

Myers, T.M. Thompson, T.J. Baring, S.O. Cummings, G.S. 

Dutton, A.H. Hayden, J.M. Lobert, G.A. Holcomb, W.T. 

Sturges, and T.M. Gilpin, in Climate Monitoring and 

Diagnostics Laboratory No. 21 Summary Report 1992, edited 

by J.T. Peterson and R.M. Rosson, pp. 59-75, NOAA 

Environmental Research Laboratories, Boulder, CO, 1993. 

Thompson, T.M., J.W. Elkins, J.H. Butler, S.A. Montzka, R.C. 

Myers, T.J. Baring, S.O. Cummings. G.S. Dutton, J.M 

Gilligan, A.H. Hayden, J.M. Lobert, T.H. Swanson, D.F. Hurst, 

and C.M. Volk, in Climate Monitoring and Diagnostics 

Laboratory No. 22 Summary Report 1992, pp. 72-91, edited by 

J.T. Peterson and R.M. Rosson, NOAA Environmental 

Research Laboratories, Boulder, CO, 1994. 

Trepte, C.R., and M.H. Hitchman, Tropical stratospheric circulation 

deduced from satellite aerosol data, Nature, 355, 626-628, 1992. 

111 

Volk, C.M., J.W. Elkins, D.W. Fahey, R.J. Salawitch, 

G.S. Dutton, J.M. Gilligan, M.H. Proffitt, M. Loewenstein, 

J.R. Podolske, K. Minschwaner, J.J. Margitan, and K.R. 

Chan, Quantifying transport between the tropical and 

midlatitude lower stratosphere, Science, 272, 1763-1768, 

1996. 

WMO (World Meteorological Organization), Scientific 

Assessment of Ozone Depletion: 1994, WMO, Geneva, 1995. 

Yung, Y.L., J.P. Pinto, R.T. Watson and S.P. Sander, 

Atmospheric bromine and ozone perturbations in the lower 

stratosphere, J. Atmos. Sci., 37, 339-353 , 1980. 

Yvon, S.A., and J.H. Butler An improved estimate of the oceanic 

lifetime of atmospheric CH3Br, Geophys. Res. Lett., 23, 53-56, 

1996. 

Zander, R., E. Mahieu, P. Demoulin, C.P. Rinsland, D.K. 

Weisenstein, M.K.W. Ko, N.D. Sze, and M.R. Gunson, Secular 

evolution of the vertical column abundances of CHClFz 

(HCFC-22) in the Earth's atmosphere inferred from groundbased IR solar observations at the Jungfraujoch and at Kitt 

Peak, and comparison with model calculations, J. Atmos, 

Chem, 18, 129-148, 1994. 
6. Cooperative Programs 

Evaluation of Arctic Meteorological Buoys 

GERALD F. APPELL 

NOAA, National Ocean Service, Ocean Systems Development Group, Silver Spring, Maryland 20910 

INTRODUCTION 

The United States Interagency Arctic Buoy Program 

(USIABP) was formed in 1991 to establish and maintain a 

network of drifting meteorological buoys in the Arctic. 

The USIABP is a collaborative program funded by nine 

government agencies/programs and managed by the 

National Ice Center in Suitland, Maryland. USIABP 

supports the International Arctic Buoy Program (IABP) 

which consists of many countries participating in the 

collection of meteorological data from Arctic drifting 

buoys. 

The buoys are strategically deployed to define the 

surface synoptic scale atmospheric pressure, air 

temperature, and sea ice drift fields. The data are available 

in real time, via ARGOS satellite transmissions, to 

operational weather forecasting centers. Data are also used 

for research into climate change. At the inception of the 

program, 25 buoys were gathering temperature and 

pressure data in the Arctic with 72% reporting on the 

Global Telecommunications System (GTS). In early 1994, 

47 buoys were in operation with 96% reporting on the 

GTS. 

The IABP uses many different buoys with different 

sensors, configurations, and sampling schemes. Many of 

the temperature measurements reported by the buoys were 

suspect when compared with atmospheric model 

predictions. In 1993 it was decided by the USIABP to halt 

deployment of new buoys until the sources of temperature 

measurement errors were investigated. A program was 

established to evaluate the available "off-the-shelf" Arctic 

buoy systems being used by the IABP. As part of this 

evaluation, a long-term test site was established at the 

CMDL facility in Barrow, Alaska (BRW). 

In 1995 the USIABP resumed procurement and 

deployment of buoys based on a buoy design derived from 

tests at BRW. 

THE FIELD TEST SITE 

In August 1993, a Coastal Climate buoy and a DSI-TAD 

buoy were placed at BRW. A data acquisition system was 

placed at the site consisting of a Telonics ARGOS uplink 

receiver and a Compaq notebook computer. Buoy 

transmissions are received and logged on the computer. 

Weekly interrogations of the computer are done from 

Silver Spring, Maryland, and data files are downloaded. In 

December 1993 a Canadian MetOcean CALIB buoy was 

added to the array, and in March 1994 a Norwegian ICEX 

buoy was placed at the site. 

In August 1994 a meteorological station was placed at 

the buoy array site. This site collects temperature data 

from aspirated sensors at the 1 m and 2 m levels. It also 

112 

collects solar radiation, barometric pressure, and wind 

data. The purpose of this system is to explore the 

horizontal and vertical temperature distribution compared 

with the CMDL sensors (20 m horizontal separation, 

CMDL sensors at 2 m and 15 m levels). Data are collected 

from the station via GOES satellite or dial-up phone link. 

A fifth buoy was added to the site in August 1994. This 

buoy is a Canadian MetOcean buoy similar in design to the 

Coastal Climate buoy. 

In May 1995 the sixth and last buoy was added to the 

site. This buoy was specified, designed, and built based on 

the experience and knowledge gained from the BRW tests. 

This buoy was manufactured by Coastal Climate and was 

based on the successful design of their original ice buoy. 

All of the air deployable buoys were removed from the site 

in 1995 with sufficient data acquired. At the close of 1995 

three buoys remained at BRW, the two Coastal Climate 

buoys and the one MetOcean buoy. 

DATA ACQUISITION AND ANALYSIS 

All buoys in the test program undergo a temperature 

sensor calibration at the National Weather Service Test 

Facility in Sterling, Virginia, before shipment to Barrow, 

Alaska. 

Each buoy has its own measurement scheme, sampling 

interval, data format, and data transmission interval. Data 

collected in Silver Spring, Maryland, is processed and 

reduced into a standard 1-hour averaged data format. 

CMDL meteorological data are sent monthly on a computer 

diskette for comparison with buoy data. An INTERNET 

link was established with BRW in 1994 for retrieval of ice 

buoy data. Compressed files from the buoy data 

acquisition system are placed on the laboratory computer 

for retrieval via FTP. This has saved the expense of 

downloading data via telephone. 

Measurements are analyzed and compared with the 

meteorological station and CMDL standards. Temperature 

differences between sensors and/or standards are analyzed 

to learn the effects of sensor height differences, solar 

radiation, and wind. Results show significant differences 

are attributed to the measurement height of the sensors 

above the surface and to solar radiation effects. 

In 1994, based on BRW test results, a specification was 

developed to procure new ice buoys. A contract was 

awarded to Coastal Climate Company for five new systems. 

The performance of the original Coastal Climate buoy 

placed at BRW has been superior to the others regarding 

accurate temperature measurements. This new 

specification required an improved sampling and ARGOS 

reporting scheme for the buoys. The ICEX, DSI-TAD, and 

MetOcean CALIB buoys were removed from the site in 

early 1995 after conclusion of tests. These buoys were 
deemed unacceptable based on proximity of sensors to the 

ground and susceptibility to blowing snow coverage. 

Analysis of data acquired in 1995 showed that the new 

Coastal Climate buoy performed as expected. The 

quality of temperature data obtained from the three 

remaining buoys is comparable. These buoys all measure 

temperature at a fixed height of 2 m above the surface 

and provide sufficient shielding of solar radiation. In 

August 1996, the original Coastal Climate buoy will have 

113 

operated continuously in Barrow for 3 years, meeting its 

design life. 

FUTURE PLANS 

It is planned to discontinue the buoy test program in 

Barrow in August 1996. Sufficient information on buoy 

performance has been acquired to assure that improved 

sensors will be available to the USIABP. 
Asian Transport of Aerosols to Mauna Loa Observatory, Spring 1994 

THOMAS A. CAHILL AND KEVIN D. PERRY 

Air Quality Group, Crocker Nuclear Laboratory, University of California, Davis 95616 

A partial National Park Service Interagency Monitoring 

of Protected Visual Environments (IMPROVE) site was 

established at Mauna Loa Observatory (MLO) in 1989 to 

measure the mass and composition of fine particles (i.e., 

DP <2.5 μm diameter). While this site has always 

produced data on the more common trace elemental species 

such as zinc (see previous CMDL summary reports), 

analytical advances in early 1993 greatly increased 

sensitivity and allowed a much wider suite of trace 

elemental species to be measured. While the IMPROVE 

site at MLO quickly confirmed prior findings of regular 

Asian dust transport each spring, it also demonstrated that 

elevated levels of trace elements also occur during the dust 

episodes. In this summary, we will compare the present 

results to recently published aerosol summaries at MLO, 

examine the intense Asian dust episodes that occurred 

during the spring of 1994, and outline intensive 

measurements being made at MLO during the spring of 

1996. 

Comparisons with other long-term aerosol records 

became possible when Zieman et al. [ 1995] summarized 

their high volume air sampler (Hi-Vol) data from MLO. 

The Hi-Vol sampler was operated for a period of l week 

during nighttime/downslope winds and collected particles 

<30 μm in diameter. For comparison purposes, we have 

summed the two weekly IMPROVE sampling periods (i.e., 

Wednesday through Friday and Saturday through Tuesday) 

to give mean weekly values during downslope winds. 

The excellent agreement for sulfates in Table l indicates 

that these particles are predominantly <2.5 μm in diameter. 

The results for soil, however, are typically different. For 

example, Hi-Vols normally collect about four times more 

soil mass than the IMPROVE PM2.

5 air sampler. Thus, 

one might expect the Hi-Vol to collect -2.9 μg m-3 of soil 

during the spring Asian dust episodes and -0.4 μg m-3 

during the entire year. Table l shows that less than half of 

this soil mass was observed during the dust season. This 

implies that the soil at MLO during the spring is much 

finer than typical local soils, which is consistent with 

transport. Braaten and Cahill [ 1986] found a mass median 

diameter for Asian soils of -1.2 μm diameter, but did not 

measure particles above -11 μm. Thus, while it is likely 

that the Hi-Vol data from Zieman et al. [ 1995] contains 

some local soils, most of the soil is probably transported 

from distant sources during the dust episodes. The data for 

zinc and selenium implies that. most of the mass of these 

species is <2.5 μm in diameter, which is also consistent 

with transport from Asia. 

The second topic involves the intense dust storms that 

occurred during the spring of 1994. Figure l shows the 

concentration of fine soil, soot (b(abs), measured 

optically), organic matter (inferred from hydrogen), and 

arsenic during this time period. Although the soil 

concentration on April 9 is about twice the maximum in 

most prior years, it is the other elements that make this 

episode interesting. For example, the maximum arsenic 

concentrations at MLO during the spring of 1994 were 

roughly equivalent to the median of the peak arsenic 

concentrations at the other 70 or so IMPROVE sites at 

mainland parks and monuments. The high arsenic 

concentrations at MLO were accompanied by other trace 

elements similar to those produced from non-ferrous 

smelter activity (Table 2). Ten-day backward isenotropic 

air trajectories for this episode pass directly over northern 

China, site of most Chinese smelting activity. 

While we expected to find traces of Asian industrial 

activity in the aerosol record at MLO, we did not expect 

such high concentrations of arsenic. Prior research had 

shown that significant dilution of soil mass occurred 

between the Asian sources and MLO. Such high arsenic 

concentrations could only be achieved if either the 

concentrations were very high at mainland sites, or the 

trace elements did not suffer as much dilution as the soil 

dust. The former hypothesis seems unlikely. For example, 

TABLE l. Comparison of Downslope Aerosol Sampling at MLO 

Mass RCMA* S04 Organics Soil b (abs) Zn Se 

(μg m-3) (μg m-3) (μg m-3) (μg m-3) (μg m-3) 10-4 m- 1 (ng m-3) (ng m-3) 

Dust Season: 

UC Davis 1.94 1.62 0.37 0.36 0.72 1.92 0.47 0.029 

Zieman et al., 0.37 1.27 0.51 0.038 

1995 

Overall: 

UC Davis 0.84 0.68 0.29 0.22 0.10 0.62 0.18 0.021 

Zieman et al., 0.26 0.55 0.33 0.031 

1995 

Note: All UC Davis data is from 1993 and 1994. 

*Mass is gravimetric, reconstructed mass (RCMA) is the sum of measured species. The difference is mainly water. 

114 
2 • • 12 16 ti 2J 2S JO 2 I I 131120237130 .. 1 ,, , .. 11 21 25 21 

March April May 

1000 

;:; 

• .E 

"' 1000 .s. 

~ 

8 ..,. rt.I 

.. 

c 

;;:: 

2 • I 12 11 UI 23 26 30 2 I I 1:1 ts 20 23 TT 30 4 7 11 ,. 11 21 2' 21 

March AprU May 

;:; 2000 

• .E .s 1500 

.!! " 

c 1000 .. 

e' 

0 ..,. .. 

c 

;;:: 

2 • I 12 II 11 :z:J 2'1 lO '2 I • 13 Hl20 ZJ '11 :)1:1 4 7 11 u 119 :I' ! 25 2t 

March April May 

;:; 

~ 1.5 co 

.s. 

.!! 1 c 

.. 

" .=: •• .. 

c 

;;:: 

2 • • 12 18 ti 2J 21 30 2 • I 131620232730 4 1 ,, ,, 11 21 ~ 21 

March April May 

Fig. 1. Aerosol concentrations at Mauna Loa Observatory, 

spring 1994. All concentrations are given in nanograms 

m-3. For details of the parameters, see Malm et al. [ 1994]. 

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 m-3 range over a wide 

area of the mainland during periods of strong ventilation 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 

II5 

TABLE 2. Comparison of Trace Elements From 

Potential Sources of Arsenic 

1000• 1000* 1000* 1000* 

Se/S04 Cu/S04 Zn/S04 As/S04 

Volcanoes: 

Kilauea, 1.9 0.39 0.37 0.32 

Nov. 21, 1992 

Copper Smelters: 

Average Arizona 1.7 20.0 28.0 6.0 

"Smelter No. S" 0.02 1.0 3.8 2.3 

Mauna Loa 

(downslope) 

April 9, 1994 <0.08 0.9 3.8 2.4 

Note: All values have been normalized to sulfate. 

for very fine (Dp <0.5 μm) 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 

μm), and (d) 14carbon 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. 

TABLE 3. Comparison of Fine Soil Dust Transport 

Efficiencies from China (April 19, 1981) 

to MLO (May 12, 1981)* 

Beijing Mauna Loa Ratio 

Dp<O.S μm 0.6 μg m-3 0.17μgm-3 31% 

0.5<Dp<3.0 μm 80 μg m-3 0.22 μg m-3 0.3% 

3.0<Dp<l6 μm 136 μg m-3 0.09 μg m-3 0.07% 

*Note that these are two different dust storms, so that the 

proportionality is only very approximate, but the ratios of coarse 

to fine dust should be reasonably s~milar. 
REFERENCES 

Braaten, D.A. and T.A. Cahill. Size and composition of Asian dust 

transported to Hawaii. Atmo. Environ., 20, 1105-1109, 1986. 

Malm, W.C., J.F. Sisler, D. Huffman, R.A. Eldred, and T.A. 

Cahill, Spatial and seasonal trends in particle concentration 

and optical extinction in the United States. J. Geophys. Res., 

99, 1347-1370, 1994. 

Zieman, J.J., J.L. Holmes, D. Connor, C.R. Jensen, W.H. Zoller, 

D.M. Hermann, J.R. Parrington, and G.E. Gordon, 

Atmospheric aerosol trace element chemistry at Mauna Loa 

Observatory, l, 1979-1985, J. Geophys. Res., 100, 25,979-

25,994, 1995. 

116 
Ultrahigh Resolution Infrared Solar Spectra 

From Mauna Loa Observatory: New Results 

S.J. David, F.J. Murcray, A. Goldman, and R.D. Blatherwick 

University of Denver, Department of Physics, Denver, Colorado 80208 

INTRODUCTION 

A modified ultrahigh spectral resolution (0.0035 

cm-I) Fourier transform interferometer (FTIR) solar 

spectrometer system was installed at Mauna Loa 

Observatory, Hawaii (MLO) in May 1991 and was 

operated routinely by the observatory staff from 

November 1991 to November 1995. This instrument 

provided data on the column abundance of several 

atmospheric chemical compounds for the Network for 

Detection of Stratospheric Change (NDSC). Normal 

operation was one sunrise set of data each week, 

usually collected on Wednesdays. 

During August 1995, a new, almost completely 

automatic FTIR system was installed at MLO. The 

solar tracker has a weather-tight hatch that is computer 

controlled. The new system requires a person to fill the 

detector dewars with liquid nitrogen; it then records 

solar spectra when weather conditions are acceptable. 

Weather permitting, data are collected 5 days-a-week at 

both sunrise and sunset. Data cartridges need to be 

changed weekly and desiccant changed monthly. 

Here, data are presented from the complete 4-year run 

of the original interferometer, and comparisons between 

the two systems are made for data from the overlap 

period. 

RESULTS AND DISCUSSION 

To date, we have analyzed the infrared spectra for total 

column amounts of several gases over a 4-year period 

co 

..... 

UJ 

0 

en 

Q) 

E 

E 

0 

~ C') 

0 

9. 

8. 

7 . 

6. 

5. 

4. 

3. 

2. 

1. 

0, 

11/01 

..... 

..... 

05/0 11/0 05/03 

at MLO. Gases included in this data base are 0 3, N20, 

HN03, F22 and HCI. 

The ozone spectral lines were chosen to be isolated 

and only weakly temperature dependent. The two fitted 

spectral regions, around 1146 and 1163 cm· I, included 

two prominent ozone absorptions and a strong line due 

to NzO. Nitrous oxide is reported to be increasing 

slightly, but is essentially constant on our scale. 

Infrared ozone column amounts are very consistent with 

the Dobson observations [David et al., 1993]. Figure l 

shows the total columns measured for 0 3 and N20. We 

see ozone has an annual cycle with lows in the winter 

and highs in the late spring to early summer. It is 

worth noting that 03 hit a low in early 1995 that is 

consistent with a record low measured by the Mauna 

Loa Dobson spectrophotometer. 

The HN03 spectral interval chosen contains three Pbranch manifolds of the n5 band located between 868.3 

and 869.6 cm· I; see David et al. [ 1994] for a 

description of the HN03 analysis. Figure 2 shows the 

total column measured for HN03. Currently, we are 

seeing a decrease of approximately 9% yr· I. Our 

measurements started just after Mount Pinatubo erupted 

in July 1991; therefore, the decrease is expected , 

however, HN03 should level off soon. 

We analyzed HCI u~ing a two-step process. First, we 

looked at 2925.5 to 2926.5 cm·I which included H20 

and CH4 in the fit. Then we zoomed in on the H35CJ 

(1-0) band of the R(l) line at 2925 89 cm· I. Our 

measurements show an increase in the column of HCl of 

approximately 2.5% yr·I. 

-+- Ozone * N20 

, 1/02 05/ 11/03 05/05 11 /04 

Fig. I. Total column amounts of ozone and N20 over Mauna Loa Observatory. 

ll7 
9. x 

8.5 x x 

8.0 xx 

7.5 x 

x x 

iO 7.0 xx ~ 

w x x x< 6.5 x (/) * Q) x 

E 6. 

E ~ C") 5.5 

x x ~ x x x x 

x x ~ x x x x 

~ x,c: xx ><><*' x x XX x 

>< x x * xx x xX x~ x x x 

0 x :><x ~ x x x 

I 

z 5.0 x ~xx 

45 

x x x 

~ xx x x *' >< ~ 

x ~x 

4.0 """ x

3.5 

3.0 

11 /01 05/02 11/01 05/03 11 /02 05/04 11/03 05/0 11)04 

Fig. 2. Total column amount of HN03 over Mauna Loa Observatory. 

