1900 

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Climate Monitoring and 

Diagnostics Laboratory 

Summary Report No. 25 

1998-1999 

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U.S. Department of Commerce 

National Oceanic and Atmospheric Administration 

Oceanic and Atmospheric Research 
Climate Monitoring 

and Diag_nostics Laboratory 

Summary Report No. 25 

1998-1999 

Russell C. Schnell, Editor 

Daniel 8. King, Editor 

Rita M. Rosson, Assistant Editor 

Boulder, Colorado 

January 2001 

U.S. DEPARTMENT OF COMMERCE 

Donald L. Evans, Secretary 

National Oceanic and Atmospheric Administration 

Scott B. Gudes, Acting Administrator 
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 within the Office of Oceanic 

and Atmospheric Research (OAR) of the National 'o ceanic 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 such as fluorocarbons that may cause 

depletion of the global ozone layer. 

This report is a summary of activities of CMDL for calendar years 1998 and 1999. It is 

the 25th 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 I through 22), reports were issued annually. For 1994-1995 we 

began 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 several 

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 OAR: 

http://www.oar.noaa.gov; NOAA: http://www.noaa.gov. 

This report is organized into the following major sections: 

I. Ob~t:r va y, Meteorology, and Data Management Operations 

2. Carbon Cycle 

3. Aerosols and Radiation 

4. Ozone and Water Vapor 

5. Halocarbons and Other Atmospheric Traces Species 

6. Cooperative Programs 

These are foll owed by a list of CMDL staff publications for 1998- 1999. 

Inquiries and/or comments are welcomed and should be addressed to: 

Director, R/CMDL 

NOAA/Climate Monitoring and Diagnostics Laboratory 

325 Broadway 

Boulder, CO 80305-3328 

(303) 497-6074 

e-mail : dhofmann@cmdl.noaa.gov 

Ill 
Jim Peterson joined the Geophysical Monitoring for Climatic Change (GMCC) Di vision 

of the NOAA Air Resources Laboratory in 1977. He became Director of GMCC in 198 1 and 

served in that position until the Di vision was re-organized into CMDL in 1990. He was the Deputy 

Director of CMDL until he retired from federal service in January 1999. For the following 2 years 

he had a Research Scientist Emeritus position with the Cooperative Institute for Research in 

Environmental Sciences (CIRES). 

iv 
Contents 

Preface . .. .... .... .. ... . . . . .. . . . . . . ... ..... .... ... .. . . . .. .. . .. .. .. .. . . . .. ... .... . .... .. .. .... .... .... .. .. ... .. . . . . . . .... ..... . .. ..... .. ... . .... ............ ...... .. ........ u1 

CMDL Organization, 1999 .................. .. .. .. ........ ........ ............................................... .. ... ......................................... v1u 

CMDL Staff, 1999 .. . .. ... .. . . . . . . .. ... .. . . . . .. . ... . . . .. . .. . ...... . .. .. . . . . ... . . .. ...... ... ............ ... .. . .. . . . .. ... ... .. .. . . . .. . .. .. .. . .. ........ ... .. ... . .. . . .. ix 

CMDL Station Information .. ... . .. ........................ ...... .. ... .... . .. . ... . .. . . .. . . .. .. .. . .. . .. .. ... .. .. . ..... .. . . . .. .. . . . . .. . .. .. ... .. ..... ... .. . . .. .. .. x 

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

I. I. Maun a Loa Observatory .. . .. . . .. . .. .. . . .. .. .. .. .. . .. . .. ... .. .. . .. .. . .. . . . .. .. .. .. .. .. .. .. . .. . . .. .. .. .. .. .. .. .. .. .. .. . . . . . .. .. .. .. .. . .. . .. . .. .. .. . I 

1. 1. 1. Operations .. ...... .. .. .. .. .. ....... .......... ...... .......... .... ......... .... ........... ............... ... .... ............................. I 

I. 1.2. Programs .. .. ... .. . . . . .. .. ... .. .. .................. .......... ...... .... .. .. ... . .. .. . .. ...... ... ... ... ....... ..... . .. . .. .. .. .. . ........ ....... 2 

1.2. Barrow Observatory .............................................. ............................................... ................................... 6 

1.2. 1. Operations .. .................... ................. ....................... ......................... .......... ................................. 6 

l.2.2. Programs ....................................... ....................... ........................................... .. ......................... 7 

1.3. Samoa Observatory................................................................................................................................. 9 

1.3. l. Operations ...................... ......................................................................... ............... .................... 9 

1.3.2. Programs ...... ......................................... ........ .................................................. ........................... 9 

1.4. South Pole Observatory ............................. .............................................................................................. 11 

1.4.1. Operations ................. ................................................................................................................. 11 

1.4.2. Programs ................................................................................ .................................................... 11 

1.5. Meteorological Measurements ................................................................................................................ 13 

1.5. 1. Meteorology Operations.............................................................................................................. 13 

1.5.2. Station Climatologies.................................................................................................................. 14 

1.6. References................................................................................................................... ............................ 23 

2. Carbon Cycle . . . .. .. . .. ... .. ... . . .. .. . . . . . . . . . .. .. . ... . . .. . ......... ..... .. .. . .. . .. . . . .. ..... .................. ...... . . . . .. .. . . . ... .. ... .. ........ ... . . . . .. .. ... 24 

2. 1. Overview.......................................................................................................................................... ...... . 24 

2.2. Carbon Dioxide ....................................................................................................................................... 25 

2.2. 1. In Situ Carbon Dioxide Measurements ....................................................................................... 25 

2.2.2. Flask Sample Carbon Dioxide Measurements ............................................................................ 26 

2.2.3. Carbon Dioxide Standards and Reference Gas Calibrations........................................................ 29 

2.2.4. Measurements of Stable Isotopes of Atmospheric C02...................................... .... .................. ... 30 

2.3. Methane................................... ................................................................................................................ 32 

2.3.1 . In Situ Methane Measurements................................................................................................... 32 

2.3.2. Measurements of Methane in Discrete Samples ......................................................................... 33 

2.3.3. Measurement of "c/2

C of Methane by Mass Spectrometry........................................................ 34 

2.3.4. •Jc/2

C and D/H Isotopic Ratio Analysis of Methane by Infrared Spectroscopy ......................... 35 

2.4. Carbon Monoxide........................................................ ................................................ ........................ ... . 35 

2.4. l. Measurements of Carbon Monoxide............................................................................................ 35 

2.4.2. CO Reference Gases.................................................. .. ................................................................ 37 

2.5. Nitrous Oxide and Sulfur Hexafluoride................................................................................................... 38 

2.6. Measurements on Tall Towers ............................................................................................................... . 39 

2.7. Aircraft Program .... ....................... ...................................................................... .............................. ...... 4 1 

2.8. Air-Sea Gas Exchange............................................... ............................................ ........... ..... .. ................ 4 1 

2.9. Data Integration (Globalview).............................................................. .. ................................................. 43 

2.1 0. Inverse Modeling....... .............................................................................................................................. 45 

2. 11. References . ............ ... ... .. .......... ..... ... .. . . . . . .. . . . ...... ............. .... .... ..... ... .. .......... .................. ... .. ..... ...... .. .. .. .... 45 

v 
3. Aerosols and Radiation ............... .................... ............................................. .. ... .......................... ........... .... ....... 47 

3. 1. Aerosol Monitoring .................... .... ... ............. .. ..... ........ ..... .................... ........ ........................... .............. 47 

3. 1.1. Scientific Background.. ....... .................................................................. ........ .. ..... .................... .. . 47 

3. 1.2. Experimental Methods................................. ........................................... ........ ............................. 48 

3. 1.3. Annual Cycles....... ............................. ... ........... ............................. ............................ .... .............. 48 

3. 1.4. Long-Term Trends .. .. .............................. ...... .................................... ........... ............... .. .............. 52 

3. 1.5. Spec ial Studies...... ......................................................... ......................... .................................... 52 

3.2. Solar and Thermal Atmospheric Radiation........................... ..................... .......... .. ........................ .......... 58 

3.2. 1. Radiation Measurements............................................. ...................................................... .......... 58 

3.2.2. Solar Radiation Calibration Facility.. ................. ... ................................................................... ... 61 

3.2.3. Aerosol Optical Depth Remote Sensing..................................................................................... . 62 

3.2.4. MLO and Boulder UV Spectroradiometers ......... ............................................................. ........... 63 

3.2.5. Broadband UV................................................................. .. .. ....................... .......... .. .. ................... 64 

3.2.6. Baseline Surface Radiation Network.... ......................... .. ........... ................................................. 64 

3.2.7. Barrow Snow Melt Date...... ............. ...... .... ..................... ................................... ............. .. .. ...... .. 65 

3.2.8. Arctic UV Monitoring........... ... .. .................... ................. .. .... ... .. ......................................... ........ 67 

3.2.9. Pyrgeometer Comparison .............. .. .. .................................................... ... ................................... 69 

3.2.10 Rayleigh Optical Depth Calculations............................................................................ ..... .......... 70 

3.2. 11 Data Processing................................................... ........................................................................ 72 

3.3. References......................................... ................. ...................................................... ............................... 73 

4. Ozone and Water Vapor ..................................................................................................... .................. ..... ....... 75 

4. 1. Continuing Programs ........ ........... ..................... ..................................... .............. ................................... 75 

4. 1.1. Total Ozone Observations .................................................... ...................................................... 75 

4. 1.2. UmkehrObservations............................................. .. .................................. ................................. 75 

4.1.3. Calibration of Dobson Spectrophotometers...... ........................................................................... 75 

4.1.4. Surface Ozone................................................................ .................................................. ... ........ 76 

4.1.5. Ozonesondes........................................................... ........ .. .. .. .................. ..................................... 78 

4. 1.6. Atmospheric Water Vapor............................................................. ................. ........................ ..... 79 

4. 1.7. Atmospheric Transport ....................................................... .......... ............... .......... ...................... 80 

4.1.8. StratosphericAerosols...................................................................................................... ........... 81 

4.2. Special Projects.............. ....... ............................................................................................... ........ ... .. ...... 82 

4.2. 1. Evidence for the Infl uence of Biomass Burning on Tropospheric Ozone in 

Both the Eastern and Western Tropical Pacific....................................................................... 82 

4.2.2. Water Vapor and Ozone Observations at San Cristobal, Galapagos.. ........ .......... .................. ...... 83 

4.2.3. Evidence of 0 1 Titration During BRW Winter Dark Periods...................................................... 86 

4.2.4. Analysis of CO and 0 , Data from Cape Point Observatory (1994- 1998) ...... .............................. 87 

4.2.5. Laboratory Testing of ECC Ozonesondes .. ....... ................................................ ..... ..................... 88 

4.2.6. South Pole: Triple Ozonesonde Flights ................ ....................................................................... 89 

4.3. References.............................. .... ................................................ ......... ...... ........................... ................... 90 

5. Halocarbons and other Atmospheric Trace Species.............................................. .................... .. .. .................... 91 

5.1. Continuing Programs ................................................... ........................................................................... 91 

5.1.1. Introduction.......................... ............ .................................................. ......................................... 9 1 

5.1.2. Flask Samples............................................................................................... ... ... .. ....................... 92 

5. 1.3. In Situ Gas Chromatograph Measurements....................... .................................... .. .................... I 00 

5. 1.4. Gravimetric Standards. ........................ .. ........................... .. .. .................................................. .. ... 102 

5.2. Airborne Projects............................................ ..................................... .................................................... 103 

5.2. l. Airborne Chromatograph for Atmospheric Trace Species (ACATS-IV) .................................... I 03 

5.2.2. Lightweight Airborne Chromatograph Experiment (LACE) ........... .. .. .. ...................................... 107 

5.2.3. PAN and other Trace Hyrohalocompounds Experiment (PANTHER).................... ....... ... .......... 108 

5.3. Ocean Projects.............. .................. .. ...................... ...... ..... ................................................ ...................... 108 

5.4. References. .. ............................................... ..................... ........................... ................ ............................. 111 

vi 
6. Cooperative Programs............................ ........................................................................ .. ................................ 113 

UV Spectrorad iometer Monitoring Program: Influence of Total Ozone, Cloud Cover and Surface 

Albedo on UV Doses in Barrow, Alaska 

G. Bernhard, C. R. Booth, J.C. Ehramjian, S.A. Lynch, and V. V. Quang.................................... 113 

W hole Air Sampling at Barrow, Alaska 

D.R. Blake and F.S. Rowland. ..................................................................................................... 116 

Corre lation Between Anthropogenic Aerosols and Gases at MLO 

T.A. Cahill, S.S. Cliff, T. M. Cahill, and K.D. Perry................................................................. .. 117 

NIWA Lauder NDSC UV N isible Measurements at the Mauna Loa Observatory 

? . Johnston...................................... ............................................................................................ 11 8 

Operation of Brewer Instruments at Mauna Loa Observatory 

J. B. Kerr.... ............................................................................................. ..................................... 119 

Isotopic Studies of Carbon Monoxide at Mauna Loa 

J.E. Mak...................................................................................................................................... 120 

Interpre ting Seasonal Cycles of Atmospheric Oxygen and Carbon Dioxide Concentrations 

at American Samoa Observatory 

A.C. Manning, R.F. Keeling, and L.E. Katz.. .............................................................................. 121 

Artific ial Windshie lding of Precipitation Gauges in the Arctic 

R.J. McClure............................ ................................................................................................... 127 

Investigation of the Transfer Function between Atmosphere and Snow Concentrations 

of Hydrogen Peroxide at South Pole 

J.R. McConnell and R. C. Bales................................................................................................... 128 

Stratospheric Ozone Climatology from Lidar Measurements at Mauna Loa 

S. McDermid, T. Leblanc, R. Cageao, and D. Walsh............................. ..................................... 130 

Microwave Measurements of Middle Atmospheric Water Vapor from Mauna Loa, 1996-2000 

G.E. Nedoluha, R.M. Bevilacqua, R.M. Gomez. and B. C. Hicks.................... ............................ 133 

Carbon Flux Using Eddy Covariance Methodology in Arctic Coastal Wet Sedge Tundra 

W. C. Oechel, R. Zulueta, and H. Kwon..................................................... .................................. 135 

Preliminary Intercomparison Results from the NDSC Microwave Ozone Profiling Instrument 

at Mauna Loa Observatory 

A. Parrish, J. S. Boyd, B.J. Connor, l.S. McDermid, S. Oltmans, J J. TsoLt, and JM. Zawodny. 137 

Advanced Global Atmospheric Gases Experime nt (AGAGE) 

R.G. Prinn. R.F. Weiss, D.M. CLtnno/d P.J. Fraser, and P.G. Si111111011ds............................... .... 140 

Winter Sampling of Shallow Firn Air at the South Pole to Understand Processes Affecting Firn 

Atmosphe ric Histories and Ice Core Gas Records 

J.P. Severinglw11s ........................................................................................................................ 143 

Barrow Magnetic Observatory 

J. Townshend....... ........................................................................................................................ 147 

7. Publications and Presentations by CMDL Staff, 1998- 1999 ........................ .. .. ........... ...... ....... ........................ 148 

8. Specialized Abbreviations and Acronyms .......... ....... ................................................................................... .... 152 

vii 
CMDL Organization, 1999 

The CMDL organization structure features five research areas organized according to scientific discipline as 

follows: (I) Carbon Cycle; (2) Halocarbons and Other Atmospheric Trace Species; (3) Ozone and Water Vapor; (4) 

Aerosols and Radiation ; and (5) Observatory Operations. At the end of 1999, the laboratory staff consisted of 51 

civil service personnel (excluding part-time student assistants), 33 CIRES/University of Colorado personnel, and I 

NOAA Corps officer as well as several visitors and people on special appointments. 

Director, CMDL 

David Hofmann 

(303) 497-6966 

Program Management Specialist Physical Science Administrator Administrative Officer 

Ann Thorne Russell C. Schnell Sandra Lawrence 

(303) 497-6074 (303) 497-6733 (303) 497-6070 

I I 

Carbon Cycle Halocarbons and Other 

Atmos. Trace Species 

Pieter Tans James W. Elkins 

(303) 497-6678 (303) 497-6224 

Ozone and Water Vapor Observatory Operations Aerosols and Radiation 

and Data Management John Ogren 

Samuel Oltmans Russell C. Schne ll 

(303) 497-6210 

Ellsworth Dutton (303) 497-6676 (303) 497-6733 (303) 497-6660 

I I I 

Barrow Observatory Mauna Loa Observatory Samoa Observatory South Pole Observatory 

Daniel J. Endres John Barnes Douglas Holt Donald H. Neff 

(907) 852-6500 (808) 933-6965 (684) 622-7455 (303) 497-6655 

viii 
Director's Office 

David Hofmann, Direc1or 

Sandra Lawrence. Adminislrali\•e Officer 

Ri1a Rosson. Edi1onal Assis1an1 

Russell C. Schnell. Physical Sci. Admin. 

Brenda Seader. Ad1111nis1ra1ive Assisian1 

Ann Thome. Pgm. Managcmen1 Specialis1 

Special Projecls 

Lori Bruhwilcr. Physical Scienlisl 

Eric Hackathorn, Compuler Specialis1 

Aerosols and Radi ation 

EllS\\ Orlh Duuon. f\lc1corologis1 

John Ogren. Physical ScienliM 

Beverly OUonnell. Secretary 

Elizabelh Andrews, CIRES 

Gail Anderson. USAF 

BarT) Bodhame. :\le1eorologis1 

Da' id Delene. CIRES 

David Jackson. Elcc1ronic Technician 

Anne Jefferson. CIR ES 

Da\ 1d Longenecker. CIRES 

Donnld Nelson. Mc1corolog1s1 

Kaue O'Gara. CIRES S1uden1 

Painck Sheridan. Physical Sc1cn1is1 

Roben S1one. CIRES 

Renee Talusko, Physical Scientis1 

James Wendell , Elcc1ronic Technician 

Norman Wood. CIRES 

Ozone and Water Vapor 

Samud Ohmans. Phys1c1s1 

Be\·erly ODonnell. Sccre1ary 

Gloria Carbaugh. Physical Scienlisl 

Mark Clark. CIRES 

Roben Evans, Research Scien1is1 

Joyce Harris. Res. Physical Scien1 is1 

Bryan Johnson, Res. Che111is1 

CMDL Staff, 1998/1999 

Michael ONeill. CIRES 

Doro1hy Quincy. CIRES 

Eric Rice, CIRES Studen1 

David Sherman. CIRES 

Brian Vase!, CIRES S1uden1 

Holger Vomel, CIRES 

Carbon Cycle 

Pieicr Tans. Chief 

Linda Sachetti, Secre1ary 

Pe1er Bak\' in, Physicisl 

Andrew Burr, Phys. Science Aid 

J. Cervelli. CIRES S1uden1 

Thomas Conway, Research Chemisl 

Angela Crowley. CIRES S1udcn1 

Ed Dlugokencky, Research Chemis1 

Laura Dukach, CIRES S1uden1 

Sara Fle1cher. CIRES Gr. Res. Asst. 

Brad Gore, CIRES 

Douglas Guenlher. ll~ES 

Michael Hahn. CIRES 

M. Johnson. CIRES S1udcn1 

Duane Ki1zis. CIRES 

Pa1ncia Lang. Physical Scien1is1 

Kenne1h Masa11c, Re>. Phy >ic1>I 

John Miller. CIRES Gr. Res. Asst. 

Paul Novelli, Res. Che1111s1 

Na1al1e Pay nler, CIRES 

James T. Pe1erson. CIRES 

Brin Siephens, CI RES 

Kirk Thoning, Physicis1 

Michael Trudeau. CIRES 

Conglong Zhao. CI RES 

Halocarbons & Other Atmos. 

Trace Species 

James Elkins. Chief 

Debra Hansen, Secre1ary 

fames Buller. Research Chcrnis1 

Lori Del Negro. NRC Pos1 Doc. 

ix 

Geoffrey Duuon, CIRES 

Brad Hall, Physical Scien1is1 

Dale Hurs1. CIRES 

Daniel King. CI RES 

Eric Kline. CIRES 

Loreen Lock. CIRES 

Douglas MacTaggan, CIRES 

Debbie Mondccl, CIRES 

Sieve Mon1zka. Res. Chemisl 

Fred f\loore. CIRES 

David Nance, CIRES 

Eric Ray. CIRES 

Pavel Romashkin. CI RES 

Thayne Thompson. Physicisl 

Observatory Operations 

Russell C. Schnell, Phy. Sci Admrn1s1ra1or 

Linda Sacheui. Secre1ary 

Bradley Haller, CIRES 

Thomas Mefford. CIRES 

Darnel Endres. S1a1ion Chief, Barrow 

f\Ialcom Gaylord. Elcc1ronic Engrneer 

John Barns. Dircc1or. l\Iauna Loa 

Judllh Pereira. Program Suppon Technician 

John Chm, Physicisl 

DarT) I Kum) uki. Elcrnonic Engineer 

Leslie Pajo. Office Au1oma11on Clerk 

S1even Ryan, Physical Scien1is1 

Roben Uchida, Electronic Technician 

Alan Yoshinaga, Chemisl 

Douglas Hoh. S1a1ion Chief. Samoa 

Enc Sandberg, Elect. Engineer 

Donald Neff, South Pole 

Andrew Clark, Chemisl 

Joel Michalski, NOAA Corps 
Name: 

Latitude: 

Longitude: 

Elevation: 

Time Zone: 

Office Hours: 

Telephone 

Office hours: 

Fax: 

Postal Address: 

Frdght Address· 

Name: 

Latitude: 

Longitude: 

Ele,·ation: 

Time Zone: 

Office Hours: 

Telephone: 

Oftice hours: 

After hours: 

Fax: 

Postal Address: 

Freight Address: 

CMDL Station Information 

Barrow (BRW) 

71.323°N 

156.609°W 

8m 

GMT -9 

8:00 am-5:00 pm 

(907) 852-6500 

(907) 852-4622 

Officer in Charge 

NOAA/ERL/CMDL 

Pouch 888 

Barrow, AK 99723 

Officer in Charge 

NOAA/ERUCMDL 

617 Cun111ngham 

Barrow, AK 99723 

Samoa (Si\IO) 

l4.232°S 

170.563°\V 

77 m 

GMT-I! 

8:00 am-5:00 pm 

011 (684) 622-7455 

011 (684) 699-9953 

0 11 (684) 699-4440 

Officer 111 Charge 

U.S. Dept. of Commerce 

NOAA - CMDL Samoa Obscnator} 

Pago Pago. American Samoa 96799 

Same as above 

x 

Mauna Loa (MLO) 

19.539°N 

155.578°W 

3397 m 

GMT-10 

8:00 am-5:00 pm 

(808) 933-6965 

(808) 933-6967 

U.S. Dept. of Commerce 

NOAA - Mauna Loa Observatory, Rm. 202 

P.O. Box 275 

Hilo, Hl 96721 

U S. Dept. of Commerce 

NOAA - Mauna Loa Obsenator) 

154 Waianuenue Ave. 

Hilo, HI 96720-2452 

South Pole (SPO) 

89.997°S 

102.0°E 

2837 m 

G~IT +12 

8:00 am - 5:00 pm 

Relayed through CMDL Boulder 

Officer in Charge 

NOANCMDL Clean Air Facility S-257 

South Pole, Antarctica 

PSC 468 Box 402 

FPO AP 96598-5402 

Same as above 
1. Observatory, Meteorology, and Data Management Operations 

1.1. MA UNA L OA OBSERVATORY 

J. BARNES, J ClllN, D. KUNIY~KI, L. PAJO, J. PEREIRA. 

S. RYAN, B. UCHIDA, AND A. YOSlllNAGA 

1.1.1. OPERATIONS 

The mos1 noticeable changes to the observatory over the past 

2 years involved moving instruments into the new Network for 

Detection of Stratospheric Change (NDSC) building that was, for 

the most part, completed in late 1997. The first to move, mainly 

from the Keeling building, were several solar radiation 

instruments from CMDL and the cooperative programs. The 

largest instrument, the new National Institute for Waler and 

Atmospheric Research (NIWA) ultraviolet/visible (UVNIS) 

spectropho1ome1er, was mounted a1 1he !Op of a chimney above 

the solar radiation room. The older spectropholometer that had 

been in service for 5 years at MLO was moved to Boulder. The 

CMDL lidars were the next instruments to be moved. The 

separate frames for the ruby and Nd:YAG lidar systems were 

redesigned and combined IO form a single struclllre situa1ed in 

1wo rooms of the NDSC building. A third room func1ions as a 

control room. The Cr-.IDL Carbon Cycle Greenhouse Gases 

(CCGG) group instruments (carbon dioxide. me1hane, and 

carbon monoxide) are no\\ in their own room thal includes a new 

llask sampling system. The CMDL Halocarbons and other 

A1mospheric Trace Species (HATS) group instruments were 

likewise moved into their own room thm was modified with 

extra thermos1at-controlled ventilation to main a constant 

temperature. Sample lines into the NDSC building from 1he 40-

m tower were routed into both the CCGG and HATS rooms. 

The computer network hardware and an electrical shop area take 

up two additional rooms. Significant modifications were made 

to the electrical system by adding ceiling ou1lets in several of 1he 

rooms. A portion of the building is re5erved for the Je1 

Propulsion Laboratory/National Aeronautics and Space 

Administralion (JPUNASA) ozone lidar currently housed in two 

trailers. Some work was done on the JPL rooms, and the lidar 

will be moved in the summer of 2000. 

The U.S. Army installed an amenna for a new radio repeater 

system. The system introduced an intermittent noise in the 

NIWA UV/V IS spectrome1er tha1 was difficult to trace. The 

antenna will be moved down and awa) from 1he observatory and 

will use a directional antenna to eliminate the interference. 

University groups initiated two new weekly sampling programs; 

the Division of Geological and Planetary Sciences at Caltech 

ins1alled an interplanetary dust collector, and the State University 

of New York installed a CO isotope sampler. The weekly 

samples are collected in 1000-psi cylinders that must be shipped 

as hazardous material. The Department of Energy (DOE) radon 

program was terminated and the instrument removed from 1he 

tower base and shipped back to New York. Two new NIWA 

spectrometers for N01 and BrO were installed in a chimney in 

the solar radiation room in the NDSC building. 

Calibrations of 2-4 weeks duration by visiting instruments IO 

the observa1ory continued to increase. There were many repeal 

visits, as well as several new groups. For the most part, the 

instruments are ariou~ solar radiation measurements of varying 

complexity. Computer network connections were added to the 

visitor building 10 accommodate these programs. Three Japanese 

astronomers visi1ed the MLO site to see if it would be a suitable 

loca1ion for radio astronomy experiments. The U.S. Air Force 

conducted radio frequency (RF) and sun viewing tes1s a1 MLO w 

assess the suitabilily of the si1e for a solar observatory. MLO is 

attractive to new astronomy groups since the Mauna Kea 

faci lities are full under the current usage plan. NOAA 

Environmental Technology Laboratory (ETL) and CMDL took 

advantage of the low water vapor above MLO during the El Nifio 

to conduct unique infrared (IR) measurements by insialling an 

ETL Fourier transform infrared (FTIR) spectrometer in the 

Microwave building that was operaled during March and April 

1998. 

Movie and magazine groups used !he observatory road to film 

a shoe commercial and four car commercials. Since 1he film 

crew vehicles can cause damage to the fragile road, sizable fees 

were charged for road access 1ha1 direc1ly funded road repair. 

There was a long drought on the Big Island in 1998 due to El 

Nifio reducing the northeastern trade winds dramatically, 1hus 

reducing orographic rain on the Big Island. There were brush 

fires in 1998 and 1999 that impac1ed the observatory 

observations, and for the firs! time in many years, snow 

prevented access to 1he observatory in December 1999. A 

me1eorologis1 was hired by the Universily of Hawaii to forecast 

the summit and upper air weather for Mauna Kea These 

forecas1s have been useful for lidar observing conditions and 

visiting solar radiation groups. 

The only change in staffing at MLO was the retirement of 

Judy Pereira. She was with the observatory for over 30 years 

and will be greatly missed. 

Outreach 

There was an increase in \isitors to the observatory in 1he past 

2 years, many of whom used the ln1erne1 10 make arrangemems 

and gel information. A group from the U.S. Department of 

Energy and the Japan Minis1ry of lnterna1ional Trade and 

Industry visi1ed twice; these visitors were attending meetings on 

a carbon dioxide sequestration experiment that \\ill be conducted 

on the western side of the Big Island. Tours were also given to 

the Department of Commerce (DOC) Deputy Secretary. the 

NOAA Administration Deputy Assislant Secretary. and 1he 

NOAA Ocean and Atmospheres Depu1y Under Secre1ary. 

Several classes from the University of Hawaii al Hilo toured 

MLO. 

The MLO slation chief lec1ured on climate change and 

pollution 10 a group of 50 senior citizens at the Kilauea Volcano 

Visitors Center and to a group at the Volcano National Park. He 

also judged the Hawaii County Science Fair. Two high school 

summer students were mentored each summer on short daia 

analysis projects. A local high school teacher and a high school 

science student also worked summers on the lidar program. 

The VOGNET program continued in 1998- 1999. For this 

program, s1udents make regular observations of volcanic 

aerosols from a network of schools spaced around the island in 

order to study the distribution and relative levels of volcanic 

haze or "vog" in Hawaii. Each school uses a Gardner 

condensation nuclei (CN) counter and a 2-wavelength 

sunphotometer to make several measurements per day. By the 

end of 1999 the s1udents had made over 6000 observations in 3.5 

years. In the summer of I 998 an inexpensive automa1ed CN 

counter was developed al r-.tLO 1hat uses common plumbing 

hardware, solenoid valves, a laser poinler, and a PC. This 

machine has been deployed al si1es around 1he island t0 
characterize the 24-hr cycle of vog concentration. An improved 

version was built by students at Hawaii Preparatory Academy as 

a science fair project that advanced through district and state 

fairs to evemually win third prize in the environmental division 

of the International Science Fair in Philadelphia in the spring of 

1999. 

Computers/Network 

There were many changes to the MLO computer network 

during 1998-1999. In September 1998 the VAX was shut down 

and sem to Boulder and replaced by two NT servers. One is 

dedicated to function as an e-mail server, and the other is a main 

tile. print, and primar) admin istrative server for the Hilo office. 

The old NT server is now a dedicated web server. In January of 

1998 we received about 60.000 MLO Web page hits per month, 

and by the end of December 1999 we were receivi ng about 

190,000 per month. 

In February 1998 the Hilo office switched to a 128-k frame 

relay circuit. In March of the same year the mountain site 

switched over to a 56-k frame relay circuit. Because of 

limitations of the telephone company's circuitry, 128 k at the 

mounta111 site is not available. 

The network hubs and routers were moved from the Keeling 

building to the computer room in the NDSC building. The site's 

fiber optic cables were reconfigured with new topology. The 

NDSC building was also wired with fiber optic cabling to each 

room, and 10 base-T hubs are now being used with the existing 

coax-fiber network in \ arious locations at the site. 

At the end of 1999 i\1LO installed a five-camera security and 

sky-observation network operation at the observatory. The 

original camera is still located at the High Altitude Observatory 

facing the northern sk) The ~econ d camera is mounted about 

half\\ J) up the high towa facing the eastern sky. The third 

camera, ~ponsored b) JPUNASA, 1s facmg the southwestern 

sk) . The fourth camera, sponsored by the Atmospheric 

Environment Service (AES) (Canada), is an all-sky camera 

vertical with the radiation deck. The fifth camera, located on the 

NDSC sundeck, is used to moni1or the Brewer" s !racking of the 

sun. All of the camera images can be seen on MLO's web site. 

About 80'7c of the hits to the MLO web site are looking at these 

live images (www.cmdl.noaa.gov/obop/mlo). 

Remote control of much of the observatory's equipment was 

a major focus in I 999. A system to remotely turn "on" or "off' 

the lidar cooler was implemented as well as remote control of 

po\\er to computers and other devices. Software control or 

monitoring through the network is available to the following 

systems: S02, new Scripps C02 computer, solar dome 

comroller, AES Brewers, surface ozone, the camera computers, 

the power comroller computer, the moumain server, and the 

main observer's computer. Links to monitor the CCGG and 

Chromatographs for Atmospheric Trace Species (CATS) gas 

chromatographs (GC) are available from MLO's website. 

Network usage of administrative programs has increased. 

Payroll ume and attendance is now done through the Hilo 

network instead of the phone line. Travel, training, and 

purchase orders are also completed through the network 

connection with the Boulder support group. In 1999 the 

Smithsonian Institution left MLO's Hilo network after 

receiving their own internet line. The U.S. Fish and Wildlife 

Service (FWS) has since been connected to the network and 

has taken the IP addresses of the Smithsonian Institution. A 

wireless bridge connects the FWS office to MLO's network 

across the street. 

2 

1.1.2. PROGRAMS 

Table I. I summarizes the programs in operation or terminated 

at MLO during 1998-1999. Relevant details on some of the 

respective programs are as follows: 

Gases 

Carbon dioxide. The CMDL Siemens Ultramat-3 IR C02 

analyzer, along with the associated equipmem and the other 

CCGG measuremem instrumems (CH4 and CO), were moYed on 

November 13, 1998, from the original concrete block building 

built in 1957 to the newly constructed NDSC facility. The new 

location is well lighted, temperature regulated, and is 

approximately I 5 m southeast of the old concrete block building. 

On November 13, 1998, a new target reference gas was added imo 

the C02 sys1em for its once daily calibration between WI, the lo\\ 

span reference gas, and W2, the high span reference gas. The 

target reference gas has a C02 concentration value in between WI 

and W2 reference gases. The Scripps Institution of Oceanography 

(SIO) Applied Physics IR C02 analyzer (see listing under 

Cooperative Programs, Table I.I) and its associated equipmem 

remained in the same location. Both the CMDL and SIO C02 

programs were operated without major problems throughout 1998-

1999. Routine maintenance and calibrations were undertaken on 

both instruments as scheduled. SIO was required to purchase a 

freezing unit for its C02 program because of the CCGG equ1pmem 

relocation. 

The weekl) C02, CH4, and other gas sampling programs, us111g 

flasks at MLO and at Cape Kumukahi, were carried out according 

to schedule throughout the year without major problems. The 

Martin and Kitzis Sampler (MAKS) sampling unit for Cape 

Kumukahi was discontinued in early 1998 and was replaced with a 

new Air KilLis sample1 (AIRKIT) ~a111ph11g unit. Since November 

20, 1998, the 0.5-L flasks were replaced with the 2.5-L flasks for 

the weekly samplings through the C02 anal)Ler at MLO. 

C02 emissions from the Mauna Loa volcano measured at 

MLO resumed their steady decline in 1998-1999 after a brief 

factor-of-2 rise in 1994-1995 that was probably due to new 

emissions from the upper southwest rift. Because emissions 

from the Yolcanic vents at the Mauna Loa caldera and along the 

northeast rift zone at Mauna Loa have fallen by over 2 orders of 

magnitude since 1984, the tables tor MLO outgassing that 

appeared in prior reports have been discontinued. They will be 

reinstated should MLO outgassing become active again, as 1s the 

case following major eruptions. 

Carbon monoxide. The Trace Analytical RBA3 reduction 

gas analyzer for the continuous measuremem of CO mixing ratio~ 

returned from CM DL (Boulder) on November 12, 1998, and was 

back in operation at MLO on November 13, 1998. 1l1e stream 

selection valve malfunctioned in early 1999 and caused a brief 

downtime; otherwise, the system has been operating cominuously. 

Methane. The HP6890 methane GC system operated without 

problems during 1998-1999. Occasionally the !lame died out during 

the normal runs and relighting was difficult. An increase in the 

hydrogen gas now in the GC from 45 mL min·' to 47 mL min·' 

corrected the problem. Since April 1996, CMDL has purchased the 

nitrogen carrier gas (99.999% pure, SJZe 200 cylinder, 6.5 m3 

volume) and the oxidizer from Gaspro in Hilo for the CH4 program 

at discounted prices. The oxidizer is 40% oxygen in balanced 

nitrogen with an analytical accuracy of ±2% and an analysis 

precision of ±I%, (size 200 cylinder 5.7 m3 volume). The usages 

of these gases are one cylinder of nitrogen per 5 weeks and one 

cylinder of oxidizer per 2.5 weeks. 
TABLE I. I. Summary of Measurement Programs at MLO in 1998- 1999 

Program 

Gases 

c o , 

co 

COi. C HJ, co. and 11C. 1

' 0 of COi 

Cll, 

so~ 

Surface o , 

Total O , 

0 1 profiles 

NiO. CFC-I I, C FC- 12. CFC- 11 3. 

C H1CC13, CCI,, SF0• HCFC-22, 

HCFC-14 1b, HCFC- 142b, CH1Br, C H,CI. 

C H,CI,, C H Ch. c,HCh, c,c1,. H- 130 I. 

H- 12 11 . H-2402. HFC-134a 

CFC- I I, CFC-12. CFC- 113. N10 , 

CCI,. CH ,CCh 

N10 

CFC- I I. CFC- 12. CFC-113, N10 . ClhCCli. CCI,. 

CH,Br. CH,CI. H-12 11 . SF •. HCFC-22 

A" ro.wlJ 

Condcnsa1ion nu ch!1 

Op11cal propenic'> 

Aerosol lighl absorp11011 (b lack carbon) 

Sl1Jlu>phc11c and upper troposphcnc aerosols 

Solar Rat/111111111 

Global irradiancc 

Diffuse irrad1ancc 

UV solar rad1 a11on 

Column wa1er vapor 

Meteorology 

Air 1empera1ure 

Air 1empera1urc 00-70 km) 

Tcmpcra1urc g rad1cn1 

Dewpoini 1c111pe ra1ure 

Rela1ivc hu1111dll) 

Press ure 

Wind (speed and d ircc li on ) 

Prec ipi1a1ion 

To1al precipitable waler 

lns1rumen1 

Si emens Ullramal-3 IR analyzert 

2.5-L glass nasks. lhrough analyzer 

Trace Analy1ical RGA3 

rcduc1ion gas analyzer no. RSt 

2.5-L glass flasks, l\IAKS pump unil 

AIRKIT pump uni1 , 2.5-L g lass flasks+ 

3-L C\ac ualcd glass nasksi 

HP6890GCt 

TECO model 43S pulscd-fluorcscencc analyzer; 

4. 10, 23. 40 mt 

Dasib1 1003-AH UV absorplion OLone 111oni1ort 

Dobson spcc1ropho1ome1cr no. 76t 

Dobson spcc1ropho1omc1c r no. 76 t 

(a u1oma1ed Umkchr melhod) 

Balloonborne ECC sonde 

850-mL. 2.5-L, and 3-L Slainless Slecl nasks 

HP5890 aulomaled GCt 

Shimadzu au10111n1cd GCt 

Au1oma1cd CA TS GC 

Pollak CNC 

TS I CNCt 

Three-wavelcng lh nephelome1cr: 450. 550. 700 nm 

Ac1halome1ert 

Nd:Y AG lidar: 532-. I 064-nm wavelengths 

Eppley pyranomc1crs wi1h Q, 

OG I. and RG8 fiherst 

Eppley pyrhe liome1er wi 1h Q fil1ert 

Eppley pyrheliome1er wilh Q. OG I. 

RG'.!, and RG8 fiherst 

Eppley/Kendall ac1ivc cavlly radi omelcrt 

Eppley pyrgeomeicr wi1 h shading disk 

and Q fillert 

Yankee Environmen1al UV B pyranornc1er 

(280-320 nm)t 

J-202 and J-314 sunpho1omelers wi1h 

380-, 500-. 778-, 862-nm narro\\ band fillers 

PMOD lhrec-wavelenglh sunpho1ome1ert: 

380. 500, 778 nm; narrowband 

Two-wavelenglh !racking sunpho10111e1er: 

860. 940 nmt (2 ins1rumen1s) 

Asp1ra1ed lhermis1o r. 2-. 9-, 37-m heigh1st 

max .-min. lhcrmomele rs. 2.5-m hc1 gh1 

Ltdar 

Aspirated lhermislors. 2-. 9-. 37-m he1 gh1st 

Dewpoinl hygromelcr, 2-m hc igh1 t 

TSL 2-m heigh1t 

Capac ilance lransducert 

8.5-, 10-, and 38-m heig h1st 

Rain gauge, 20 cm 

Rain gauge, 20 m~ 

Rain gauge, tipping bucke1t 

Foskelt JR hygrometert 

3 

Sampling Frequenc} 

Conlinuous 

I pair wk"

1 

Con1inuous 

I pair wk"1 

I pair wk"1 

I pair wk·1 

Conlinuous 

Conlinuous 

Continuous 

3 day"1. weekdays 

2 day" 1 

I wk-1 

I sample wk·' 

I sample h·

1 

I sample h"' 

I sample h-1 

I day"1 

Continuous 

Continuous 

Conlinuou s 

I profile wk"1 

Conlinuous 

Conlinuous 

3 day·

1 

I mo·

1 

Conlinuous 

Continuous 

3 day"1

. weekdays 

Conlinuous 

Conlinuous 

Continuous 

I day"1

, weekdays 

I profile \\k 1 

Conlinuo us 

Conlinu ous 

Conlin uous 

Conlinuous 

Conlinuous 

5 wk·' 

I wk· 1 

Conlinuous 

Continuous 
TABLE I. I. Summary of Measurement Programs at MLO in 1998-1999-<:ontinued 

Program 

Preup11t1trt111 Che1111stry 

pH 

Conduc tivity 

C11opera111•e Programs 

C02 (SIO) 

C02, 11C, N20 (SIO) 

C02. co. CH •. 11C/ 12C (CS IRO) 

C H,, C HiCCi), CH,Cl, HCFC-22, CFC- 12, 

CFC-I I, CFC-113, CO. C02, N20. C HCI,, 

CCI, (OG IST) 

0 2 analyses (S IO) 

02 anal)ses (URI) 

CH4 (llC/12C) (Uni v of Washington) 

To tal suspended pa rticula tes (DOE) 

Ultraviolet radiation (CSU-USDA) 

Radionuclide deposit ion (DOE) 

Aerosol chemistr) (Univ. of Calif.-Davis) 

Sulfate, nitrate, aerosols (Uni v. of Hawaii) 

Radon (ANSTO) 

AERONET sunphotometers (NASA Goddard) 

G lobal Positioning System (GPS) Test Bed 

(FAA and Stanford Uni versity) 

Earthquakes HVO/USGS Menlo Park 

Earthquakes Nort hwestern University 

CO isotopes (SUNY) 

Cosmic dust (CAL TECH ) 

Instrument 

pH meter 

Condu ctivity bridge 

Applied Physics IR analyzert 

5-L evac uated glass fl asks* 

Pressuri zed glass fla sk sample 

Pressuri zed stainless steel flasks * (Ended 6/99) 

5-L glass flasks through tower line and pump unit* 

3-L glass flasks through tower line and pump unit :;: 

(Ended 12/98) 

35-L evacuated fla sk (Ended 12/98) 

High-volume sampl er 

Multi-wavelength radiometer (direct. diffuse, shado" band) 

Ion-exchange column (Started l /98) 

Prog rammed filt er sampler 

Filter system 

Aerosol scavenging of Rn daughters!: 

2-filter system 

Automated solar-powered sunphotometers 

GPS-dcri vcd column water vapor profiles 

Seismomctcr 

Seismome ter 

I 000 psi cylinder 

Magne tic co llector 

/\'e/l\11rkj11r De1ec111111 of Stratosphenc Chc111ge (NDSC) 

Ultrav10J.:t radiation UV spec trometer (280-450 nm), I-nm resolu tiont 

(NOAA and NIWA) 

Stratospheric o, profile. 20-64 k m 

(Uni,· o f !\lass . Amherst) 

Stra tosphe n c ·o, profiles ( 15-55 km). 

h!mperature (20-75 km). 

:icro~o l profiles (15-40 km) (JPL) 

Stratospheri c water \apor profiles. 40-80 km. 

10-15 km resolution CNRL) 

UV/,isiblc radiatio n (NIWA and NOAA) 

UV/visible radiation (NIWA and NOAA) 

Column o,. UV (AES. Canada) 

Solar spectra (Uni ,·. of Den\'er) 

All instru men ts arc at l\ILO unless indic ated. 

• l\lLO and Kumukah1 

l\111111ech Corp .. 11 0.8-GHt mi crowave ozone 

spec troscopy 

UV lidart 

M 1II1 meter" a\C spectrometer 

Slant column N02 spec trometer 

Column BrO spectrometer (Began I 0/99) 

Brewe r spectrophotometers (Two instruments) 

FTIR spec trometer, automatedt 

tDma from this instrume nt record ed and processed b) microcomputers 

+Kumukah1 onl y 

Kul ni l\lauka 

Sampling Frequenc) 

Continuous 

I pair wk· 1 

3 pair mo·1 

3 wk·' 

3 (2 mor' 

2 (2 mo)'1 

2 mo I 

Continuous ( I filt er wk·I J 

Continuo us 

Quarter!) sample 

Integrated 3-day sample, 

I continu ous and 

I do\\ nslope sample 

(4 days)'' 

Dail y, 2000-0600 LST 

Continuous, integrated 

30-min samples 

Continuous 

Continuous 

Cont inuo us 

Continuo us 

I wi.. ·

1 

I wk·' 

Con tinuous 

3 profiles h 1 

J-4 profiles" k 1 

Continuous 

Continu ous, da) 

Continuous, da) 

Da i I) 

5 days wk·' 

The l! ~ data continued to sho\\ clear!) defined cycles of 

\'a1'} tng frequencies. The typical diurnal cycle \\as well correlate<l wtth up- and downslope \\inds. with the marine boundary 

layer atr hanng higher ~ concentrattons. :-.tultt-day or 

\) nopttc-scalc CH~ cycles were also observed, \\ hich apparent I) 

relate to different atr mass source regions. 

Sulfur dioxide. A ne\\ system. using a TECO -BS pulsec.1-

lluorescence analyzer, was developed in Hi lo in early 1998 and 

installed at MLO in April. By the end of June the system was 

fully operational. Every hour SO~ is measured sequenti ally from 

inlets at 4.10, 23, and 40 meters on the tower, followed b) a zero 

measurement. A single-point calibration is made once per da) 

by injecting calibration gas into the airstream at the 40-m intake. 

All of the inlet lines are thermostaticall) maintained at 20°C. In 

August 1999 a break in the 40-m intake occurred, and sampling 

was restricted to the lower three levels for the rema111der of the 

year while the damaged line section was removed and repaired. 

4 

This is the lirst time multi-point continuous \erttcal profiles 

of an atmospheric constiiuent have been measured at l\ILO. The 

S02 profiles show several features that change along with the 
diurnal cycle of upslope/downslope winds. During the daytime, 

pollution from the Kilauea volcano is commonly brought to MLO 

in the upslope wind by late morning. Turbulent mixing causes the 

concentrations at all four tower levels to be similar. After sunset 

the surface temperature inversion develops, and the downslope 

wind commences. Residual pollution from Kilauea at that time 

has a S02 profile with concentrations increasing with height. After 

midnight, pollution episodes from Mauna Loa volcano are seen 

10% of the time, as indicated by increases in C02 by up to several 

ppm. These are accompanied by increases in S02 of up to several 

hundred ppt above a baseline of tens of pp! with concentrations 

decreasing with height, indicating the gas is trapped beneath the 

surface temperature inversion. ll1roughout 1998-1999, the 

molecular ratio of S02 to C02 in the Mauna Loa volcanic plume 

remained at about 5 x 10·5

. This ratio is being monitored closely 

as an eruption precursor. An increase in the ratio is expected if 

magma migrates closer to the surface. 

Ozone 111011itori11g. The 1998-1999 MLO ozone monitoring 

program consisted of three measurement foci: continuous MLO 

surface ozone monitoring using a Dasi bi model 1003-AH UV 

absorption ozone moniwr: daily total and Umkehr ozone profile 

measurements using a computer-based automated Dobson 

instrument (Dobson no. 76); and ozone profile measurements 

based on weekly ascents of balloonbome electrochemical 

concentration cell (ECC) ozonesondes released from the NWS 

station at the Hilo airport. 

Dobson no. 76 was operated daily during weekdays 

throughout the period with daily morning and afternoon Umkehr 

checks. Summer intercomparisons with standard Dobson no. 83 

occurred in 1998 and 1999. The instrument was maintained as 

needed with repairs to the pedestal unit, stainless steel wedge 

band replacement, dome (hatch and shutter) work, and 

mi~cellaneous motor, belt, and tension spring dju tment ~. 

The Dasibi program operated normally throughout the period, 

and the data transmission software and hardware were upgraded 

in June 1999. The Dasibi was calibrated, and yearly maintenance was carried out by MLO-based staff in 1998 and 1999. 

Absorption tubes were cleaned by other MLO-based staff in 

August 1999 at which time ND checks were also completed. 

The Dasibi unit also was connected to its own uninterruptible 

power supply (UPS) at this time. 

Ozonesondes were launched weekly whenever supplies were 

available from Boulder. In 1998 there were 44 ozonesonde 

nights, and in 1999 there were 47. The new "2Z" sondes were 

used beginning April 1998. These sondes send telemetry in a 1-s 

packet versus 6 seconds for the old "6A .. type that results in 

much less susceptibility to radio interference. As a result, data 

acquisition is consistentl y over 90% instead of the <20% that 

occurred on some flights of the old sondes. 

Halocarbo11s and other atmospheric trace species. In 1998 

the Radiatively Important Trace Species (RITS) unit had airline 

pump board changes, a Keithley replacement, UPS battery 

replacements, and computer hardware repairs. In September 

1998, the RITS GC and a new four-channel CATS GC were 

installed in the new NDSC building. The new CATS GC went 

through hardware changes throughout the year until June 1999 

''hen it stabilized. CAL2 was shut down in Jul y. 

Radon. Radon has been measured continuously since 1989 

by the Australian Nuclear Science and Technology 

Organization (ANSTO). Since March 1998, monthly manual 

calibrations have been made with a commercial radon source. 

5 

Aerosols 

Condensation nuclei. The Thermo Systems Incorporated 

(TS!) unit is a continuous expansion CN counter (CNC) in 

which condensation occurs in butyl alcohol vapor in a 

chamber, and single-particle counting statistics are used as a 

basis for calculating CN concentrations. The TS I was in 

Boulder from November 1998 to October 1999 for repairs and 

maintenance. The Pollock CNC continues to be used as a 

primary daily calibration. 

Aerosol light scattering. The four-wavelength 

nephelometer in operation at MLO for decades was retired in 

July 1998 and was replaced by a fast-response three-wave 

nephelometer measuri ng at 450, 550, and 700 nm. The old and 

new nephelometers operated together for more than I year. 