2.0-

iO 

~ 

w 

0 1.5- ...... ... (/) ~ ....... Q) ... E "' E 1.0-

C\J 

C\J 

LL 

0.5-

... 

... 

.,./"'--: 

... .. 

... 

... ... ... 

-

...... 

... ...... 

... 

Fig. 3. Total column amount ofF22 over Mauna Loa Observatory. 

Finally, we measured the 2n2 Q-branch of CHF2CI 

(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-toold ratio, we find approximately 1 % difference for 0 3 

and N20 with the new instrument slightly higher, 

approximately 2% difference for the F22, and 

approximately 5% difference for the HN03 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. 

118 

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 SJ., F.J. Murcray, A. Goldman, C.P. Rinsland, and D.G. 

Murcray, The effect of the Mt. Pinatubo aerosol on the HN03 

column over Mauna Loa, Hawaii, Geophys. Res. Lett., 21, 

I 003-1006, 1994. 
A Preliminary Comparison of ()13C Measurements in C02 

From Mace Head, Ireland 

A. GAUDRY AND P. MONFRAY 

Centre des Faibles Radioactivites, LMCE, CEA l'orme des Merisiers, 91191 Gif sur 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 Gif sur Yvette, France 

S.G. JENNINGS 

Department of Physics, University College of Galway, Ireland 

BACKGROUND 

The 13C composition of atmospheric C02 makes it 

possible to estimate biospheric fluxes of C02, as plant 

photosynthesis discriminates against 13C02, whereas 

isotopic fractionation during C02 dissolution into the 

ocean is small. However, to infer the partitioning of 

anthropogenic C02 between its oceanic and terrestrial 

sinks requires measurements of very high precision. 

Fluxes of C02 that are readily measured via changes in the 

atmospheric C02 mixing ratio have a smaller impact on 

ol3C. For instance, adding 1 ppm (analytical precision is 

-0. l ppm) of purely "biogenic" C02 to the atmosphere 

changes the o13C of that reservoir by only 0.05%0 

(analytical precision is -0.02%0). The isotopic effect of 

adding l ppm of "oceanic" C02 is even smaller. 

Although the internal precision of mass spectrometers is 

about 0.0 l %0, systematic experimental errors may bias 

measurements of the o13C of air samples [Francey et al., 

1995]. Drift of the reference gases used to calibrate 

measurements can also introduce biases [Trolier, 1994]. 

lntercomparisons 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 

o13C 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 C02 

[Lefevre, 1996]. but it is also reached by continental air, 

especially in winter. The seasonal cycle of ol3C at Mace 

Head has a fairly large amplitude (0.9%o), so o13C values 

can be compared over a rather wide range, from about 

-8.3%0 in winter to about -7.4%o in spring and summer. 

The results of this intercomparison are summarized and 

discussed below. 

119 

SAMPLING AND ANALYTICAL TECHNIQUES 

CFR-LMCE began continuous atmospheric C02 

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 0-ring stopcocks, filled to 1 bar with air 

dried to a dewpoint of -55°C) have been measured for the 

13C composition of C02• 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; o13C 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 

ol3C measurements. The recognized effects include 

[Francey et al., 1995] memory effects (when a sample has 

a very different o13C 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 determination of the N20 interference. The CFR flask measurements are calibrated against one sample of carefully purified 

C02, called SNAIL. SNAIL was calibrated against NBS-19, 

a carbonate provided by International Atomic Energy 

Agency (IAEA) [Hut, 1987] and two standard pure C02 

gases, GS 19 and GS20, provided by the University of 

Groningen, Netherlands. The o13C of SNAIL standard was 

determined to -9.67 ± 0.04%0 (relative to VPDB-C02). 

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 

C02, CH4, and CO by CMDL, and for ol3C and ol80 of 

C02 by INSTAAR. At INSTAAR, C02 (with N20) is 

extracted from about 750 bar·cm3 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 
mass 44) are corrected for the presence of N20 and for the 

contribution of species containing 170 to the ion currents. 

The experimental technique and data analysis are described 

by Trolier et al. [ 1996]. The INSTAAR flask 

measurements are calibrated against a suite of whole-air 

reference gases, which in turn are calibrated against 

VPDB-C02 and V·SMOW. The estimated precision of 

individual 1)13C and l)ISQ measurements are 0.03%0 and 

0.05%0 respectively; the uncertainties in the absolute 

calibrations are -0.02%0 and -0.1 %0 respectively. 

INTERCOMPARISON 

Figure 1 shows the time series of 1)13C 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: (I) 

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 l hour apart. The 

average difference for these samples (CFR - INSTAAR) is 

-0.04 ± 0.09%0 (the error estimate is the standard deviation, 

lcr, 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 

-7.l 

·1.4 

. •• 

,,,. 0 oO 

·~ 

"" 

·tl.l 4 

.... 

0 

0 0 

MACE HEAD STATION 

\\ 

0 0 0 0 • ,, 

·. . ~· ~o~ ~ 

0 :~ ~ 

0 .~ 

·8.6 - ------- ,,., 19915 1992 1992 s 199J 1993...5 1994 1994.S "" 

Fig. 1. Time series of ()IJC of atmospheric C02 measured from 

samples of air taken at Mace Head, Ireland, by the CMDL 

Cooperative Flask Sampling Network (open circles) and CFRLMCE (filled circles). The CMDL samples were analyzed by 

INSTAAR at the University of Colorado. 

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 INST AAR and CFR) and the smoothed curve. 

These differences are shown in Figure 2. The mean 

difference between the CFR 1)13C values and the INSTAAR 

smoothed curve is -0.05 ± 0.08%0 for 26 samples. This 

analysis has been repeated using only INST AAR 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%0 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 

l)t3C measurements at Mace Head, obtained by LMCE and 

MACEHEAO STATION 

0.1 -

i us ~ 

0 

~ 0.1 •o 0 0 

;; 0 

0 •o . i 0 •o 0 0 0 o• ... , oo cno o 0 0 00 

~ 

.. 0 o" 0 0 0 oo.g .. ~ 

f 00 ~ . 0 . o • "bo 0 

0 .. 0 0 00 %oc:)•eo "'• 0 

i 0 00 0 D 0 

.e Oo o 0 ~ 

-0.0S <JO .. •8 o• D 

-i 0 0 \\ oO DD D ,p. 0 0 .~. . ~ ~ D DOQ .... 0 

t 0 . ·. 0 

0 

-0.IS 

• 0 

.... • • 0 

'"' 1991.5 1992 19'25 199) lf'Jl.S '"' 1994.S "" 1~5.5 

Fig. 2. Differences in ()13C between the INSTAAR and CFR 

flask samples, and a smoothed curve fit through the INSTAAR 

time series. The INSTAAR data are shown with open circles, and 

the CFR-LMCE data by filled circles. 

120 

MACE HEAD STATION (background condilions} 

···1 0.15 

0.1 

•• 0 

.. D o 

-0.0S :· 

.... ;: I • -0.21992 

~ s 1993 J99JS 

.. 0 

. 

0 

• 

e> oeo ~ 

~ .. • (lo • oo • 

• • 0 

. . 

19'J4 1994 s "" 

Fig. 3. Same as Figure 2, except that only CFR/LMCE data 

collected under "background" atmospheric conditions are used in 

the analysis of the differences. 
INSTAAR-CMDL, covering approximately two annual 

cycles, is encouraging. An apparent offset of about -0.03 

±0.07%0 exists between the groups, with the CFR data 

being lighter. The limited duration of parallel sampling, 

and the small number of simultaneous samples, prevents a 

quantitative evaluation of drifts between the groups or a 

comparison of the range of the measurements observed 

during an annual cycle. While the intercomparison will be 

strengthened by continuing parallel sampling, simultaneous 

sampling and independent checks would be useful 

additions. The latter point will be partially addressed by a 

round-robin intercalibration being organized by the IAEA 

[Allison et al., 1994] involving groups from Australia 

(CSIRO); the United States (INSTAAR, CMDL, and SIO); 

France (CFR-LMCE); and others. 

REFERENCES 

Allison C.E., R.J. Francey, L.P. Steele, and F. de Silva, The 

IAEA interlaboratory calibration program: Air standards for 

the IAEA round-robin exercise, 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. 

Ciais P., P.P. Tans, M. Trolier, J.W.C. White, and R.J. 

Francey, A large northern hemisphere terrestrial C02 sink 

indicated by 13C/12C of atmospheric C02, Science, in press, 

1996. 

Francey R.J., C.E. Allison, L.P. Steele, R.L. Langenfelds, E.0 . 

Welch, J.W.C. White, M. Trolier, P.P. Tans, and K.A. 

Masarie, Intercomparison of stable isotope measurements of 

C02. 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. I 06-110, 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 ~p map for the 

North Atlantic ocean, JGBP-10, working paper 11, 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., 94, 8549-

8565, 1989. 

Trolier, M., Calibrating the INSTAAR-NOAA/CMDL record of 

stable isotopic composition of atmospheric C02. 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 P.A. 

121 

Gemery, Monitoring the isotopic composition of atmospheric 

C02: Measurements from the NOAA global air sampling 

network, J. Geophys Res., in press, 1996. 
Measurement of Short Period Magnetic Pulsations at Barrow: 

A Key Location in the STEP Polar Network 

KAN JI HAY ASH! 

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 timeresolution 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 @ I Hz) 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 

122 

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. 
Total Nitrate and MSA Variation at Mauna Loa 

8. J. HUEBERT AND L. ZHUANG 

Department of Oceanography, University of Hawaii. Honolulu 96822 

INTRODUCTION 

Much of the NO and N02 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 oddnitrogen'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 labora400 

"5_300 

a. 

Q) 

+-' 

~ 200 ~ 

z 

co 

+-' 

0 100 ..... 

0 

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. 

RES UL TS AND DISCUSSION 

In 1993 we published a description of gradient 

measurements of nitric acid and aerosol nitrate at MLO 

[Lee et al., 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-I. 

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 

1995 

0 100 200 

Julian Day 

300 

Fig. I. Nightly concentrations of total nitrate in 1995. 

123 
Q) 

-ca 

L.-

~ 

z 

(ij 

-0 

Iz 

a. 

a. 

300 

250 

200 

150 

100 

50 

0 

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 Cl or Na, 

which are clear indicators of boundary-layer air in our 

samples. 

124 

1 

~ a. 

':0.8 

<( 

Cl) 

~ 

Q) 0.6 

C> 

~ Q) 

~ 0.4 

>-

.r::. 

c 0.2 

0 

:E 

0 

1 3 5 7 9 11 

Month 

160 

120 

80 

40 

Q) 

+"' 

~ ~ 

z 

"'C 

c: 

ca 

Cl) 

Cl) 

z 

Q) 

C> 

~ Q) 

~ >-

.r::. 

+"' 

c: 

0 

~ 

• MSA _._ N03 ----A- NSS 

Fig. 3. Monthly average MSA, sulfate, and total nitrate for 1995. 
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, M.A. Carroll, D.D. Montzka, 

B. Huebert, R.B. Norton, J. Walega, F. Grahek, and 

125 

S. Schauffler, Partitioning and Budget of NOY 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. 
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 7Be and 

210Pb. 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 m3 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 210Pb, 7Be, 95zr, mes, and 144Ce 

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 7Be and 

210Pb data for the SPO site in 1994 is due to the loss of samples 

126 

TABLE 1. Average Surface Air Concentrations of 

Radionuclides 

Date 

1994 

Jan. 

Feb. 

March 

April 

May 

June 

July 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

1995 

Jan. 

Feb. 

March 

April 

May 

June 

July 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

1994 

Jan. 

Feb. 

March 

April 

May 

June 

July 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

1995 

Jan. 

Feb. 

March 

April 

May 

June 

July 

Aug. 

Sept. 

Oct. 

Nov. 

Dec. 

7Be 210pb 95zr 137Cs 144Ce 

(mBq m·3) (mBq m·3) (μBq m·3) (μBq m·3) (μBq m·3) 

n.d. 

2.1 ±0.3 

2.4 ± 0.3 

2.3 ± 0.2 

2.2 ± 0.2 

0.5 ±0.l 

n.d. 

0.5 ±0.l 

0.9 ±0.2 

1.1±0.2 

1.6 ± 0.2 

1.8 ± 0.2 

2.0± 0.2 

1.6 ± 0.2 

1.7 ± 0.2 

1.6 ± 0.2 

I.I ± 0.2 

1.3 ± 0.2 

0.7 ±0.1 

0.6±0.l 

1.9 ± 0.3 

1.3 ± 0.1 

1.6 ± 0.2 

1.9 ± 0.2 

6.3 ± 0.7 

4.4 ± 0.5 

5.8 ±0.6 

8.9 ±0.9 

5.4 ± 0.6 

5.6 ± 0.6 

4.4 ± 0.5 

4.1 ±0.5 

4.6 ± 0.5 

6.0 ± 0.6 

6.1 ±0.6 

8.0 ±0.8 

0.3 ±0.l 

5.6 ± 0.6 

7.0 ± 0.7 

6.8 ±0.7 

7.1 ±0.8 

7.8 ± 0.9 

5.4 ± 0.6 

6.9 ± 0.8 

5.8 ± 0.6 

7.0 ± 0.8 

3.6 ± 0.4 

5.8 ±0.6 

BRW. 

.74 ± .09 <87 

.83 ± .09 <9 

1.12±.12 <6 

.48 ± .05 <4 

.24 ± .03 <6 

.04 ± .01 <25 

.05 ± .02 <31 

.07 ± .01 <30 

.10± .02 <56 

.22 ± .03 <13 

.48 ± .05 <20 

.69 ± .07 <4 

.84 ± .09 <4 

.71 ± .08 <20 

.53 ± .06 <13 

.35 ± .04 <7 

.12±.02 <15 

.09 ± .01 <6 

.07 ± .01 <2 

.06 ± .01 <6 

.22 ± .03 <9 

.18±.02 <8 

.41 ± .05 <8 

1.21 ± .13 <13 

MLO 

.26 ± .04 <17 

.13 ± .02 <12 

.33±.05 <II 

.47 ± .06 <9 

.32 ± .04 <6 

.21±.03 <II 

.18 ± .03 <12 

.15 ± .04 <17 

.18 ± .04 <I l 

.30 ± .04 <13 

.18±.02 <5 

.30 ± .04 <28 

.03 ±.01 

.32± .04 

.43 ± .04 

.45 ± .07 

.45 ± .05 

.41 ± .05 

.20± .03 

.24 ± .05 

.25 ± .05 

.31 ± .05 

.18 ± .03 

.20± .03 

<7 

<4 

<13 

<14 

<ii 

<22 

<45 

<14 

<14 

<16 

<ii 

<29 

<3 

<2 

<2 

<I 

<I 

<I 

<2 

<2 

<3 

<2 

<2 

<I 

<I 

<l 

<I 

<I 

<2 

<2 

<I 

<I 

<2 

<I 

<I 

<2 

<2 

<3 

<3 

<3 

<2 

<3 

<3 

<4 

<3 

<2 

<I 

<3 

<2 

<I 

<I 

<4 

<2 

<3 

<5 

<3 

<4 

<5 

<2 

<4 

<10 

<8 

<6 

<5 

<6 

<7 

<I l 

<I l 

<5 

<9 

<3 

<4 

<6 

<7 

<6 

<8 

<9 

<5 

<2 

<6 

<10 

<5 

<8 

<I 

<11 

<14 

<14 

<16 

<9 

<14 

<15 

<17 

<15 

<10 

<5 

<6 

<8 

<5 

<6 

<18 

<10 

<18 

<8 

<16 

<16 

<23 

<9 

<8 
TABLE l. Average Surface Air Concentrations of during shipment back to EML; occasional gaps in 7Be data for 

Radionuclides - Continued other sites are the result of unavoidably long delays between 

collection and analysis of samples allowing the relatively short7Be 210pb 95zr mes 144Ce lived 7Be (t112 = 53 days) to radioactive decay below detection 

Date (mBq m-3) (mBq m-3) (μBq m-3) (μBq m-3) (μBq m-3) levels. 

SMO Seasonal cycles in the concentrations of 7Be and 210Pb at the 

1994 four sites are consistant with previous observations [Larsen et 

Jan. 2.3 ± 1.2 55± 12 <504 <2 <6 al., 1995]. Concentrations of artificial radionuclides were below 

Feb. 2.0± 0.2 64± 13 <13 <2 <ii detection limits in all analyzed samples from the four sites. 

March 1.6 ± 0.2 34± 12 <5 <I <5 There were no known large scale releases of anthropogenic 

April 1.1±0.1 27 ± 19 <6 <2 <9 radionuclides into the atmosphere in regions likely to influence 

May 1.7 ± 0.2 44± 20 <10 <2 <10 surface air concentrations at BRW, MLO, and SPO, thus the 

June 2.7 ± 0.3 52 ± 11 <12 <2 <3 anthropogenic radionuclide data for these three sites are as July 2.3 ± 0.2 46 ± 11 <3 <I <4 expected. A potential source of anthropogenic radioactivity at 

Aug. 3.1±0.3 56±21 <5 <2 <10 SMO was a series of subsurface detonations of low-yield nuclear Sept. 2.5 ± 0.4 105 ± 20 <74 <3 <6 devices conducted by the French government at Muraroa and Oct. 1.5 ± 0.2 63 ± 15 <6 <I <6 

Nov. 2.0± 0.2 55 ± 11 <15 <2 <3 Fangataufa atolls, -3000 km ESE of SMO between September 

Dec. 0.9 ± 0.1 39± 10 <8 <2 <8 1995 and February 1996. In spite of reassurances on the part of 

1995 2.2 ± 0.2 36±15 <18 <4 <5 the French government, there was widespread public concern 

Jan. 1.7 ± 0.2 51 ± 8 <8 <I <2 regarding the possibility of environmental releases of artificial 

Feb. 1.7 ± 0.2 47 ± 15 <5 <2 <7 radioactivity from these tests. Surface air concentrations of 95zr, 

March 2.2 ± 0.2 53 ± 13 <I I <I <6 I37Cs, and 144Ce in monthly composite samples from SMO 

April 1.3 ± 0.2 60± 14 <50 <3 <5 (Table 1) remained below detection limits in the last 3 months of 

May 2.9 ± 0.4 69±14 <10 <2 <10 1995 supporting the contention that no release of anthropogenic 

June 2.5 ± 0.3 65 ±20 <9 <2 <10 radioactivity into the atmosphere occurred. During the period of 

July 2.4 ± 0.3 55 ± 12 <6 <I <8 testing at Muraroa and Fangataufa, air filters collected at SMO 

Aug. 3.2 ± 0.4 86± 15 <5 <I <8 were returned to our laboratory by express courier service, and 

Sept. 2.7 ± 0.3 84± 22 <8 <2 <II monthly composite analyses were supplemented by analyses of 

Oct. 1.8 ± 0.2 51±11 <6 <2 <8 individual air filters; artificial radionuclide activities were below Nov. 3.2 ± 0.3 77 ± 9 <6 <I <2 detection limits in all of these samples as well. Dec. 

SPO 

1994 Acknowledgment. We wish to thank the CMDL staff at BRW, MLO, 

Jan. 6.1 ±0.7 36± 12 <10 <2 <9 SMO, and SPO for the collection of air filter samples for SASP. 

Feb. n.d. 28 ±12 <399 <2 <43 

March 5.9 ± 1.0 30± 6 <141 <I <12 REFERENCES 

April 4.2 ± 1.3 39 ± 18 <427 <4 <II 

May 2.2 ± 0.6 34 ± 15 <72 <2 <12 Rehfeld, S. and M. Heimann, Three dimensional atmosgheric transgort June 4.1 ±0.7 34± JO <86 <3 <16 simulation of the radioactive tracers 2 JOpb, 7Be, 1 Be, and 9 Sr, July n.s. n.s. n.s. n.s. n.s. Max-Planck-lnstitut fur Meteoro/ogie Rep. No. 144, Hamburg, 1994. Aug. n.s. n.s. n.s. n.s. n.s. Larsen, R.J., C.G. Sanderson and J. Kada, EML surface air sampling Sept. n.s. n.s. n.s. n.s. n.s. program, 1990-1993 data, U.S. DOE Rep. EML-572, U.S. Dept. of 

Oct. n.s. n.s. n.s. n.s. n.s. Energy, Environmental Measurements Laboratory, New York, 1995. 