Aerosol absorption . The aethalometer performed 

satisfactori ly during most of 1998-1999. Since August 1998, 

transfer of the aethalometer data to Boulder has been done 

every week. The internal hoses that were cracked because of 

ozone attacking the rubber were replaced in July 1999. 

Stratospheric and upper troposph eric aerosols. Weekly 

observations continued with the Nd:Y AG lidar throughout 

1998 and 1999. The optical framework was redesigned for the 

move into the NDSC building in February 1998. The lidar for 

the telescopes, lasers, and controls each have their own room in 

the new building. Only 2 weeks were needed to mo ve and get 

the Nd:Y AG system operating in the new building. On the 

other hand, the ruby system (694-nm wavelength) showed a 

severe loss of signal after the move. Since the Nd:YAG system 

measures aerosol profiles at 532 and I 064 nm, which give an 

interpolated 694 nm value, it was decided to discontinue the 

ruby observations as there was already over a year of overlap 

between the two systems, and the interpolated 694 nm profile 

b 111un: al:l:Urate than the mea~un:d 694 nm signal. 

The Nd:YAG laser power supply fai led in February 1998. 

Fixing the problem required a service call from SpectraPhysics in California. In February 1999 a potentiometer failed 

on the laser and was repaired by MLO staff. Other 

maintenance consisted of tlashlamp and cooling water changes. 

Solar Radiation 

The solar radiation program continued with the same 

instrumentation described in the previous summary report 

[Hof111a1111 et al., 1998]. Normal Incident Pyroheliometer data 

(which goes back to 1958) is calibrated periodi cally against an 

active cavity radiometer. Eight of these comparisons were 

done in 1998 and six in 1999. Mauna Loa Observatory is also 

used to calibrate handheld sunphotometers usi ng the Langley 

technique; 23 instruments were calibrated in 1998, and 28 were 

calibrated in 1999. The observatory is also used to calibrate 

CMDL's Yankee UVB instruments; four were calibrated in 

1998, and three were calibrated in 1999. 

Meteorology 

A computer-based "New Met System" measures station 

pressure, temperatures at the 2-, 9-, and 37-m levels, dewpoint 

temperature at the 2-m level, and wind speeds and directions at 

the 8.5-, 10-, and 38-m levels of the MLO Observation Tower. 

Precipitation is measured with a tipping bucket rain gauge. 

This new system has remained in operation unaltered and 

operating with high reliability to date. 
Precipitation Chemistry 

The MLO modified program of precipitation chemistry 

collection and analyses continued throughout I 998- 1999 within 

the basic MLO operational routine. This program consists of 

collections of a weekly integrated precipitation sample from the 

Hilo National Weather Service (NWS) station and the 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 I. I. New 

programs and changes not discussed in the NDSC section are 

presented here. 

In March I 996 MLO began calibrating automated 

sunphotometers for the NASA Aerosol Robotics Network 

(AERONET). Thirteen instruments were calibrated in 1998, and 

fifteen were calibrated in 1999. In September 1997 the Federal 

Aviation Administration (FAA) installed high qualit) Global 

Positioning Satellite <GPS) and meteorology sensors on the 

MLO Observation Tower in a study of atmospheric effects on 

GPS positioning. From this program MLO will receive nearly 

continuous column water vapor measurements. In November 

I 997 the Colorado State University (CSU) and U.S. Department 

of Agriculture (USDA) UV-B monitoring instruments were 

installed and continue to operate. 

Network for the Detection of Stratospheric Change (NDSC) 

All NDSC mstruments operated in previous years continued 

observations. Two additional spectrometers operated by the 

National Institute for Water and Atmospheric Research (NIWA) 

(New Zealand) were added in December I 999 for column 

measurements of NO~ and BrO. The NOAA lidar, owncsonde, 

and Dobson operations, which are also part of the MLO NDSC 

facility, are described in other sections of this report. 

UV/VIS spectroradiometer. This new instrument was put 

into operation in the NDSC building in November I 997. Weekly 

quality control calibrations were performed with a mercury lamp 

and a 45-\V quartz lamp. An absolute-standard I 000-W FEL 

lamp calibration was performed twice each year. Jn fall 1999 an 

intermiuem noise source in the background level was traced to 

the new U.S. Army radio repeater. Tracing the problem required 

a visit from a NI\V A engineer. The problem was fixed 

temporaril) by reducing the radio transmitter power and using a 

directional antenna. The permanem solution is to move the 

antenna down and away from the observatory; this will be 

completed in summer 2000. 

Microwa11e ozone spectroscopy system. The University of 

Massachusetts microwave instrument measures the vertical 

profile of ozone from 20 to 70 km with a vertical resolution of I 0 

km or less up to 40 km, degrading to I 5 km at 64 km. The ozone 

altitude distribution is retrieved from the details of the pressurebroadened line shape. 

UV lidar. During the last 2 years the JPL UV lidar conducted 

several extensive studies of the dynamics of the middle 

atmosphere above MLO. Using the lidar, one can observe 

gravity waves, planetary waves, atmospheric tides, and 

mesospheric inversions. Temperature climatologies were 

developed using these results. Work was also done on the new 

space in the NDSC building. It is assumed that the more stable 

concrete noor in the NDSC building will allow JPL to slightly 

improve data quality. JPL will also use the opportunity offored 

by the move and the rebuilding of the lidar to extend the range of 

its measurements to lower altitudes. The additional space will 

certainly make the lidar easier to operate and maintain. 

6 

N01, BrO spectrometers. Since July 9, I 996, stratospheric 

nitrogen dioxide (N02) has been measured at MLO using the 

twilight zenith technique with a NIWA UV/V IS spectrometer. 

Data have been analyzed, quality confirmed, and then submiued 

to the NDSC archive. The new N02 and BrO spectrometers 

began operation in December I 999. 

Brewer spectrophotometer. A single monochromator Brewer 

instrument was installed by the Canadian AES at MLO and 

began routine measurements of 0 3 and UV-B radiation on March 

2.i, 1997. A second instrument was added in November 1997. 

The measurements are supplememed by all-sky images that are 

recorded every I 0 minutes in order to assist in the analysis of the 

UV-B data. Overviews of the automatic operation of the 

instrument and data retrievals have since been carried out 

remotely from AES in Downsview, Ontario, over the Internet. 

The data are archived at the World Ozone and Ultraviolet 

Data Centre (WOUDC) in Toronto. Up-to-date preliminary data 

are available over the Internet from AES. Publication of some 

new results is planned after thorough analysis of a longer data 

record is completed. 

Solar FTIR spectrometer. The University of Denver FTIR 

spectrometer routinely monitors HCI, HNOJ> 0 3, N20, HCFC22, HF, CH4, NO, HCN, CO, C2H2, and ~. Because of the 

automatic nature of the instrumem, the program is able to look at 

diurnal variations in the species. Data are not collected on 

Sundays or Monday mornings unless special operators arc on site 

to add liquid nitrogen to the instrument. 

1.2. B ARROW 0BSERVA TORY 

D. E~DRES AND :-.t. GAYLORD 

1.2.1. OPERATIONS 

During the summer of I 88 I Lt. P.H. R.iy (U.S. Navy) was 

sent to Barrow, Alaska, with a small party to collect data on 

meteorology, natural history, magnetism, and other phenomena. 

This program lasted 3 years. A permanent weather observing 

program was started in I 946 and continues today under the 

National Weather Service. The United States Geological Surve} 

(USGS) began a permanent magnetic observatory program in 

1949 that cominucs today as one of 14 magnetic observatories in 

the United States. In January of I 973 the National Oceanic and 

Atmospheric Administration (NOAA) began a program of 

observations to detect changes in levels of background 

constituents that may force climate change. A network of four 

stations was planned with Barrow as the northernmost site. 

The Barrow Observatory, Barrow, Alaska (BRW) celebrated 

25 years of operation in January I 998. From a small program 

started in I 973 the station has grown to the point where almost 

every major global change study that passes through the Arctic 

has some connection with BRW because of the number (over 40) 

and longevity (some over 20 years) of programs and the qualit} 

of data produced there. Station personnel are often called upon 

to help with a wide range of scientific studies from a variety of 

sources. BRW has enjoyed the longest period of personnel 

stability to date with the station chief passing I 5 years and the 

electronic engineer passing 5 years of service. 

Outreach 

In March I 998 the station was visited by a delegation from the 

U.S. Postal Service, including the Postmaster General, when they 

were in town to celebrate the first-day issue of Arctic animal 
series stamps and to announce the approval of funds for the 

construction of a new post office in Barrow. Also in the group 

were several members of the U.S. Senate staff from the 

appropriations committee. 

Three television documentaries were filmed at BRW over the 

past 2 years. A film crew from Japan was in town for 2 days and 

filmed station acti vities. A crew from Italy filmed for a day for a 

popular science program in Italy geared towards 8- 12 year olds. 

The British Broadcasting Corporation (BBC) filmed at the 

station for 2 days for a documentary dealing with the possible 

consequences of climate change. An American Broadcasting 

Corporation (ABC) affiliate was in town to film several 5 minute 

segments for broadcast in San Diego during the weather segment 

of the news. 

BRW station personnel were called on by the local high 

school to help judge the science fair. In 1997 a Barrow project 

was sent to state where it placed near the top, and in 1998 a 

project won first place at the state level. The local community 

college, lllisagvik, tapped the expertise of the station technician 

to help with curriculum development for technical trades. 

The station chief continues to be involved with the Barrow 

Arctic Science Consortium and is a member of the Barrow 

Environmental Observator) Management Committee, and 

attended a meeting sponsored by the National Science 

Foundation held in December 1998 to have as many Arctic 

research programs as possible discuss the needs and future of 

support needed. Based on material developed at the workshop, a 

report was issued (Arctic Research Co11sorti11111 of the U.S. 

(ARCUS), 1999]. 

Station Concerns 

A new 1998 Ford pick-up replaced the 1992 Ford picJ..-up. The 

old truck was sold in place and saved CMDL the cost of backhaul 

for the old truck. Two nC\\ snow machines were secured as 

replacements for the two older machines purchased in 198-l. 

Roadwork continued with all but the last 9 1 111 being completed 

by the fall of 1999. Plans call for completion by summer of 2000. 

Road construction costs in Barrow arc astronomically high, so an 

agreement was worked out with lllisagvik, the local community 

college. to have students in the heavy equipment operators class 

build the road and a consortium of government agencies provide 

the materials. Costs were shared by CMDL, the Department of 

Energy Atmospheric Radiation Measurement (ARM) Program, the 

L'SGS. and the , ational Science Foundation (NSF). The road is 

approx11nately 9 15 m (3000 ft) long and one lane wide. TI1c road 

had sunk into the tundra to the poim where several places were 

lower than the surrounding tundra, causing blockage by drifting 

snow every winter. The road was closed to vehicular traffic from 

about October umil about June each year and snow machines were 

used to get to the station from the Distant Early Warning <DEW) 

line site. The new road will eliminate a less than ideal travel 

slluation. 

Funds \\Cre secured for Phase 2 of the master plan for upgrades 

at BRW. Phase 2 calls for a new garage to be built in place that 

\\ill house compressed gas cylinders as well as cargo and vehicles. 

Warm storage is in high demand as building costs are prohibitively 

high. The ability to park the vehicles in a warm place during the 

day saves on wear and tear to a very large degree. 

The computer network at BRW was greatly enhanced by the 

wnnection to a T-1 line provided by the ARM program. The Tl line was pan of a reciprocal agreement with the ARM program 

that allowed them access to land withdrawn by NOAA and 

personnel support whenever possible. Equipment needed to 

record data for wcathersondcs launched by the ARM program is 

housed at BRW, and BRW personnel helped write programs to 

transfer data to the ARM program computer located at the 

Ukpeagvik lnupiat Corporation (U!C) Naval Arctic Research 

Laboratory (NARL) facility. Balloons are launched once per day 

by ARM program personnel, and the data are formatted and 

transferred once per day by BRW personnel. 

7 

1.2.2. PROGRAMS 

Table 1.2 lists programs for 1998-1999 at BRW. Operational 

highlights follow. 

Aerosols 

The upgraded aerosol cquipmem was described in the CMDL 

Summary Report No. 24, 1996-1997 [Hof111a1111 et al., 1998]. It 

worked well during the entire 2-yr period with the cxcep11on of 

the Thermal Systems Inc, (TSI) CN counter. It was discovered 

that the TS! data was being affected by the cooling fans in the 

aerosol rack. The instrument was being cooled to the point that 

the alcohol was not evaporating and data counts were too low. 

Station personnel built an acrylic enclosure to minimize cooling 

by the rack fans. Data collected at BRW continue to show a 

springtime high in CN concentrations along with the buildup of 

the Arctic haze. 

Solar Radiation 

Barrow snowmelt date cominucs to be one of the most talked 

about programs at the station. An annual graph is provided by 

the CMDL Solar Radiati on group in Boulder and is the most 

sought after graph on site. The graph shows the melt trends from 

the NWS office 111 the town of Barrow, the melt date as measured 

by BRW radiation mstrumcnts, and the date of the first egg from 

a study of Guillemot birds on a nearby island. The Guillemot 

will not lay eggs on Cooper Island, the nesting grounds for the 

birds, umil the snow co\·cr is minimal. All three graphs shO\\ a 

trend towards an earlier melt date. 

An Epply pyranomctcr was installed at about the I 5-m level 

on the tower in 1998. It measures upwelling radiation and will 

be helpful for albedo mcasuremems. A shade was installed to 

block the tower and station from the field of view of the 

instrument, minimizing any error due to obstructions from the 

direction of the station. 

Carbo11 Cycle 

Carbo11 dioxide. C02 mixing ratios as high as 375 ppm were 

seen during 1998-1999. Values as low as 355 ppm were also 

noted. TI1e high values were among the highest average values 

ever. 

The Siemens Ultramat 5-E continues to serve as the main C02 

station instrument and worked well the entire period without any 

major problem. Calibrations were performed at regular intervals. 

Methan e. The HP6890 gas chromatograph continued to run 

well with minimal intervention. Data show a clearly defined 

frequency with high values occurring in the winter months and 

low values in the summer. 

Carbon monoxide. A Trace Analytical gas chromatograph has 

been the station instrument since 1991 and continued to run with 

minimal routine maintenance that included changing a scrubber for 

Hg and replacing the UV lamp in the detector section. 

Flask samples. Flask samples were collected as available and 

as scheduled. There were no major problems with the flask 

program. Isotopic composition measurements of C02 continues, 

and data from this program can be found in other sections of this 

summary report. 
TABLE 1.2. Summary of Measurement Programs at BRW in 1998- 1999 

Program 

Gases 

C02 

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

180 /160 of C02 

CH. 

Surface Oi 

Total Oi 

N20, CFC- I I, CFC-12, CFC-11 3, 

CH1CC'3, cc1. 

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

CH1CCl3, CCI •• SF6 , HCFC-22. 

HCFC-141 b, HCFC-142b, C H,Br, 

CH3CI, CH2Cl2, CHCI" C2HC'1, 

C2CI,, H- 130 I, H-12 11 , H-2402, HFC- I 34a 

CFC-I I, CFC-12, CFC- 11 3, N10 

CCI,. CH1CCl1 

Instrument 

Siemens Ultramat SE analyzer 

3-L glass fla sks 

0.5-L glass flasks, through analyzer 

0.5-L glass flasks, P3 pump unit 

Carle automated GC 

Dasibi ozone meter 

Dobson spectrophotometer no. 9 1 

850-mL, 2.5-L, and 3-L stainless steel flasks 

850-mL, 2.5-L, and 3-L stainless steel flasks 

HP5890 automated GC 

N20 Shimadzu automated GC 

CO Trace Analytical GC 

CFC- I I, CFC- 12, CFC-1 13, N20, CH3CCI,, CCl4 , Automated CATS GC 

CH3Br, CH3CI. H- 12 11, SF6, HCFC-22 

Aerosols 

Condensation nuclei 

Optical propertie s 

Black carbon 

Solar Radiation 

Global irradiance 

Direct irradiance 

Albedo 

Te rrestrial (IR) Radiation 

Upwellin g and downwelling 

Meteorology 

Air temperature 

Dewpoinl te111pc.:ra1ure 

Pressure 

Wind (speed and direc1ion) 

Preci pi tat ion 

Cooperative Programs 

Total surface partic ulates (DOE) 

Precipitation gauge (USDA) 

Magneti c fie lds (USGS) 

Hg (ATDD) 

co2. 13C, N20 <S IO) 

CH, (Uni v. of Calif.. Irvine) 

0 2 in air (Princeton Uni v.) 

C0 2 fl ux (San Diego State Univ.) 

Magnetic fi e lds (NAVS\VC) 

t\fagne tic micropulsati ons (Uni v. of Tokyo) 

UV monitor (NS F) 

Stud y thaw depth in permafrost (SUNY) 

Total VOC and heavy metals 

(Hokkaido Univ.) 

Pollak CNC 

TS I CNC 

Four-wavelength nephelometer 

Aethalometer 

Eppley pyranomelers wi1h Q and RG8 fillers 

Tracking NIP 

Eppley pyrheliometer with Q. OG I, 

RG2 , and RG8 filters 

Eppley pyranometer 

Eppley pyrgeometers 

Thermistor, 2 leve ls 

Max.-min. thermometers 

Dewpoi n1 hygrome1er 

Capacitance transducer 

Mercurial barometer 

R.M. Young Aerovane 

Rain gauge, tipping bucke t 

High-volume sampler (I fi lter wk'

1

) 

Nipher shield, Alter shield, 2 bucke ts 

3-Component fluxgate mag netometer and to tal fi eld 

proton magnetometer 

Dec lination/inclination magnetometer sample 

Tckran 2537 A Hg vapor analyzer 

5-L evacuated glass flasks 

Stainless steel flasks 

3-L glass flasks 

C02 and H20 infrared gas analyzer and son ic 

anemometer 1

He senso rs 

Mag netometer and cassette recorder 

UV spectromete r 

Temperature probe 

Fi Iler samples 

8 

Sampling Frequency 

Continuous 

I pair wk· I 

I pair wk·l 

I pair wk·l 

I sample ( 12 min)' I 

Continuous 

3 day· I 

I sample mo· I 

I sample mo· I 

I sample h·' 

I sample h· 1 

I sample (6 min)· I 

I sample 11· 1 

I day· 1 

Continuous 

Continuous 

Continuous 

Continuous 

Continuo us 

Discrete 

Continuous 

Continuo us 

Continuous 

I day·' 

Continuous 

Continu ous 

Discre te 

Continuous 

Continuous 

Continuous 

I mo· ' 

Continuo us 

6 sets 1110· 1 

Continuous 

I set wk' 1 (3 fla sks ser ') 

I pair wk·' 

I set (3 mo)' 1 

Continuous, check 

site I wk·l 

I (2 wk )· I 

I (3 wk)' 1 

I scan per 0.5 hour 

Continuous 

I (2 wk)'' 
Meteorology 

A maximum wind speed of 2 1 m s" 1 was recorded during 

1998-1999. The high temperature was 20°C and the low was 

-41°C. Equipment ran well, with only routine calibration and 

maintenance required. All sensor probes were calibrated and 

adjusted as scheduled or needed. 

Ozone 

Total column. The Dobson ran well the entire period with 

only one problem. A clutch in the Q l lever wore out causing 

the lever to fall to the lowest position. The clutch was rebuilt 

by station personnel and seemed to work well. Dobson no. 9 1 

continues to be the station instrument. Values as high as 440 

Dobson Units (DU) and as low as 290 DU were recorded . Data 

collection is not possible during the winter months when the 

sun is below the horizon, but regular calibrations are performed 

to ensure proper operation of the instrument. 

Surface ozo11e. The Dasibi ran well with only routine 

calibrations. Surface ozone is one of the longest running 

programs at BRW and continues to be of value for trend 

analyses. With the addition of a new cooperati ve program to 

measure Hg vapor, surface ozone has taken on a new value. 

There appears to be a strong correlation between surface ozone 

values and Hg \'alues measured at BRW in the spring. 

HATS 

A new system for in situ measurements was installed during 

1998 known as the Chromatograph for Atmospheri c Trace 

Species (CATS). There were a few startup problems to be 

worked out, most notably the chiller for the cryo-cooled 

samples was replaced once, and leaks in the tubing were fixed. 

The compliment of gases now measured in situ for the HATS 

group numbers 11 , nearly doubling the number of species over 

the old system. One of the new gases measured is sulfur 

hcxafloridc, SF6. SF6 is used mostly as a replacement for 

polychlorinated biphenyls (PCB) in transformers and has a 

lifetime in the atmosphere of 3200 years. It is one of the most 

potent greenhouse gases known. 

Cooperative Projects 

BRW cooperative programs are listed in Table 1.2. Only 

projects with major changes are discussed in this section. 

A new project was started with the NOAA Atmospheric 

Turbulence and Diffusion Division (ATDD). The project 

measures precipitable Hg and complements the system in 

place at Alen, Canada. Springtime values seem to have a 

strong correlation with surface ozone and sunrise. Funding 

for this project is through the Environmental Protection 

Agency (EPA). 

Filters that are analyzed for heavy metals were collected for 

Hokkaido University every 2 weeks. A second set of packed 

tubes is collected monthly and is analyzed for volatile organic 

compounds. 

The ARM program is in the final stages of setup, and data 

arc now being collected. The ARM program will complement 

the CMDL program by measuring global change parameters 

that CMDL cannot. Between the two programs, BRW will 

most likely be one or the most comprehensive climate change 

research sites in the world. 

A hi- vol filter collector for the University of Alaska, 

Fairbanks (UAF) was stopped when the pump died. The 

project is on hold until funding can be secured for a new pump. 

All other cooperati\'C research programs continued as before 

with no major problems and no major changes. 

9 

1.3. SAMOA OBSERVATORY 

D. HOLT, J. MICHALSKI, AND E. SANDBERG 

1.3.1. OPERA TIO NS 

Operations at the American Samoa Observatory (SMO) were 

relatively uneventful during 1998-1999, with the station chief 

completing his term and changes in station engineer at the end of 

1998. 

The most signifi cant change to the station came with a 

cooperative agreement between NOAA and the new cellular 

phone company, Blue Sky Communications. Blue Sky saw 

Matatul a Point as an ideal location for one of its many cellular 

phone towers. Since NOAA's own meteorological tower was 

nearing the end of its useful life, it became an excellent 

opportunity to allow Blue Sky use of the property while allowing 

NOAA to use Blue Sky's new tower. The tower was completed 

in May 1999, and throughout the year the experiments that 

depended on the old tower were gradually moved to the new one. 

This process continued into 2000. 

Effective Internet access to the observatory was still not 

available. Despite meetings with the local phone company and 

Peace Sat, a Pacific Islands initiative to connect schools and 

government agencies to the lriternet, no effective connection 

scheme was found, although there is optimism that a connection 

will be possible sometime in 2000. 

The backup diesel generator remains operational but is in 

urgent need of maintenance and pan replacements. Although the 

diesel unit is in decent condition, the radiator, water pump and 

electronic controls all require immediate attention. 

The station facilities are also in need of renovation. Because the 

roof has some mmor leaks, a complete repainting is necessary. 

The interior of the main laboratory is in need of repainting and 

other upgrades, including new electrical wiring and lighting. 

Finally, the old Plcxiglass windows have turned translucent from 

UV exposure and will to be replaced in 2000. 

1.3.2. PROGRAMS 

Table 1.3 summarizes the programs at SMO for 1998-1 999. 

Operational highlights arc as follows: 

Carbon Dioxide 

In situ monitoring and Airkit samples continued wnhout 

interruption during this reporting period. 

Surface Ozo11e 

The Dasibi ozone monitor failed completely in March 1999. 

Because the newer Thermo Electron Instrument (TEI) UV 

photometric ozone analyzer was operational, the loss of the 

Dasibi was not critical. Plans for a new or repaired Dasibi are on 

order for 2000. 

Total Ozone 

The Dobson spectrophotometer continued to operate reliably 

during this reporting period. In December 1998 a new dome was 

installed to replace the old dome that had rusted so badly that it 

could no longer turn to face the sun. 

Ozo11eso11de Balloons 

Weekly ozonesondc flights continued during this reporting 

period using the National Weather Service (NWS) balloon 

inflation facility at the Tafuna airport. 
TABLE 1.3. Summary of Measurement Programs at SMO in 1998- 1999 

Program 

Gases 

COi 

C02. C H, 

C02, CH,, CO, and UC. IRO of C02 

Surface OJ 

Total Oi 

N10 , CFC- I I, CFC- 12. CFC-11 3. 

CHiCC!i, CCI, 

N10, CFC- I I, CFC-12, CFC- I 13. 

C HiCCli. CCI,, SF •. HCFC-22, 

HCFC-141b. HCFC- 142b, C H3Br, CH,Cl, 

C H2Ch. CHCI,, C2HCii, C2CI,, H-130 I, 

H- 121 I, H-2402. HFC- I 34a 

CFC- I I, CFC- 12, CFC- I I 3, N20. 