Nov. n.s. n.s. n.s. n.s. n.s. Larsen, R.J., C.G. Sanderson, H.N. Lee, K.M. Decker and H.L. Beck, Dec. n.s. n.s. n.s. n.s. n.s. Fission products detected in Alaska following the Tomsk-7 accident, 

1995 J. Environ. Radioact., 23, 205-209, 1994. 

Jan. n.s. n.s. n.s. n.s. n.s. 

Feb. 11.2 ± 1.4 51 ± 9 <41 <I <9 

March 11.3 ± 1.6 54± 17 <166 <5 <32 

April 5.9 ± 0.8 29± 9 <36 <I <12 

May 5.0 ±0.8 41±19 <52 <3 <23 

June 4.9 ±0.7 48 ±40 <56 <4 <26 

July 3.8 ± 0.5 33 ±JO <ii <1 <10 

Aug. 4.6±0.6 40± 8 <20 <I <8 

Sept. 4.3 ±0.7 44±35 <56 <5 <25 

Oct. 7.1±0.8 47 ± 15 <77 <4 <7 

Nov. 10.9 ± 1.2 83 ±24 <37 <5 <26 

Dec. 10.8 ±I.I 70± 14 <16 <3 <14 

n.d. = not detected 

n.s. = no sample 

127 
Global Distribution of Chloroform in the Marine Boundary Layer 

M.A.K. KHALIL 

Department of Physics, Portland State University, Portland, Oregon 97207-0751 

R.A. RASMUSSEN 

Department of Environmental Science, Oregon Graduate Institute, Portland, Oregon 97291 

Atmospheric chloroform comes from many natural and 

anthropogenic sources. We discuss its latitudinal 

distribution in the atmospheric boundary layer based on 

data taken at six sites, between January 1986 and January 

1995, operated by the CMDL program. The 

interhemispherical ratio of concentrations is about 2.1 + 

0.2 and the globally-averaged concentration is 17.3 + l.3 

pptv ( + values are 90% confidence limits). 

In recent years there has been a growing interest in the 

global budgets of chlorine containing trace gases in the 

atmosphere because of their role in depleting the 

stratospheric ozone layer and in affecting tropospheric 

ozone. The most important of these gases are the 

chlorofluorocarbons, but other gases such as methylchloride, chloroform, trichloroethylene, perchloroethylene, dichloromethane and similar compounds also 

contribute to the reservoir of relatively long-lived chlorine 

containing gases with lifetimes between a month and 

several years. Little is known about the global budgets and 

biogeochemical cycles of these gases. 

In this paper we describe the salient features of the 

global distribution of chloroform (CHC13). Chloroform is 

emitted in substantial quantities from the oceans and soils. 

In addition, there are many anthropogenic sources, 

including emissions from chlorination of water, chemical 

manufacturing, and combustion processes [Graedel, 1978; 

Khalil et al., 1983, 1990]. 

Between 1986 and 1994 we obtained flask samples from 

eight sites distributed around the world. This sampling is 

part of our cooperative project with the CMDL program 

supplemented with our own sites. The sites are Barrow, 

Alaska (BRW) (7l.16°N, 156.5°W), Cape Meares, Oregon 

(CM 45.5°N, 124°W), Cape Kumukahi and Mauna Loa, 

Hawaii (CK and MLO 19.3°N, 154.5°W), Samoa 

(SA 14. l 0

S, l 70.6°W), Cape Grim, Tasmania (CG 42°S, 

145°E), Palmer Station (PS 64.46°S, 64.05°W) and the 

South Pole (SP 90°S). Data from these sites are reported 

in Figure 1. It is important to note that these 

concentrations represent a long-term climatology of 

chloroform concentrations and that these measurements 

represent the marine boundary layer. There is evidence 

that over land, concentrations can be substantially higher 

at some latitudes. 

Table l shows the concentration of chloroform at the five 

main sites where there are enough data to estimate mean 

128 

35 

• Cl> l Cl> 

,... 30 .;, 

a> 

Cl> • 

> 1 25 

c. ' ~ 

c 20 ~ 

~ c 

T Cl> 15 0 

c T 0 

0 • I (") 

10 1 ..J 

u .J.. • :I: 

u 

5 

-1.0 -0.6 -0.2 0.2 0.6 1.0 

Sine ol Latitude 

Fig. 1: The long-term concentration of chloroform in the marine 

boundary layer. Data shown here were taken between January 

1986 and January 1995. From north to south (sine latitude = + 1, 

the sites are Barrow, Alaska; Cape Meares, Oregon; Cape 

Kumukahi, Hawaii; Samoa; Cape Grim, Tasmania; Palmer 

Station, Antarctica; and the South Pole. 

TABLE l. Annual and Long-Term Averages of 

Chloroform Concentrations (pptv) 

BRW CM CK SA TA SP 

1986 26 33 15 9 8 19 

1987 26 35 16 9 10 7 

1988 30 35 16 11 11 8 

1989 37 42 16 9 11 12 

1990 36 34 19 13 24 14 

1991 28 32 18 11 15 12 

1992 24 30 20 8 11 9 

1993 24 28 17 8 14 NA 

1994 23 26 18 9 12 NA 

Average 28.3 32.8 17.3 9.7 12.9 11.4 

Sine latitude 0.95 0.71 0.33 -0.24 -0.67 -0.9 
annual concentrations for each of the years between January 

1986 and January 1995. The results show that there are no 

secular trends, although the concentrations do tend to 

increase and decrease over short periods of time. The 

trends, over the entire period, are generally not statistically 

significant at the 5% level. Concentrations seemed to have 

increased between 1986 and 1990 and then have been 

falling to the present. 

Acknowledgments. This work was supported in part by grants 

from NSF (ATM-8109047) and DOE (DE-FG06-85ER603 l). 

Additional support was provided by the Biospherical Research 

Corporation and the Andarz: Co. We thank the staffs of the 

CMDL program, the Baseline Cape Grim Station, and CSIRO for 

129 

collecting samples. We thank Don Stearns, Jim Mohan, Bob 

Dalluge, Rohith Gunawardena (001), Martha Shearer and Francis 

Moraes ( PSU), for their contributions to the project. 

REFERENCES 

Graedel, T.E., Chemical Compounds in the Atmosphere, 

Academic Press, NY, 440 pp., 1978.Khalil, M.A.K., R.A. 

Rasmussen, and S.D. Hoyt, Atmospheric chloroform: Oceanair, exchange and global mass balance, Tel/us, 358, 266-274, 

1983. 

Khalil, M.A.K., R.A. Rasmussen, J.R. French, and J. Holt, The 

influence of termites on atmospheric trace gases, J. Geophys. 

Res., 95, 3619-3634, 1990. 
NSWC Pt. Barrow Geomagnetic Observatory 

DANIELS. LENKO, JOHN F. SCARZELLO, AND DAVID TAYLOR 

Naval Surface Warfare Center, Electromagnetic Fields Branch, Bethesda, Maryland 20903-5640 

OBJECTIVE 

The purpose of the observatory is to measure and 

characterize geomagnetic field variations using a sensitive 

magnetometer array for a period of at least one sunspot 

cycle. 

BACKGROUND 

The system was first installed in the spring of 1991. The 

three magnetometer sensor suites were placed on Air Force 

Long Range Radar Site Pt. Barrow property and cables 

connected the sensors to a PC in the CMDL Barrow 

Observatory building that controls the array and stores the 

magnetic information onto transportable media that is 

mailed to Maryland for analysis. 

SENSORS 

Configured to form two orthogonal gradiometer axes, 

magnetic N-S and E-W, with a 150 m baseline, each of the 

three magnetic sensor sites consists of actually two types 

of magnetometers. The first and most sensitive is the He-3 

total field magnetometer which is an optically pumped, 

nuclear magnetic resonance sensing device. It provides a 

very accurate "absolute" measurement of the ambient 

magnetic field in the bandwidth from DC to about 0.1 Hz. 

In terms of sensitivity, the He-3 sensor can resolve 

submilligamma magnetic data when two sensors are 

configured as a gradiometer; here, a second He-3 sensor is 

used to cancel out earth's magnetic field. The dynamic 

130 

range accommodates magnetic fields over 100,000 gamma, 

but the He-3 sensor is gradient sensitive which can shorten 

the measurement time between pumpings. The second 

magnetic sensor included in each location is a triaxial 

fluxgate magnetometer. The three orthogonal axes 

measure magnetic fields in a bandwidth from DC to about 

1 Hz. The digital data is appended to each of the He-3 

sample updates (2.34 times a second) and the fluxgate 

sensor can resolve about 0.1 gamma. 

STATUS 

The geomagnetic noise collected by the previously 

mentioned system has been characterized and used to 

develop and test noise reduction algorithms in an effort 

to enhance advanced detection methods. Specifically, Pt. 

Barrow ambient magnetic data has been "played" into 

detection software as a training data set. Also, on 

occasions, data from the observatory was used to 

correlate magnetic noise events at other locations 

throughout the world. In terms of the observatory 

hardware, the arctic environment is quite harsh and, 

therefore, cabling and sensor maintenance is in order. 

Also, computer and/or storage media upgrades will be 

performed as funds permit. 

FUTURE 

In order to complete the current sunspot cycle, NSWC 

plans to support the Pt. Barrow Observatory through the 

end of the decade. 
Exposure Experiment, South Pole 

JOHNE MAK 

State University of New York at Stony Brook, Stony Brook, New York 11794-5000 

CARL A.M. BRENNINKMEJJER 

Max Planck lnstitt fur Chemie, Mainz, Germany 

JOHN R. SOUTHON 

Center for Accelerator Mass Spectrometry, Lawrence Livermore National Laboratory, Livermore, California 94551-9900 

We are continuing with the exposure experiment for 14C 

production rates at the South Pole. 

The scope of this project is to directly detect and 

quantify the production rate of atmospheric 14C. Carbon14 is not only used for dating organic materials, it can also 

be used as a tracer of OH chemistry (in the form of 14CO). 

In the latter case, if the in:ventory of 14CO is measured and 

the production rate known, then the sink rate, which is 

oxidation by OH, can be calculated. Although cascade 

calculations have constrained the 14CO production rate to 

120%, it is of interest to measure this rate directly. 

Carbon-14 is produced from the reaction: 

14N(n,p)14C 

which is immediately followed by: 

14C + 0 2 ~ 14CO + 0 (>90% yield). 

The methodology takes advantage of gas-handling techniques previously developed by these authors. A known 

131 

amount of CO carrier gas was mixed in with zero air and 

compressed into a suite of cylinders, some of which were 

placed I 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 14C 

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 14C 

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 14C detection has been 

achieved and the first time a ground effect has been 

accounted for by direct measurement. This is an ongoing 

cooperative project. 
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 al., 1995]. 

However, these model studies of past atmospheres lack 

sufficient data for validation . Ice cores provide 

temperatures and CH4 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 al., 1995]. A glacial ice record of atmospheric 

formaldehyde, an intermediate species in the oxidation of 

CH4 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 H20 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 H20 2 detector makes 

atmospheric measurements at approximately I 0-minute 

intervals using a glass coil scrubber to transfer the 

132 

peroxide from the continuous stream of air to water and 

then a chemical fluorescence method to determine the 

concentration in the water [Bales et al., 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 H20 2 and, on a subset of the samples for 

51so, and some ionic species. 

RESULTS 

Average atmospheric H20 2 concentrations for the 3-

week period in spring 1994 were approximately 320 pptv 

and, as expected, no die! cycle was observed [Fuhrer et 

al., 1996]. Occasional rapid changes in atmospheric H20 2 

were observed and a qualitative comparison with air parcel 

trajectories suggest a correlation of atmospheric H20 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 H20 2 concentrations from a pit collected in 

January 1996 are shown in Figure I. Note the very 

obvious annual cycles in H20 2. Along with the other three 

snowpits from 1995 [McConnell et al. , 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 al., l 996a]. Some revisions to the 

model are required because snow accumulation at the 

South Pole is much more sporadic [McConnell, et al., 

1996b]. 

The H20 2 concentrations in the surface snow samples 

are shown in Figure 2. Along with complimentary 

laboratory data [Conklin, et al., 1992], these surface snow 

samples have been used to estimate the annual cycle in 

atmospheric H20 2 concentration [McConnell et al., 

1996c]. The results indicate that the surface snow 

provides a good proxy of the atmospheric H20 2 

concentration throughout the year at the South Pole. 

Evaluation of the surface snow data continues. 
0 

25 

'E 50 

.e 

.r:. 75 .. 

Cl. 

Cll 

c 100 

125 

150 

0 

Fig. 1. Variations 

depth at South Pole. 

:=: 

.c 

Cl. 

Cl. 

~ 

0 .. :c 

800 

600 -

400 

200 

0 

94.50 

100 200 

H20 2 (ppbw) 

300 400 

in hydrogen peroxide concentrations with 

95.00 95.50 96.00 

Year since 1900 

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 

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-tosnow transfer process, both for H20 2 and for reversibly 

deposited chemical species in general. 

REFERENCES 

Bales, R.C., M.V. Losleben, J.R. McConnell, K. Fuhrer, and A. 

Neftel, H20 2 in snow, air, and open pore space in firn at 

Summit, Greenland, Geophys. Res. Le/I., 22(10), 1261-1264, 

1995. 

Conklin, M.H., A. Sigg, A. Neftel, and R.C. Bales, Atmospheresnow transfer function for hydrogen peroxide: microphysical 

considerations, J. Geophys. Res., 98(Dl0), 18,367-18,376, 

1992. 

Fuhrer, K., M. Hiltterli, and J.R. McConnell, Overview of the 

recent field expeiiments for the study of the air-snow transfer 

of H20 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. 

133 

McConnell, J.R., R.C. Bales, J.R. Winterle, H. Kuhns, and C.R. 

Stearns, A lumped parameter model for the atmosphere-tosnow transfer function for hydrogen peroxide, J. Geophys. 

Res., in press, l 996a. 

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, l 996b. 

McConnell, J.R.; 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 AS! Series I, Vol. 30, pp. 265-297, 1995. 
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 stratospheric 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 (NASAGSFC) 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. Boom, J. R. TUSSON IV' AND J. c. EHRAMJJAN 

Biospherical Instruments Inc, San Diego, California 92110-2621 

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 al., 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 monochromator, 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 el 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 

South Pole 90.00°S o• 

McMurdo 77.51°S J66.40°E 

Palmer 64.46°S 64.03°W 

Ushuaia, Argentina 54.49°S 68.t9°W 

Barrow, Alaska 71.18°N 156.47°W 

San Diego, California 32.45°N 117.ll 0 W 

*CADIC: Centro Austral de Investigaciones Cientificas, Argentina 

tUkpeagvik Inupiat Corporation-National Arctic Research Laboratory 

1.8 

1.6 

1.4 

1.2 

'E 1 .!,! 

~0.8 

0.6 

0.4 

0.2 

(a) 

298.507 - 303.03 nm lnlegraled Spectral lrradlance 

-Barrow, Alaska 

-south Pole 

oJ-:....:~~--'"-~--=....,,~~-""'.........;:.....,...-"""""'-~~.....,....---. 

5000 

4500 

4000 

3500 

'E 3000 

~ 2500 

:>. 

2000 

1500 

1000 

500 

0 

(b) 

1-Jan-93 1-Jan-94 1-Jan-95 1-Jan-96 1-Jan-93 

Established Location 

Feb. 1988 Clear Air Building 

March 1988 Arrival Heights 

May 1988 Clean Air Building 

Nov. 1988 CADIC* 

Dec. 1990 UIC-NARLt 

Oct. 1992 Biospherical Instruments, Inc. 

UV-A (320 - 400 nm) lrradlance 

-Barrow, Alaska 

-south Pole 

1-Jan-94 1-Jan-95 1-Jan-96 

Fig. I. 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 1 b, 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 

High spectral resolution scanning UV spectroradiometers 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, 

1.8 • 

" 1.6 

!j 

~ 1.4 

" g 1.2 t 

~ 

~ 1 

;;; 

y o.e 

~ 0.6 

~ gi 0.4 

£ 0.2 

-+-298.507 • 303.03 nm lnlegraled Speclral lrradiance 300 

-Tovsozone 

320 

340 

360 

400 

420 

- 440 

~~..___.~~~~~--'+~~ ........ ~~ ......... ~~ ....... ~~-+ 450 

15-Apr 26-Apr 7-May 18-May 29-May 9-Jun 20-Jun 1-Jul 

1995 

Figure 2. Comparison of the 298.507 - 303.03 nm integrated spectral 

irradiance and TOYS 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. 

136 

1,4 - •- 298.507 • 303.03 nnm lnlegrtaed Spectral lrradlance 

-Hlslorlcal Minima & Maxima 

ol...-----~~;:::::~.:,......:.,.:'S,,~ 

1-Sep 1-0ct 31-0cl 

1994 

30-Nov 30-Dec 

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 (μW/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. l 0 

Barrow 199.5 June I, 1992 49.6 

South Pole 129.4 December 3, 1992 67.8° 

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 aellv1ty was 

funded by contract SCK-M 18914-02 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 llisagvik College), D. Endres and M. 

Gaylord (CMDL). The Ukpeagvik lnupiat Corporation of Barrow 

provided installation assistance. Operators at Palmer, the South 

Pole, and McMurdo were provided by ASA. 
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), I I5-I I6, I993. 

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 I 8-22, 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, I 996a. 

Booth, C.R., T.B. Lucas, T. Mestechkina, J.R.Tusson IV, J.P. 

Schmidt, D.A. Neuschuler, and J.H. Morrow, NSF Polar 

Programs UV Spectroradiometer Network 1994-1995 

Operations Report, I 82 pp., Biospherical Instruments Inc., San 

Diego, CA, I 996b. 

Booth, C.R., and S. Madroni ch, Rndiati on amplificati on Fac tors: 

Improved formulati on accounts for large increases in 

ultraviolet radiation associated with Antarcti c ozone depletion, 

in Antarctic Research Se ries, edited by C.S. Weiler and P.A. 

Penhale, 62, pp. 39-42, I 993 . 

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, J 992. 

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. 

137 

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. Ultrnviolet 

radia ti on and its effects on organisms in aquatic environments, 

in E11 virm1111e11ral UR Plro1obiology , 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, Anl. J. U. S., 1989 Review, 25(5). 

24I-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, I 7-30, 1994. 

McKenzie, R.L., M. Blumthaler, C.R. Booth, S.B. Diaz, J.E. 

Frederick, T. Ito, S. Madronich, and G. Seckmeyer, Surface 

Ultraviolet Radiation, in Scie11tific 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, H.P. 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. 

ofGeophys. Res., 97, 7383-7397, I992. 

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, IOl3-IOI7. I992. 
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 I 

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. Strontium90 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 90Sr 

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 gammaemitting radionuclides instead of the radiochemical 

procedure previously used to make a single 90Sr 

measurement. Gamma radionuclides of particular interest 

include both anthropogenic (137Cs, 95zr, and t44Ce) and 

natural isotopes (?Be and 210Pb). This technique will 

allow EML to continue to monitor for atmospheric releases 

of fission products. In addition, the development of a 

database on 7Be and 210pb 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 ionexchange resin and sealing the sample in a 90-cm3 

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 anthropogenic gamma radionuclides. In all, twenty samples from 

SMO were analyzed. 

RESULTS 

Radionuclide deposition data from SMO obtained in this 

study is presented in Table I. The results are shown in 

units of becquerels per square meter (Bq m-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 210Pb, 137Cs, t44Ce and 95zr when 

their activity was not detected. In addition, precipitation data in centimeters is provided for most sampling 

intervals. 

DISCUSSION 

The results presented in Table I 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 t 37Cs activity detected in two samples 

is only slightly higher than the detection limit. Cesium137 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 anthropogenic 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 I 37Cs in 

these two samples was probably due to resuspension of 

previously deposited material. Of the natural radionuclides, 7Be was detected in most of the samples, but 

210pb was only detected in seven of the twenty samples. 