CCI,, CH1CCli 

N10 

CFC- I I, CFC-12. CFC- I 13, N20, CH3CC11, CCl4, 

CH3Br, CH,CI, H-12 11 , SF •• HCFC-22 

Aerosols 

Condensation nuclei 

Solar Radia1w11 

Global irradiance 

Direc t irradiance 

Di ff use irradiance 

Meteorology 

Air temperat ure 

Dewpoint temperature 

Pressure 

Wind (speed and direction) 

Precipitation 

Cooperatil'e Proi.:rams 

C01, 13C, NiO (S IO) 

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

CFC- 11 3, N10, CCI,, C H,CCI" CH, (S IO) 

Various trace gases (OG IST) 

Bulk deposition (DOE) 

Total suspended particulates (DOE) 

Total s uspended particulates (SEASPAN) 

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

Light hydrocarbons (UCI) 

0 2 (Pri nceton Univ.) 

02 (SIO) 

SIO - Scripps Institu tion of Oceanography 

Instrument 

Siemens Ultramat-5E analyzer 

0.5-L glass nasks, through analyzer 

2.5-L glass nasks, MAKS pump unit 

2.5-L glass nasks, AirKit 

Dasibi ozone meter 

TEI UV photometric ozone analyzer 

Dobson spectrophotometer no. 42 

850-mL, 2.5-L. and 3-L stainless steel nasks 

850-mL, 2.5-L, and 3-L stainless steel nasks 

HP5890 automated GC 

Shimadzu a utomated GC 

Automated CA TS GC 

Pollak CNC 

Eppley pyranometers with Q and RG8 filters 

Eppley pyrheliometer with Q filter 

Eppley pyrheliome ter with Q, OG I. 

RG2, and RG8 filters 

Eppley pyrgeometer with shading disk and Q filter 

Thermistors (2) 

Polished mirror 

Capac itance transducer 

Mercu rial barometer 

R.M. Young Windbird 

Rai n gauge, tipping bucket 

Rain gauge. plastic bulk 

5-L evacuated glass nasks 

HP5880/HP5890 Series II gas chromatograph 

Stainless steel nasks 

Ion exchange column 

High-volume sampler 

High-volume sampler 

30-L pressu ri zed cyli nder 

1-L evacuated stainless steel nasks 

2.5-L glass nasks 

3-L glass n asks 

OGIST - Oregon Graduate Institute of Science and Technology 

DOE - Department of Energy 

SEAS PAN - Sea-Air Exchange Experiment 

UCI - Uni versity of Californi a, Irvine 

URI - Uni versity of Rhode Island 

10 

Sampli ng Frequency 

Continuous 

I pair wk·

1 

I pair wk· 1 

I pair wk·

1 

Continu ous 

Continuous 

4 day· I 

I sample wk· 1 

I sample wk·1 

2 sample h-1 

2 sample h-1 

I sample h-1 

I day· 1 

Conti nuous 

Continuous 

Discrete 

Conti nuous 

Continuous 

Continuous 

Continuous 

I wk·I 

Conti nuous 

Continuous 

I day·I 

I set wk· I (3 n asks ser 1 > 

3 h-1 

I set wk·I (3 nasks set·t> 

Continuous ( I fi lter mo·I) 

Continuous ( I filter wk·I) 

Continuous ( I filter wk· I) 

Biweekly 

3-4 n asks qw t 

2 pair mo-I 

2 sets mo-I (3 nasks set· I> 
Halocarbons and Other Atmospheric Trace Species 

The new Chromatograph for Atmospheric Trace Species 

(CA TS) gas chromatograph was installed in December I 998 and 

ran alongside the older Radiatively Important Trace Species 

(RITS) system. lntercomparison continued through this 

reporting period, and plans for the removal of the RITS system 

will be carried out in 2000. 

Aerosols 

The only aerosol measuring instrument at Samoa is a Pollak 

counter. Daily Pollak observations were conducted throughout 

the year. 

Solar Radiation and Meteorology 

The solar radiation and meteorological instruments continued 

to operate with no significant problems. A member of the 

Ci\IDL Ozone and Water Vapor (OZWV) group visited during 

October I 999 to add an IR pyranometer and to take a current 

theodolite observation of obstructions to the horizon. 

Cooperative Programs 

A complete list of SMO cooperati ve projects is found in Table 

I .3. All operated essentially without problems during this 

reporting period. 

1.4. SOUTH POLE OBSERVATORY 

N. HILL ASD J. MICHALSKI. NOAA CORPS 

1.4.1. OPERATIONS 

The CM DL South Pole Observatory (SPO) is located at the 

geographic south pole of Antarctica at an elevation of 2838 m 

above sea level. The Amundsen-Scott South Pole Station is an 

integral part of the U.S. Antarctic Program run by the National 

Science Foundation (NSF) and was administered by Antarctic 

Support Associates (ASA}, who provided logistical and 

operational support. 

The vast majority of CM DL's projects at SPO are housed 

\\ 1th1n the Clean Air Facility (CAF) that takes up the majority of 

the Atmospheric Research Observatory (ARO) building located 

400 m grid northeast of the main station. The clean air sector is 

defined as an area grid northeast of ARO between grid 340° and 

11 0°. Because the wind blows from this direction more than 

90% of the time at the South Pole, the CAF is ideally situated to 

sample air uncontaminated by the rest of the station. Acti vity 

within the clean air sector is strictly prohibited. 

CMDL's meteorological tower sits on the edge of the clean air 

sector at grid 340° from ARO. Meteorological sensors, sampling 

lines and thermal radiation instruments arc located there. 

CMDL's stratospheric ozonesondc program is conducted from 

the Balloon Inflation Facility (BIF) located grid south of the 

main station. This facility is shared with ASA's meteorological 

department. 

The Amundsen-Scott station receives support from regular 

aircraft flights for only 3 months out of the year from November 

through January. The station, including CMDL's observatory, is 

completely isolated from the rest of the world from February 

through October. During this period, temperatures are too low 

for aircraft to operate safely. As a result , air samples taken 

during the austral winter cannot be returned for analysis until the 

station reopens each November. Data collected in situ arc 

transferred to the home institution regularly via a satellite link to 

the Internet. 

Station power is generally quite reliable but outages do 

occasionally occur. The CAF is equipped with stable power 

supplies for some of the more sensitive equipment. 

1.4.2. PROGRAMS 

Table 1.4 summarizes the programs at SPO for 1998- 1999. 

Operational highlights are as follows: 

Carbon Cycle 

The Siemens continuous carbon dioxide analyzer ran without 

significant problems or changes. Sample flasks were filled 

through the analyzer twice per month and once per week with the 

Martin and Kitzis Sampler (MAKS) portable pump unit. 

Aerosols 

The four-wavelength nephelometer ran continuously without 

any problems. Discreet measurements were made daily with the 

Pollak condensation nucleus counter (CNC). The Thermo 

Systems Inc. (TS!) CNC went off-line on March 23, I 998, after 

the condenser temperature became unstable. Repairs to this unit 

were not possible with the spare parts available. The TSI 

remained off-line for the remainder of the winter until a new 

instrument could be flown to the observatory in November. 

Solar and Terrestrial Radiation 

During the austral summer, all of the solar and terrestrial 

radiation measuring equipment ran without any significant 

problems. In January of 1998 the data acquisition soft ware was 

altered to record I -min averages instead of 3-min averages, as 

had been the case before. After sunset each year the short-wave 

(solar) instruments were taken off-line for the winter. 

11 

Ozone and Water Vapor 

The Dasibi surface ozone monitor ran continuously without 

any significant problems. Discrete measurements of total 

column ozone were taken three times daily during the summer 

months using a Dobson ozone spectrophotometer. Whenever 

possible, total ozone values were obtained in the winter \\ ith the 

Dobson using the full moon as a light source. 

The balloonborne stratospheric ozonesonde program 

continued to run well. Profiles of ozone up to approximately 30 

km were obtained once per week except during the months of 

severe stratospheric ozone depletion (August-November) when 

flights were graduall y increased to one every other day. 

Halocarbons and Other Atmospheric Trace Species 

The two Shimadzu mini-gas chromatographs (GC) continued 

to run without significant interruption. A new automated fourchannel custom-built Chromatograph for Atmospheric Trace 

Species (CATS) was installed in January I 998 to run 

concurrently with the Shimadzus. This new GC is intended to 

replace the older, more limited mini GCs. In addition to the 

automated sampling, sample flasks were tilled twice per month 

to be analyzed in Boulder. 

Meteorology 

The meteorology program ran well with no significant 

problems. Weather observations by station personnel took place 

daily or during changing conditions. 

Cooperative Programs 

SIO. The Scripps Institution of Oceanography (SIO) conducts 

long-term monitoring of C02, 13C/12

C ratio, and N20. Twice per 
TABLE 1.4. Summary of Measurement Programs at SPO in 1998-1999 

Program 

Gases 

C02 

C02. CH, 

Su rface o, 

Total 0 3 

Ozone profiles 

NiO, CFC- I I, CFC- 12, CFC-11 3, 

C HiCCli, CCI,, SF6, HCFC-22, 

HCFC-141 b, HCFC- I 42b, C H3Br, CH3Cl, 

C H2Cl2. C HCli, C2HCI,, C2CI,, H-1 30 l , 

H-12 11 . H -2402, HFC-13-la 

CFC- I I, CFC-12, CFC- 11 3, N20, CH,CCl3, 

CCI, 

CFC- I I, CFC-12, CFC- I 13. N20. CH1CCh. 

CCI,, CH1Br, CH1CI, H- 121 l. SF0, HCFC-22 

Aerosols 

Condensation nuclei 

Optical properties 

Solar Rt1dwtum 

Global irradiancc 

Direct irradiancc 

Alb~<lo 

Diffuse irradiance 

Terrestrtt1/ (IRJ Rt1dit11t1111 

Up\\elling and downwelling 

Meteorology 

Air temperature: 

Pressure 

Wind (speed and direction) 

Frost-point temperature 

Cuoperatitoe Programs 

C02. 11C. NiO (S lO) 

0 2, Ni (S IO) 

To tal surface particulate (DOE) 

lntcrhemispheric 11C/ 12C (CSIRO) 

H102 (Univ. o f Arizona) 

Isotope production (SUNY) 

Trace spec ies in the shallow snow firn (S 10) 

instrument 

URAS-2T and Siemans IR analyzer 

2.5-L g lass nasks, through analyzer 

2.5-L g lass nasks, MAKS pump unit 

Dasibi ozone meter 

Electrochemical cell (ECC) 

Dobson ozone spectrophotometer nos. 80 and 82 

Balloonbo rne ECC sonde 

850-mL, 2 .5-L, 3-L stainless steel nasks 

Shimadzu automated GC 

Automated CA TS GC 

Po llack CNC 

TSI CNC 

Four·\\ avelength nephelomc:ter 

Eppley pyranometers with Q and RG8 filters 

Eppley pyra nometer wi th Q filter 

Net radiometer 

Eppley pyrheliometer with Q, 00 I, RG2, and ROS 

fi hers 

Eppley pyrheliometer wi th Q and RG8 filters 

Eppley pyranometer with Q and RG8 filters, 

downward fa cing 

Eppley pyranometer wi th shading disk and Q filter 

Epple) pyrgeometers 

Platinum resistor, 2- and 20 m heights 

Capacitance transducer 

Mercurial barometer 

Bendix Aerovane 

Hygromete r 

5-L evacuated g lass nasks 

Air sampling pump and nasks 

Hi gh-volume pump and filte rs 

Pump unit , 0.5-L and 5-L flasks 

Snow sample collection 

Pressurized cyli nders 

Sampling lines, pump, 2-L glass fla sks 

Sampling Frequency 

Continuous 

I pair week·' 

I pair twice mo" 

Continuous 

Continuous 

3 day·I 

I wk'

1

, summer, autumn. 

winter; 3 wk·

1

, spring 

I pair mo·1 

2 sample wk·

1 

l sample h'

1 

2 day" 1 

Continuous 

Continuous 

Continuous, summer 

Continuous, summer 

Continuous, summer 

3 day·

1 

Continuous, summer 

Continuous 

Continuous 

Continuous 

Continuous 

Continuous 

l wk·I 

2 day' 1 

Continuous 

Continuou s 

2 mo·

1 (3 n asks sample.1

) 

2 mo·

1 (3 flas ks set·' ) 

Continuo us (4 fi lte rs mo. 1

) 

2 mo·• (2 nasks sel' 1

) 

I wk·'. 2 wk·

1• spring 

NIA, checked once mo·' 

2 yr"' 

month, th ree evacuated glass flasks were exposed to ambient air. 

Three glass flasks were pressurized '' ith ambient air on the first 

and fifteenth of each month for the long-term monitoring of 0 2 

and N2• Air samples were taken at depth intervals from within a 

15-m hole drilled in the snow firn. The sampling hole was 

located within the clean air sector approximately 30 m grid east 

of the Atmospheric Research Observatory. Air samples were 

returned to SIO and analyzed for atmospheric trace species. 

Samples were taken once in the summer and once in the winter. 

DOE. The U.S . Department of Energy (DOE) conducts longterm monitoring of the spatial and temporal distribution of 

specific and anthropogenic radionuclides in the surface air. The 

DOE pump ran continuously without significant problems: filters 

were changed once per week. Also, a monthly sample blank was 

collected once per month. 

12 

CSIRO. The Commonwealth Scientific and Industrial 

Research Organization (CSIRO) monitors the ratio 13C/12C in 

atmospheric C02 for use in a two-dimensional global carbon 
cycle model. One glass flask was pressurized with ambient air 

every 2 weeks. 

SUNY. State University of New York (SUNY). Fi ve airfilled 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 by 

SUNY. The cylinders were inspected and cleared of snow once 

per month. Occasionally, the platforms required raising to keep 

clear of drifting snow. 

University of Ariw11a. Snow samples were taken weekly for 

the Univiversity of Arizona to study the snow/atmosphere 

exchange of H20 2. Additionally, snow heights were measured 

from a "sampling grid" inside the clean air sector. 

1.5. METEOROLOGICAL MEASUREMENTS 

T. M EFFORD 

1.5.1. METEOROLOGY OPERATIONS 

llltroductio11 

The climatology of surface meteorological observations at the 

four CMDL observatories is based on hourl y averaged 

measurements of the vector wi nd direction and speed, barometric 

pressure, ambient and dewpoint temperatures, and precipitation 

amount. The meteorological sensors used were selected for their 

high accuracy, as well as their ability to withstand the extreme 

conditions of the polar regions. Data are recorded as I-min 

averages. so the variability within the hourly averages can be 

determined. To the extent that is possible, World Meteorological 

Organization (WMO) siting standards [WMO, 1969] are 

followed. Thermometers are also positioned at the top of the 

sampling towers at l::IKW, MLO, and SPO to measure the 

temperature gradient and to determine the stability of the surface 

boundary layer. 

A detailed description of the PC-based data acquisition system 

may be found in Pe1erson and Rosson [ 1994). Table 1.5 

describes the instrument deployment as of December 3 1, 1999. 

At BRW the complement of sensors measuring meteorological 

variables remained unchanged. In early 1998 and again in early 

1999, the aspirator fan on the dewpoint hygrothermometer was 

replaced. In mid-June 1999 the dewpoint hygrothermometer 

sensor head was replaced since the old one failed at the 

beginning of June. In December 1999 a filter capacitor on the 

main power supply of the dewpoint hygrothermometer was 

replaced. 

At MLO the RS-485 card, which is used by the meteorological 

data acquisition computer to communicate with the sensor 

interface modules, was replaced in March 1998. In March 1999 

the sensor interface modules in the dewpoint hygrothermometer 

and the anemometer that measures the I 0-m winds were 

replaced. In August 1999 the wind speed transmitter on the 

Bendix aerovane was replaced. 

At SMO the biggest change was the move of the anemometer, 

the dewpoint hygrothermometer, and the platinum resistance 

probe from the meteorological sampling tower to the newly 

constructed cellular phone tower near the main building. This 

move took place between July 8 and 24, 1999. Table 1.6 

describes the heights of the sensors before and after the move to 

the new tower. The pressure transducer and the rain gauge 

remained in the same locations. 

At SPO the RS-485 card was replaced in earl y January 1998. 

The aspirator fan in the dewpoint hygrothermometer was 

replaced in early April 1998 and then again later in the month. 

Data Ma11ageme11t 

The meteorological data acquisition system gathers data from 

sensors that operate continuously at each of the four CMDL 

observatories. Data are transferred to Boulder on a daily basis 

via the Internet, except for SMO. The SMO data are transferred 

to Boulder on a weekly basis. Preliminary hourly averages of 

vector wind direction and speed, barometric pressure, ambient 

and dewpoint temperatures, and precipitati on amounts are sent to 

the stations on a daily basis except for SMO, where it is sent on a 

weekly basis. 

A comparison of the number of data points recorded against that 

expected for the year was used to monitor the system's 

performance. Table 1.7 shows the performance of each system in 

1998 and 1999. On average the meteorological data acquisition 

system for the four observatories operated 95.62% and 92.03% of 

TABLE 1.5. CMDL Meteorological Sensor Deployment December 31, 1999 

BRW MLO SMO SPO 

Serial Elevation, Serial Elevation, Serial Elevation, Serial 

Sensor No. m No. m No. Ill No. 

Primary anemometert 14S84 10.S 23 186 10.2 IS94S 22.9 14S83 

Secondary anemometert IS946 38.2 

Pressur<: transducer+ 374199 9.5 374 198 3398.4 374200 78.S 3S8960 

Mercurial barometer 641 9.S 278 3398.4 961 78.S 121SA 

Air temperature A§ 2.4 2.0 18.9 

Air temperature B§'( lS.7 37.4 18.9 

Air temperature C** 2.9 2.0 18.9 

Dewpoint temperature GOOOl 2.9 G0004 2.0 G0008 18.9 G0007 

Rai n gauge -4 0.8 -4 

Heights are in meters above surface, except fo r the pressure transducer and mercurial barometer, which is with respect to mean sea level. 

t Propeller Anemometer, model no. OS 103, R. M. Young Company, Traverse City, Michigan. 

+Pressure Transducer, model no. 270, Setra Systems, Acton, Massachusetts. 

§Platinum Resistance Probe, Logan 41 SO Series, Logan Enterprises, Libeny, Ohio. 

Elevation, 

Ill 

10.0 

284 1.0 

284 1.0 

1.6 

22.0 

2.0 

2.0 

'(Thermometer, positioned at the top of the local sampling tower to facilitate an estimation of boundary layer stability, except at SMO where both 

sensors were at the same height. **Hygrothermometer, Technical Services Laboratory model no. 1088-400, Fon Walton Beach, Florida. 

13 
TABLE 1.6. SMO Sensor Instrument Heights on the 

Old Sampling Tower and the New Cellular Phone Tower 

Old Sampling Tower 

Instrument Sensor Heights (m) 

Primary anemometer 13. 7 

Air temperature A 14.0 

Air temperature B 

Air temperature C 12.8 

Dewpoint temperature 12.8 

New Cellular Phone 

Tower 

Sensor Heights (m) 

22.9 

18.9 

18.9* 

18.9 

18.9 

*Second Platinum Resistance Probe was installed on October 22, 

1999. 

TABLE 1.7. CMDL Meteorological Operations Summary 

Expected Number Percent Data Number of Missing 

Station of Data Points Capture Data Points 

1998 

BRW 4,204.800 99.51% 20,7 16 

MLO 6,832,800 91.06% 611,062 

SMO 3,679,200 95.02% 183,258 

SPO 4,20-l.800 96.89% 130,940 

Average 95.62% 

1999 

BRW 4,20-l,800 98.70% 54,832 

MLO 6,832,800 89.82% 695,350 

SMO 3,778,560 83.60% 619,545 

SPO 4,20-l,800 96.01 % 167,660 

Average 92.03% 

the time for 1998 and 1999, respectively. Because of the remoteness 

of the observatories, power outages are common and are the main 

reason for data loss. Hardware failure, system restarts, and system 

maintenance are the other reasons for data loss. At BRW, during the 

winter time periods, rime, snow, and ice occasionally would build up 

on the sensors and have to be removed by the station personnel. 

• WS >• ll 

30% • SO<=VIS <• '0 0 

0 05<-VIS <•SO 

O CALM 2 f.V, 

20% 

10% 

0% 

N NE E SE s SW w NW 

1998 

1.5.2. STATION CLIMATOLOGIES 

The 23-yr station climatologies are an important record for the 

interpretation of measured val ues of aerosols, trace gases, 

atmospheric turbidity, solar radiation, and the long-term changes 

in the records themselves. The records also serve to outline 

periods of local contamination. 

Barrow 

In Figure I. I histograms of hourly average vector wind 

direction and speed at BRW are presented in 16 direction classes 

and 3 speed classes. Winds from the "clean air" sector, northnortheast to southeast occurred 68.5% of the time in 1998 and 

64% in 1999 as compared with 61.3% for the 21-yr period from 

1977 through 1997 (Figure 1.2). Wind speeds in excess of I 0 

ms·

1 in 1998 (8.7%) and 1999 (5.9%) were less frequent than in 

the 21-yr climatology (11.3%). The average wind speed of 5.5 

ms't in I 998 was the fifth lowest average, while the 4.8 ms' 1 in 

I 999 was the lowest average in the 23 years at the station (Table 

I .8). 

The average air temperature of - 8.7°C in 1998 (Table 1.8), 

was considerably warmer than the 21-yr average of -12.4°C, 

while 1999 (- 12.3°C) was very close to average. A new record 

high temperature was recorded in May 1998, and the record high 

temperature was tied in March 1998. The barometric pressure in 

1998 was 1.8 hPa below the 21 -yr average, while the average for 

1999 was close to normal. September 1999 set a new record 

high pressure for the month, while new record lows were set in 

August 1998, January 1999, and May 1999. The summertime 

precipitation amounts for 1998 (54 mm) and 1999 (40 mm) were 

both below the long-term average of 61 mm. 

Maruia Loa 

The climatology of MLO is best understood when it is 

considered in two distinctive wind regimes, the night 

(downslope) period ( 1800-0559 Hawaiian Standard Time 

(HST)) and the day (upslope) period (0600-1759 HST). The 

2 1-yr night and day wind histogram illustrate the two distinct 

wind regimes (Figure I .3). 

For the night regime, the 2 I-yr wind histogram (Figure 1.3) 

shows that 91.5% of all winds observed had a southerly 

c.:>mponent. The percentage of occurrence of southerly winds in 

1998 was 90.4% (Figure I .4) and 92.5% in 1999 (Figure 1.5). 

W\'JS >z l') 

30% • SO<= WS u X>O 

D 05<• WS <•50 

OCALM 23% 

20% 

10% 

0% 

N NE E SE s SW w NW 

1999 

Fig. 1.1. Histogram of surface winds for BRW for 1998 (lefl) and 1999 (right). Percent frequency of winds is shown for each of 16 direction classes and 3 

wind speed (WS) classes. Percent frequency of calm winds (WS <0.5 ms"

1

) is indicated in the legends and is shown as an open bar on each histogram. 

14 
• ws ,.10 

30% -.----------------~ 50<•WS<•10D 

N NE E SE s SW 

D 0.5<•\'IS <• 50 

D CAl.M 12% 

w NW 

1977. 1997 

Fig. 1.2. Histogram of surface winds for BRW 1977 through 1997. Percent frequency of winds is shown for each of 16 direction classes and 3 wind speed 

(\VS) classes. Percent frequency of calm winds (WS <0.5 ms·1) is indicated in the legend and is shown as an open bar on the histogram. 

• WS >• 10 8 WS >= 10 

30% • SOoWSolOO 30% • SO<•WS <._ 100 

DOSoWS 050 0 0 5 <•\'IS <"' 5 0 

DCALM 28% D CALM 509' 

20% 20% 

10% 10% 

N NE E SE s SW w NW N NE E SE s SW w NW 

1977 • 1997 Day 1977 • 1997 Night 

Fig. 1.3 Histograms of surface ,,;nds for M LO for 1977 through 1997 day (left) and night (right). Percent frequency of winds is shown for each of 16 

d1rccuon classes and 3 " ind speed (\VS) classes. Percent frequency of cairn winds (\VS <0.5 ms.1) is indicated in the legends and is shown as an open bar on 

each histogram. 

•WS >• 10 

30% ~-------------------< 50 <•\'IS<• 100 

D05<• WS <•50 

DCALM 309' 

N NE E SE s SW w NW 

1998 Day 

• WS >• 10 

30% -.----------------~ 50 <• WS <= 10 0 

0 05< .. wS <:;: 50 

DCALM 6.1% 

10% 

N NE E SE s SW w NW 

1998 Night 

Fig. 1.4. Histograms of surface winds for MLO for 1998 day (left) and night (right). Percent frequency of winds is shown for each of 16 direction classes 

and 3 "ind speed (WS) classes. Percent frequency of calm winds (WS <0.5 ms.1

) is indicated in the legends and is shown as an open bar on each histogram. 