Beryllium-7 is a cosmogenic radionuclide produced in the 

earth's upper atmosphere, while 210pb is a daughter in the 

primordial 238U decay series and its atmospheric presence 

follows the release of 222Rn from the earth's surface. The 

deposition of 7Be and 210pb ranged from undetectable to 

271.8 and <0.7 to 8.8 Bq m-2 respectively. The 7Be 

deposition appears to be related to both the amount of 

precipitation and duration of the collection period. The 

138 
TABLE I. Gamma Radionuclide Deposition at SMO from September I 995 Through February 1996 

Precipitation 7Be Error 

Collection Date (cm) (Bq m·2) (%) 

3rd Quarter 199 5 66.0 271.8 6 

Sept. 1-20, 1995 18.I 90.8 9 

Oct. 4-11, 1995 4.3 88.5 8 

Oct. 11-18, 1995 0.8 14.9 16 

Oct. 18-25, 1995 8.4 ND 0 

Oct. 25-Nov. 3, 1995 1.0 21.4 10 

Nov. 3- 8, 1995 8.0 22.4 14 

Nov. 8-15, 1995 13 .1 27.7 9 

Nov. 15-22, 1995 3.1 21.4 II 

Nov. 22-29, 1995 13 .2 45 .1 9 

Nov. 29-Dec. 6, 1995 2.2 33.7 13 

Dec. 6-15, 1995 I. I 20.I 14 

Dec. 15-20, 1995 0.0 ND 

Dec. 20-29, 1995 2.7 54.6 8 

Dec . 29-Jan. 3, 1996 2.7 30.0 14 

Jan. 3-10, 1996 8.1 46.5 7 

Jan. 10-24, 1996 18 .6 48.7 7 

Jan. 24-31 , 1996 0.9 IO.I 22 

Jan. 31-Feb. 7, 1996 NA 24.I 16 

Feb. 7-14, 1996 NA 27.2 13 

ND - Not detected 

NA - Data not available 

210pb 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 concentration of 210pb 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 210Pb deposition and precipitation because of the large 

number of nondetects. Real 2 IOpb deposition values 

occurred during periods of lesser precipitation which may 

suggest that there is a higher 222Rn flux during these 

periods. Further measurements and comparisons with 

atmospheric concentrations of 210pb may reveal if this 

interpretation is valid. In the future, EML will analyze 

deposition samples collected at SMO and MLO to address 

this observation. 

21opb Error 210pb Error 144Ce 95zr 

(Bq m·2) (%) (Bq m·2) (% ) (Bq m·2) (Bq m· 

2) 

8.8 25 < 0.6 < 0.7 < 1.8 

< 1.5 < 1.0 < I.I < 2.7 

< 1.5 < 1.0 < I.I < 2.9 

< 1.3 < 0.8 < 1.0 < 2.2 

< 1.7 < 1.0 < 1.2 < 2.9 

5.9 40 < 0.7 < 0.9 < 2.0 

< 2.0 < 1.6 < 2.0 < 4.8 

< 1.0 0.9 14 < 0.8 < 1.6 

< 0.7 < 0.4 < 0.5 < 1.2 

< I. I 0.7 18 < 0.9 < 1.9 

< 1.3 < 0.8 < 0.9 < 2.0 

3.4 36 < 0.9 < 1.0 < 2.4 

2.8 37 < 0.8 < 0.9 < 2.1 

< 1.6 < 1.2 < 1.5 < 3.4 

8.5 38 < 1.2 < 1.4 < 3.0 

4.7 45 < 0.6 < 0.8 < 1.8 

3.6 38 < 1.0 < 1.3 < 2.9 

< 1.5 < I.I <1.4 < 3.3 

< 1.2 < 0.8 < 0.9 < 2.0 

< 1.2 < 0.7 < 0.8 < 2.1 

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. I, 

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 

I 990, 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 !-

minute averages. Operation is continuous except for an 

annual break of about I 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 I 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 0s) 

was equal to 2.5 (about 66°), i.e., between 08 I 4 and 0857 

LST in October and December, respectively. These are 

given as ratios of the irradiance in each channel to the 

140 

., 

~ c 

0 

., 

~ 

e. 

., 

c 

0 

N 

0 

~ 'E 

;::) 

c 

0 

1l 

0 

e. 

~ N 

0 

~ 

c 

::::> 

c 

0 

., 

.0 

180 

Nov. 1994 Dec. 1994 Jan. 1995 

260 

220 

Nov. 1994 1 Dec. 1994 Jan. 1995 180.J__.:_.:=..:..;_c=..;:..;,..,;.__::..::..:.:._;_;:~_.__--==o.;--=~"'--L 

e. 220 ., 

5 

(5 

3.50 10~ 

3.00 10" :g 

e 

2.5010" i 

c 

2.00 10" ~ 

"' t: 

1.50 10" ~ 

0 

1.00 10""' :g_ 

en 5.00 10·5 

0.011 

0.010 0 

... 0.009 ~ 

s 

0.008 c 

'ti "' 

0.007 ~ 

0.006 ~ 

0 

0.005 8. 

en 

0.004 

0.055 

0.050 :2' 

! 

II> 

u 

c: 

., 

'a 

~ 

~ 

0 

~ c/) 

0.030 

Fig. J. Time series of total ozone and UV-B irradiance ratios at 

MLO during winter 1994-1995. Early morning (secant 2.5) 

irradiance on clear-sky days in three bands (5- nm full bandwidth 

at half height) with nominal center wavelengths of 295 nm (upper 

panel), 300 nm (middle panel) and 305 nm (lower panel) relative 

to 325 nm. Note different ratio scales in each panel. 

irradiance in the 325-nm channel. The time series of 

Dobson spectrometer ozone measurements at MLO is 

shown for comparison. Over the period of decreasing 

ozone, November to December, there is a steady climb in 

the irradiance ratio in each channel. The increase from 

minimum to maximum irradiance was a factor of 3.0, 1.9, 

and 1.6, respectively, in the 295-, 300- and 305-nm 

channels. There is a strong correlation between ozone 

and the irradiance ratio in each channel. A linear 

regression of the 305 nm/ 325 nm ratio on total ozone 

(interpolating the ozone series as necessary for missing 

dates) had a coefficient of determination (R2) of 0.86. 

The R2 for the 295- and 300-nm ratios were 0.85 and 0.86, 

respectively. 
These results reinforce the conclusion of Hofmann et al. 

[1996] that incident solar UV-B was significantly elevated 

during the record low total-column ozone event at MLO 

(December-January 1994 ). Measurements during both 

early morning (sec es = 2.5) and midmorning (sec es = 1.5) 

show specific increases in irradiance during this period 

that are highly correlated with the decrease in total column 

ozone. Since the mean optical path length of solar 

irradiance through the stratosphere is longer at sec es = 2.5 

compared to 1.5, a given decrease in ozone should result in 

a larger relative increase in irradiance at higher secant. 

This was indeed the case for the 300- and 305-nm 

channels, for which there was less of an increase from 

minimum to maximum (factor 1.5 and 1.8, respectively) at 

sec e. = 1.5 [Hofmann et al. , 1996). However, for the 

295-nm channel, the factor increase was actually higher at 

the shorter secant (3 .2). For this channel, early morning 

and midmorning measurements may not be strictly 

comparable. This is because the effective center wavelength, i.e., the filter center wavelength adjusted for the 

greater proportion of longer-wavelength solar irradiance 

within the pass band [Correll et al., 1992), is likely to be 

141 

at a significantly longer wavelength in the early morning 

versus midmorning. 

REFERENCES 

Correll, D. L., C. 0 . Clark, B. Goldberg, V. R. Goodrich, D. R. 

Hayes Jr., W. H. Klein and W. D. Schecher, Spectral ultravioletB radiation fluxes at the earth's surface: long-term variations at 

39°N, 77°W, J. Geophys. Res .. 97, 7579-7591, 1992. 

Hofmann, D.J., S.J. Oltmans, B.A. Bodhaine, G.L. Koenig, 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, W.D. Komhyr, R.D. Evans, B.J. 

Johnson, D.M. 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(12), 1533-1536, 1996. 

Neale, P.J., D.L. Correll, V.R. Goodrich, and D.R. Hayes Jr., UVB optical depths at Mauna Loa: Relative contribution of ozone 

and aerosols, in Summary Report 1993, edited by J.T. 

Peterson, and R.M. Rosson , NOAA Environmental Research 

Laboratories, Boulder, CO, pp. 132-134, 1994. 
Advanced Global Atmospheric Gases Experiment (AGAGE) 

R.G. PRINN 

Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 

R.F. WEISS 

Scripps Institution of Oceanography, University of California, La Jolla, California 92093 

F.N. ALYEA AND D.M. CUNNOLD 

Georgia Institute of Technology, Atmospheric Sciences, Atlanta, Georgia 30332 

P.J. FRASER AND L.P. STEELE 

CS/RO, Division of Atmospheric Research, Victoria, Australia 3 I 95 

P.G. SIMMONDS 

University of Bristol, School of Chemistry, Bristol, United Kingdom BSB ITS 

INTRODUCTION 

Continuous high-frequency gas chromatographic 

measurements of two biogenic/anthropogenic gases (CH4 

and NzO) and five anthropogenic gases (CFC13, CF2Cl2, 

CH3CC13, CF2ClCFC12, and CC14) are being carried out at 

globally-distributed sites to quantitatively determine the 

source and sink strengths and circulation of these 

chemically and radiatively important long-lived gases. 

Hydrogen, carbon monoxide, and a wide range of 

hydrochlorofluorocarbons (HCFCs), hydrofluorocarbons 

(HFCs) and other halocarbons are also measured at certain 

stations. The station locations are Cape Grim, Tasmania 

(41°S, 145°E), Cape Matatula, American Samoa (SMO) 

(14°S, 171°E), Ragged Point, Barbados (13°N, 59°W), 

Trinidad Head, California (41°N, 124°W), and Mace Head, 

Ireland (53°N, 10°W). The program, which began in 1978, 

is divided into three parts associated with three changes in 

instrumentation: the Atmospheric Lifetime Experiment 

(ALE) which utilized Hewlett-Packard HP5840 gas 

chromatographs, the Global Atmospheric Gases 

Experiment (GAGE) which utilized HP5880 gas 

chromatographs, and the Advanced (AGAGE) phase now 

underway which uses a new fully-automated system from 

the Scripps Institution of Oceanography (SIO) containing a 

custom-designed sample module and HP5890 and Carle 

Instruments gas chromatographic components. Also, as 

part of AGAGE, a new Finnigan gas chromato-graph/mass 

spectrometer system for measuring HCFCs and HFCs is 

now operating at Mace Head and a second such instrument 

will be installed at Cape Grim in late 1996. 

1994-1995 UPDATE 

The data for the seven long-lived gases measured in 

GAGE and AGAGE during 1994-1995 continue to be of 

very good quality with significant improvements in the 

frequencies, prec1s10ns, and accuracies of the 

measurements resulting from the transition from GAGE to 

AGAGE. Some significant conclusions have been reached 

over the past year as a result of analyzing the data. 

First, Prinn el al. [1995] showed that the atmospheric 

concentration of the volatile anthropogenic chemical 

CH3CC13, which was steadily increasing at 4.5 ± 0.1 % per 

year until mid-1990, has subsequently decreased at a rate 

of 2.2 ± 0.4% per year (all stated uncertainties are 1 cr). 

142 

This recent rapid decrease is consistent with its short 

lifetime and recent industrial emission reductions. The 

observed decreases began in early 1991 in the northern 

hemisphere and in mid-1992 in the southern hemisphere, 

reflecting the predominantly northern hemispheric 

emissions of this industrial chemical and the approximately 

I-year interhemispheric exchange time. The measurements, combined with industrial emissions, were used in an 

inverse method to deduce a globally averaged CH3CC13 

lower atmospheric lifetime (200 to 1000 mbar) of 4.6 ± 0.3 

years and a total atmospheric lifetime (0 to 1000 mbar) of 

4.8 ± 0.3 years. Assuming a lifetime for loss of CH3CC13 

to the oceans of 85 years, we deduced a global weightedaverage lower atmospheric OH concentration of (9.7 ± 0.6) 

x 105 radicals cm-3. The rate of change of this OH 

concentration is 0.0 ± 0.2% per year, implying that the 

oxidation capability of the lower atmosphere has not 

changed significantly from 1978 to 1994. Our conclusions 

concerning the OH concentrations and trend depend on the 

accuracy of the industrial emission estimates and our new 

absolute calibration. For methane (CH4), these OH 

concentrations imply lower atmospheric and total 

atmospheric lifetimes of 8.0 ± 0.5 and 8.9 ± 0.6 years, 

respectively. The deduced lifetimes for CH3CCl 3 and CH4 

are substantially less and the deduced OH concentrations 

substantially more than previous estimates. This 

substantially lowers the potential of these two gases (and 

most other hydrogen-containing gases) for affecting the 

ozone layer and climate compared to previous estimates. 

Second, observations at the ALE/GAGE stations of 

CC12FCCIF2 have been reported by Fraser et al. [1996]. 

The observations from Cape Grim have been extended back 

to 1978 using archived air samples. The global 

atmospheric abundance of CC12FCC1F2 is indicated to have 

been growing exponentially between 1978 and 1987 with 

an e-folding time of approximately 7.6 years; it has been 

growing less rapidly since that time. On January 1, 1994, 

the mean inferred northern hemispheric mixing ratio in the 

lower troposphere was 84.4 ± 0.4 ppt (parts-per-trillion dry 

air mole fraction) and the southern hemispheric value was 

80.6 ± 0.4 ppt; the global growth rate in 1991-1993 is 

estimated to have averaged approximately 3.1 ± 0.1 ppt per 

year. The differences between the northern and southern 

hemispheric concentrations are calculated to be consistent 

with almost the entire northern hemispheric release of this 

gas. The annual release estimates of CCl 2FCC1F2 by 
industry, which include estimates of eastern European 

emissions, consistently exceeds those deduced from the 

measurements by approximately 10% from 1980 to 1993. 

The uncertainties in each estimate is approximately 5%. 

This difference suggests that up to 10% of past production 

might not yet have been released. The measurements 

indicate atmospheric releases of CC12FCC1F2 have been 

decreasing rapidly since 1989 and in 1993 amounted to 

78 ± 27 xl06 kg or 42 ± 15% of the 1985-1987 emissions. 

Third, using GAGE/AGAGE observations Cunnold et al. 

[ 1996] showed that global concentrations of CC1 3F reached 

a maximum in 1993 and decayed slightly in 1994, while 

CCl2F2 concentrations increased approximately 7 ppt in 

1993 and 1994. These changes suggest that world 

emissions decreased faster in these 2 years than industry 

production figures would suggest and faster than expected 

under the Montreal Protocol and its amendments. An 

analysis of regional pollution events at the Mace Head site 

suggest that industry may be underestimating the decline of 

emissions in Europe. It is argued, however, that the 

decline in European emissions is not biasing the 

background Mace Head measurements (or the GAGE 

global averages). Combining the chlorofluorocarbon 

measurements, including CCl2FCCIF2, with GAGE/ 

AGAGE measured global decreases in CH3CC13 and CC14 

after 1992 and with Cape Grim archived air measurements 

of CHC1F2, the measurements suggest total anthropogenic 

atmospheric chlorine loading from these six gases 

maximized in 1992 at 2.95 ± 0.04 ppb (parts-per-billion 

dry air mole fraction) and that it had decreased by 0.02 ± 

0.01 ppb by the beginning of 1995. 

During 1996, operations at the American Samoa 

Observatory (SMO) will make the transition from the 

GAGE instrument to the new AGAGE system; it is to be 

installed in the new laboratory building. During 1994-

1995 the GAGE HP5880 continued to be operated by the 

CMDL station personnel in collaboration with the Scripps 

Institution of Oceanography (SIO) group. Operations were 

quite smooth and uneventful during this period with most 

problems being of a routine maintenance and repair nature. 

The new instrument systems for AGAGE represent a 

significant technological advance. All operations and data 

acquisition are by a Sun Microsystems workstation using 

custom software for signal processing integration and 

storage of the data and chromatograms. The instrument 

measures its own nonlinearity for all the AGAGE gases on 

a regular basis using a pressure-programmed constantvolume injection system and a single gas standard. All 

channels of the instrument are fitted with precolumns to 

avoid column contamination by late-eluting gases and, as a 

result the frequency of measurement, has been increased 

three-fold versus GAGE. Precision is also greatly improved 

over the GAGE instruments. The system works interactively 

with its uninterruptible power supply (UPS). With the new 

installation at SMO completed, the new AGAGE instruments 

will be operational at all five AGAGE stations. 

Another major component of the AGAGE program is the 

development of new absolute calibration scales. This work 

is being done using an extension of the "bootstrap" 

calibration method used earlier at SIO. In the AGAGE 

work, gravimetrically-determined aliquots of pure CFCs 

are mixed with about 12 L of gravimetrically-determined 

pure N20. A small aliquot (-0.4 cm3) of this mixture is 

then introduced into a 35-L electropolished stainless steel 

canister to which about 10 torr of water vapor has been 

added to reduce wall reactions and adsorption. The 

canister is then filled with about 40 atmospheres of 

repurified "zero air" to bring the N20 mole fraction to a 

near-ambient value. The resulting N20 concentration is 

then calibrated gas chromatographically against existing 

SIO standards, ar.d the CFC concentrations are determined 

by multiplying the measured N20 mole fraction by the 

gravimetric CFC/ N20 ratios of the original mixture. In 

this way we have been able to obtain improved accuracy 

for all AGAGE gases, but especially for the lower vapor 

pressure and more adsorptive gases. AGAGE and CMDL 

are now engaged in an active intercalibration program 

(through the IGAC/NOHALICE activity) for all of the 

AGAGE gases as well as for methyl halides and some 

HCFCs. 

DATA ACCESS 

The ALE/GAGE/AGAGE data are archived at the 

Department of Engery Carbon Dioxide Information 

Analysis Center, Oak Ridge, Tennessee, and are available 

to interested scientists. Potential users of the data may 

contact CDIAC on the Internet (CDP@ORNL.GOV). 

Acknowledgments. The AGAGE is supported by NASA Grants 

NAGW-732 and NAGW-2034 , NOAA Contract NA85-

RAC05103, CSIRO Australia, Australian Bureau of 

Meteorology, the U.K. Department of Environment, and the 

Alternative Fluorocarbons Environmental Acceptability Study. 

We thank Mark Winey and the other NOAA staff at SMO for 

their continued excellent local support for our instrumentation 

there. 

REFERENCES 

Cunnold, D.M., R. Weiss, R.G. Prinn, D. Hartley, P.O. 

Simmonds, P.J. Fraser, B. Miller, F.N. Alyea, and L. Porter, 

GAGE/AGAGE measurements indicating reductions in global 

emissions of CCJ3F and CC12F2 in 1992-1994, J. Geophys. 

Res., submitted, 1996. 

Fraser, P., D. Cunnold, F. Alyea, R. Weiss, R. Prinn, P. 

Simmonds, B. Miller, and R. Langenfelds, Lifetime and 

emission estimates of I, 1,2-trichlorotrifluorethane (CFC-113) 

from daily global background observations June 1982-June 

1994, J. Geophys. Res .. IOI, 12,585-12,599, 1996. 

143 

Prinn, R.G., R.F. Weiss, B.R. Miller, J. Huang, F.N. Alyea, D.M . 

Cunnold, P.J. Fraser, D.E. Hartley, and P.O. Simmonds, 

Atmospheric trends and lifetime of CH3CCl3 and global OH 

concentrations, Science, 269, 187-192, 1995. 
The 13C/12C of Atmospheric Methane 

PAUL QUAY, JOHN STUTSMAN, AND DAVID WILBUR 

School of Oceanography, University of Washington, Seattle 98195 

INTRODUCTION 

Since 1989 we have been measuring the 13C/ 12C of 

atmospheric CH4 on air samples collected at three CMDL 

·sites (Pt. Barrow at 71°N, 156°W, Mauna Loa at 19°N, 

155°W and Samoa at 14°S, 170°W) and on the Washington 

coast at 48°N, 126°W. 