15 
TABLE I .8. BRW I 998 and I 999 Monthly Climate Summary 

Jan. Feb. March April May June 

Prevailing wind 

direction 

Average wind 

speed (m s·1

) 

Maximum wind 

speed* (m s·1) 

Direction of max. 

wind* (deg) 

Average station 

pressure (hPa) 

ENE 

6.4 

13 

76 

1022.9 

NE E 

5.2 5.0 

14 13 

56 108 

10 14..l 1011 .6 

Maximum pressure· I 037 I 032 I 038 

(hPa) 

Minimum pressure* 998 994 994 

(hPa) 

Averageair -26.2 -26.0 -19.0 

temperature (°C) 

Maximum temperature• -19 -1 1 - I 

c

0

c> 

Minimum temperature• -39 -36 -3 1 

c·q 

Average dewpoinl -29.0 -29.0 -2 1.3 

temperature (0C) 

i\tax imum dewpoinl -22 -13 -3 

temperature (°C) 

Minimum dewpoint -42 -40 -34 

1empera1ure (

0

C) 

Precipitation (mm) 0 0 0 

Prevailing \\ md 

direcuon 

A vcragc \\ind 

speed (m s·') 

i\tax1mum wind 

speed* (m s'1

) 

Direction of max. 

wi nd"' (deg) 

Average slat ion 

pressure (hPa) 

SW 

3.8 

14 

84 

10 15.4 

NE NE 

4.6 3.7 

10 13 

89 67 

1008.5 1019.3 

i\taximum pressure• 1048 1026 104 1 

(hPa) 

i\linimum pressure 974 997 997 

(hPa) 

Average air -29.0 -26.9 -27.0 

lernperalllrc (°C) 

i\l axirnum 1ernpcra1u re* -9 - 18 -17 

c·c> 

i\linimum temperature• -42 -4 1 -4 I 

c

0

c> 

Average de\\ poim -3 1.7 -29.5 -29.7 

1empera1urc (°C) 

i\lax11num de\\ poim -9 -20 -19 

lempera1ure (°C) 

i\hn1111um de\\ point -46 -45 -46 

temperature ( C) 

Prec1pi1a1ion (mm) 0 0 0 

ENE ENE E 

4.8 6.1 4.4 

14 14 9 

80 62 88 

1008.2 10 12.0 10 15.4 

1029 1023 1024 

993 997 1006 

- I 1.4 -4.8 1.5 

-2 8 18 

-23 -18 -3 

-12.9 -6.2 0.6 

-3 4 10 

-26 -2 1 -4 

0 

E E E 

5.2 4.8 4.3 

13 II 9 

102 104 6 1 

10 18.I 10 16.6 10 14.0 

1037 1035 1020 

99 1 992 100 1 

- 19.8 -5.8 0.1 

-4 6 

-30 -17 -8 

-2 1.8 -6.9 -0.4 

-5 0 2 

-33 -19 -4 

0 6 

July 

1998 

E 

6.4 

12 

92 

10 13. 1 

1023 

1000 

5.3 

IS 

-I 

4.3 

II 

-2 

15 

1999 

E 

5.2 

11 

75 

10 14.6 

1027 

997 

3.9 

17 

-2 

2.2 

12 

-2 

9 

Aug. Sept. Oct. 

E ESE ENE 

5.4 5.0 6.5 

16 14 2 1 

2 19 103 55 

1003 .9 1007.2 10 10.1 

IO l8 102 1 1024 

983 987 983 

5.3 2.8 -4.0 

14 9 3 

- I -4 -19 

4.0 1.3 -6.I 

13 7 2 

-3 -8 -22 

2 1 14 

E E E 

6. 1 4.5 62 

16 13 15 

92 354 104 

1010.2 1008.9 10 15.1 

102 1 1035 103 1 

100 1 985 1000 

4.5 0.4 -8.0 

20 8 -I 

-1 -8 -19 

3.0 -1.4 -10 .7 

12 6 -3 

-4 -10 -2 1 

19 0 

Nov. Dec. Year 

ENE SSW ENE 

6.7 3.3 5.5 

15 12 2 1 

64 79 55 

10 11.0 10 19.1 10 12..l 

1028 1044 1044 

998 991 983 

-10.4 -19 .9 -8.7 

0 -I 18 

-22 -37 -39 

-12.5 -22.0 - 11.0 

0 -I 13 

-25 -4 1 -42 

0 0 54 

ESE SE E 

4.1 5.0 4.8 

17 12 17 

11 3 127 11 3 

10 10.6 101 8. 1 10 14 2 

1035 1041 1048 

993 997 974 

- 18.4 -27.9 - 12.3 

-9 -17 20 

-29 -37 -42 

-20.9 -30.7 -14.8 

-11 -20 n 

-32 -40 -46 

0 0 40 

lnslrumenl heights: wind, 10.5 m; pressure. 9.5 m (MSL); air 1empcra1urc, 2.9 m; dewpoim lempcralure, 2.9 m. Wind and lcrnpermurc instruments 

arc on a lower 25 m northeast of the main building. 

• Maximum and minimum values arc hourly averages. 

16 
• WS >• 10 • WS » 10 

30% • 5.0 <• ws <• 10 0 30% • SO uWS <• 10.0 

D0.5 <• WS <• 5.0 C 0.5 <•\'IS <"" 5.0 

CCAl.M 2.3ll CCAl.M 5011. 

20% 20% 

10% 10% 

N NE E SE S SW W NW N NE E SE S SW W NW 

1999 Day 1999 Night 

Fig. 1.5. Histograms of surface winds for MLO for 1999 day (left) and night (right). Percent frequency of winds is shown for each of 16 direction classes 

and 3 wind speed (\VS) classes. Percent frequency of calm winds (WS <0.5 ms.1

) is indicated in the legends and is shown as an open bar on each histogram. 

Pressure gradient controlled winds (\VS ~ I 0 ms· 1) from 

predominately westerly and southeasterly directions, occurred 

4.6% of the time in 1998 and 3.8% in 1999, both of which were 

below the 21 -yr average of 7 .3%. The annual average wind 

speeds for both 1998 and 1999 were below the long-term 

average (Tables 1.9 and I. I 0). The upslope, or northerly 

component, winds (north-northwest through east-northeast) that 

occurred 2.5% of the time in 1998 and 1999, are the result of the 

daytime upslope now extending into the early evening hours. 

For the day regime the 1998 and 1999 wind histograms 

(Figures 1.4 and 1.5) indicate that winds from the westnorthwest through east-southeast occurred 63.6% of the time 

in 1998 and 59.9% of the time in 1999 compared with 58.4% 

for the 21-yr climatology (Figure 1.3). Pressure gradient 

controlled winds (\VS ~ I 0 ms· 1

) occurred 3.6% of the time in 

1998 and 2.9% of the time in 1999, both of which were lower 

than the 21-yr average of 6%. In 1998 and 1999 the pressure 

gradient winds, which are usually associated with storms, 

followed the expected pattern of fewer occurrences during the 

day regime. The day wind histogram is more uniforml y 

distributed in the light wind classes than the night wind 

histogram. This is due to the variable wind directions during 

the transition periods at dawn and dusk, most of which are 

included in this regime. 

The average ambient temperatures for 1998 and 1999 

(Tables 1.9 and I. I 0), combining both day and night regimes, 

were 8.2°C and 7.2°C, respectively, both of which were above 

the long-term average of 7. I °C. April 1999 and October 1999 

both tied the minimum record temperature for the month. The 

average barometric pressure for 1998 (68 1.1 hPa) was above 

the long-term average of 680.4 hPa, while 1999 (680.0 hPa) 

was below the long-term average. The months of February, 

April , and July in 1998 each tied their maximum values for the 

month. The precipitation amounts in 1998 (66 mm) and 1999 

( 106 mm) were both much lower than the long-term average 

of480 mm. 

Samoa 

A comparison of SMO's 1998 and 1999 wind histograms 

(Figure 1.6) to that of the 21-yr period (Figure 1.7) shows a 

considerably lower percentage (46%) of clean air sector winds 

(north-northwest through southeast) in 1998 while 1999 

17 

(72.4%) was considerably higher than the long-term average 

of 60.3%. The occurrence of winds in the 10 ms·' or greater 

class was 5.4% in 1998 and 4.7% in 1999, while the expected 

occurrence based on the 21-yr average is 4.8%. The annual 

average wind speed for 1998 (5.9 ms"1

) was above normal, 

while 1999 (4.5 ms.

1

) (Table 1.11 ) was slightly below the 

long-term-average of 4.9 ms· 1

• 

The average ambient temperatures for 1998 (26.2°C) and 

1999 (26.7°C) were cooler than the 21-yr average of 27. 1°C. 

Record minimum temperatures were tied in July 1998 and 

October 1999. The average barometric pressures for 1998 

(I 002. 1 hPa) and 1999 (I 001.8 hPa) were higher than the 21-

yr average of 1000.3 hPa. High-pressure records were tied in 

the months of May, August, September, and October of 1998. 

A new high-pressure record was set in July 1998 that also ties 

the all time record high in 23 years of observations at SMO. 

The precipitation amounts in 1998 ( 11 72 mm) and 1999 (1858 

mm) were drier than the normal amount of 2 108 mm. 

South Pole 

The distribution of the surface wind direction in 1998 and 

1999 (Figure 1.8) shows a percentage of "clean air" sector 

(grid north-northwest through east-southeast) winds of 93.2% 

in 1998 and 92.7% in 1999 similar to the 21-yr average of 

93.9% (Figure 1.9). The percentage of winds in the I 0 ms·

1 or 

greater class was 2.6% for both 1998 and 1999 compared to 

3.9% for the long-term average. The annual average wind 

speeds for 1998 (5.2 ms.

1

) and 1999 (5.0 ms. 1) were slightly 

less than the long-term average wind speed of 5.4 ms· 1. 

The average temperatures for 1998 (-50.0°C) (Table 1.1 2) 

and 1999 (-49.9°C) were cooler than the long-term average of 

-49.0°C. January 1998 and December 1999 both tied their 

record minimum temperatures for the month. The minimum 

temperature in 1998 of -75°C occurred in May and September. 

The minimum temperature in 1999 of -74°C occurred in July. 

The annual average barometric pressure for 1998 (677 A hPa) 

was 1.9 hPa lower than the 21-yr average of 679.3 hPa. while 

the average barometric pressure for 1999 was equal to the 

long-term average. May 1998 tied its record low-pressure 

record, and June 1999 set a new high pressure reading for the 

month, surpassing the old June record by 4 hPa. 
T A BLE 1. 9. M LO 1998 Monthly Climate Summary 

Jan. Feb. March April May June July Aug. Sepl. Oc1. 

Prevailing wind 

direction 

WSW SW SSE 

Average wind 5.2 3.2 4.9 

speed (ms·') 

Maximum wind 16 9 13 

speed" (m s·') 

Direction of max. 2-+9 306 149 

wind* (deg) 

Average station 679.6 682.0 680.9 

pressure (hPa) 

Maximum pressure* 683 686 684 

(hPa) 

Minimum pressure* 671 678 677 

(hPa) 

Average air 5.4 6.1 5.2 

temperature (0C) 

Maximum temperature* 12 13 I 0 

(OC) 

Minimum empera ure~ 

(oC) 

Average dewpoint 

temperature (°C) 

Maximum dewpoint 

temperature (°C) 

Minimum dewpoint 

temperature (°C) 

Precipitation (mm) 

Prevailing wind 

direction 

-3 

-24.3 

-33 

7 

NW 

-2 

-20.6 -19.1 

7 2 

-33 -35 

0 0 

NNW SE 

Average wind 4.6 3. 1 4.3 

speed (ms") 

Maximum wind 15 12 13 

speed* (m s·') 

Direction of max. 256 310 132 

wind• (deg) 

Averagcstation 679.7 681.9 681.1 

pressure (hPa) 

Maximum pressure* 683 686 685 

(hPa) 

Minimum pressure* 672 678 677 

(hPa) 

Average air 9.7 10.2 9.6 

temperature (°C) 

Maximum temperature* 17 17 15 

(oC) 

Minimum temperature* 

(OC) 

Average dewpoint 

temperature (°C) 

Maximum dewpoint 

temperature (°C) 

Minimum dewpoint 

temperature (

0

C) 

Precipitation (111111) 

-2 

-17.0 

4 

-32 

0 0 

-12.7 -11.2 

7 7 

-3 1 -32 

0 0 

SE SSE SSE 

Night 

SSE SSE SSE SSE 

4.5 2.7 3.6 4.3 2.9 3.0 4.6 

13 9 I I 14 8 10 12 

157 159 169 169 176 159 159 

680.8 680.9 681.5 682.0 68 1.5 680.5 681.4 

684 683 684 686 684 682 685 

678 678 679 679 678 678 678 

5.2 6.5 8.1 6.9 6.8 6.6 6.4 

12 13 17 15 14 12 12 

-I 0 2 2 

-22.0 -17.4 -15.I -13.3 -12.0 -12.9 -13.0 

3 5 5 6 8 7 6 

-38 -3 1 -30 -34 -29 -27 -3 1 

0 0 0 0 0 

Day 

N NNW NE NE NNW NE NE 

4.2 2.9 3.3 4.3 3.0 2.7 3.8 

13 9 10 12 10 8 11 

159 137 155 169 141 157 164 

681. 1 681.1 681.7 682.2 681.7 680.6 681.4 

685 684 684 685 684 683 685 

678 678 679 679 678 678 678 

9.7 10.5 12.3 11.6 10.7 10.5 10.3 

I 5 17 20 18 17 18 I 7 

0 2 5 3 3 2 

-1 1.6 -7.7 -7. 1 -7.4 -3.4 -2.8 -6.3 

6 7 6 8 9 8 8 

-34 -30 -30 -32 -28 -27 -29 

3 0 4 17 3 13 

Nov. Dec. Year 

SSE SSE SSE 

5.2 4.8 4.0 

14 15 16 

159 164 249 

680.8 680.4 68 1. I 

684 684 686 

677 676 67 1 

5.4 4.8 6.2 

10 10 17 

0 -3 

-10.7 -15.5 -16.0 

6 4 8 

-33 -3 1 -38 

7 0 16 

SE SE NNW 

4.4 3.9 3.7 

13 14 15 

149 162 256 

680.8 680.3 681 .2 

683 684 686 

677 676 672 

8.7 8.0 10.2 

15 15 20 

-2 

-7.3 -9.3 -8.3 

8 5 9 

-33 -31 -34 

7 0 50 

Instrument heights: wind. I 0.2 m; pressure, 3398.4 m (MSL); air temperature, 2.0 m; <lewpoint temperature, 2.0 m. Wind and temperature instruments 

are on a tower I 5 m southwest of the main building. 

*Maximum and minimum values are hourly averages. 

18 
TABLE I. JO. MLO 1999 Monthly Climate Summary 

Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. Year 

Night 

Prevailing wind SE S SSE SE SSE SE SSE SE SSE SE SE SE SSE 

direction 

Average "ind 4.S 2.S 4.6 3.2 3.6 3.6 4.6 S. I 3.S 4.6 4.4 S.2 4.3 

speed (m s·

1

) 

Maximum wind 14 S 13 10 10 9 13 14 IS 13 11 13 IS 

speed* (m s·') 

Direction of max. 130 180 I S7 I S6 163 143 I S6 126 I 17 IS I 161 137 117 

wind* (deg) 

Average station 679.4 679.7 678.9 679.1 680.4 680.9 680.S 681.2 680. 1 680.S 680.2 678.7 680.0 

pressure (hPa) 

1-.laximum pressure• 683 683 682 682 683 684 683 684 683 683 683 682 684 

(hPa) 

Minimum pressure• 67S 677 676 676 678 678 678 678 678 675 678 673 673 

(hPa) 

Average air 3.9 2.6 3.1 2.4 5.7 7.3 7.3 7.3 6.3 6.6 S.O 3.3 S. I 

temperature (°C) 

1-.laximum temperature• 10 9 8 II 12 14 14 12 12 II 10 8 14 

c

0

c> 

Minimum temperature* 0 -2 -2 -3 2 3 3 3 0 2 0 -2 -3 

<°CJ 

Average dewpoint -13.5 -1 1.7 - 13.7 -13.4 -11.6 -13.4 -17.3 -10.9 -IS.2 -13.3 -14.4 -6.2 -12.9 

temperature (°C) 

Maximum dewpoint 5 6 6 3 s s 6 8 6 s 4 s 8 

Minimum dewpoint -32 -27 -27 -30 -26 -30 -3 1 -30 -28 -26 -32 -2S -32 

temperature (°C) 

Precipitation (mm) 6 3 0 0 0 0 0 0 0 23 35 

Day 

Prevailing wi nd SE NE SE NNW NE NE SE SE NW NE NE SE NE 

direction 

Average wind 4.6 1.8 3.7 3.1 3.4 3.6 3.9 4.7 3.3 3.9 4.0 S.2 3.9 

speed (m s·

1

) 

Maximum wind 18 S I I 8 10 10 12 15 13 13 12 14 18 

speed* (m s·') 

Direction of max. 145 20 I 147 16 1 156 3 2 136 122 I 15 148 152 I S2 145 

"ind• (deg) 

A\•erage station 679.3 679.7 679.0 279.2 680.S 680.9 680.7 681.2 680.1 680.4 680. I 678.6 680.0 

pressure (hPa) 

Maximum pressure' 683 683 682 682 683 684 684 68S 683 683 682 682 68S 

(hPa) 

Minimum pressure• 67S 676 677 677 678 678 679 678 678 676 677 673 673 

(hPa) 

Average air 7.3 6.3 7.2 6.4 10.0 12.1 11.9 11.8 10. 1 10.7 8.9 6.8 9.2 

temperature (°C) 

Maximum temperature• 16 13 12 14 IS 17 18 18 17 18 14 14 18 

(°CJ 

Minimum temperature• -I -2 -2 -2 3 4 s 4 2 3 2 -2 -2 

c·ci 

Average dewpoint -8.6 -6.7 -7.5 -6.S -6.3 -7 .S -8.3 -4.5 -4.S -6.I -9.2 -S.3 -6.7 

temperature (°C) 

Maximum dewpoint 6 9 I 0 s 6 8 8 12 8 8 s 7 12 

temperature (

0 C) 

Minimum dewpoint -29 -28 -26 -28 -24 -30 -27 -29 -29 -25 -26 -25 -30 

temperature (°C) 

Preci pitation (mm) 2 23 9 11 2 0 0 5 0 16 71 

Instrument heights: \\ 111d. I 0.2 m: pressure. 3398.4 m (MSL): air temperature, 2.0 m: <.lewpoint temperature. 2.0 m. Wind and temperature instruments 

are on a tower 15 111 southwest of the main building. 

•Maximum and minimum values are hourly averages. 

19 
•WS » 10 • WS >= 10 

40% ,-----------=,-------~·5.0 <• WS « 10.0 

D0.5 « WS <= 5.0 

D CALM 1.5% 

40% ,---------------------1• 5.0<•WS « 100 

0 0 .5 <= WS <= 5.0 

C CALM 25% 

20% 

N NE E SE s 

1998 

SW w NW N NE E SE s 

1999 

SW w NW 

Fig. 1.6. Histograms of surface winds for SMO for 1998 (lefl) and 1999 (right). Percent frequency of winds is shown for each of 16 direction classes and 3 

wind speed (\VS) classes. Percent frequency of calm winds (WS <0.5 ms1

) is indicated in the legends and is shown as an open bar on each histogran1. 

• WS >= 10 

40% ,---------------------1•50 <-WS <- 10.0 

C0.5oWS oSO 

C CALM 28% 

N NE E SE s SW w NW 

1977 - 1997 

Fig. 1.7. Histogram of surface winds for SMO 1977 through 1997. Percent frequency of winds is shown for each of 16 direction classes and 3 wind speed 

(WS) classes. Percent frequency of calm winds (WS <0.5 ms'1

) is indicated in the legend and is shown as an open bar on the histogran1. 

• ws >= 10 • ws >= 10 

30% •S.0 <= WS <= 10.0 30% • SO<: WS <= 100 

DO.S<=WS < .. so a OS<.zWS <==50 

CCALM 05% C CALM 0 • % 

20% 20% 

10% 10% 

0% 

N NE E SE s SW w NW ~ N NE E SE s SW w NW 

1998 1999 

Fig. 1.8. Histograms of surface winds for SPO for 1998 (left) and 1999 (right). Percent frequency of winds is shown for each of 16 direction classes and 3 

wind speed (WS) classes. Percent frequency of calm winds (\VS <0.5 ms'1

) is indicated in the legends and is shown as an open bar on each histogram. 

20 
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. 

NW 

5.6 

13 

135 

998.4 

1002 

Minimum pressure* 992 

(hPa) 

Average air 27.2 

temperature (

0 C) 

Maximum temperature• 29 

c

0

c ) 

Minimum temperature* 25 

c

0

c) 

Average dcwpoint 25.0 

temperature (°C) 

Maximum dewpoint 26 

temperature (°C) 

Minimum dewpoint 23 

Temperature (0C) 

Precipitation (mm) 150 

Prevailing wind 

Direction 

Average wind 

Speed (rn s·1) 

Maximum \\ind 

Speed* (rn s'1

) 

Direction of max. 

SE 

3.9 

11 

348 

TABLE 1.11 . SMO 1998 and 1999 Monthly Climate Summary 

Feb. March April May June 

SSE SSE SSE SSE SE 

4.1 4.4 5.9 6.1 8. 1 

II 12 10 11 13 

155 132 132 165 141 

999.8 1000.1 1003.0 1003.7 1003.7 

1006 1004 1006 1007 1007 

995 996 999 1000 999 

27.0 27.0 26.5 25.8 25.6 

30 30 29 27 27 

25 24 23 24 23 

23.8 23.5 22.9 22.0 22.4 

26 26 26 25 24 

22 20 19 18 18 

42 347 18 27 56 

NNW SE ESE SSE SE 

3.7 4.0 3.5 4.2 4.1 

10 9 10 14 12 

330 109 11 5 155 IOI 

July 

1998 

SSE 

6.5 

II 

138 

1004.6 

1009 

1000 

24.4 

26 

2 1 

20.0 

24 

14 

22 

1999 

ESE 

4.8 

9 

139 

Aug. Sept. Oct. 

SSE SSE SE 

7.5 8.0 5.9 

12 13 10 

146 157 127 

1004.2 1004. I 1002.6 

1009 1009 1008 

1000 1000 999 

25. 1 25.7 26.4 

27 27 29 

23 23 24 

22.2 22.7 23.0 

25 25 25 

19 19 18 

10 63 IOI 

ESE SE ESE 

5.5 6.7 5.9 

13 19 13 

151 126 131 

Nov. Dec. Year 

SE NNW SSE 

3.8 5.2 5.9 

10 13 13 

95 344 14 1 

1000.8 999.4 1002.1 

1004 1004 1009 

998 995 992 

27.2 27.2 26.2 

29 30 30 

24 23 2 1 

23.6 23.5 22.8 

25 26 26 

2 1 20 14 

36 300 1172 

SE N SE 

4.2 3.7 4.5 

10 9 19 

3 12 27 1 126 

Wind* (deg) 

Average station 

Pressure (hPa) 

1000.5 1000.2 1000.8 100 1.5 1002.0 1002.9 1003.0 1~.0 1003.3 1002.6 100 1.4 1000.3 1001.8 

Maximum pressure* I~ 1004 1004 1005 1005 1006 1006 1008 1007 1007 1005 1004 1008 

(hPa) 

Minimum pressure ~ 997 995 997 998 999 1000 1000 100 1 999 999 998 997 995 

(hPa) 

Average air 26.2 26.8 27.5 27.8 26.3 26.7 26.6 26.4 26.2 26.I 26.5 27.3 26.7 

Temperature (°C) 

Maximum temperature • 29 29 30 30 30 29 28 28 28 28 28 29 30 

c

0

c> 

Minimum temperature* 23 23 24 24 22 24 23 22 23 21 22 24 2 1 

c·q 

Average dewpoint 24.3 24.7 25.0 25.4 24.4 24.5 23.9 22.7 22.4 22.7 22.9 22.9 23.8 

temperatu re (

0 C) 

Maximum de\\ point 26 26 27 27 26 26 26 25 24 24 25 25 27 

temperature (°C) 

Min11num dewpotnt 2 1 22 22 23 2 1 22 22 19 18 20 20 18 18 

temperature (°C) 

Prec1pttation (mm) 228 160 87 38 360 97 33 75 282 147 195 155 1858 

Instrument heights: wind, 13.7 m; pressure, 78.5 m (MSL); air temperature, 18.9 m; dewpoint temperatu re, 18.9 m. Wind and temperature 

instruments are on Lauagae Ridge, 110 m northeast of the main building. 

*Maximum and mi nimum values are hourly averages. 

21 
TABLE 1.12. SPO 1998 and 1999 Monthly Climate Summary 

Jan. Feb. March 

Prevailing wind N NE NE 

direction 

Average wind 4.5 4.4 5.2 

speed {ms·') 

Maximum wind 9 9 9 

speed* {ms·') 

Direction of max. 359 3 13 

wi nd* (deg) 

A\erage station 686. 1 683.8 678.2 

pressure {hPa) 

Maximum pressure~ 698 694 687 

(hPa) 

Minimum pressurex 680 675 664 

(hPa) 

Average air -27 .5 -38.4 -53.0 

temperature (°C) 

Maximum temperature• -20 -26 -42 

(oC) 

Minimum temperature• -38 -52 -62 

(OC) 

Average dewpoint -30.4 -41.7 -56.3 

temperature (°C) 

Maximum dewpoint -23 -29 -4S 

temperature (0C) 

Minimum dewpoint -42 -S5 -66 

Temperature {°C) 

Precipitation (mm) 0 0 0 

Prevailing v. ind 

Direction 

Average wind 

Speed (m s·'i 

/\1aximurn " ind 

Speed• (m s·') 

Direction of max. 

Wind• (deg) 

NNW 

4.7 

12 

341 

E ENE 

4.6 4.6 

12 10 

9 336 

Average station 690.5 685. 1 681.0 

Pressure (hPa) 

Maximum pressure· 703 695 692 

{hPa) 

/\1inimum pressure 680 674 673 

(hPa) 

Average air -26.0 -4 1.0 -54.0 

Temperature (°C) 

Maximum temperature* -19 -22 -39 

<°CJ 

Minimum temperature* -34 -49 -69 

{°CJ 

Average dewpoint -28.5 -44.5 -57.6 

temperature {°C) 

/\laximum dewpoint -1 9 -24 -42 

temperature (°C) 

Minimum dewpoint -37 -S3 · 73 

temperature {°C) 

Precipitation (mm) 0 0 0 

April May June July Aug. Sept. Oct. 

1998 

ENE ESE E NNE NE ENE NE 

4.9 6.1 5.0 6.2 5.S S. I 5.2 

II 14 10 14 12 11 10 

3 351 346 9 353 28 26 

668.0 675.3 680. 1 673.2 672.6 67S.9 675.6 

681 685 689 684 683 687 696 

658 653 666 659 660 664 662 

-62.2 -58.0 -54.6 -59.1 -63.0 -62.2 -53.8 

-46 -35 -37 -44 -47 -46 -39 

-73 -75 -69 -74 -73 -75 -66 

-64.6 -61.0 -57.8 -6 1.8 -65.8 -65.4 -56.8 

-49 -37 -40 -46 -49 -49 -41 

-76 -78 -73 -76 -76 -79 -69 

0 0 0 0 0 0 0 

1999 

NE N ENE E NE E N 

5.7 6.1 5.3 5.3 6.0 5.1 5.4 

12 12 II 12 14 12 12 

358 10 25 348 32 6 357 

67 1.5 674.5 688.8 675.0 674.8 679.4 67 1.9 

686 692 7 11 690 691 699 688 

660 658 673 660 657 665 659 

-60.6 -56.8 -58.2 -62.7 -56.4 -62.0 -51. I 

-53 -36 -42 -46 -38 -44 -33 

-72 -73 -71 -74 -69 -72 -69 

-64.3 -60.4 -6 1.6 -66.3 -60.3 -65.8 -S4.I 

-56 -38 -4S -50 -4 1 -47 -3S 

-76 -77 -7S -78 -74 -75 -72 

0 0 0 0 0 0 0 

Nov. Dec. Year 

N NNE N 

6.6 3.6 5.2 

14 9 14 

3 18 35 1 

678.5 682.9 677.4 

693 692 698 

667 670 653 

-36.4 -28.6 -50.0 

-23 -2 1 -20 

-48 -34 -75 

-39.2 -31 .5 -52.9 

-26 -24 -23 

-50 -37 -79 

0 0 0 

NNE E ENE 

4.0 3.6 5.0 

9 8 1-1 

17 296 32 

679.9 679. 1 679.3 

698 693 7 11 

662 669 657 

-39.4 -31.5 -49.9 

-32 -24 - 19 

-SI -41 -74 

-43.2 -34.9 -53.2 

-34 -27 -1 9 

-SS -4S -78 

0 0 0 

Instrument heights: wi nd , I 0.0 m: pressure, 284 1 m (MSL): air temperature, 2.0 m: dewpoint temperature, 2.0 m. Wind and temperature instruments 

are on a tower 9 1.4-m grid north-northwest of the Atmospheric Research Observatory. 

*Maximum and minimum values arc hourly averages. 

22 
8 WS >• 10 

30% • S.O <-VIS<• 100 

DOS <•WS <•50 

DCAlM 05'11 

20% 

10% t0% ~~ N NE E S E s SW w --~ NW 

1977. 1997 

Fig. 1.9. Histogram of surface winds for SPO 1977 through 1997. Percent frequency of winds is shown for each of 16 direction classes and 3 wind speed 

(WS) classes. Percent frequency of calm winds (WS <0.5 ms-1

) is indicated in the legend and is shown as an open bar on the histogram. 

Ack11owledgme11t. The Observatory Operations group wishes to 

thank Brad Halter who was responsible for maintaining 

meteorological sensor hardware and electronics maintenance in 

add111on to his many other contributions to CMDL. 

1.6. REFERENCES 

Arctic Research Consoni um of the U.S. (ARCUS), The Future of w1 

Aruic Resource: Reco111111e11datio11s Jro111 1he Barroll' Area Research 

Support \Vorkshop, 10-1 pp., ARCUS, Fairbanks, AK, 1999. 

23 

Hofmann, D.J., J.T. Peterson, and R.M. Rosson (Eds.). Climate 

Mo11i111ri11g and Diag1wstics u1bora1ory S1111111u11y Report No. 24 

1996-1997, 166 pp .. NOAA Environmental Research Laboratories, 

Boulder, CO, 1998. 

Peterson, J.T., and R.M. Rosson (Eds.). Clima1e Mo111tor111g and 

Diag1ws1ics Laboratory No. 22 Su111111ary Report 1993, 152 pp., 

NOAA Environmental Research Laboratories, Boulder, CO, 1994. 

World Meteorological Organization (WMO), Guide to Me1eorolog1rnl 

f11 .w·u111e111t11im1 a11d Observing Praclices, No. 8, Tech Paper J, 

347 pp., World Meteorological Organization, Geneva, 1969. 
2. Carbon Cycle 

P.P. TANS (EDITOR), P.S. BAKWIN, L. BRUHWILER, T.J. CONWAY, E.J. DLUGOKENCKY, D.W. GUENTHER, D.R. Km1s, P.M. LANG, 

K.A. MASARIE, J.B. MILLER, P.C. NOVELLI, K.W. THONING, M. TRUDEAU, B.H. VAUGHN*, J.W.C. WHITE*, ANDC. ZHAO 

2.1. OVERVIEW 

It is the goal of the CMDL Carbon Cycle Greenhouse Gases 

(CCGG) group to improve the understanding of the factors that 

determine the atmospheric burdens of major trace gases 

influencing the earth 's climate, in parti cular C0 2, CH4, and CO. 

The anthropogenic impact on each of these species is large, but 

natural cycles are involved as well. The international climate 

change negoti ations during December 1997 in Kyoto, Japan, 

highlighted the fact that the world has tentati vely started to 

take steps to try to control the steadily increasing climate 

forcing by anthropogenic greenhouse gases. One of the factors 

required for effecti ve policies is a quantitative understanding of 

what controls the atmospheric concentrations. 

Our main tool for studying the global budgets of the trace 

gases is the measurement of atmospheric spatial concentration 

patterns and their changes over time. Two experimental 

methods have been employed from the start of the Geophysical 

Monitoring for Climatic Change program, the forerun ner of 

CMDL: continuous measurements in remote clean air 

locations, namely the four CMDL observatories, and weekly 

pairs of discrete flask samples, also at remote clean air 

locations. Initially the samples were analyzed only for C02, 

but gradually more species have been added (Table 2.1 ). The 

isotopic ratio measurements are being carried out at the 

Institute for Arctic and Alpine Research (INSTAAR) of the 

University of Colorado in close cooperation with the CCGG 

group. Anomalous 170 enri chments are measured in a small 

subse1 of the flasks by a group at the University of California, 

San Diego. The global air samples provide a unique resource 

for narrowing uncertainties of greenhouse gas budgets as well 

as other atmospheric problems. The feasibility of adding 

additional measurements continues to be investigated. 

Information on sources and sinks of the trace gases is 

obtained from their rates of change and from their spatial 

distributions. Numerical models of atmospheric transport, 

operating in both two and three dimensions, provide the 

quantitati ve link. Since this is working "backwards" from 

observed concentrations to the sources causing them, this 

problem is in the class of so-called inverse problems. The 

greatest limitation is sparseness of data, especially in regions 

close to important sources and sinks. Therefore, the spatial 

coverage of the global cooperative air sampling network has 

gradually expanded. Isotopic analyses were added because 

different sources/sinks may be characterized by different 

isotopic "signatures." 

To overcome the limitation of having only measurements 

from the remote marine boundary layer, two new approaches 

were initiated. One is to continuou sly measure a number of 

chemi cal species and atmospheric physical parameters at 

different heights on very tall towers. Mixing ratios (also called 

mole fractions) in the continental boundary layer are highly 

variable, making them more diffi cult to interpret and require 

much more auxiliary data than the traditional marine air 

' flls1i1111e for Arctic and Alpine Research. U11i1•ersity of C11/11rad11 

24 

TABLE 2. 1. Species Analyzed in Samples of the 

Global Air Sampling Network 

Start Precision 

Species Date Method (One Sigma) Collaborators 

C01 1976 NDIR 0.05 ppm (0.02%) 

CH. 1983 GC/FID <I ppb (0.07%) 

co 1988 GC/HgO 0.5 ppb (0.5- 1%) 

Hi 1988 GC/HgO 2 ppb (0.4%) 

C02

13C 1990 IRMS 0.0t3o CU/INSTAAR 

C02'80 1990 !RMS 0.03%0 CU/INSTAAR 

N10 1996 GCIECD 0.2 ppb (0.07%) HATS Group 

SF. 1996 GC/ECD 0.03 ppb (1%) HATS Group 

C02

17

0 1997 IRMS 0.0330 UC San Diego CH}~C 1998 GC/IRMS 0.06%0 CU/INSTAAR 

CU, University of Colorado 

INSTAAR, Institute for Arctic and Alpine Research, University of 

Colorado, Boulder 

UC, University of California 

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 Ro11lcler for analysis. In 

order to provide significant regional-scale constraints on the 

budgets of the gases measured, it is hoped that this method will 

be greatly expanded, especially over North America. 

Since the global coverage of the sampling ne1work is 

unmatched, CMDL plays an active role in bringing together the 

measurements from many different laboratories around the 

world. Toward this end, measurements of standard reference 

gases, as well as actual field samples, are being intercompared. 

The CMDL link with the Commonwealth Scientific and 

Industrial Research Organization (CSIRO, Australia) is 

particularly strong in this regard. For C02 and CO, CMDL 

provides calibrated reference gas mixtures under the auspices of 

the World Meteorological Organization (WMO). 

A common global database for C02, named Globalview-C02, 

is continually assembled, updated, and is currently based on the 

measurements from laboratories in 14 countries, hopefully 

without significant calibration or methodological discrepancies. 

Its intended use is for three-dimensional (inverse) modeling. 

The first data base release was in 1996 and has been updated 

once a year since then (http://www.cmdl.noaa.gov/ccgg/ 

globalview/co2/default.html). Plans are to maintain and enlarge 

this database, as well as assemble similar ones for isotopic ratios, 

CH4, CO, etc. 

Full individual data records and monthly means can be obtained 

for each species for each sampling site from the CMDL World 

Wide Web page (http://www.cmdl.noaa.gov), the ftp file server's 

"pub" directory (ftp.cmdl.noaa.gov), from the WMO World Data 

Center for Greenhouse Gases in Tokyo and from the Carbon 

Dioxide In formation Analysis Center in Oak Ridge, Tennessee. 
2.2. CARBON DIOXIDE 

2.2.1. lN SITU CARBON DIOXIDE MEASUREMENTS 

The mixing ratio of atmospheric C02 was measured with a 

continuously operating non-dispersive infrared analyzer (NDIR) 

at each of the four CMDL observatories during 1998 and 1999, 

as in previous years. Monthly and annual mean C02 

concentrations are given in Table 2.2. These values are 

provisional, pending final calibrations of station standards. 

Preliminary monthly average C0 2 mixing ratios, selected for 

background conditions for the entire record through 1999, are 

plotted versus time for the four observatories (Figure 2.1.) 

A new data acquisition system was installed at the Samoa 

Observatory, American Samoa (SMO) in July of 1998. This 

system uses an Intel CPU-based Unix workstation for controlling 

the C0 2 NDIR measurements. This system replaced the Control 

and Monitoring System (CAMS) data acquisition unit that 

experienced frequent failures. 

At the Mauna Loa Observatory, Hawaii (MLO) in November 

1998, the continuous C02, CH4, and CO systems were moved 

into the Network for the Detection of Stratospheric Change 

(NDSC) building. The computer used for controlling the data 

acquisition was upgraded to an Intel CPU-based Unix 

workstation. The C0 2 analytical system was upgraded using a 

new design (Figure 2.2). These design upgrades were installed 

TABLE 2.2. Provisional 1998 and 1999 Monthly and Annual 

Mean C02 Mole Fractions From Continuous Analyzer 

Data (μ mol mol·1

, Relative to Dry Air 

WMO Mole fraction Scale) 

Month BRW MLO SMO SPO 

1998 

Jan. 369.32 364.99 363.72 361.98 

Feb. 370.29 365.80 363.25 362. 10 

March 370.59 366.95 363.44 362.26 

April 371.27 368.44 363.04 362.58 

May 371.33 369.32 362.90 

June 369. 18 368.79 363.39 

July 36 1.53 367.59 364.83 363.92 

Aug. 357.04 365.63 364.89 364.56 

Sept. 36 1. 14 363.84 364.98 364.86 

Oct. 365.65 364.19 365. 14 364.9 1 

Nov. 368.96 365.36 365.72 364.93 

Dec. 372.56 367.0 1 366. 15 364.88 

Year 367.40 366.49 364.52 363.61 

1999 

Jan. 373.52 367.93 366.55 364.86 

Feb. 373.62 368.80 367.05 364.78 

March 374. 10 369.38 366. 1 l 364.69 

April 374.63 370.77 366.68 364.86 

May 374.81 370.59 366.52 365.06 

June 372.28 370. 12 367.70 365.38 

July 362.85 369.07 367.03 365.70 

Aug. 356.7 1 366.65 367.08 366.09 

Sept. 359.40 364.70 366.54 366.35 

Oct. 364.86 365. 17 366.80 366.48 

Nov. 370.34 66.50 367.33 366.60 

Dec. 372.50 367.89 367.69 366.52 

Year 369.14 368.1 3 366.92 365.6 1 

25 

)7) .. -

llDL-~~'--~~'--~~'--~~L--~~L--~~'--~--' 

1910 19'1S lleO '~ 19111 

YNI 

Fig. 2. 1. Preliminary selected monthly mean C01 mole fractions in dry 

air expressed in ppm (μmo l/mol) at the four CMDL observatories. 

at the South Pole Observatory, Antarctica (SPO) in December of 

1998, and the same changes are planned for the Barrow 

Observatory, Alaska ( BRW) and SMO in 2000. 

This design involved new modul ar hardware to ensure each 

module in the C0 2 system can be replaced easily in case of 

failure. Three new rack-mountable boxes were installed and are 

shown in Figure 2.2 as dashed lines. The first contains the 

hardware for controlling the ambient air sample flow rates and 

pressure from the intake lines and pumps. This box is shared 

with the CH4 and CO analysis systems. The second box controls 

the flow rate and elects the sample or standard gas that flows to 

the C0 2 analyzer. The third box is used for tilling fl asks from 

the ambient air sample lines. 

I

·" ~· 

W1 W2 T 

. .;. "'-::-~ ~ 8-* Prelala'e Aowmeter _,,, 0-10Vm 

- ..... 

C02NOIR 

.-. 

II, II i I 

H20T..., 

. f 

_,f Solenoid valves r ___ :,. 

·, Flowoontrdler flowoontrolle< 

/ 

_0-200oc/mln _ L_ 0-10c:cl{rin 

Fig. 2.2. System schematic for continuous measurement of C0 2. 
Several changes occurred in the way the C02 system operated 

after the upgrade. The four C02 station standards were removed. 

These gases were used to calibrate the two working tanks at 

weekly intervals in order to check for any drift in mixi ng ratio 

for the working tanks. Results of calibrations over many years 

show that the aluminum cylinders used for containing the C0 2 

standard gases were stable. Results from these calibrations did 

not yield enough information to justify the extra effort to 

prepare, maintain, and analyze the results for the station 

standards. In place of the weekly calibrations using the station 

standards, a daily I-hr long "Target" cali bration was introduced 

using a separate Target standard gas. These dail y cali brations 

can be used to track any changes in working gas mixing ratios 

and possibly any changes in the behavior of the C02 analyzer. 

The tubing used for carrying the gases within the system was 

changed to 1.6 mm (1116 in.) OD stainless steel. This tubing is 

much easier to handle than the previous 3.2 mm ( 1/8 in.) OD 

stainless steel and is the same type of tubing used for the CH4 

and CO chromatographic systems. Mass flow controllers are 

now used for controlling the flow rate, instead of a mechanical 

pressure controller previously used. This provides much more 

stable flow rates to the analyzer and increased precision since the 

C02 analyzer is sensitive to flow rate changes. 

90°N 

60°N 

30°N 

oo 

3o·s 

5o·s 

VONGOLIA 

• UIDHAY IS!MD 

• !.'AUNA LOA 

CAPE KUUUKAHI 

i / ' ~ I •'. CHRISTMAS ISLAND 

f 

' ./ . I ' PACIFlC OCEAN CRUISEf}_STER . ISLAND 

~·;; ~'RING HEAD 

2.2.2. FLASK SAMPLE CARBON DIOXIDE 

MEASUREMENTS 

Because the sources and sinks of carbon cycle gases (C02, 

CH4 , and CO) are highly variable over space and time, the 

CMDL global cooperative air sampling network (Figure 2.3) 

provides greater geographic coverage to complement the highfrequency in situ measurements at the four observatories. Air 

samples are collected approximately weekly at 48 land-based 

sites and aboard commercial shi ps. The samples are measured at 

CMDL for C02, CH4, CO, H2, N20, and SF6, and at INSTAAR 

for 13C and 180 of C02• In 1998, 7800 samples were analyzed, 

and in I 999, 7500 samples were analyzed. Samples from seven 

sites are measured for 13

C of CH4 at INSTAAR (section 2.3.3), 

and samples from three sites are measured for 170/160 of C02 at 

the University of California, San Diego. The isotopic and 

mixing ratio measurements are used to calculate sources and 

si nks by numerical inverse techniques or to constrain source/sink 

estimates obtained from process models. 

After several years of intermittent sampling because of 

logistical problems, weekly sampling resumed at Christmas 

Island (CHR) with a new sample collector in November 1998. 

Sampling on the island of Kaashidhoo, Republic of Maldives, 

ALERT ZEPPEUN 

~ 

HAU£Y BAY 

KAZAKSTAN (2) 

• 

CROZET • 

SYOnA 

AMST£RD.W 

.. 

90°N 

60°N 

30°N 

o· 

3o·s 

5o·s 

SOUTH POLE 

goos +-~---.--~--.--.,.----,--~-.----i..:=..t---.--.,.---,--~--,.---~-.---~--r go·s 

100°E 140°E 1 so0 14o·w 100°w 60°W 20°w 20°E 60°E 1 oo·E 

Fig. 2.3. Locations of the Carbon Cycle Greenhouse Gases Group measurement programs including the baseline observatories (squares). cooperative 

global air sampling network (circles), discontinued sites of same (open circles with cross), aircraft venical profiles (stars), and the very tall tower site 

(triangle). 

26 
began in March 1998. Samples are collected at the Kaashidhoo 

Climate Observatory (KCO) in cooperation with the Maldivian 

Ministry of Home and Environmental Affairs and the Scripps 

Institution of Oceanography (SIO). The Kaashidhoo Climate 

Observatory was established as part of the Indian Ocean 

Experiment (INDOEX) project. It is hoped that sampling will 

continue at KCO, although no samples have been received since 

July 1999. Sampling at Point Arena, California, began in 

January 1999, thanks to the cooperation of the lighthouse keeper. 

This site replaces Cape Meares, Oregon, that was discontinued in 

March 1998. Since October 1999 monthly samples are collected 

at Baring Head, New Zealand. The samples are part of an 

intercomparison project with the National Institute for Water and 

Atmospheric Research (NIWA) (New Zealand). One member of 

each flask pair is analyzed at both NIWA and CMDL to evaluate 

the agreement of the two laboratories' analytical methods. Flask 

sampling at the tall tower site in Grifton, North Carolina (!TN) 

ended in June 1999 when the tower measurement program was 

terminated. In October 1998 the sampling program in the South 

China Sea (SCS) was interrupted when the MN Frontier 

Express came off the Singapore-Hong Kong route. Sampling 

will resume if a suitable replacement ship can be found. The 

three-letter codes for two sites were changed to make them 

consistent with WMO conventions. The code for Mace Head, 

Ireland, is now MHD (formerly MHT) and the code for the site 

in Qinghai Province, China (formerly QPC) is now WLG 

(Waliguan Observatory). 

The 1998 and 1999 annual mean C02 mixing ratios calculated 

from smooth curves fit to the data for 48 sites acti ve during 

1998-1999 are given in Table 2.3. Annual means for the 

shipboard data are given in Tables 2.4 and 2.5. 

The globally averaged C0 2 mixing ratios and the long-term 

trend [Tho11i11g et al. , 1989) calcul ated from the global air 

sampling network data for 1979 through 1999 are plotted as 

smooth curves in Figure 2.4a. The global C02 growth rate as a 

function of time is calculated by taking the derivati ve of the 

trend curve (Figure 2.4b). The average C02 growth rate for 

1979-1999 is 1.5 ppm yr" 1

. The C02 growth rate varied from 0.5 

ppm yr" 1 in 1982 and 1992 to 3.5 ppm yr" 1 in 1998, and there is 

no significant overall trend in the growth rate over this period. 

The C0 2 growth rate as a function of latitude and time is shown 

in Figure 2.5. In this figure it is apparent that much of the 

interannual vari ability of the growth rate arises from coherent 

variations on hemispheric to global scales. In some cases the 

growth rate variations originate in the equatorial region and then 

propagate toward higher latitudes in both hemispheres. Also, the 

highs and lows tend to be more extreme at mid- and highnorthern latitudes. The growth rate anomaly that began in 1997 

and peaked at record high values in earl y 1998 is unusual in that 

it appears nearly simultaneously and nearl y as intensely 

throughout both hemisr,heres. 

The C02 and li1 C data were combined with a twodimensional atmospheric transport model [Tans et al., 1989) to 

calculate the C02 sources and sinks underlying the growth rate 

variations. The model results for 1990-1999 are summarized in 

Table 2.6. The 1990-1997 average sources and sinks are shown 

with one sigma standard deviations to indicate the interannual 

variability during that period of time. In 1998 the net global C02 

sink was only 0.5 Gt C compared with an average of 3.4 Gt C 

during the previous 8 years. Marked decreases in both the net 

oceanic and net terrestrial biospheric sinks contributed to this 

change that resu lted in an atmospheric increase of 6.2 Gt C. In 

27 

TABLE 2.3. 1998- 1999 Annual Mean C0 2 Mole Fractions 

From Network Sites 

Code Station 1998 1999 

ALT Alen, N.W.T., Canada 367.2 368.9 

ASC Ascension Island 365.0 366.3 

ASK Assekrem, Algeria 366.6 368.2 

AZR Terceira Island, Azores 365.6 368.8 

BAL Baltic Sea 369.8 371.0 

BME Bermuda (east coast) 366.9 368.7 

BMW Bemiuda (west coast) 366.3 368.5 

BRW Barrow, Alaska 367.4 369.8 

BSC Black Sea, Constanta, Romania 372.2 376.4 

CBA Cold Bay, Alaska 369.3 37 1.2 

CGO Cape Grim, Tasmania 363.7 365.5 

CHR Christmas Island, Kiribati [) 368.3 

CRZ Crozet Island 363.6 [) 

EiC Easter Island, Chile 363.3 365.0 

GM! Guam, Mariana Islands 366.7 367.9 

GOZ Gozo Island, Malta [) [) 

HBA Halley Bay, Antarctica 363.4 365.5 

HUN Hegyhatsal, Hungary 369.3 370.8 

ICE Yestmanaeyjar, Iceland 366.9 368.5 

ITN WITN, Grifton, Nonh Carolina 370.3 [] 

IZO lzana Observatory, Teneri fe 367. 1 368.5 

KCO Kaashidhoo, Maldives 366. 1 [ ) 

KEY Key Biscayne, Florida 367.7 369.3 

KUM Cape Kumukahi, Hawaii 366.9 368.3 

KZD Plateau Assy, Kazakstan 369.4 37 1.0 

KZM Sary Taukum, Kazakstan 365.6 368.0 

LEF WLEF, Park Falls, Wisconsin 367.9 370.1 

MHD Mace Head, Ireland 366.3 368.4 

MID Midway Island 366.6 368.2 

MLO Mauna Loa, Hawaii 366.6 368.3 

NMB Bobabeb, Namibia [) 366.5 

NWR Niwot Ridge, Colorado 366.5 368.4 

PSA Palmer Station, Antarctica 363.7 365.7 

PTA Point Arena, California [] 370.8 

RPB Ragged Point, Barbados 366.3 367.6 

SEY Mahe Island, Seychelles 365.4 366.7 

SHM Shemya Island, Alaska 367.1 368.8 

SMO American Samoa 364.6 366.9 

SPO South Pole, Antarctica 363.8 365.6 

STM Ocean Station M 366.7 368.7 

SYO Syowa Station, Antarctica 364.5 365.7 

TAP Tae-ahn Peninsula, South Korea 370.6 373. 1 

TDF Tierra del Fuego, Argentina 363.6 365.6 

UTA Wendover, Utah 366.9 369.1 

UUM Ulaan Uul, Mongolia 367.5 368.7 

WIS Sede Boker, Negev Desen, Israel 367.9 369.3 

WLG Mt. Waliguan, China 365.7 368. 1 

ZEP Ny-Alesund, Svalbard 367.2 370. 1 

The square brackets indicate insufficient data to calculate the annual mean. 

The 1999 annual means are provisional. 