The 13C/12C of atmospheric CH4 is a tracer that can 

distinguish between CH4 input from bacterial and 

nonbacterial CH4 sources. Bacterial CH4 is microbially 

produced in anoxic environments likes swamps, bogs, rice 

paddies, and the rumens of cows. Non-bacterial CH4 sources include thermogenically produced natural gas and 

CH4 produced during biomass burning. Bacterial CH4 has 

a ot3C of about -60%0 (versus PDB) whereas the o13C of 

natural gas and CH4 from biomass burning are about -40 

and -24%0, respectively [Quay et al., 1991]. 

The spatial and temporal variations in the 13C/ 12C of 

atmospheric CH4 depend on the variations of the relative 

strength and 13C/ 12C of the CH4 sources and sinks. Over 

-47 rr===---------------, 

[Darrow 1. 

-47.2 

-47.4 

8-47.6 

:3. 

(.) -47.8 - -· <') 

~ -48 . 

-48.2 

-48.4 

r 

• 

-48.6 .i--------+-------------' 

1988 1989 1990 1991 1992 1993 1994 1995 1996 

x -47 .--------------------, 

Olympic Pn. 

-47.2 

• 

0 

~ -47.4 

.£. 

• 

(.) 

<') 

~ -47.6 "O 

-47.8 ·1 

l 

-48 ~-----------------~ 

1988 1989 1990 1991 1992 1993 1994 1995 1996 

interannual time scales the trends in the 13C/ 12C of 

atmospheric CH4 indicates changes in the source 

composition, i.e., the relative strength of bacterial versus 

non-bacterial CH4 sources. Chan~es in the loss rate of 

CH4 have little effect on the 13C/ 1 C. Because CH4 will 

likely contribute about 15% of the radiative forcing during 

the next century [Wigley and Raper, 1992], it is important 

to quantify the strength of the individual CH4 sources and 

to determine whether the CH4 source strengths are 

changing with time. This latter point has been underscored 

by the recently observed slowdown in the rate of CH4 

increase in the atmosphere [Dlugokencky et al., 1994]. 

METHODS 

The air samples are collected at approximately 2-week 

intervals. using pre-evacuated stainless steel flasks either 

15 or 30 litres in volume. The CH4 is extracted from air in 

our laboratory using the procedure developed by Stevens 

and Rust [1982]. Briefly, the air is metered into a high 

-46.9 .--------------------, 

-47.1 

0 

~ -47.3 

.£. 

(.) 

<') 

~ -47.5 "O 

-47.7 

MauruJ Loa 

-47.9 ~-----------------_.J 

1988 1989 1990 1991 1992 1993 1994 1995 1996 

-46.7 .-------------------~ 

Samo~ 

-46.9 

0 

.£: ·47.1 

.£. 

(.) 

("') 

:a; -47 ,3 "O 

-47.5 -

-47 ,7 -'---------------+-------' 

1988 1989 1990 1991 1992 1993 1994 1995 1996 

Fig. I. The time series of the 1)13C of atmospheric CH4 measured at Pt. Barrow, Olympic Peninsula, Mauna Loa, and Samoa since 1988. 

144 
vacuum extraction line through a series of liquid nitrogen 

traps to remove H20, C02, and N20. The air then passes 

through a bed of Schutze's reagent, 120 5 on silica, to 

oxidize CO to C02 which is trapped cryogenically. Then 

the CH4 in the air is combusted over platinized silica at 

800°C to C02 which is then trapped cryogenically. The 

yield of the procedure determined from standards is 100 ± 

2% (n = 114). The 13C/12C of the C02 derived from CH4 

is measured on a Finnigan MAT 251 gas ratio isotope mass 

spectrometer. The overall measurement precision is about 

±0. l %0. We obtain a ol3C of -41. 73%0 (versus PDB) for 

NBS-16. 

RESULTS AND DISCUSSION 

The seasonal cycle in the ol3C of CH4 is greatest at 

71°N (Barrow) with an amplitude of -0.6%0, and decreases 

southward to 14°S (Samoa) where the seasonal trend is at 

about our measurement precision, i.e., 0.1 %0 (Figure 1 ). 

The seasonal trends at 71 °N and 48 °N can be approximated roughly by a single harmonic with an annual 

period. Episodes of high CH4 concentrations associated 

with very depleted ol3C values occur at these two sites in 

September and October of each year and are due to input 

of bacterial methane. The trend toward higher summertime 

ol3C values is expected as a result of increased CH4 

oxidation by OH because the 12CH4 molecules react at a 

slightly faster rate ( l.0054x) than the 13CH4 molecules 

[Cantrell et al., 1990]. It is also likely that there is 

seasonal change in the average o13C of the CH4 sources. 

The annual mean ol3C values increase southward from 

about -47.7%0 at 71°N to -47.2%0 at l4°S. 

We calculate a global average ol3C of CH4 of 

approximately -47.3%0. The mean global ol3C value, when 

combined with the 14C content of atmospheric CH4, yields 

estimates of the proportion of bacterial, nonbacterial, and 

145 

fossil CH4 source strengths [e.g., Quay et al., 1991]. We 

estimate that bacterial CH4 sources contribute about 75%, 

fossil CH4 sources about 15%, and biomass burning about 

10% of the total CH4 input. 

Although the seasonal cycle in ol3C dominates the time 

series measurements in the northern hemisphere, there is 

evidence for a slight interannual increase. Measurements 

at all four time-series locations indicate an increase in 

ol3C and, when combined and area weighted, yield a 

global rate of approximately 0.02%0 per year since 1989. 

A ol 3C increase indicates that the ratio of nonbacterial to 

bacterial CH4 source strength is increasing slightly. The 

interhemispheric gradient and interannual trend in the 

isotopic composition of methane yields useful constraints 

of the magnitude of CH4 sources and the rate at which the 

source strengths are changing with time. 

REFERENCES 

Dlugokencky, E.J., L.P. Steele, P.M. Lang, and K.A. Masarie, 

The growth rate and distribution of atmospheric methane, J. 

Geosphys. Res., 99, 17,021-17,043, 1994. 

Cantrell, C.A., R.E. Shetter, A.H. McDaniel, J.G Calvert, J.A. 

Davidson, D.C. Lowe, S.C. Tyler, R.J. Cicerone and J.P. 

Greenberg, Carbon kinetic isotope effect in the oxidation of 

methane by the hydroxyl radical, J. Geophys. Res., 95, 22,455-

22,462, 1990. 

Quay, P.D., S.L. King, J. Stutsman, D.O. Wilbur, L.P. Steele, I. 

Fung, R.H. Gammon, T.A. Brown, G.W. Farwell, P.M. 

Grootes, and F.H. Schmidt, Carbon isotopic composition of 

atmospheric methane: Fossil and biomass burning source 

strengths, Global Biogeochem. Cycles, 5, 25-47, 1991. 

Stevens, C.M. and F.E. Rust, The carbon isotopic composition 

of atmospheric methane, J. Geophys. Res., 87, 4879-4882, 

1982. 

Wigley, T.M.L. and S.C.B. Raper, Implications for climate and 

sea level of revised IPCC emission scenarios, Nature, 357, 

293-300, 1992. 
Aerosol Measurements on American Samoa 

DENNIS L. SAVOIE AND JOSEPH M. PROSPERO 

University of Miami, Rosenstiel School of Marine and Atmospheric Sciences, Miami, FL 3314-1098 

An aerosol sampling program was established at the 

CMDL station on American Samoa in 1983 as part of the 

Sea/Air Exchange Program (SEAREX) network [Savoie et 

al., l 989a]. Our data record starts in March 1983 and 

continues to the present. The main focus of these studies 

is on non-seasalt (nss) S04=, No3-, methane sulfonate 

(MSA) and various seasalt components. Measurements of 

210Pb yield concentrations that are among the lowest 

reported for temperate and tropical ocean regions 

[Turekian et al., 1989], suggesting that the island is 

minimally impacted by continental sources Al and Sb 

concentrations at Samoa are among the lowest reported for 

tropospheric aerosols [Arimoto et al., 1989; Prospero et 

al., 1989], and concentrations of Pb are about an order of 

magnitude lower than those in the North Pacific westerlies 

[Maring et al., 1989; Rosman et al., 1990]. Consequently, 

the concentrations of nss-S04= and No3- at Samoa should 

largely reflect the input from natural sources in the region. 

SAMPLING AND ANALYSIS 

Aerosol samples are collected by drawing air through 

20 x 25-cm Whatman-41 filters at a nominal flow rate of 1.1 

m3 min-I; the filters are mounted at the top of a tower at the 

eastern edge of the promentory where the CMDL site is 

located. The sampling pumps are controlled by wind sensors 

that activate the pumps only when the wind is off the ocean 

at speeds greater than 1 m s-1. Filters are returned to Miami 

for analysis; see Savoie et al., 1994 for procedures. 

Nss-S04= is obtained as the difference between total S04= 

and seasalt S04=, the latter being calculated as total Na+ 

times 0.2516, the S04=/Na+ mass ratio in bulk seawater. 

MEAN CONCENTRATIONS AND TEMPORAL VARIATIONS 

The monthly mean concentrations of nss S04=, MSA, 

N03-, and Na+ are presented in Table 1. The monthly 

TABLE I. Aerosol Concentrations Measured at American Samoa From March 19, 1983, to January 3, 1996 

Month 

January 

February 

March 

April 

May 

June 

July 

August 

September 

October 

November 

December 

Mean 

Med. 

0.114 

0.103 

0.120 

0.111 

0.091 

0.087 

0.091 

0.085 

0.089 

0.083 

0.103 

0.096 

0.103 

0.092 

0.108 

0.098 

0.152 

0.142 

0.148 

0.139 

0.128 

0.123 

0.148 

0.137 

Annual-Wkly 0.116 

0.104 

Annual-Mon 0.116 

0.100 

Nitrate 

μg m-3 

Std. 

16% 

0.057 

0.066 

0.055 

0.069 

0.038 

0.057 

0.060 

0.050 

0.036 

0.061 

0.044 

0.067 

0.038 

0.070 

0.042 

0.061 

0.054 

0.105 

0.059 

0.093 

0.049 

0.092 

0.068 

0.088 

0.055 

0.068 

0.023 

0.087 

N 

84% 

38 

0.155 

34 

0.179 

46 

0.118 

46 

0.116 

49 

0.118 

49 

0.135 

50 

0.141 

49 

0.149 

50 

0.189 

46 

0.185 

54 

0.166 

45 

0.215 

556 

0.165 

12 

0.137 

Sodium, 

μg m-3 

Mean Std. 

Med. 16% 

6.05 3.72 

4.79 3.64 

6.12 2.98 

5.42 3.67 

4.70 1.60 

4.21 3.43 

5.09 1.94 

4.56 3.35 

5.18 1.84 

5.23 3.61 

4.99 1.56 

4.75 3.25 

5.46 1.85 

5.10 4.07 

6.18 2.10 

5.61 4.53 

5.72 2.45 

5.06 3.83 

4.70 1.51 

4.53 3.41 

5.13 1.65 

4.71 3.75 

6.28 2.82 

5.60 

5.44 

4.95 

5.47 

4.92 

3.97 

2.25 

3.59 

0.58 

4.55 

N 

84% 

38 

9.02 

34 

8.39 

46 

5.97 

46 

6.65 

49 

6.22 

49 

6.73 

50 

7.15 

49 

8.01 

50 

7.47 

45 

6.00 

54 

6.27 

45 

8.15 

555 

7.12 

12 

5.46 

Mean 

Med. 

0.365 

0.377 

0.428 

0.417 

0.381 

0.385 

0.275 

0.265 

0.272 

0.276 

0.293 

0.299 

0.272 

0.288 

0.252 

0.276 

0.433 

0.421 

0.458 

0.425 

0.328 

0.352 

0.358 

0.368 

0.339 

0.345 

0.343 

0.360 

NSS Sulfate, 

μg m-3 

Std. 

16% 

0.213 

0.168 

0.313 

0.197 

0.151 

0.249 

0.164 

0.162 

0.238 

0.171 

0.167 

0.206 

0.171 

0.139 

0.235 

0.052 

0.195 

0.286 

0.166 

0.281 

0.162 

0.240 

0.220 

0.222 

0.210 

0.185 

0.072 

0.276 

N 

84% 

38 

0.572 

32 

0.655 

46 

0.546 

46 

0.396 

49 

0.406 

48 

0.414 

50 

0.426 

48 

0.476 

50 

0.614 

45 

0.631 

54 

0.450 

45 

0.528 

551 

0.497 

12 

0.418 

Mean 

Med. 

24.9 

21.7 

23.4 

23.7 

20.6 

20.7 

17.3 

13.7 

24.7 

23.7 

20.8 

18.5 

25.0 

20.8 

25.0 

27.3 

31.3 

33.2 

25.7 

23.2 

20.7 

22.7 

24.0 

22.5 

23.4 

22.1 

23.6 

22.6 

MSA, 

μg m-3 

Std. N 

16% 84% 

11.1 18 

15.6 38.0 

9.1 14 

13.5 30.6 

8.0 16 

13.7 25.6 

10.6 20 

9.8 28.9 

12.8 19 

11.3 36.5 

10.6 20 

13.4 25.9 

12.5 16 

14.7 39.7 

13.3 15 

10.2 31.0 

12.1 17 

19.1 41.9 

9.1 15 

18.5 36.2 

5.3 24 

14.5 26.3 

10.7 13 

14.5 

10.8 

12.9 

3.5 

20.2 

32.7 

207 

33.3 

12 

24.6 

Values in bold are the monthly mean concentration, the standard deviation, and the number of samples in the set. The values in 

italics are the median concentration and the concentrations of the samples at the 16% and 84% level in the frequency distribution. 

146 
averages listed in Table 1 and the plots of the weekly 

concentrations (Figure 1) show evidence of seasonal 

cycles. The strongest cycle is exhibited by No3· for which 

Lhe highest monthly mean (0. l52 μg m·

3 in September) is 

71 % higher than the lowest (0.089 μg·m·' in April). Th'e 

seasonal cycle for nss-S04"' is similar to that for No3· but 

the seasonal difference is somewhat less; the October mean 

(0.458 μg m-3) is 56% higher than the April mean (0.294 

μg m-3). For both species, the seasonal cycles presented 

here do not differ significantly from those based on the 

1983 through 1987 samples [Savoie et al., l 989b]. 

There is no clearly evident pattern in the monthly 

averages for MSA even though there are significant monthto-month variations. This lack of a clear trend may be due 

in part to the fact that the data set for MSA is not as large 

as that for the other species. Nonetheless, the maxiumum 

occurs in September (mean, 31 .31 ng m· 3

) and the 

minimum in April (17 .30 ng m-3). 

There is no evidence of any long-term changes in aerosol 

co ncentrations at the site. The means in Table 1 are quite 

simi lar to those previously reported by Savoie et al. 

[ l 989a,b] for 215 samples, 0.36 μg·m· 3 for nss SQ4= and 

0.1 I 0 for No3•. Even the comparatively small data set (n = 

22) used by Saltzman et al. [ 1985] provided comparable 

means: nss-S04=, 0.41 μg·m- 3; MSA, 26 ng·m- 3

; N03-, 

0. 118 μg·m- 3; and Na+, 5.6 μg·m· 3• 

.., -

E 

..... 

C> 

::l. 

-Q) 

-~ 

-

z 

0.3 

0.2 

0.1 

i 

I 

! 

~ 

t 

~ I 

I 

3 6 9 12 

Month of the Year 

Fig. 1. Weekly aerosol concentrations for American Samoa 

(from March 19, 1983 to January 3, 1996) grouped by month. 

The data are shown with box plots. The length of each box shows 

the range within which the central 50% of the values fall, with 

the box borders at the first and third quartiles; the cross-bar 

shows the median [for details see Tukey, 1997) 

147 

The relationship between nss-S04= and MSA also 

appears to be quite stable over time. Savoie et al. [1994] 

investigated the relationships among the various species 

and found that the geometric mean (GM) ratio nssso4=/MSA (18.1 ± 0.9) is only about 7% higher than the 

GM ratio of 16.9 in the 22 American Samoa samples 

originally used by Saltzman et al. [1985]. As reported in 

Savoie et al. [1994] the ratio obtained at American Samoa 

is similar to that obtained at other ocean stations in the 

tropics and sub-tropics. Thus, within this region, MSA 

should provide reasonable estimates of the biogenic 

component of the total nss-S04=. 

Acknowledgments. We are indebted to the NOAA Climate 

Monitoring and Diagnostics Laboratory for permitting us to 

sample at their station and to the numerous people who have been 

involved in the actual field work, principally C. Farmer and E. 

Wilson-Godine!. The aerosol research was supported by National 

Science Foundation grants ATM870341 I and ATM9013125 and 

NASA contracts NAG8-621 and NAG8-841 to the University of 

Miami. 

REFERENCES 

Arimoto,R., R.A. Duce, and B.J. Ray, Concentrtions, sources and 

air-sea ·exchange of trace elements in the atmosphere over the 

Pacific Ocean. in Chemical Ocea11ography, vol. 10, edited by 

J.P. Riley, R. Chester, and R.A. Duce, pp. 107-149, Academic, 

San Diego, CA., 1989. 

Maring, H., C. Patterson, and D. Settle, Atmospheric input fluxes 

of industrial and natural Pb from the westerlies to the midNorth Pacific, in Chemical Oceanography. vol. 10, SEAREX: 

The Sea/Air Exchange Program, edited by J. P. Riley, R. 

Chester, and R. A. Duce, pp. 84-106, Academic, San Diego, 

CA, 1989. 

Prospero, J.M., M. Uematsu, and D.L. Savoie, Mineral aerosol 

transport to the Pacific Ocean, in Chemical Oceanography, 

vol. JO, SEAREX: The Sea/Air Exchange Program, edited by 

J.P. Riley, R. Chester, and R.A. Duce, pp. 187-218, Academic, 

San Diego, Calif., 1989. 

Rosman, K.J.R., C.C. Patterson, and D.M. Settle, The 

distribution of lead between seasalt, dust, and lead-rich 

aerosols in the mid-South Pacific easterlies at American 

Samoa, J. Geophys. Res., 95, 3687-3691, 1990. 

Saltzman, E.S., D.L. Savoie, J.M. Prospero, and R.G. Zika, 

Atmospheric methanesulfonic acid and non-seasalt sulfate al 

Fanning and American Samoa, Geophys. Res. Lei/., 12, 437-

440, 1985. 

Savoie, D.L .. J.M. Prospero, and E.S. Saltzman, Nitrate, nonseasalt sulfate and methanesulfonate over the Pacific Ocean, in 

Chemical Oceanography, vol. 10, SEAREX: The Sea/Air 

Exchange Program, edited by J.P. Riley, R. Chester and R. A. 

Duce, pp. 219-250, Academic, San Diego, CA, 1989a. 

Savoie, D.L., J.M. Prospero, J.T. Merrill, and M. Uematsu, 

Nitrate in the atmospheric boundary layer of the tropical South 

Pacific : Implications regarding sources and transport, J. 

Atmos. Chem., 8, 391-415, 1989b. 

Savoie, D.L., J.M. Prospero, R. Arimoto, and R.A. Duce, Nonseasalt sulfate and methanesulfonate at American Samoa, J. 

Geophys. Res., 99 (D2), 3587-3596, 1994. 

Tukey, J.W., Exploratory Data Analysis, 688 pp., AddisonWesley, Reading, MA, 1977. 

Turekian, K. K., W.C. Graustein, and J.K. Cochran, Lead-210 in 

the SEAREX program: An aerosol tracer across the Pacific, in 

Chemical Oceanography, vol. 10, SEAREX: The Sea/Air 

Exchange Program, pp. 51-81, edited by J. P. Riley, R. 