1999 the oceanic sink was still only a third of the decadal 

average while the terrestrial sink rebounded strongly, leading to 

a near-average atmospheric increase. The two-dimensional 

model results also indicate that the 1998 growth rate anomaly 

was driven predominantly by variations in the tropical zone, 

defined from l 7°S to l 7°N in our model, including a large 

increase in the terrestrial source during late 1997. 
TABLE 2.4. 1998-1999 Annual Mean C02 Mixing 

Ratios From Pacific Ocean Cruises 

C0 2 {ppm) 

Latitude 1998 1999 

30"N 366.7 370.0 

25°N 367.5 370.1 

20"N 367.0 369.3 

15°N 367.3 368.6 

IO"N 366.9 369.5 

5°N 367.0 368.7 

Equator 366.8 368.7 

5•5 365.9 368. l 

10"5 365. I 367.6 

15°5 364.5 367.3 

20"5 364.5 366.6 

25•5 364. 1 366.3 

30"5 364.0 365.9 

35°5 364.2 366.2 

TABLE 2.5. 1998 Annual Mean C02 Mole Fractions 

From South China Sea 

Latitude 

2 1°N 

l 8°N 

15°N 

12°N 

9°N 

6°N 

3°N 

w 

0 

~ 

f-

~ 

1 

.5 

0 

w 

z 

(f) 

-.5 

- 1 

C02 {ppm) 

1998 

369.2 

368.0 

367.6 

367.4 

367.0 

367.5 

367.9 

......... 

E 

Cl. 

Q_ 

N 

0 

u 

.......... 

' >-

{o) GLOBAL MIXING RATIO AND TREND 

360 

350 

340 

{b) GLOBAL GROWTH RATE 

3 

E 2 

Cl. 

Q_ 

N 

0 

u 0 ----- ------·-- ------------- --

79 80 8 1 82 83 84 85 86 87 88 89 90 9 1 92 93 9-4 ~ 96 97 98 99 Y£AA 

Fig. 2.4. (a) Globally averaged C02 mixing rario and long 1erm 1rend for 

1979 through 1999 based on measurements from remote marine 

boundary layer sites in the global air sampling network. (b) The time 

variation of the global COi growth rate calculated as the derivative of the 

trend curve in (a). 

90°N 

w 

0 

30°N ~ fEQ ~ w 

w 

30°S ~ 

90°S 

w 

0 

79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 

YEAR 

Fig. 2.5. C02 growth rate as a fu nction of latitude and time based on marine boundary layer sites. Yellow, orange, and red indicate high growth rates 

(red is >3.5 ppm yr"1

). Purple and black (black is <0.0 ppm yr" 1

) represent low growth rates. The transition between blue and green is the average C01 

growth rate of - 1.5 ppm yr" 1

• 

28 
TABLE 2.6. Annual CO, Source and Sink Strength From 

a Two-Dimensional Atmospheric Transport Model 

Fossi I fuels 

Atmospheric increase 

Oceanic uptake 

Terrestrial biospheric uptake 

GtC=I015g 

1990-1997 1998 1999 

6.3 (0.2) 

2.9 (0.9) 

-2.0 (0.7) 

-1.4 (0.9) 

6.7 

6.2 

-0.6 

0.1 

6.8 

3.1 

-0.7 

-3.1 

Numbers in parentheses denote interannual variations (I a). 

2.2.3. CARBON DIOXIDE STANDARDS AND REFERENCE 

GAS CALIBRATIONS 

The 15 primary WMO standards, ranging in C02 mixing ratio 

from approximately 250 to 520 μmo! mo1' 1

, were calibrated at 

regular yearly intervals by the CMDL manometric system [Zhao 

et al., 1997]. From September 1996 through December 1999 

there were a total of 172 individual manometric determinations 

of the C02 mole fractions (Table 2.7). For comparison the C02 

mole fractions were measured by SIO infrared absorption 

relative to the WMO X93 mole fraction scale (Table 2.7). The 

mean precision of the manometric measurement (standard 

deviation) is 0.13 μmo! mor' . The concentrations analyzed by 

SIO and CMDL in the atmospheric C02 concentration range of 

300 to 400 μmo! mol' 1 are in good agreement; therefore, the 

switch from SIO to CMDL for the maintenance of the WMO 

Mole Fraction Scale does not result in a large shift of the scale. 

The function of the primary standards is to provide continuity to 

the WMO scale as well as a quality-control check on the 

performance of the manometric system. The assigned values of 

the primaries are ultimately determined through the manometric 

analyses repeated at yearly intervals. The column in Table 2.7 

labeled "Old scale" contains the concentration assignments of the 

WMO primary cylinders until the fall of 1999. They are based 

on both CMDL manometric measurements and on the SIO 

infrared determinations but biased toward the larger number of 

SIO data. After the last round of CMDL manometric 

measurements that finished in January 2000, the values of the 

WMO primaries were reassigned and are now completely based 

on the CMDL manometric measurements. The average shift of 

the WMO Mole Fraction scale in the range of 350-400 ppm is 

+0.06 ppm (last column of Table 2.7, not using cylinder no. I 03). 

Because we want to maximize the useful life span of the 

primaries, the primary calibration scale is transferred by way of 

NDIR measurements approximately twice a year to a set of 

secondary standards (not using no. I 03). The secondaries, which 

typically have a useful lifespan of 3-4 years, are in tum used to 

calibrate all other cylinders in which each cylinder is always 

compared to a set of four bracketing secondaries. Therefore, the 

user will see a gradual shift of the calibration scale over a 3-yr 

period of about +0.06 ppm. During 1998 about 432 cylinders 

were assigned a value on the WMO Mole Fraction Scale in this 

way. The reproducibility, in the range between 250 and 520 

μmol mol' 1

, has generally been better than 0.1 μmol mol' 1• In 

the range of 325-425 ppm the reproducibility (one sigma) has 

been 0.0 14 ppm [Kitzis and Zhao, 1999]. 

On request, calibrations can be performed with the 

manometric system well outside of the range of atmospheric C02 

values. Because there is some demand for calibrations well 

above 520 μmo! mor 1

, new primary C02 standards were created 

at the high end of the range at approximately 600, 700, 1000, 

1500, 2000, 2500, and 3000 μmol mol' 1

• This will allow CMDL 

to perform C02 calibrations using the comparative infrared 

absorption technique rather than the time consuming manometric 

determinations. 

Cylinders prepared by CMDL with a specified C02 

concentration undergo the following procedures at the clean air 

pumping station at high elevation (3475 m) on Niwot Ridge, 

Colorado (NWR), 30 km east of Boulder, Colorado. 

New or Recently Hydrotested Cylinders: (!) Cylinder is 

vented and then pressurized twice with dry natural air to about 

20 atm (300 psi) and vented again. (2) Cylinder is filled to about 

TABLE 2.7. Summary of Manometric Measurements of the WMO Primary C02 Standards Expressed as μ mol mot·• in Dry Air (ppm) 

Cylinder Difference 

Serial CMDL SIO Old Scale (mano-old) 

Number N* (ppm) (%) (ppm) (z) (ppm) (ppm) 

110 9 246.66 0.11 246.65 0.25 246.64 0.02 

102 13 304.40 0. 11 304.38 0.09 304.38 0.02 

Ill 14 324.01 0.13 324.01 0.08 324.00 0.01 

130 9 337.27 0.11 337.26 0.08 337.27 0.00 

121 II 349.39 0.11 349.34 0.1 1 349.34 0.05 

103 15 353.37 0.08 353.17 0.11 353.22 0.15 

139 II 360.9 1 0.06 360.81 0.15 360.83 0.08 

105 10 369.40 0.12 369.33 0.17 369.33 0.07 

136 7 381.32 0.15 381.25 0.18 381.27 0.05 

146 11 389.52 0.15 389.51 0.20 389.51 0.01 

IOI 13 396.35 0.17 396.24 0.20 396.24 0.11 

106 9 412.08 0.15 41 1.96 0.24 411.96 0.08 

123 II 423.09 0.18 422.91 0.30 423.03 0.06 

107 16 453.18 0.18 452.79 0.43 452.92 0.26 

132 13 521.35 0.17 521.00 0.83 521.08 0.27 

*Number of CMDL manometric calibrations for each cylinder 

29 
34 atm (5 I 0 psi) with dry natural air and stored for several 

weeks. (3) Before the final fill the cylinder is first vented and 

then spiked with either I 0% or zero C02 in air, depending on the 

desired final mixing ratio. (4) Final cylinder is filled with 

ambient and dried natural air to 135 atm (2000 psi) during which 

the ambient C02 mixing ratio is monitored. (5) When water 

vapor content of the filled cylinder is measured, it must be less 

than 5 ppm, and it is usually less than 1 ppm. Drying is 

accomplished with magnesium perchlorate, Mg(Cl04)i. The 

pump is a Rix oil-less diving compressor. 

Previously Used Cylinders: Steps I and 2 are replaced by 

venting and one fill with dry natural air to a pressure of 20 atm. 

Other trace gases, such as CH4 and CO, can be targeted to 

specified values in the same cylinders. 

2.2.4. MEASUREMENTS OF STABLE ISOTOPES OF 

ATMOSPHERIC C02 

Since 1989 the Stable Isotope Laboratory at INSTAAR has 

measured the stable isotopic composition of C02 from weekly 

flask samples of air obtained from the CMDL network of sites. 

A selection of only six sites and two ships in 1990 began the 

measurement effort that has grown to include approximately 45 

stationary sites in the CMDL program as well as all of the 

shipboard samfiles. During 1999 over 11,000 isotopic analyses 

of o13C and o 80 were made at INSTAAR that included 7500 

flasks and 3200 tank air standards used for calibration. 

Combined with the C01 mole fraction measurements made by 

CMDL, the isotopi c measurements offer a unique tool to 

111 vestigate the sources and sinks of global carbon inferred from 

the spatial distribution of C02. The tracking of large scale 

sources and sinks is an important part of the basis for our 

understanding of the carbon cycle and is one of the key tools 

necessary for making credible predictions about the future C02 

loading of the atmosphere. 

The degree to which isotopic measurements made on 

atmospheric samples are useful is limited by the precision of the 

mass spectrometer used. For example a change of just 0.02%0 in 

813C globally translates into a shift of 1.0 x 109 metric tons of 

carbon between an oceanic or terrestrial source to the 

atmosphere. Hence the measurements need to be of the highest 

precision attainable. In 1990 the program began making 

measurements with a VG SIRA Series 2 mass spectrometer. 

This instrument and extraction system produced an overall 

reproducibility Of 0.03%0 for 013

C and 0.0530 for 01R0 (lcr Of 

nine replicates). A Micromass Optima mass spectrometer was 

purchased and tested in 1996, fitted with a custom manifold and 

extraction system, and has been used since late 1996 exclusively 

for making flask measurements. The overall reproducibility for 

the Optima system is (lcr for replicate analyses) ±0.012%0 813C 

and ±0.031 %c for ~0. The Optima system incorporates an 

automated 40-port custom manifold and a sample extraction 

system using all stainless steel parts and is based on the methods 

that were proven on the SIRA instrument. 

The increased capacity attained with the 40-port manifold 

allowed us to make over 45 ,360 separate analyses on flasks and 

reference gases since the instrument was brought on-line in 

1996. Instrument down time experienced during 1999 is 

calcul ated to be 2%. The combined effect of improved 

precision, increased capacity, and decreased down time, has 

resulted in more high-quality isotopic measurements that help 

characteri ze the present day carbon cycle. 

AdditWn of Aircraft Samples 

Very few changes or improvements were necessary to the 

mass spectrometer, sample preparation system, or protocols 

used in analysis during the last year. However, a few small 

hardware and software modifi cations were made to allow 

aircraft sampling kits to be analyzed for 8 13C and 8 18

0 of C02• 

Protocols identical to normal flask measurements are used with 

the exception that longer pump times are added to evacuate the 

longer manifold connections to the aircraft suitcases. Tank air 

from the Niwot Ridge site was used to fill and test the aircraft 

kits, and results indicated a reproducibility slightly less than 

that of normal flasks. However, on repeated analyses of the 

same 20 aircraft flasks of tank air, the mean 8 13C values 

remained stable (-0.05%0 change) while the mean 8 180 values 

drifted (-0.3830 change), showing what appear to be signs of 

moisture in the flasks from previous samples. These effects 

increase until the water in the flask has equilibrated with the 

C02• These preliminary tests indicate that care should be taken 

to keep the aircraft sample flasks dry initially and to use some 

type of air drying system, particularly when sampling at lower 

altitudes. Thus far, over 400 aircraft flasks have been 

analyzed, and plans continue to allow for increased capacity to 

analyze these types of samples. 

Data Quality Checks 

The measurement protocol that began in late 1996 calls for 

three aliquots of air from a standard cylinder in the middle of 

every 40-flask run on the mass spectrometer. This additional 

cylinder, called the "quality control tank," provided an 

independent check on the performance of the entire system, all 

the way from the manifold, through the extraction system, to the 

ionization in the source of the mass spectrometer, and the final 

data reduction and corrections for N20 and 170 made in 

software. In this manner, the day-to-day quality of data 

produced can be monitored before each run and steps to correct 

problems can be taken immediately. Figure 2.6 shows the 

standard deviation (lcr) for the 8 13C value measured on three 

aliquots of air from a quality control tank measured at midpoint 

during each analysis run plotted as a 10-point running mean. 

The average standard deviation during the entire period 

(November I 998 to May 2000) is 0.010%o and is usually less 

than 0.015%0. The unusually high values (>0.0230) around run 

number 470 may be because of contamination from a reference 

gas regulator and a change in capillaries. The dramatic 

improvement (mean = 0.0061 %0) after run number 720 resulted 

from a cleaning and rebuilding of the mass spectrometer source. 

The more transient fluctuations in between these periods are 

likely the result of water contamination in the manifold 

originating from flasks that contain moist air. 

30 

The same information is shown in Figure 2.7 for 8 180 in the 

quality control tank. The average standard deviation is 0.0-Wlcc. 

The Standard deviation Of 01R0 displays a similar but lagged 

response to the source rebuild relative to the 8 13C record. This 

may be due to the extra time required to remove contaminants 

(including water) from the system following the rebuild. 

Two other key tools in data quality checks have been the 

circulation of the so-called "Classic" standards with three other 

laboratories and the flask lnterComparison Program (ICP). 

INST AAR has and will continue to participate in these 

programs. The Classic standards are five tanks of air with a wide 

range of greenhouse gas constituents, including isotopic 

compositions of C02 that range over several permil. Regulators 
,,......, 0040 

b 0035 

c 0030 0 

:;::; 

ro 0,025 

·:;: 

(]) 0020 "O 

"O 0015 .... 

ro 

(Post-source rebuld) I ~·00003 

"O 0010 c 

ro 0005 U5 0000 450 500 550 600 650 700 750 800 850 

Run number 

Fig 2.6. Ten-point running mean of the standard deviation of the quality 

control tank li13C as a function of run number. The data cover the period 

from November 1998 to May 2000. 

020 

b 

....... 

c 015 

0 

~ > 

(]) 0 10 

"O 

"O 

.... 

ro 

"O 005 c 

ro -(f) 

500 

(Post-sO<Jrce rebuild) 

Mean• 00301 

550 600 650 700 750 800 

Run number 

850 

Fig 2.7. Ten-point running mean of the Slandanl deviation of the quality 

control tank 811'0 as a function of run number. The data cover the period 

from November 1998 10 f\lay 2000. 

are shipped with the tanks lo ensure similar circumstances for 

measurement b) the four different laboratories. This program is 

an important intercomparison tool, but one circuit among four 

laboratories takes many months to complete. The JCP protocol, 

where two or more laboratories sample the same air in flasks that 

go to both laboratories for analysis, provides a method for 

ongoing frequent comparison that has a higher chance of 

illuminating discrepancies between laboratories. However, the 

ICP measurements cannot be repeated, and thus the results carry 

larger error bars. Such programs are essential to the success of 

global integration of isotopic data. 

Sampli11g Humid Air 

Jn samples collected at humid, tropical locations without 

drying, the 0/ 0 measurements are highly variable and 

consistently more depleted in 180 because of the exchange of 

oxygen atoms between C02 and H20 molecules on the walls of 

the flasks. Systematic tests at INSTAAR [Gemery et al., 1996] 

showed that the exchange takes place during storage in the flasks 

when the relati ve humidity of the air sample is above 50%. 

There is also some dependence on the physical characteristics of 

each flask. The problem with wet air can be seen in the 

percentage of flask pairs that are considered similar enough to be 

retained in the data set. In order for a value to be retained, flask 

pair difference must be less than 0.0930 for 813C analyses and 

0.15'7oo for 8180 analyses. The average percentage of flask pairs 

that have been retained at 45 (fixed) stations is 93.4% for 813C 

and only 69.7% for 8180 analyses. The reason for the lower 

success rate in 8180 pair agreement is closely tied to the moisture 

problem as seen in the low pair agreements at sites with high 

humidity (for example, see Figure 2.8). 

31 

80 • 60 • 

• -· •O .. • 

' • 

(]) 20 

1j • • • ::J 

- • 0 ~ 

1\1 .. ....J -20 • 

• ·•O • • 0 

• 0 -60 • • DO 

-80 • 0 

20 40 60 80 100 

Percentage of flask pairs retained 

Fig. 2.8. li'"O (filled circle) and li11C (open square) pair agreement in 

flask samples from the CMDL flask sampling network, plotted by 

latitude. 

Field testing of a new prototype air sampling apparatus began 

at SMO in September 1994 and at Cape Kumukahi, Hawaii 

(KUM) in May 1995. The new Air Kitzis sampler (AIRKIT) 

differs from the older Martin and Kitzis Sampler (MA KS) in two 

important ways: (I) 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 (Figure 2.9). While large 

improvements in the reproducibility were gained when shifting 

analyses from the SIRA to the OPTIMA mass spectrometer, 

future improvements are expected for both o13C and 8180 as 

more flask samples in the network are dried and wet air issues 

are overcome. 

Seaso11ality a11d Temporal Tre11ds i11 Isotopes of C02 

A sample of the isotope data is given in Figure 2.10, which 

shows time series of the C02 mole fraction, 813C, and 8180 at 

Barrow, Alaska, from 1990 through 2000. The striking 

anticorrelation between the seasonal cycles of mixing ratio and 
N ·I Cl 

0 

u 

"-:::> -l 

0 .:: .) 

"' 0 

·l 

0 • 

oO 

.. 

. . 