Chester and R. A. Duce, Academic, San Diego, Calif., 1989. 
An Operational lntercalibration Experiment Between CMDL and CSIRO to 

Measure Several Atmospheric Trace Species 

L.P. STEELE, R.J. FRANCEY, R.L. LANGENFELDS, C.E. ALLISON, AND M.P. LUCARELLI 

CS/RO Division of Atmospheric Research. Aspendale, Victoria, Australia 

P.P. TANS, E.J. DLUGOKENCKY, T.J. CONWAY, P.C. NOVELLI, AND K.A. MASARIE 

NOAA, Climate Monitoring and Diagnostics Laboratory, Boulder, Colorado 80303 

J.W.C. WHITE AND M. TROLIER 

University of Colorado, Institute of Arctic and Alpine Research, Boulder, Colorado 80309 

INTRODUCTION 

Atmospheric trace species that are important to the 

question of global and climate change have been measured 

by both CMDL and CSIRO for many years through their 

networks of flask sampling sites. There has been some 

overlap of these networks, particularly at the locations of 

the baseline observatories. A desirable, even essential goal 

is to be able to "seamlessly merge" the trace species data 

obtained by the two laboratories, creating a larger and selfconsistent data set that can be reliably used for modeling 

and interpretive studies of trace gas budgets, with 

particular emphasis on the global carbon cycle. The 

advantages of this approach have already been 

demonstrated through several studies of the carbon cycle 

which make use of the isotopic measurements of carbon 

dioxide [e.g., Ciais el al., l 995a,b,c]. The initial phases of 

an intercomparison of stable isotope measurements of C02 

by both laboratories has been provided by Francey el al. 

[1994). 

The most commonly adopted method of determining the 

degree of agreement in the measurement of atmospheric 

trace gases by different laboratories has been the periodic 

exchange of standard gases, usually contained in highpressure cylinders. This method was in use for many years 

by those laboratories measuring atmospheric C02, and is 

endorsed by the World Meteorological Organization 

[Pearman, 1993]. While these types of experiments can 

yield important information, they suffer from the 

disadvantages that the frequency of intercalibration is too 

low, perhaps occurring only once every few years, and the 

analysis methodology sometimes differs from that 

employed in the routine observing programs. 

OPERATIONAL INTERCALIBRA TION 

In an attempt to improve upon the existing methods of 

trace species intercalibration between CSIRO and the 

CMDL Carbon Cycle Group (CCG), we proposed an 

experiment in 1991 that was agreed upon between the two 

laboratories. It began in late 1991 and is ongoing. The 

glass flasks that are filled with air (in pairs) approximately 

once a week for CCG at the Cape Grim baseline station are 

routed through CSIRO's GASLAB on their way back to 

Boulder. One member of every second pair of flasks (i.e., 

one in every four flasks) is measured in GASLAB for 

several trace species (C02, CH4, CO, H2, and 13C and IBO 

in C02). The flask sample measured in this way is clearly 

148 

marked, therefore, it can be identified when the air samples 

reach Boulder. All flask air samples, including the one 

measured in GASLAB, are then measured for the same 

suite of trace species in the CCG laboratories. This type of 

experiment is possible only because the analytical methods 

used in GASLAB consume relatively small volumes of air, 

typically less than 200 mL for the full suite of 

measurements. The techniques used for the GASLAB 

measurements are outlined in Francey el al. [1996). A 

crucial requirement for this experiment to be successful is 

that the trace composition of the samples measured in 

GASLAB must not be altered in any way by this process. 

The design of the experiment should allow any such 

alteration to be identified. 

Exchanges of data from this experiment between the two 

laboratories were initially sporadic. Visual inspection 

indicated that there was reasonable agreement for CH4, 

CO, and 13C02. An offset of about 0.6 ppm between the 

C02 records was thought to be due to an offset in the 

calibration scales being used by the two laboratories. A 

thorough analysis of the full data set is being prepared for 

publication. This analysis and improvements in procedures 

to allow regular and systematic comparison of the results 

by staff of both laboratories has been greatly facilitated by 

support from both laboratories for an extended visit by one 

of the authors (KAM) to CSIRO Division of Atmospheric 

Research during 1996. 

REFERENCES 

Ciais, P., P.P. Tans, M. Trolier, J.W.C. White, and R.J. Francey, 

A large northern hemisphere terrestrial C02 sink indicated by 

the 13C/12C ratio of atmospheric C02, Science, 269, 1098-

1102, I 995a. 

Ciais, P., R.J. Francey, P.P. Tans, J.W.C. White, and M. Trolier, 

An analytical error estimate for the ocean and land uptake of 

C02 using 1)13C observations in the atmosphere, NOAA Tech . 

Memo. ERL CMDL-8, NOAA Environmental Research 

Laboratories, Climate Monitoring and Diagnostics Laboratory, 

Boulder, Colorado, 13 pp., I 995b. 

Ciais, P., P.P. Tans, J.W.C. White, M. Trolier, R.J. Francey, J.A. 

Berry, D.R. Randall, P.J. Sellers, J.G. Collatz, and D.S . 

Schimel, Partitioning of ocean and land uptake of C02 as 

inferred by 1)13C measurements from the NOAA Climate 

Monitoring and Diagnostics Laboratory Global Air Sampling 

Network, J. Geophys. Res., I 00, 5051-5070, I 995c. 

Francey, R.J., C.E. Allison, L.P. Steele, R.L. Langenfelds, E.D. 

Welch, J.W.C. White, M. Trolier, P.P. Tans, and K.A. Masarie, 

Intercomparison of stable isotope measurements of C02, in 

Climate Monitoring and Diagnostics Laboratory No. 22 
Summary Report 1993, edited by J.T. Peterson and R.M. 

Rosson, pp. 106-110, NOAA Environmental Research 

Laboratories, Boulder, CO, 1994. 

Francey, R.J., L.P. Steele, R.L. Langenfelds, M.P. Lucarelli, C.E. 

Allison, D.J. Beardsmore, S.A. Coram, N. Derek, P.R. de 

Silva, D.M. Etheridge, P.J. Fraser, R.J. Henry, B. Turner, E.D. 

Welch, D.A. Spencer and L.N. Cooper, Global Atmospheric 

Sampling Laboratory (GASLAB): Supporting and extending 

the Cape Grim trace gas programs, in Baseline Atmospheric 

Program (Australia) 1993, edited by R.J. Francey, A.L. Dick, 

149 

and N. Derek, pp. 8-29, Bureau of Meteorology and CSIRO, 

Division of Atmospheric Research, Melbourne, Australia, 

1996. 

Pearman, G., Survey of the results of the 1991-1992 round-robin 

interlaboratory intercomparison, in Report of the Seventh 

WMO Meeting of Experts on Carbon Dioxide Concentration 

and Isotopic Measurement Techniques, Rome, Italy, 

September 7-10, 1993, edited by G.I. Pearman and J.T. 

Peterson, pp. 104-107, World Meteorological Organization, 

Global Atmosphere Watch, Report No. 88, 1993. 
USGS Barrow Observatory 

JACK TOWNSHEND 

U.S. Geological Survey, College Obesrvatory, Fairbanks, Alaska 99775-5160 

The Barrow Magnetic Observatory is the northernmost of 

U.S. Geological Survey (USGS) I 2 continuously-recording, 

digital magnetic observatories. As such, it serves as a 

singularly important site in a global network of observing 

stations whose combined data define the planetary magnetic 

field and track its secular change. Ground stations such as 

the Barrow Observatory are controls for field modeling by 

harmonic analysis, essential reference stations for airborne 

and satellite surveys, and absolute calibration locations for 

field survey instrumentation. 

The primary instrumentation operated is an EDA FM100BR Triaxial fluxgate magnetometer, an EDA PPM-105 

proton free-precession magnetometer, an Observatory 

Magnetometer Interface System (OMIS), and several piermounted instruments for absolute control observations. 

In late summer 1996 the USGS plans on upgrading the 

present fluxgate magnetometer and installing an additional 

instrument called a "quasi-absolute magneto-meter." 

In August I 993 the USGS and CMDL negotiated a 

Memorandum of Agreement (MOA) to have CMDL 

personnel at Barrow service the USGS BRW equipment, 

make instrument observations, and provide some logistic 

support. This agreement is renewed annually. 

The Barrow Magnetic Observatory receives its 

authorization to operate from the USGS Branch of 

Earthquakes and Geomagnetic Information in Golden, 

Colorado. 

Parts of the NOAA-USGS MOA are presented below to 

provide some history and background of our joint Barrow 

operations. 

For many years, the Naval Arctic Research Laboratory 

(NARL) was the source of electrical power, road 

maintenance, transportation, and lodging support. Effective 

October I, 1984, this support was no longer assured as the 

Navy began the process of transferring ownership of NARL 

to the Ukpeagvik lnupiat Corporation (UIC). 

Individual withdrawal applications for land occupied by 

each agency's project was approved by BLM and published 

in the Federal Register. Withdrawal file numbers are 

NOAA-F-81469 and USGS-F-8 I 490. Transfer of the land to 

the USGS and NOAA was made effective April 2, 1991, and 

published in the Federal Register, Volume 56, Number 63, 

page 13413, dated April 2, 1991. 

A third-party agreement was set up between NOAA, 

USGS, and the Department of the Air Force, now located 

150 

at l ITCW/LGOX, 6900 9th St. Suite 301, Elmendorf AFB, 

Alaska 99506-2270, to provide support for electrical power, 

road service, transportation, vehicle repair, lodging, and 

meals through their DEW System Station at Barrow, Alaska 

(Pow-Main). This agreement (Inter-Agency MOA between 

NOAA and USGS) will be an attachment to the "Support 

Agreement" between USAF, NOAA and USGS. NOAA is 

authorized by the USGS to be signatory to the "Support 

Agreement" with the USAF, since they want only one 

signature on the document. 

Subsequently NOAA and USGS agreed to get power from 

the Barrow Utilities and Electric Co-op, Inc., (BUEGI), 

through the Ukpeagvik lnupiat Corporation/ 

Northern Arctic Research Laboratory (UIC/NARL) facility. 

NOAA and the USGS shall continue to acquire electrical 

power from the Barrow Utilities and Electric Co-op., Inc. 

(BUECI). 

Under the terms of the MOA, NOAA agrees to have the 

CMDL personnel at Barrow do the following: 

Weekly 

Check facilities for any noticeable damage or unusual 

conditions and report anything that may seem out of the 

ordinary to the College Observatory, Fairbanks, check the 

Observatory instruments and equipment, and make routine 

rotations on specific forms supplied. Make four sets of 

magnetic absolute observations with a Declination 

Inclination Magnetometer (DIM); make one set of Scale 

Value Observations on the Observatory Magnetometer 

Interface System (OMIS) Fluxgate Magnetometer; change 

digital magnetic, and analog paper tapes; and send all data, 

computations, observations, and tapes to the USGS office. 

Unscheduled 

Perform minor trouble shooting and make adjustments to 

equipment when USGS technical personnel provide 

instructions by telephone. 

For the services supplied by NOAA in the previously 

mentioned items, the USGS will reimburse NOAA for the 

time required to perform the work, travel time required to 

get to and from USGS facilities and instruments, and a 

reasonable amount for unplanned circumstances because of 

emergencies, weather, etc. Supplies and materials are not 

included in this agreement. USGS will pay for or reimburse 

NOAA for supplies or materials needed. 
The New ANSTO Radon Detector at MLO 

S. WHITTLESTONE 

ANSTO, PMB I, Menai, NSW 2234, Australia 

INTRODUCTION 

After 6 years, many of the questions posed at the 

commencement of the Australian Nuclear Science and 

Technology Organization (ANSTO) CMDL radon program 

at the Mauna Loa Observatory, Hawaii (MLO) have been 

answered. By 1994 the radon detector was obsolete. It is, 

therefore, timely to review the output from the program 

and describe a new radon detector designed to meet the 

needs of the future . 

The program commenced in June 1989. Its aim was to 

assess the value of radon as a tracer for air masses which 

have been subject to recent contact with land and, 

therefore, not representative of the global baseline. By the 

end of 1991 it was evident that radon is indeed the best 

readily-measured indicator of perturbation of air masses by 

contact with land beyond Hawaii [Whittlestone et al., 

1992]. Because it is chemically inert, radon concentration 

is unaffected by the complex reactions affecting most other 

atmospheric species during transport. Samples of trace 

gases sampled in the baseline wind sector are strongly 

correlated with radon concentrations (Figure 1 ). For the 

first time there was a quantitative continuous measure of 

the influence of the Asian continent on air samples at MLO 

when jet streams transport air from Asia in only a few days 

[Kritz, 1990]. 

Radon has been useful in the study of dry deposition 

because its decay products are very small and highly 

reactive. Radon acts as a uniform source of ultrafine 

reactive particles that have a short half life and so indicates 

deposition only over a limited area. Measurements at sea 

level at Cape Grim, Australia, indicated very strong 

180 2 

170 0 

310 

~ 

CFC11 pptv. add 260 

N20 ppbv 

10 

305 ~ ~ CFC12 add 460 

0 

200 400 200 400 

RADON mBq m·3 

Fig. I. Dependence of trace gas concentrations on radon 

concentration in the baseline wind sector at MLO. 

151 

deposition in the lower marine boundary layer. Studies at 

MLO showed higher concentrations of ultrafine radon 

decay products were present at the altitude of MLO but 

that they were subject to strong deposition close to MLO in 

certain weather conditions [Schery and Whittleston e, I 995; 

Schery et al., 1992]. 

Several other studies have made use of radon . For 

example it was valuable in validation of use of air mass 

trajectory cluster analysis of variations of methane at MLO 

[Harris et al., 1992]. Data were provided for MLOPEX-11 

and were part of an evaluation of Pb-212 as a tracer for 

local ground contact [Whittlestone et al., 1996a,b]. 

Radon has proved to be useful to other programs at 

MLO. However, the detector required a degree of skilled 

technical supervision that was not sustainable in the long 

term. It was desirable to be able to obtain radon 

measurements with no more effort than wind speed and 

direction. To meet this need, a new radon detector design 

was incorporated into the MLO detector. This design, 

although it was markedly simpler and more rugged than the 

previous one, provided improved time response, better 

sensitivity, lower power consumption, and freedom from 

routine maintenance. 

Because of the simplicity of the new instrument, it is 

possible to obtain high-quality preliminary data in real 

time. Steps have been taken to make the radon data readily 

available from the CMDL computer. 

THE RADON DETECTOR 

Figure 2 is a schematic diagram of the detector. It is an 

implementation of the design described in Whittlestone et 

Signal to data logger 

Photomultiplier 

ZnS screen 

2000L delay 

chamber 

~ 

Airflow 

diffuser 

625 mesh wire 

' 

Exhaust 

lntcmal fl ow 

loop blower 

40m air 

r· 

Delay to 

remove 

thoron 

External 

flow loop 

blower 

Fig. 2. Schematic diagram of the ANSTO radon detector at 

MLO. 
[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 

min-I. 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-I 

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-t 

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 

Sensitivity: 

Limit of detection: 

Time response: 

Routine maintenance: 

Power consumption: 

Specification 

0.5 c s-l per Bq m-3 

20 mBq m-3 (30% counting error in 

1 hour count) 

45 minutes to 50% after step in radon 

concentration 

Minimal 

40W 

152 

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 washout 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., Olugokencky, 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(05), 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, 428, 46-61, 1990. 

Schery, S.O., and S. Whittlestone, Evidence of high deposition of 

ultrafine particles at Mauna Loa Observatory, Atmos. Environ., 

29(22), 3319-3324, 1995 

Schery, S.O., R. Wang, K. Eak, and S. Whittlestone, New models 

for radon progeny near the earth's surface, J. Radiat. Pro/. 

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.O. Schery, and Y. Li, Thoron and radon fluxes 

from the island of Hawaii, J. Geophys Res., 101(09), 14,787-

14, 794, l 996a. 

Whittlestone, S., S. 0. 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, l 996b. 
A Comparison of C02 and 13/12C Seasonal Amplitudes in 

the Northern Hemisphere 

T. P. WHORF, C.D. KEELING, AND M. WAHLEN 

Scripps /11s1i1111io11 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 C02 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 C02 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 C02 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 C02 changes in 

the form of possible changes in the growth of plants on a 

very large spati al scale. The Alert measurements have 

been collected under a cooperative program hetween SIO 

and the Atmospheric Environment Service of Canada. The 

SIO carbon dioxide program also continues to monitor C02 

concentrations at Christmas Island (2°N), Baring Head, 

New Zealand (4 1°S), Raoul Island, Kermadec Islands 

(29°S), and La Jolla, California (LJO , 33°N), the last of 

which start ed in 1969 and now includes both continuou s 

and flask measurements. 

Since 1978 the 13C/12C isotopic ratio of atmospheri c 

C02 has been determined from the same 5-L flask samples 

of C02 that have been measured for C02 concentration . In 

the early years isotopic ratio was measured at MLO, SPO, 

and LJO and by the mid- I 980s 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 Isotopi c Physics Laboratory in the Netherlands 

[Keelin g et al., 1989]. Samples si nce then have been 

analyzed using a VG PRISM Series II mass spectrometer at 

SIO. 

Changes in the amplitude of the seasonal cycle in C02 

concentration at MLO were first observed and reported in 

the early 1980s [Bacastow et al., 1985]. A more recent 

analysis of seaso nal cycle variations observed at MLO has 

shown an increase in amplitude of 20% since the midl 960s, an earlier drawdown of C02 in the late spri ng and 

early summer by up to a week since the late 1970s, and a 

correlation between amplitude changes there and temperatures averaged over the northe rn hemisphere [Keeling et 

al. , 1996]. Here we discuss seasonal c hanges in the 

I 3C/l 2C isotopic ratio of atmospheric C02 and how they 

compare with changes in amplitude of C02 concentration. 

DATA AND ANALYSIS 

Measurements of 13C/12C used in this study come from 

the same 5-L flask sampl es that have all been analyzed for 

C02 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 th an three sigma from our smooth curve 

fit. This fit, described in Keeling et al. [1 989]. uses four 

harmonics to describe the seasonal variations plus a cubi c 

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. 

153 

Isotopic data are obtained from samples of C02 

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, 130, of atmospheric C02 

[Keeling et al., 1989, p. 170]. Similar data have been 

obtained at the other SlO site locations. In 16 years of 

MLO 130 isotopic data, ove r 700 daily samples have been 

analyzed amounting to approximately 44 per yea r, 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 lo track any changes in the 

spectrometer output and thereby correct for them. These 

standards were recently calibrated against NBS 19 (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 dupli cated 

measurements of these daily gas standards on the mass 

spectrometers at the Ne the rlands and at SIO. 

RESULTS 

Figures 2-4 show relative seasonal amplitudes computed 

annually by least-square fitting the annua l function 

g( l + Atm) multiplied by the four harmon ics derived in the 

overall fit to the data of each year independentl y. In this 

expression, g denotes the annual rel ative amplitude, 101 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 func tion is thus phase 

locked to the fit of the overall data set. Amplitudes are 
-8. q 

-8.2 PTB 

-8.0 

-7.8 

-7.6 

-7.q 

-7.2 

-8.0 

-7.8 

-7.6 

-7.q 

-7.2 

BO B2 Bl! B6 BB 90 92 9'1 96 YEAR 

Figure I. Time trend of the reduced isotopic ratio, t 31), of 

atmospheric C02 in per mil difference from the intern atio nal 

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 C02 and 138 for our northern hemisphere 

si tes, (ALT, BRW, LJO, MLO, and KUM) in whic h the 

C02 station data have been fit over the same time periods 

as there exists data for 138, typically beginning around 

1980 except for ALT data, which begins later. This is so 

that the relati ve 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 C02 fits, they number approximately 90% of the 

number for C02, except at La Jolla where it is about 60%. 

In addition, the figures showing BRW, LJO, and MLO 

flasks have C02 data extending back in time to before the 

beginning of the isotopic data. In these cases, fits to these 

longer records have yielded earlier C02 relative amplitudes 

which have subsequently been adjusted so as to be 

referenced to the same time as in the shorter fit and then 

154 

SEASONAL AMPLITUDE AT STATION ALERT 

I. 2S 

I. 20 • C02 9 (a) 

o Cl3 [: til I. IS '' " Q : \ ::::> 5 I. 10 0.. 

~ <I.OS 

w 

> f: I. 00 

j 

w 

0:: .9S 

. 90 

70 7S 80 8S 90 9S 

YEAR 

SEASONAL AMPLITUDE AT POINT BARROW 

I. 20 

I. IS • C02 (b) 

o Cl3 ~ l.10 

::::> 

j I.OS 0.. 

~ 

< 1.00 

~ .9S !'-

j 

w 

0:: .90 

.as 

70 7S 80 8S 90 9S 

YEAR 

SEASONAL AMPLITUDE AT LA JOLLA PIER 

I. IS 

I. to • C02 (c) 

~I.OS 

::::> 5 1.00 0.. 

~ 

< .9S 

~ .90 !'-

j 

w 

0:: .6S 

.60 

70 7S 80 6S 90 9S 

YEAR 

Figure 2. Comparisons of relative seasonal amplitudes for C02 

concentration and 131) at the threo! most northerly stations (a) 

Alert (ALT), (b) Point Barrow (BRW) and (c) La Jolla (LIO), 

each referred to the midpoint of its isotopic record (open circles). 

The large solid circles for LJO are continuous data. 
I. IS 

I. 10 w 

Cl ::::>I.OS 

E-

::J 

~ 1.00 

< 

.BS 

.BO 

. 7S 

6S 70 7S BO BS 90 

YEAR 

SEASONAL AMPLITUDE AT CAPE KUMUKAHI 

1.25 

1.20 C02 

:::> 

~I. IS o C13 

.

~ . 5 1.10 .. . . . . c:>.. 

~I.OS 

~ E- 1.00 

j 

w 

P:: .9S 

.90 

70 7S BO BS 90 

YEAR 

(a) 

95 

(b) 

9S 

Figure 3. Comparisons of relative seasonal amplitudes for C02 

concentration and 131) at (a) Mauna Loa (M LO), nask 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 partl y due to a strong shift in trend following the 1983 El 

Niiio. 

included in these figures. Increasing amplitudes are more 

apparent in these longer records. Gain factors calculated 

for the longer records shown al these three sites and 

referenced to 1970 near the start of these fits are BRW: 

1.03 ± 0.16% yr·l, LJO: 1. 21 ± 0.17% yr-I, and MLO 

flasks: 0.82 ± 0.15% yr· I. 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 C02 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 sign ificantly higher quality than 

other early years containing sparse flask data. 

The fluctuations in 138 seasonal amplitudes occurring 

over several year periods show a strong tendency to fo llow 

the C02 fluctuations during the same times, especially at 

BRW and LJO. A significant part of semi-decadal to 

155 

1.20 

I. IS 

~I. 10 

:::> 

51.os 

c:>.. 

~ 1.00 

I-

~ .9S 

j 

μ:J 

P:: .90 

.85 

70 75 BO BS 90 95 

YEAR 

Figure 4. Comparison of seasonal amplitudes of C02 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 fl uctuations may be a result of the effect of 

interannual variations connected with El Niiio 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 Do with C02 concentration for our northern hemisphere 

sites show a rate of change in 138 wi th respect to C02 of 

close to 0.05 per mil per ppm, as would be expected by a 

predominantly terrestrial component in C02. An 

interesting but unexplained observation is that mu lti-year 

seasonal changes at ALT in both 138 and C02 seem to be 

out of phase with changes at BRW by a couple of years, 

particularly near 1992. 

Comparison of seasonal changes in 138 and C02 

concentration do not seem to fo llow each other as closely 

at MLO as at BRW and LJO. This may stem from part of 

the seasonal cycle in C02 concentration being produced by 

oceanic processes that influence it without significantl y 

affecting the amplitude of 138. A difference in the trends 

of the seasonal amplitudes in concentration and 138 is also 

ap parent at MLO as evidenced by the differing gain factors 

138 and C02. 

Gain factors for C02 concentration and 138, compared 

over the same time intervals and referred to 1970, are 

expressed as annual rates of change in Table I. Annual 

rates referred to 1980 would be about 8-10% smaller than 

if referred to 1970. No significant change in the seasonal 

cycle of 138 is apparent in the MLO flask record since 

1980, whereas the increase in seasonal amplitude of C02 

concentration over the same period exceeds the standard 

error by more than a factor of two. 

An additi onal observation of seasonal amplitude c hanges 

in C02 between MLO (conti nuous data) and KUM (Figure 

4) where respective gain factors over the same period are 

shown in Table I, shows no increase in seasonal amplitude 

at KUM since 1979. Also, no significant increase in 

amplitude is evident in the isotopic data. Since KUM, 
TABLE. I. Annual Rate of Increase in the 

Seasonal Amplitud e of Atmospheric C02 and 138 at Various Locations 

Rate of 

Approx. Inclusive Years Increase* 

Location Latitude Type of Observations (in percent) 

Alert 82°N C02 1985- 1995 1.2 1 ± 0.36 

131) 1985-1995 2.48 ± 0.63 

Point Barrow 71°N C02 1974-1995 1.03 ± 0.16 

C02 1982- 1995 1.10 ± 0.29 

131) 1982-1995 0.58 ± 0.35 

La Jolla 33°N C02 1970- 1995 1.21±0. 17 

C0 2 1978-1995 1.16 ± 0.33 

131) 1978-1995 0.65 ± 0.42 

Mauna Loa 

(flasks) 20°N C02 1968-1995 0.82 ± 0.15 

C02 1980-1995 0.61±0.25 

131) 1980-1995 -0.16±0.37 

Mauna Loa 

(continuous) 20°N C02 1958- 1995 0.62 ± 0.04 

C02 1979-1995 0.34 ± 0. 12 

Kumukahi 20°N C02 1979-1995 -0.43 ± 0.23 

131) 1979-1995 0.11±0.41 

*With reference to January I, 1970, except for Alert referred to 

January 1, 1980. 

situated close to sea level, supplies principall y 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 138 

and C02 concentration at MLO may also be occurri ng at 

BRW and LJO as shown by lower gain factors for 138 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 13C/12C isotopic data have recently received 

final calibrations and have been analyzed to look for 

simil arities and signifi cant divergences in seasonal 

amplitude from the C02 concentration daia. At several 

northerly sites including BRW and LJO, isotopic changes 

in seasonal ampli tude appear to track the C02 amplitude 

changes quite well over periods of several years, 

suggesting that a dominant component in the seasonal 

signal of C02 is terrestrial plant activity. At other sites 

such as MLO in Hawaii, differences between trends in 138 

and C02 concentration suggest an oceanic component. At 

this time, when subtle changes are just becoming apparent 

in concurrent concentration and 13C/12C records of 

atmospheri c C02, 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 ampl itude first 

became apparent in our longest records. 

Ack11owledg111e11ts. This work was supported by Grant 

ATM91-21986 of the National Science Foundation, Grant 

DE-FG03-9SER62075 of the U.S. Department of Energy 

and Grant NAGW-2987 of the U.S. National Aeronautics 

and Space Administration. In additi on, through Contract 

SORANR 100090, NOAA provided for the cost of 

maintaining our primary standard reference gases used to 

maintain accuracy in our measurements of atmospheric 

C02. We are grateful to CMDL for providing assistance in 

our sampling program and for maintenance of our 

continuous recordi ng instrument at MLO. 

156 

REFERENCES 

Bacastow, R.B., Keeling, C.D., Whorf, T.P., Seasonal Amplitude 

Increase in Atmospheric C02 Concentration at Mauna Loa, 

Hawaii, 1959-1982, J. Geoplrys. Res. , 90, 10,529-10,540, 1985. 

Keeling, C.D., Bacastow, R.B., Carter, A.F., Piper. S.C., Whorf, 

T.P., Heimann, M. , Mook, W.G., and Roeloffzen, H. , A threedimensional model of atmospheric C02 transport based on 

observed winds: 1. Analysis of observational data, in Aspects of 

Cli111t11e Variability i11 rlre Pacific a11d the \Vestem Amerirns, 

edited by D. H. Peterson, Geophysical Monograph, American 

Geophysical Union, 55, 165-236, Washington, DC, 1989. 

Keeling, C.D., Wharf, T.P., Wahlen, M., van der Plicht, J., 

lnterannual extremes in the rate of rise of atmospheric carbon 

dioxide since 1980, Nmure, 375, 666-670, 1995. 

Keeling, C.D., Chin, J.F.S., Wharf, T.P., Increased activity of 

northern vegetation inferred from atmospheric C02 

measurements, Nature, 382, 146- 149, 1996. 

Reinsch, C. H., Smoothing by spline function s, N11111erisclre 

Mathematik, 10, 177 -183, 1967. 
7. Publications by CMDL Staff, 1994-1995 

Arends, B.G. , G.P.A. Kos, R. Maser, D. Sche ll, W. 

Wobrock, P. Winkler, J.A. Ogren, K.J. Noone, A. 

Hallberg, I.B. S venningsson , A. Wiedensoh ler, H.-C. 

Hansson, A. Berner, I. Solly, and C. Kruisz, 

Microphysics of c louds at Kleiner Fe ldberg, in The 

Kleiner Feldberg Clo ud Experiment 1990, S. Fuzzi 

(ed.), Kluwer Academic, Dordrecht, 59-85, 1994. 

Austin, J., D.J. Ho fmann , N. Butchart, and S.J. Oltmans, 

Midstratospheri c ozone minima in polar regions, 

Geophys. Res. Lett., 22(18), 2489-2492, 1995. 

Bakwin , P.S., P.P. T ans, and P. Novelli , Carbon monoxide 

budget in the Northern Hemisphe re, Geophys. Res. Leu., 

21(6), 433-436, 1994. 

Bakwin, P.S., P.P . Tans, W. Ussler, Ill, and E. Quesne ll, 

Measurements of carbon dioxide on a very tall tower, 

Tellus, 47B, 535-549, 1995. 

Bergin , M.H., C.I. Davidson, J.E. Dibb, J.L. Jaffrezo, H.D. 

Kuhns, and S.N. Pandis, A simple model to estimate 

atmospheric concentrations of aerosol chemical s pecies 

based on snow core chemistry at Summit , Greenl and, 

Geophy. Res. Lett., 22(24), 3517-3520, 1995. 

Bergin , M. H., J.-L. Jaffrezo, C.I. Davidson, J. E. Dibb, S.N 

Pandis, R. Hillamo, W. Maenhaut, H.D. Kuhns, and T. 

Makela, The contributi ons of snow, fog, and dry 

deposition to the summer flux of anions and cations at 

Summit, Greenland, J. Gcophys. Res., 100( D8), 16, 275-

16, 288, 1995. 

Bertman , S.B., J. M. Roberts, D.D. Parrish, M.P. Buhr, 

P.D. Goldan , W.C. Kuster, F.C. Fehsenfeld, S.A. 

Montzka, and H. Westberg, Evolution o f alkyl nitrates 

with air mass age, J. Geophys. Res., lOO(Dl 1 ), 22, 805-

22, 813, 1995. 

Bodhaine, B.A., Aerosol ab sorption measurements at 

Barrow , Mauna Loa, and the South Pole, J. Geophys. 

Res., 100(D5), 8967-8975, 1995. 

Bodhaine, B.A., and E.G. Dutton , Reply [Comment on "A 

long term decrease in arctic haze at Barrow, Alaska" by 

B.A. Bodhaine and E.G. Dutton). Geophys. Res. Leu., 

22(6), 741-742, 1995. 

Bridgman, H.A., and B.A. Bodhaine, On the frequ ency of 

long-range transport events a t Poi nt Barrow, Alaska, 

1983-1 992, Atmos. Environ., 28(21), 3537-3549 , 1994. 

Buhr, M., D. Parrish , J. Elliot, J. Holl oway, J. Carpenter, 

P. Goldan, W. Kuster, M. Trainer, S. Montzka, S. 

McKeen, and F. Fehsenfeld, Evaluation of ozone 

precursor source types usi ng principal component 

analysis of ambient air measurements in rural Alabama, 

J. Geophys. Res., lOO(Dll ), 22, 853 -22, 860, 1995 . 

Butler, J.H , The potential role of the ocean in regulating 

atmospheric C H3Br, Geophys. Res. Lei/., 21(3), 185-

188 , 1994. 

Butl er, J.H. , Methyl bromide under sc rutin y, Natu re, 376, 

469-470, 1995. 

Butler, J.H ., J.W. Elkins, B.D. Hall, S.A. Montzka, S.O. 

Cummings, P.J. Fraser, and L.W. Porter, Recent trends 

157 

in the global atmospheric mixing ratios of halon-1301 

and halon - 1211, in Baseline Atmospheric Program 

Australia 1991 , ed ited by A.L. Dick and J .L. Gras 

Department of the Environment, Sport, and Territories 

Bureau of Meteorology in · cooperation with CSIRO 

Di vision of Atmosphe ri c Research , Melbourne, 

Australia , 29-35, 1994. 

Cess, R.D., M. H. Zhang, P. Minnis, L. Corsetti, E.G. 

Dutton, B.W. Forgan, D.P. Garber, W.L. Gates, J.J. 

Hack, E.F. Harrison, X. Jing , J.T. Kiehl , C.N. Long, J.-

J. Morcrette, G.L. Potter, V. Ramanathan, B. Subasilar, 

C.H. Whitlock, D.F. Young, and Y. Zhou, Absorption of 

solar rad iation by clouds: Observations versus models, 

Science, 267, 496-499, 1995. 

Ciais, P., R.J. Francey, P.P. Tans, J.W.C. White, M. 

Trolier, An analyti cal error est imate for the ocean and 

land uptake of C02 using 1)13C observations in the 

atmosphe re, NOAA TM ERL CMDL-8, 13 pp., 1995. 

Ciais, P. , P.P. Tans, M. Troli er, J.W.C. White, and R.J. 

Francey, A large Northern Hemisphere terrestri al C02 

sink indicated by 13C/12C of atmospheri c C02, Science, 

269, 1098-1102, 1995. 

Ciais, P., P.P. Tans, J.W.C. White, M. Trolier, R.J. 

Francey , J.A. Berr y, D.R. Rand all, P.J. Sellers, J.G. 

Collatz, and D.S. Schimel, Partitioning of ocean and 

land uptake of C0 2 as in ferred by 1)1 3C measurements 

from the NOAA Cli mate Monitori ng and Diagnostics 

Laboratory Global Air Sampli ng Network, J. Geophys. 

Res., JOO(D3), 5051 -5070, 1995 . 

Clarke, A., and R.C. Schnell, Black carbon variabi li ty in 

the Pacific free troposphere and marine boundary layer, 

Abstracts, Proc., 5th Int. Conf on Carbonaceous 

Particles in the Atmosphere, DOE Lawrence Berkley 

Lab., Berkeley, CA, August 23-26 , 1994. 

Colvile, R.N., R. Sander, T.W. Chou larton, K.N. Bower, 

D.W.F. Inglis, W. Wobrock , D. Schell, I.B. 

Svenningsson, A. Wiedensohl er, H.-C. Hansson , A. 

Hallberg, J.A. Ogren, K.J. Noone, M.C. Facchin i, S. 

Fuzz i, G. Orsi, B.G. Arends, W. Winiwarter, T. 

Schne ider, and A. Berner, Computer modeling of c louds 

at Kleiner Feldberg, in Th e Kleiner Feldberg Cloud 

Experiment 1990, edit ed by S. Fuzzi, Klu wer Academic 

Publishe rs, Dordrecht, 189 -229, 1994. 

Conway, T.J. , P.P. Tans, L.W. Waterman, K.W. Thoning, 

D.R. Kitzis, K.A. Masarie, and N. Zhang, Evidence fo r 

interannual variabili ty of the carbon cycle from the 

National Oceanic and Atmosphe ric Administration/ 

Climate Monitoring and Diagnosti cs Laboratory Global 

Air Sampl ing Network, J. Geophys. Res., 99(Dl I), 22, 

83 1-22, 855, 1994. 

Cri ll , P.M., J.G. Butl er, D.J. Cooper, and P.C. Novel li, 

Standard ana lyti cal methods for measuring trace gases in 

the environment, in Biogenic Trace Gases: Measuring 

Emissions f rom Soil and Water, Methods in Ecology, 
edited by P.A. Matson and R.C. Harriss, University 

Press, Cambridge, U .K., 164-205, 1995. 

Dessler, A.E., E.M. Weinstock, E.J. Hintsa, J.G. Anderson, 

C.R. Webster, R.D. May, J.W. Elkins, and G.S. Dutton , 

An examination of the total hydrogen budget of the 

lower stratosphere, Geophys. Res. Lett., 21(23), 2563-

2566, 1994. 

Dlugokencky, E.J., K.A. Masarie, P.M. Lang, P.P. Tans, 

L.P. Steele, and E.G. Nisbet, A dramatic decrease in the 

growth rate of atmospheric methane in the northern 

hemisphere during 1992, Geophys. Res. Lett., 2 1 ( 1), 45-

48, 1994. 

Dlugokencky , E.J., K.A. Masarie, P.M. Lang, P.P. Tans, 

L.P. Steele, and E.G. Nisbet, Reply to "Comments on 'A 

dramatic decrease in the growth rate of atmospheric 

methane in the northern hemisphe re during 1992'," 

Geophys. Res. Lett., 21(22), 2447-2448, 1994. 

Dlugokencky, E.J., L.P. Steele, P.M. Lang, and K.A. 

Masarie, Atmospheric methane at Mauna Loa and 

Barrow observatories: Presentation and analysis of in 

situ measurements, J. Geophys. Res., 100( D 11 ), 23, l 03-

23, l l 3, 1995. 

Dutton, E.G, Comparison of the solar radiative effects of 

El Chi chon and Mt. Pinatubo long-lived aerosols, 

Preprints, Eighth Confere nce on Atmospheri c Radiation , 

Nashville, TN, J anuary 23-28, 1994, American 

Meteorological Society, Boston, 426-428, 1994. 

Dutton , E.G., and S.K. Cox, Tropospheric radiative forcing 

from El Chichon and Mt. Pinatubo: Theory and 

observatio ns, Culorado State University Atmospheric 

Science Pape r No. 586, Fort Co ll ins, CO, 2 17 pp., 1995. 

Dutton, E.G., P. Reddy , S. Ryan, and J.J. DeLuisi, 

Features and effects of aerosol optical depth observed at 

Mauna Loa, Hawaii , 1982-1992, J. Geophys. Res., 

99(34), 8295-8306, 1994. 

Endres, D., OPS-derived time baffles NOAA researcher, 

Ocean Navigator, 66, 22-24, 1995. 

Fan, E.-M., M.L. Goulden , J.W. Munger, B.C. Daube, P.S. 

Bakwin , S.C. Wofsy, J.S. Amthor, D.R. Fitzj arra ld, K.E. 

Moore, and T.R. Moore, Environmental controls on the 

photosynthesis and respiration of a boreal lichen 

woodland: A growing season of whole-ecosystem 

exchange measurements by eddy correlation, Oecologia, 

102, 443-452, 1995. 

Ferrare, R.A., T.J. McGee, D. W hiteman, J. Burris, M. 

Owens, J. Butler, R.A. Barnes, F. Schmidlin, W. 

Komhyr, P.H. Wang, M.P. McCormick, and A.J. Miller, 

Lidar measurements of stratospheric temperature during 

STOIC, J. Geophys. Res., 100(D5}, 9303-9312, 1995. 

Goldan , P.D., W.C. Kuster, F.C. Fehsenfeld, S.A. 

Montzka, Hydrocarbon measurements in the 

southeastern United States: The Rural Oxidants in the 

Southern Environment (ROSE) Program 1990, J. 

Geophys. Res., 100(Dl 2), 25 , 945-25, 963, 1995. 

Hallberg, A., K.J. Noone, J.A. Ogren, l.B . Svenningsson, 

A. Flossmann , A. Wiedensohler, H.-C. Hansson, J. 

Heintzenberg, T.L. Anderson, B.G. Arends, and R. 

Maser, Phase partitioning of aerosol particles in clouds 

at Kl einer Feldberg, in The Kleiner Feldberg Cloud 

Experiment 1990, S. Fuzzi (ed.}, Kluwer Academic 

Publishers, Dordrecht, 107-127, 1994. 

Hallberg, A., J.A. Ogren , K.J. Noone, K. Okada, J. 

Heintzenberg, and J.B. Svenningsson, The influence of 

aerosol particle composition on cloud droplet formation, 

in The Kleiner Feldberg Cloud Experiment 1990, S. 

Fuzzi (ed.}, Kluwer Academic Publishers, Dordrecht, 

153-171, 1994. 

Harris, J.M., and J .D. W. Kahl , Analysis of 10-day 

isentropic flow patterns for Barrow, Alaska: 1985-1992, 

J. Geophys. Res., 99(012):25, 845-25, 855, 1994. 

Helas, G., J. Lobert, D. Scharffe, L. Schafer, J. 

Goldammer, J. Baudet, B. Ahoua, A.-L. Ajavon, J.-P. 

Lacaux , R. Delmas, and M.O. Andreae, Ozone 

production due to emissions from vegetation burning, J. 

Atmos. Chem., 22, 163- 174, 1995. 

Hofmann, D.J., S.J. Oltmans, J.A. Lathrop, J.M. Harris, 

and H. Ybmel, Record low ozone at the South Pole in 

the spring of 1993, Geophys. Res. Lett., 21(6), 421-424, 

1994. 

Hofmann, D.J., S.J. Oltmans, J.M. Harris, J.A. Lathrop , 

G.L. Koenig, W.D. Komhyr, R.D. Evans, D.M. Quincy, 

T. Deshler, and B.J. Johnson, Recovery of stratospheric 

ozone over the United States in the winter of 1993-1994, 

Geophys. Res. Lett., 21(17), 1779-1782, 1994. 

Hofmann , D.J., S.J. Oltmans, W.D. Komhyr, J.M. Harris, 

J.A. Lathrop, A.O. Langford, T. Deshler, B.J. Johnson, 

A. Torres, and W.A Matthews, Ozone loss in the lower 

stratosphere over the United States in 1992-1993: 

158 

Evidence for het erogeneous chemistry on the Pinatubo 

aerosol, Geophys. Res. Lett., 21 ( 1), 65-68 , 1994. 

Hofmann , D.J., S.J. Oltmans, B.J. Johnson , J.A. Lathrop, 

J.M. Harris, and H. Ybmel, Recovery of ozone in the 

lower stratosphere at the South Pole during the spring of 

1994, Geophys. Res. Lett., 22(18), 2493-2496, 1995. 

Hofmann , D., P. Bonasoni, M. DeMaziere, F. Evangelisti, 

G. Giovanelli, A. Goldman, F. Goutail, J. Harder, R. 

Jakoubek, P. Johnston , J. Kerr, W. A. Matthews, T. 

McElroy, R. McKenzie, G. Mount, U. Platt, J.-P. 

Pommereau, A. Sarkissian, P. Simon, S. Solomon, J. 

Stut z, A. Thomas, M. YanRoozendael, and E. Wu, 

Intercomparison of UV/visible spectrometers for 

measurements of stratospheric N02 for the Network for 

the Detection of Stratospheric Change, J. Geophys. Res., 

100(08), 16, 765-16, 79 1, 1995 . 

Hurst, D.F., D.W.T. Griffith, and G.D.Cook, Trace gas 

emissions from biomass burning in tropi cal Australi an 

savannas, J. Geophys. Res., 99( DB), 16, 441-16, 456, 

1994. 

Jaffe, D.A., R.E. Hanrath , D. Furness, T.J. Conway, E. 

Dlugokencky, and L.P. Steele, A determination of the 

CH4, NO,, and C02 emissions from the Prudoe Bay, 

Alaska oil development , J. Atmos. Chem., 20, 2 13-227, 

1995. 

Kerr, J.B., H. Fast, C.T. McElroy, S.J. Oltmans, J.A. 

Lathrop, E. Kyro, A. Paukkunen, H. Claude, U. Kohler, 

C.R. Sreedharan , T. Takao, and Y. Tsukagoshi, The 
1991 WMO international ozonesonde inte rcompariso n at 

Vanscoy, Canada, Atmos. Ocean, 32(4), 685-716, 1994. 

Komhyr, W.D. , R.D. Grass, R.D. E vans, R.K. Leonard, 

D.M. Quincy, D.J. Hofmann , and G.L. Koenig, 

Unprecedented 1993 ozone decrease over the United 

States from Dobson spectrophotometer observations, 

Geophys. Res. Lei/., 21 ( 3 ). 201-204, 1994. 

Komhyr, W.D., R.A. Barnes, G.B. Brothers, J.A. Lathrop, 

and D.P. Opperman, Electrochemi cal concentration cell 

ozoneso nde performance evaluati on during STOIC 1989, 

J. Geophys. Res., /OO(D5), 9273-9282, 1995. 

Komhyr, W.D. , B.J. Connor, I.S . McDermid, T.J. McGee, 

A. O. Parrish, and J.J. Margitan , Comparison of STOIC 

1989 ground-based lidar, mi crowave s pectrometer, and 

Dobson spectrophotometer Umkehr ozone profiles with 

ozone profiles from balloon-borne e lectrochemical 

concentration cell ozonesondes, J. Geophys. Res., 

100( D5 ), 9273-9282 , 1995. 

Lang, P.M., E.J. Dlugokencky, K.A. Masarie, and L.P. 

Steele, Atmos pheric methane data for 1989- 1992 from 

the NOAA/CMDL global cooperati ve air sampling 

network, NOAA TM ERL CMDL- 7, 49 pp, 1994. 

Lobert, J.M., J.H. Butler, T.J. Baring, S.M. Montzka, R.C. 

Mye rs, and J.W. Elkins, OAXTC 92 Ocean/Atmosphere 

Exchange of Trace Compounds 1992: Oceani c 

measurements of HCFC-22, CFC-I I, CFC- 12, CFC-1 13, 

CH3CC13, CC14 , and N20 in the marine air and s urface 

wa ters o f the west Pacific Ocean (August 3-0ctober 2 1, 

1992), NOAA TM ERL CMDL-9, 4 3 pp., NOAA 

E11 vi1 0111nt:ntal Rt:M::an.:h Laburalurit:s, Buuh.Je r, CO 

1995. 

Lobert, J.M., J.H. Butler, S.A. Montzka, L.S. Geller, R.C. 

Myers, and J.W. Elkins, A net sink for atmospheri c 

C H3Br in the East Pacifi c Ocean, Science, 267, 1002-

1005, 1995. 

Margitan, J.J., R.A. Barnes, G.B. Brothe rs, J. Butler, J. 

Burris, B.J. Connor, R.A. Ferrare, J.B. Kerr, W.D. 

Komhyr, M.P. McCormick, I.S. McDe rmid, C.T. 

McElroy, T.J. McGee, A.J. Miller, M. Owens, A.O. 

Parrish, C.L. Parsons, A.L. Torres, J.J. T sou, T.D. 

Walsh, and D. Whiteman , Stratosphe ric ozone 

intercomparison campaign (STOIC) 1989: Overview, J. 

Geophys. Res., 100(D5), 919 3-9207 , 1995. 

Masarie, K.A., and P.P. Tans, Exten sion and integration of 

atmospheric carbon dioxide data into a globally 

consistent measurement record, J. Geophys. Res., 

100(D6), 11 , 593- 11 , 610, 1995. 

Montzka, S.A., R.C. Myers, J.H. Butler, and J.W. Elkins, 

Early trends in the global tropospheric abu ndance of 

hydrochlorofl uorocarbon-1 4 1 b and l 42b, Geophys. Res. 

Lett., 21(23), 2483-2486, 1994. 

Montzka, S.A., R.C. Myers, J.H. Butle r, J.W. Elkins, and 

S.O. Cummings, Atmospheric measurements of HCFC22 at the South Pole, Ant. J .• 28(5), 267-269, 1994. 

Montzka, S.A., M.R. Nowick, R.C. Myers, J.W. Elkins, 

J.H. Butle r, S.O. Cummings, P.J. Fraser, and L.W. 

Porter, NOAA-CMDL chlorodifluorome thane (HCFC22) observations at Cape Grim, in Baseline Atmospheric 

Program Australia 1991, edited by A.L. Dick and J.L. 

Gras, Department of the Environment, Sport, and 

Te rritories Bureau of Me teo rology in cooperation with 

CS IRO Division of Atmosphe ri c Reseach, Melbourne, 

Australia, 25-28, 1994. 

Mont zka, S.A., M. Trainer, W.M. Angevine, and F.C. 

Fehsenfeld, Measurements of 3-methyl furan , methyl 

vinyl ke tone, and methacrolein at a rural forested site in 

the southeastern United States, J. Geophys. Res., 

/00(D6), 11 , 393-1 1, 40 1, 1995 . 

Moody, J.L., S.J. Oltmans, H. Levy 11 , and J.T. Merrill , 

Tran sport climatology of tropospheric ozone: Bermuda, 

1988-1991, J. Geophys. Res., 100(D4), 7 179-7 194, 

1995. 

Nemesure, S., R.D. Cess, E.G. Dutton, J.J. DeLuisi, Z. Li , 

and H.G. Leighton, Impac t of clouds on the shortwave 

radiation budget of the surface-atmosphere system for 

snow-covered surfaces, J. Climate, 7( 4). 579-585, 1994. 

Novelli , P.C., and R.M. Rosso n (eds.), Report of the WMO 

meeting of experts o n global carbon monoxide 

measurements, World Meteorological Organization , 

Global Atmos. \Vatch No. 98, WMO/TD-NO. 645, 

Geneva, Swit zerland, 82 pp, 1994. 

Novelli, P.C., K.A. Masarie, P.P. Tans, and P.M. Lang, 

Recent changes in atmosphe ri c carbon monoxide, 

Science, 263, 1587- 1590, 1994. 

Novelli , P.C., J.E. Collins, Jr., R.C. Myers, G.W. Sachse, 

and H.E. Scheel, Reevaluation of the NOAA/CMDL 

carbon monoxide reference scale and comparisons with 

CO reference gases at NASA-Lang ley anti tht: 

Fraunhofer In stitute, J. Geophys. Res .. 99( D6), 12, 833-

12, 839, 1994. 

159 

Novelli, P.C., and R.M. Rosson (eds.), Report o f the 

meeting of experts o n carbon monox ide, Boulder, 

Colorado, February 1994. WMO Repo rt 98, Geneva, 

Switzerl and, 78 pp., 1995. 

Novelli , P.C., T.C. Conway, E.J. Dlugokencky, and P.P. 

Tans, Recent changes in atmospheri c carbon diox ide, 

methane and carbon mo noxide, and the implications of 

these changes on global climate processes, World 

Meteorol. 8111/., 44, 32-37, 1995. 

Ogren, J.A., A systematic approach to in situ observations 

of aerosol prope rti es, In Aerosol Forcin g of Climate, 

R.J. Charlson and J. He intzenberg (eds.), Wiley & Sons, 

New York, 2 15-226, 1995. 

Oltmans, S.J., and H. Levy, II, Surface ozone 

measurements from a g lobal network, Atmos. Environ., 

28( 1 ), 9-24, 1994. 

Oltmans, S.J., and D.J. Hofmann, Increase in lowerstratospheri c water vapor at a mid-latitude Northern 

Hemisphere site from 1981 to 1994, Na/lire, 374, 146-

149, 1995. 

Parungo, F., Z. Li, X. Li, D. Yang, and J. Harris, Gobi dust 

storms and The Great Green Wall, Geophys. Res. Lei/., 

21( 11 ). 999-1002, 1994. 

Parungo, F., Y., Kim , C.-J. Z hu , J. Ha rris, R. Schnell, X.-

S. Li , D.-Z. Yang, X.-M. Fang, P. Yan, X. Yu, M.-Y. 

Zhou, Z. Chen, F.-L. Qi an, and K. Park, Asian dust 
storms and their effects on radiation and climate, Part I, 

Science and Technology Corporation Technical Report 

2906, Boulder, CO, 56 pp., 1995. 

Penner, J.E., R.J. Charlson, J.M. Hales, N.S. Lau lainen, R. 

Leifer, T. Novakov, J. Ogren, L.F. Radke, S.E. 

Schwartz, and L. Travis, Quantifying and minimizing 

uncertainly of climate forcing by anthropogenic 

aerosols, Bull. Am. Meteorol. Soc., 75(3), 375-400, 

1994. 

Pe terson, J.T., and R.M . Rosson (eds.), Climate 

Monitoring a11d Diagnostics Laboratory No. 22: 

Summary Report 1993, NOAA Environment al Research 

Laboratories, Boulder, CO, 152 pp , 1994. 

Prospero, J.M., R. Schmitt, E. Cuevas, D.L. Savoie, W.C. 

Graustein , K.K. Turekian, A. Volz-Thomas, A. Diaz, 

S.1 . Oltmans, H. Levy II, Temporal variability of 

summer-time ozone and aerosols in the free troposphere 

over the eastern North Atlantic, Geoplrys. Res. Lett., 

22(21), 2925-2928, 1995. 

Reagan, J., K. Thome, B. Herman, R. Stone, J. DeLuisi, 

and J. Snider, A comparison of columnar water vapor 

retrievals obtained with near-IR solar radiometer and 

microwave radiometer measurements, J. Appl. 

Meteorol., 34, 1384- 139 1, 1995. 

Ryan, S.C., Quiescent outgassing of Mauna Loa Volcano 

1958-1994, in Mauna Loa Revealed: Structure, 

Composition, History, and Ha zards, Geophysical 

Monograph 92, edited by J.M. Rhodes and J.P. 

Lockwood , American Geophysical Union, Washington, 

D.C., 95-1 15, 1995. 

Salawitch, R.J., S.C. Wofsy, P.O. We nnberg, R.C. Cohen, 

J.G. Anderson, D.W . Fahey, R.S . Gao, E.R. Keim, E.L. 

Woodbridge, R.M . Stimpfle, J.P. Koplow, D.W. Kohn , 

C.R. Webster, R.D. May, L. Pfiste r, E.W. Golllieb, H.A. 

Michelsen, G.K. Yue, J.C. Wilson, C.A. Brock, H.H. 

Jonsson, J.E. Dye, D. Baumgardner, M.H Proffill, M. 

Loewenstein, J.R. Pooolske, J.W. Elkins, G.S . Dutton, 

E.J. Hinlsa, A.E. Dessler, E.M. Weinstock, K.K. Kelly, 

K.A. Boe ring, B.C. Daube, K.R. Chan, and S.W. Bowen, 

The distribution of hydrogen, nitrogen, and chlorine 

radicals in the lower stratos phere: Implications for 

changes in 03 due to emission o f NOy from supersoni c 

aircraft, Geophys. Res. Leu., 21(23), 2547-2550, 1994. 

Schmidt , E.O., R.F. Arduini, B.A. Wielicki, R.S. Stone, 

and S.-C. Tsay, Considerations for modeling thin cirrus 

effects via brightness temperature d ifferences, J. Appl. 

Meteorol., 34(2), 447-459, 1995. 

Schnell, R.C., Are biological ice nucl ei impo rtant in 

drought processes: Past thoughts, present perspectives, 

Pro., Biological Ice N11cleation, Laramie, Wyoming, 

August 4-6, 1993 , Un iversity of Wyoming, Laramie, 30 

pp., 1994. 

Schnell, R.C., Carbon cycle species and Asian du st al 

Mauna Loa Observatory in relation to air mass origins, 

Proc., Tsukuba Global Carbon Cycle Workshop, Tsuka, 

J apan, 54-61, February 1-3, 1995. 

Schnell , R.C., Recent Chinese dust storms observed at 

Mauna Loa Observatory, Hawaii , Proc., WMO-IGAC 

Conf on tire Measurement and Assessment of 

Atmospheric Composition Change, Beijing, China, 218-

220, October 9-24, 1995. 

Schnell , R.C., D.T. Kuniyuki, B.A. Bodhaine, and A.D.A. 

Hansen, The dust component of aerosol light absorption 

measured al Maun a Loa Observatory, Abstracts, Proc., 

5th lnt. Conf 011 Carbonaceous Particles in the 

Atmosphere, DOE Lawrence Berkley Lab., Berkeley, 

CA, August 23-26, 1994. 

Stone, R.S., E.G. Dullon, and J.R. Key, Properties and 

decay of Pinatubo aerosols in polar regions compared 

with tropical observations, Preprints, Eighth Conference 

on Atmospheric Radi ation, Nashville, TN, January 23-

28, 1994, American Meteorological Society, Boston, 

432-434, 1994. 

Svenningsson, B., H.-C. Hansson, A. Wiedensohler, K. 

Noone, J. Ogren, A. Hallberg, and R. Colville, 

Hygroscopic growth of aerosol particles and its 

influence on nucleation scavenging in cloud: 

Experimental results from Kleiner Feldberg, in The 

Kleiner Feldberg Cloud Experiment 1990, edited by S. 

Fuzzi, Klu wer Academic Publishers, Dordrecht, 129-

152, 1994. 

Tans, P.P., and P.S. Bakwin, Climate change and carbon 

dioxide forever, Ambio, 24, 376-378, 1995. 

Thoning, K.W., T.J. Conway, N. Zhang, D. Kitzis, 

Analysis system for measurement o f C02 mix ing ratios 

in fl ask air samples, J. Atmos. Ocean. Tech., 12(6), 

1349-1356, 1995. 

TU1.:k, A.F., D.W. Fahey, M. Lowenstein, J.R. Podolske, 

K.K. Kelly, S.J. Hovde, D.M. Murphy, and J.W. Elkins, 

Spread of denitrifi cation from 1987 Antarctic and 1988-

1989 Arctic stratospheric vorti ces, J. Geophys. Res .. 

99(DIO), 20, 573-20, 583, 1994. 

160 

Vomel, H., D.J. Hofmann, S.J. Oltmans, and J.M. Harris, 

Evidence for midwinter chemical ozone destructi on over 

Antarctica, Geophys. Res. Leu., 22( 17), 2381-2384, 

1995. 

Vomel, H., S.J. Oltmans, D. Kley, and P.J. Crutzen, New 

evidence for the stratospheric dehydration mec hanism in 

the equatorial Pacific, Geophys. Res. Lett., 22(21), 

3235-3238, 1995. 

Vomel, H., S.J. Oltmans, D.J. Ho fmann, T. Deshler, and 

J.M. Rosen, The evo lution of the dehydration in the 

Antarctic stratospheri c vortex. J. Geophys. Res., 

100(D7), 13, 9 19-13, 926, 1995. 

Vomel, H., S.J. Oltmans, D. Kley, and P.J. Crutzen. New 

evidence for the stratospheric dehydration mechanism in 

the equato ri al Pacific. Geophys. Res. Lett. 22(21 ):3235-

3238 ( 1995). 

Waugh, D.W., R.A. Plumb, P.A. Newman, M.R. 

Schoeberl, L.R. Lait , M. Loewenstein, J.R. Podolske, 

J.W. Elkins, and K.R. Chan, Fine-scale, poleward 

transport of tropical air during AASE 2, Geophys. Res. 

Lett., 21 (23 ), 2603-2606, 1994. 

Wobrock, W., D. Schell, R. Maser, W. Jaeschke, H.-W. 

Georgii, W. Wieprechl, B.G. Arends, 1.1 . Mols, G.P.A. 

Kos, S. Fuzzi, M.C. Facchini, G. Orsi, A. Berner, I. 
Solly, C. Kruisz, l.B. Svenningsson, A. Wiedensohler, 

H.-C. Hansson, J.A. Ogren, K.J. Noone, A. Hall berg, S. 

Pahl, T. Schneider, P. Winkler, W. Winiwarter, R.N. 

Colvile, T.W. Chourl arton, A.I. Flossman, and S. 

Borrman n, The Kle iner Feldberg c loud experiment 1990 , 

An Overview, in Th e Kleiner Feldberg Cloud 

Experiment 1990, edited by S. Fuzzi, Kluwer Academic, 

Dordrccht, 3-35, 1994. 

Wofsy, S.C., K.A. Boering, B.C. Daube, Jr., M.B. 

McElroy, M. Loewenstein, J.R. Podolske, J.W. Elkins, 

G.S. Dutton, and D.W . Fahey, Vertical transport rates in 

the stratosphere in 1993 from observations of C02, 

N20, and CH4, Geophys. Res. Le11., 21 (23 ). 2571-

2574, 1994. 

Woodbridge, E.L., J.W. Elkins, D.W. Fahey, L.E. Heidt, S. 

161 

Solomon, T.J. Baring, T.M. Gi lpin , W.H. Pollock, S.M. 

Schaumer, E.L. Atlas, M. Lowenstein, J.R. Podolske, 

C.R. Webster, R.D. May, J.M. Gilligan, S.A. Montzka, 

K.A. Boering, and R.J. Salawitch, Estimates of total 

organic and inorganic chlorine in the lower stratosphere 

from in situ and flask measure me nts dur)ng AASE II, J. 

Geophys. Res., 100( D2), 3057-3064, 1995.