0 0 

c • 

% 0 

D "-o D 

~~~~~~~~~~~~~~~~~~~-'-~-..J 

1992 1993 199~ 1995 1996 1997 1998 1999 2000 2001 

\EAR 

Fig. 2.9. 1>180 values of atmospheric C02 from Seychelles (Mahe Island, 

4"40'S, 55"10E). Note the swuch to collecting dried air in September 

1998. 

-9.0~~~~~~~~~~~~~~~_J 

1.0 

90 91 92 93 94 95 96 97 98 99 00 

Year 

Fig. 2.10. Isotopic and concentration data for carbon dioxide at Point 

Barrow, Alaska. 

813e, reflects 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 

mixi ng ratio shows an increasing long-term trend because of the 

use of fossi l fuels, the trend of one is to lighter values reflecting 

the depletion in one of fossil fuel relati ve to the atmosphere. 

The seasonal cycle of o1RO lags behind C0 2 and o13e, and 

while its interannual variability shows no steady trend, the 

0 ratio appears somewhat unstable from year to year, most 

likely because of the large isotopic exchanges of oxygen between 

C0 2 and different reservoirs of water in plant leaves and in soils. 

2.3. METHANE 

2.3.1. IN SITU METHANE MEASUREMENTS 

Quasi-continuous measurements of atmospheric methane 

continued at MLO and BRW at a frequency of four ambient 

measurements each hour. The relative precision is 0.07%. 

Details of the measurement techniques and analysis of the in situ 

data through earl y 1994 were published in 1995 [Dl11goke11cky et 

al., 1995]. Daily averaged methane mole fractions (in I 0-9 mol 

mor 1

• nmol mol" 1) are plotted in Figure 2.11 for BRW (a) and 

MLO (b). The data were edited for instrument malfunction using 

a rule-based expert system [Masarie et al., 199 1]. and they were 

selected for meteorological conditions. Briefl y, the BRW data 

are constrained to the clean air sector that includes wind 

direction of020-I 10° and wind speed greater than I m s 1

• MLO 

data are constrained to periods typically with downslope winds 

that correspond to 0000-0659 local time. 

32 

1950 ,......._ 

-g_ 1900 

a. 

:i 1850 

u 

1800 

1800 

,......._ 

-g_ 1 775 

a. 

:i 1750 

u 

1725 

a 

b 

1998 1999 

YEAR 

Fig. 2. 11. Daily mean CH4 mixing ratios for (a) Barrow and (b) Mauna 

Loa for 1998 and 1999. The data are constrained fo r wind regime, and 

they have undergone a quality control step to ensure that the analytical 

instrument was working optimally when they were obtained [Masarie et 

al., 199 1]. 
2.3.2. MEASUREMENTS OF METHANE IN DISCRETE 

SAMPLES 

During 1998-1999 the determination of the global distribution 

of atmospheric methane continued from 48 sampling sites of the 

global cooperative air sampling network. Provisional annual 

mean values for 1998-1999 are given in Table 2.8. Some sites 

that began prior lo 1998 and now have longer, more complete 

records have been added lo Table 2.8. These sites are Assekrem, 

Algeria (ASK); Christmas Island. Kiribati (CHR); Bobabeb, 

Namibia (NMB); Plateau Assy, Kazakstan (KZD); and Sary 

Taukum, Kazakstan (KZM). 

During 1998 an interesting anomaly was observed in the CH4 

growth rate. particularly at mid- lo high-latitudes in the northern 

hemisphere. In Figure 2. 12 preliminary CH4 mole fractions for 

the high northern hemisphere (HNH) are plotted for 1984- 1999 

in panel a, and the ins1amaneous dcseasonalized and smoothed 

growth rate is plotted in panel b. Though the increased growth 

rate in 1998 is unmistakable in Figure 2. l 2b, a better 

appreciation of the magnitude of the anomaly may be achieved 

from Figure 2. l 2c. In that panel, residuals from a function fitted 

10 the zonal means are plotted as a function of lime. The 

function consists of a second-order polynomial and fo ur 

harmonic terms. It is reasonable 10 think of this function as a 

model of methane's average behavior in the atmosphere where 

the pol}nomial represems the long-term average trend and the 

harmonics represem the average seasonal cycle. This "model" is 

consistelll with the previous suggestion that atmospheric CH4 is 

approaching steady state [D/11goke11cky et al., 1998). The 

residuals plolled in Figure 2. I 2c represent deviations from this 

model, and they are the result of perturbations to the "average" 

balance of CH4 sources and sinks. 

Evidem in the residuals is n01se with three cycles y(1 and an 

ampluude varying from 4 to 15 ppb. During 1984-1992 the 

residuals trended upwards, but in 1992 there was a dramatic drop 

in the residuals followed by a decreasing trend through 1997. 

D/11goke11cky et al. [ 1995) suggested that the decreased growth 

rate in 1992 could not be explained entirely by decreased 

emissions from natural wetlands and that perhaps decreased 

emissions from the fossi l fuel sector in the former Soviet Union 

(FSU), coincident with the collapse of that economy, resulted in 

the observed change in growth rate. Although the following is 

quite speculative, one might expect that if decreased emissions 

from wetlands was the only cause of the observed anomaly in 

growth rate in 1992, the upward trend in the residuals should 

have resumed after the wetland emissions recovered. The fact 

that it did not may suggest that emissions from the fossil sector 

in the FSU did contribute to the observed anomaly, and that 

continuing efforts to hall leaks in the natural gas pipelines of the 

FSU may have prevented a return to emission levels prior to 

1992 for this latitude zone. Evidence for this scenario comes 

from two recent studies of CH4 emissions from Russia. 

Reshetnikov et al. [2000) estimated 24-40 Tg y( 1 CH4 emissions 

from the Russian gas industry during the late-1980s and 

early- I 990s. Dedikov et al. [ 1999). using measurements from an 

extensive program in 1996 and 1997 to determine losses from 

Russian gas production and transmission facilities, estimated that 

3.6 Tg y( 1 CH4 were emilled during that time. The dramatic 

decrease in emissions suggested by these studies is not supported 

by our measurements, but decreased production and improved 

efforts to prevent leaks likely did lead to lower emissions. 

TABLE 2.8. Provisional 1998 and 1999 Annual Mean 

CH4 Mixing Ratios From the Air Sampling Network 

Site 1998 1999 

Code Location CH4 (ppb) CH4 (ppb) 

ALT Alert, N.W.T., Canada 1825.3 1831.7 

ASC Ascension Island 1707.7 1714.8 

ASK As~ekrem, Algeria 1770.4 1779.7 

AZR Terceira Island, Azores 1796.8 1805.2 

BAL Baltic Sea 1850.7 1858.8 

BME Bemmda (east coast) 1799.3 1799.4 

BMW Bermuda (west coast) 1789.I 1795.8 

BRW Barrow, Alaska 1836.7 1841.0 

BSC Black Sea, Constanta, Romania 1919.4 1936 9 

CBA Cold Bay, Alaska 1823.5 1826.5 

CGO Cape Grim, Tasmania 1695.3 1705.7 

CHR Christmas Island. Kiribati [] 1736.0 

CRZ Crozct Island 1694.6 [ l 

EiC Easter Island, Chile 1695.8 1705.7 

GM I Guam, Mariana Islands 1754.1 1753.9 

GOZ Gozo Island, Malta (] (] 

HBA Halley Bay, Antarctica 1694.7 170.tS 

HUN Hcgyhatsal, Hungary 1887.5 1893.2 

ICE Vestmanaeyjar, Iceland 1826.9 1827.2 

ITN WITN, Grifton, North Carolina 1853.8 [ l 

IZO lzana Obs .. Tcnerife 1778.8 1782.1 

KCO Kaashidhoo, Maldives 1743.0 [ l 

KEY Key Biscayne, Florida 1788.8 1796.8 

KUM Cape Kumukahi, Hawaii 1777.5 1778.8 

KZD Plateau Assy, Kazakstan 1844.0 1845.6 

KZM Sary Taukum, Kazakstan 1808.4 1812.2 

LEF WLEF, Park Falls, Wisconsin 1841.4 1859.6 

MHD Mace Head, Ireland 1811.7 1822.4 

MID Midway Island 1786.7 1784.2 

MLO Mauna Loa, Hawaii 1755.9 1764.2 

NMB Bobabeb, Namibia (] 1715.3 

NWR Niwot Ridge. Colorado 1787.2 1793.7 

PSA Palmer Station, Antarctica 1694.9 1705.5 

PTA Point Arena. California [] 1822.1 

RPB Ragged Point. Barbados 1758.3 1767 7 

SEY Mahe Island, Seychelles 1717.5 1724.4 

SHM Shemya Island, Alaska 1822.8 1825.3 

SMO American Samoa 1697.8 1713.7 

SPO South Pole, Antarctica 1694.I 1704.7 

STM Ocean Station M 1823.6 1828.2 

SYO Syowa Station, Antarctica 1694.3 1704.7 

TAP Tae-ahn Peninsula, South Korea 1851.8 1859.5 

TDF Tierra Del Fuego, Argentina 1694.7 1706.2 

UTA Wendover. Utah 1799.9 1808.4 

UUM Ulaan Uul, Mongolia 1821.6 1825.8 

WIS Sede Boker, Negev Desert, Israel 1825.6 1828.9 

WLG Mt. Waliguan, China 1790.1 1802.4 

ZEP Ny-Alesund, Svalbard 1830.3 1832.7 

Note: square brackets indicate insufficient data to calculate the annual 

33 

mean. 

In 1998 there was a large positive anomaly in the residuals 

that shows signs of recovering at the end of 1999. Since natural 

wetlands are an important source of CH4 in this latitude zone, 

changes in their emissions are always a possibility when an 

anomalous CH4 growth rate is observed. The two most sensitive 

parameters for CH4 emissions from wetlands are soil temperature 

and soil moisture. In Figure 2.13 air temperature <n and 

precipitation anomalies are plotted for inundated wetland regions 
~ 

.0 

a. 

a. 

I 

(.) 

~ 

._ 

>. 

.0 

Q_ 

Q_ 

I 

(.) 

~ 

.0 

Q_ 

a. 

I • 

(.) 

<l 

1850 

1800 

1750 

1700 

20 

15 

10 

5 

0 

15 

10 

5 

0 

-5 

- 10 

84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 

YEAR 

Fig. 2.12. (a) Methane mole fractions for the high northern latitudes 

(30-90"N; HNH). The solid line is a function (2nd-order polynomial + 4 

harmonics) fitted to the zonal means. The dashed line is a 

deseasonalizcd trend fitted to the zonal means. (b) Instantaneous CH.. 

growth rate for HNH. It is calculated as the derivative of the dashed 

curve in 2. I 2a; (c) Residuals from function (solid line in 2.12a) fitted to 

HNH zonal averages. 

1.0 0.50 

~ 

0 .5 0.25 "O 

p 

E 

_s ..?::- >- 0 0.0 0.00 0 

E E 0 0 c c: <( <( 

..... a. 

-0.5 -0.25 ·2 

ct 

-1.0 -0.50 

84 85 86 87 88 89 90 9t 92 93 94 95 96 97 98 YEAR 

Fig. 2.13. Temperature (black) and precipitation (gray) anomalies for 

northern wetland regions during 1984-1998. 

only; these are used as a proxy for the soil parameters. There are 

clear positive T and precipitation anomalies in 1998. 

Noteworthy are the negative T and precipitation anomalies in 

1992. Using a process-model, large ( 10 Tg) anomalies were 

calculated in wetland CH4 emissions for these 2 years, negative 

in 1992 and positive in 1998 (8 . Walter, Columbia University, 

private communication, 2000). Although uncertainties on these 

estimates are large, they implicate wetlands as a contributor to 

both anomalies observed in CH4 growth rates. Additionally, 

there were large boreal forest fires in North America and Siberia 

during 1998 that potentially contributed to the CH4 growth rate 

anomaly (E. Kasischke, University of Maryland, private 

communication, 2000). Estimates of emissions from these fires 

are ongoing (see section 2.4.1 ). 

2.3.3. MEASUREMENT OF 13C/12C OF METHANE BY 

MASS SPECTROMETRY 

Partitioning atmospheric methane into its bacterial, thermal, 

and biomass burning sources is possible through global 

measurements of its stable carbon isotopic ratio 13C/12C. Ratios 

are expressed in permil (a one pan per thousand relative 

deviation from a standard isotopic ratio). Biological sources, 

such as wetlands, have a characteristic isotopic composition 

(typically -6030) that is more depleted in the heavy isotope, 13C, 

than thermal sources like natural gas (-40%0), which, in tum, are 

more depleted than the biomass burning source (-25%0). The 

measured isotopic ratio of atmospheric methane (-47%0) is a 

composite of these sources, but it is also influenced by the 

enrichment in 13C content (+5%o) that results from the 

destruction of methane by the hydroxyl radical, which is slightly 

more rapid for 12CH4 than for 13CH4• 

An automated system was designed for the analysis of 13C in 

atmospheric methane. Starting in January 1998 the system has 

analyzed pairs of fl asks, on a weekly basis, from six sites (SPO, 

Cape Grim Tasmania (CGO), SMO, MLO, NWR, and BRW) of 

the global cooperative air sampling network. From a sampling 

flask, 200 mL of air is used to achieve a precision of better than 

0.06%0 in less than 15 minutes. The measured precision is 

comparable to that of systems where at least I 00 times as much 

air is used and where the analysis takes more than I hour. 

Starti ng in June 1998 an automated flask manifold was 

introduced that allows for a greater throughput of samples than 

would otherwise be possible. The CMDL standard scale is now 

linked to a scale maintained by the University of California, 

Irvine (UC!). In the summer of 2000 a program that includes 

both CMDL and the UCl laboratories will measure 13CH4 in 

small cylinders collected at NWR. 

34 

Measurements indicate an annual average latitudinal 

difference of approximately -0.5%0 (BRW-SPO) (Figure 2.14). 

The sign of this gradient is explained by the predominance of 

methane sources, which arc generally depleted relative to the 

atmospheric average, in the northern hemisphere, whereas the 

dominant methane si nk, OH, is more evenly distributed. The 

magnitude of the gradient and how it changes seasonally are a 

result of changing OH and source emission patterns. 

Distinct seasonal variations are also evident at each of the six 

sites. At the northern hemisphere sites of BRW and NWR 

seasonal variations appear to be driven by seasonality in source 

emissions, but the variations at the southern hemisphere sites, 

CGO and SPO, appear to be driven by OH seasonality (Figure 

2.15). At MLO and SMO seasonal variations are less distinct. 
·46.6 (/) 2 Cl 0 

·46.B 

iD 

0 

a_ ·47.0 

~ 

(.) 

~ ·47.2 <O 

·47.4 

·47.6 

-1 -0.5 0 0.5 

Sine of Latitude 

Fig. 2. 14. Annual mean latitude gradient of 011C of CH,. 

-46.6 

;n 

0 ·46.8 a.. 

l 

(.) 7o -47.0. 

-47.2 ~ 

~ 

0 0 0 

0 • 

g 0 0 

JFMAMJJASON D 

1720 

1700 Q 

... 

'C' 

t6BO ~ 

t660 

Fig. ~ 15. A'eragc seasonal cycle of CH, and its 11C/12C rauo at Cape 

Gn111 (CGO) and at the south pole (SPO). 

Curiously the amplitude of the seasonal cycle of 813C al CGO 

(0.3%c) cannot be explai ned solely by destruction by OH, while 

the seasonal cycle amplitude of 813C at SPO can be. This is 

especially intriguing in light of the strong similarity in the 

amplitude of the mole fraction seasonal cycles at the two sites. 

The analysis of intra-annual variations in 13C/ 12C at individual 

sites as well as inter-annual variations at all the sites arc likely to 

contribute lo a better understanding of methane budgets on 

continental and global scales. 

2.3.4. t

3

C/12C AND D/H ISOTOPIC RATIO ANALYSIS OF 

METHANE BY INFRARED SPECTROSCOPY 

The goal of this methane isotopic measurement program is lO 

develop a robust infrared absorption spectrometer to measure 

both 13C/12C and D/H isotopic ratios in atmospheric methane 

samples with sufficient sensiti vity to resolve spatial and temporal 

trends. The instrument is being developed in cooperation with 

the Optical Frequency Measurements Group at the U.S. National 

Institute of Standards and Technology (NIST), and samples will 

be obtained from the CCGG global cooperative air sampling 

network to provide a good spatial distribution of sampling sites 

from which to obtain global methane variability data. To date, 

measurements of atmospheric methane 13C/12C and D/H values 

have been largely regional and performed almost exclusively by 

isotope ratio mass spectrometry (section 2.3.3) [Tyler et al., 

1999; Wahlen et al., 1990]. 

Since 13CH4 and 12CH3D have the same isotopic mass, their 

separate measurement requires extensive procedures to convert 

the CH, to C02 and H2. Infrared absorption spectroscopy offers 

a simple, nondestructive way to measure the stable isotopic 

composition of atmospheric methane samples. A mid-infrared 

absorption spectrometer was constructed for stable isotope ratio 

measurements of atmospheric methane. The spectrometer 

employs periodically poled lithium niobate (PPLN) to generate 

difference frequency radiation from two near-infrared diode 

lasers (one at 811 nm and the other at I 066 nm). This technique 

yields about I 0 microwatts of single mode, tunable radiation that 

probes the v3 rotational-vibrational absorption band at 3.4 

microns. The radiation is passed through a multipass absorption 

cell with a path length of 36 m and a volume of 0.3 L. Second 

harmonic wavelength modulation is used to reduce spectrometer 

noise. The current 3cr detection limit is 2 ppb of methane in 50 

torr of air for a noise-equivalent bandwidth of I Hz. 

Since the tropospheric mixing ratio of 12CH3D is close to I 

ppb and is comparabl'! to the instrument detection limit, a 

procedure to concentrate methane samples is requi1ed uo::fure 

isotopic analysis. Methane is extracted from 25 L of air using a 

cryogenic chromatographic column and is injected into the 

multipass cell with a fi nal total pressure of -70 torr. This 

procedure enriches the methane samples by -1000 times. The 

abundance of the rare isotopic species (

13CH4 and 12CH3D) are 

measured relative to 12CH4 by comparing the absorbance of an 

intrinsically strong spectral line of a rare species with a weak line 

of 12CH,. Thus far a precision of 1.7% for the isotope ratios has 

been attained. The precision is limited by long-term spectral 

baseline instabilities arising from optical interference fringes in 

the multipass cell. With spectral baseline subtraction and the 

addition of a reference absorption cell , the precision is expected 

to improve by an order of magnitude. 

2.4. CARBON MONOXIDE 

35 

2.4.1. MEASUREMENTS OF CARBON MONOXIDE 

During 1998- 1999 the study of the global distribution of CO 

in the lower troposphere continued using both air samples 

collected through the CMDL global cooperative air sampling 

network and in situ measurements at BRW and at MLO. In the 

air sampling network conversion of all sites from glass nasks 

with greased stopcocks to those accepcable for CO analysis 

(those fitted with Tenon 0-ring stopcocks) was completed by 

1998, and CO was measured at all active sites in the network. In 

situ measurements at BRW continued uninterrupted, whi le at 

MLO a rebuilt Reduction Gas Analyzer was reinstalled in late 

1998. The 1998 and 1999 provisional an nual mean mixing ratios 

from the in situ measurements at BRW ( 155.9 and 128.2 ppb, 
respectively) were equivalent to the flask results from BRW 

(154.7 and 129.5 ppb, respectively). At MLO interrupted 

measurements provide no annual mean for 1998, but the 1999 in 

situ results (annual mean = 86.5 ppb) agree well with the flask 

measurements (88.0 ppb). These provisional flask and in situ 

values are believed to be somewhat low and are likely to be 

revised upward (section 2.4.2). 

The residuals from a function approximating the annual 

oscillations and trend (the annual cycle as represented by four 

harmonics, the long-term trend by a polynomial [Tlro11i11g et al., 

1989]) were used to examine key features in global and 

hemispheric CO. A high degree of interannual variation was 

seen during 1991 -1999 (Figure 2.16). The sharp decline in 

global CO during 1992 (Figure 2. 16a) has been attributed to the 

effects of the June 1991 eruption of Mt. Pinatubo [Bekki et al., 

1994; Gra11ier et al., 1996). The sharp drawdown is particularly 

evident in the detrended residuals from the southern hemisphere 

(Figure 2. I 6b). As the effects of the eruption diminished in 

1993, CO returned to previous levels (Novelli et al., I 998a; 

Granier et al., 1996). Other variations in the time series 

( 1994-1996) may be related, in part, to vari ations in large scale 

biomass burning. 

CO mixing ratios in the southern hemisphere showed strong 

enhancement in late 1997. The anomaly was largely confined to 

the low latitudes during late 1997. Following this well-defined 

increase, CO remained somewhat high during early 1998 before 

returning to previous levels (Figure 2. I 6b). Strong fires in 

Indonesia, which burned agricultural areas, forests, and peat 

swamps from mid-1997 through early 1998, produced substantial 

amounts of CO (> 77 Tg CO; Levi11e et al. ( 1999]). The 1997 

r-... 

.D 

0.. 

0.. 

0 

u 

r-... 

.D 

0.. 

0.. 

0 

u 

r-... 

.D 

a. 

a. 

0 

u 

20 

15 

10 

5 

0 

-5 

10 

5 

0 

- 5 

-10 

30 

20 

10 

0 

- 10 

1991 1992 1993 1994 t995 t996 1997 t998 1999 

YEAR 

Fig. 2.16. Residuals from zonal average time series, after the average 

seasonal cycle and a third-order polynomi al fit to the trend have been 

subtracted, and a smooth curve fit to those residuals (solid line): (a) 

global, (b) southern hemisphere, and (c) northern hemisphere. 

fires provided at least 35% more CO to the troposphere than 

biomass burning in a typical year. As the seasonal cycle of CO 

in the southern hemisphere is largel y driven by emissions from 

biomass burning [Gra11ier et al., 2000], the fires likely 

contributed substantially to the high CO observed during late 

1997 and early 1998. In the northern hemisphere, a weak 

summer minimum in 1998 was followed by a strong fall 

maximum (Figure 2. I 6c). This period of high CO is also evidem 

in the residuals calculated from in situ measurements at BRW 

(Figure 2.17). For the first time since CMDL measurements 

began at BRW in 1988, autumn mixing ratios in the high 

latitudes of the northern hemisphere surpassed the typical 

seasonal maximum in March/April. The enhancement at Barrow 

was nearly twice that seen in the zonally averaged northern 

hemisphere time series, suggesting the boreal nature of the 

source. Estimates of the extent of burning in Canada, northern 

United States, and Russia during 1998 are twice as high as any 

previous year in the 1990s [Kasischke et al., 1999]. Variations 

in the depth of the northern hemispheric seasonal CO minimum 

(defined as the July/August average mixing ratio) are highly 

correlated with the annual land area burned in the temperate and 

boreal forests (G. Wotawa et al., Boreal forest fires and their 

contribution to northern hemispheric summertime CO 

background concentrations during the 1990s, submitted to 

Nat11re, 2000). The effect of boreal forest fires on the Arctic 

troposphere was also shown in a comparison between CMDL 

CO surface measurements at BRW and total column 

spectroscopic measurements made al Poker Flats, Alaska. In 

winter and late spring 1995 surface measurements of CO were 

greater than the equivalent colunm average. However, during 

May and through September (the primary burning season in 

Canada and Russia) the column measurements were enhanced 

relative to the surface. Emissions from forest fires were 

suspected of providing CO to the free troposphere over Alaska 

[Y11rga11ov et al., 1998). 

36 

'.D 

0. 

~ 

0 

u 

80 

70 

60 

50 

40 

30 

20 

10 

0 

-10 

-20 

- 30 

1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 

Y(AR 

Fig. 2.17. Residuals, de1ermined as in Figure 2. 16, from 1he in si1u 

measuremenls al Poinl Barrow, Alaska. The solid line is the smooth fil 

10 1he residuals. 
2.4.2. CO REFERENCE GASES 

A set of eight CO standards was prepared using gravimetric 

methods by the CMDL Halocarbons and other Atmospheric Trace 

Species (HATS) group in late 1999 and early 2000. Mixing ratios 

assigned to CMDL working standards referenced against the new 

gravimetrics were significantly greater than those previously 

assigned based upon the original scale. The CMDL reference 

scale used in our measurements of atmospheric CO is based upon 

17 standards prepared during 1989-1990 by gravimetric methods 

[Novelli et al., 1991). The scale was transferred to a set of ten 

natural air secondary standards with mixing ratios between 32 and 

201 ppb CO. The standard scale was found to be in good 

agreement with our gravimetric dilutions of a NIST 9.7 ppm CO 

Standard Research Material (SRM), and dynamic dilutions of a 

NIST 10 ppm SRM made at the U.S. National Aeronautics and 

Space Administration (NASA) Langley Research Center and at the 

Fraunhofer Institute in Garmisch-Partenkirchen, Germany. 

Over time the original gravimetric standards, made in highpressure cylinders of a smaller size, were found to drift at rates 

of up to several ppb y(1

, and the scale was maintained through 

the secondary and working standards. Drift in these standards 

was evaluated in two ways: (I) frequent intercomparison of the 

suite of standards maintained at CMDL, and (2) periodic 

preparation of new gravimetric standards. In 1991 the 

instrument with a linear response was changed to a new one that 

exh1b1ted nonlinearity below - l 2S ppb. Therefore, a multipoint 

calibration procedure was necessary to define the instrument 

response. In addition to exhibiting nonlinearity, response 

characteristics changed over time requiring frequent calibration 

of the instrument. This procedure used six to eight standards 

(mixing ratios between SO and 200 ppb) plus a blank (zero air 

passed through Schutze reagent) and daily calibration curves. A 

straight line, second-. and third-order polynomial were used to 

define instrument response [Novelli et al. , l 998a]; the first two 

curve fits were used for diagnostics, and the reported mixing 

ratios were based upon the third-order fit. 

In 1992 three gravimetric standards were prepared, and their 

assigned mixing ratios. based on the gravimetric method, agreed 

well with the CO mixing ratios assigned to the secondary 

standards [No1·elli et al., 1994). The long-term calibration 

histories of the CMDL standards showed no evidence of drift. 

Figure 2.18 shows the cali bration history of one SO ppb working 

standard (ID CCI 147 12). A significant drift was not detected 

through the first half of 1998 (Fig. 2. l 8a), however, higher 

mixing ratios determined in 1999 suggest an increase of 0.2 ppb 

yr'1 (Figure 2. l 8b). 

In 1996 a new set of five standards was prepared using 

gravimetric methods. The mixing ratios assigned to the 

secondary and working standards when referenced against the 

1996 gravimetrics were somewhat higher than those previously 

assigned. In I 999 and 2000 eight gravimetric standards with 

mixing ratios ranging from S3 to 20S ppb were prepared at 

CMDL. The mixing ratios assigned to the secondary and 

working standards referenced to the new gravimetric standards 

were greater than the 1996 results and definitely greater than the 

original values (Table 2.9). Calibration of the new gravimetrics 

using dynamic dilution of a NIST 9.7 ppm SRM confirmed their 

values based on the gravimetric preparation. This surprising 

result lead to a re-evaluation of the CO scale extending back to 

the original standards prepared in 1989 and 1990. Confidence in 

both the original scale and the 1999 gravimetric standards 

! 

8 

8 

a 54 

5J 

51 

50'--~-L~~-'-~--'-'-~---'-'-~-'-~'---'-~--'~~-' 

1992 199.J 1994 1995 1996 1997 1998 1999 2000 

b 

5J 

52 

51 

50~~~~~~~~~~~-'-~~~~~~~~~~ 

1992 1993 1994 1995 1996 1997 1998 1999 2000 

(YEAA) 

Fig. 2. 18. The calibration history of CMDL working standard CC I 14712 

(assigned a mixing ratio = 5 1.9 ppb in 1992). Each poim represents a 

calibration based upon ten or more analyses. Error bars represent one 

standard deviation. (a) History through the first half of 1998, Y = 51.9 

(±0.37) + 5.3 x 10·

1 (±0.086)(X - 1992): (b) History through 1999; Y = 

5 1.2 (±0.3 1) + 0.22 (±0.55)(X-l 992). 

37 

suggests drift in both the secondary and working standards over 

time. Calcul ations of linear drift at rates of 0.8 ± 0.3 ppb y(1 

between I 992 and 1999 are consistent with the 1996 gravimetric 

standards and with intercomparisons involving several other 

laboratories [Novelli et al., l 998b] (K. Masarie ct al., The 

NOANCSIRO Flask Air Intercomparison Experiment: A 

strategy for directly assessing consistency among atmospheric 

measurements made by independent laboratories, submitted to 

Journal of Geophysical Research, 2000). However, drift rates of 

about 1 ppb y(1 are not evident in the calibration histori es of the 

working standards because the working standards and the CMDL 

secondary standards were both drifting at comparable rates. 

To examine whether drift in a sample could be masked by 

drift in the standards, a sensitivity study examined the effects of 

drifting standards on the calibration of simulated samples. 

Artificial area responses of eight standards comprising a 

calibration curve were allowed to change while the assigned 

mixing ratios were kept constant. When upward standard drift 

was not accounted for, the calculated sample mixing ratios were 

lower than the actual value. Combinations of drift in the 

simulated standards, on the order of the apparent rates seen in the 

CMDL standards, and drift in samples at various rates between 0 

and 3 ppb yr"1

, resulted in a range of results. In general if 

samples were drifting at rates similar to those of the standards, 

the appearance of drift was largely hidden within the precision of 

the measurements. 
TABLE 2.9. Mixing Ratios Assigned lo the CMDL Secondary Standards* 

Tank 

ID 

121999 

105460 

68734 

73 11 0 

1989/1990, 

1992 

51.7 

100.5 

159.7 

200.8 

(I. I) 

(1.2) 

(I. I) 

( 1.7) 

56.2 

107.S 

164.4 

202.9 

1996 

(0.7) 

(0.9) 

( 1.0) 

(0.9) 

60.4 

11 0.9 

167.7 

205.3 

1999 

(0.5) 

( I. I) 

( 1.3) 

(0.5) 

NIST Dilution, 

1999 

61.5 

111 .3 

167.0 

207.3 

(1.2) 

(I. I) 

(1.7) 

( 1.5) 

*Mixing ratios assigned to secondary standards by comparison to gravimetric standards prepared in 1989/1990 and 1992; 1996, 1999, and by 

comparison to dynamic dilution of a NIST 9.7 ppm SRM. Uncertainties (lcr) are in parentheses. All mixing ratios are in ppb by mole fraction 

(gravimetric calibrations) or ppb by volume (NIST dilutions). 

Beginning late 1999 a number of standards were assigned 

mixing ratios referenced to both the CMDL working standards 

and the new gravimetric standards. The relationship defined by 

these calibrations (Figure 2. 19) relates mixing ratios assigned 

during mid-1999 to mid-2000 by the original (but drifting) scale 

to mixing ratios defined by the new gravimetri c standards. 

Correcting the time series data is more difficult, but several 

options are available. Most promising is a linear adjustment 

between 1992 and 1999. Results from this approach are 

consistent with both the 1996 and 1999 gravimetric standards. 

300 -

en 

en 200,_ -

0 

u 100-

~~~~~~~~~~~~~~~ ....... ~~~~ ....... 0 100 200 300 400 

CO from working standa rds 

Fig. 2.19. Scatter plot of CO mixing ratios assigned to various natural air 

mi xtures based upon the 1999 gravimetric standards versus the original 

CMDL CO scale. The dashed line shows a third order lit to the data and 

is defined by Y = 0.320 + 1.217 X - 0.00163 X2 + 2.972 x 10"" X3

. The 

solid line represents the one-to-one relationship between the 1999 

gravimetric standards and the CMDL CO working standards. 

2.5. NITROUS OXIDE AND SULFUR HEXAFLUORIDE 

Measurements of N20 and SF6 from all sites in the global 

cooperative air sampling network continued during 1998 and 

1999. A significant analysis problem was found al the end of 

1999. Measurements of N20 and SF6 appeared too high in 

network samples, but the problem was hardly noticeable in the 

record of daily test flasks. After a detailed investigation into the 

problem, the screens installed between the Valeo sample valve 

body and the end of the 1.6 mm (l/16") OD tubing connected to 

the valve were found to be the cause of the problem. These 

38 

screens are used to prevent particles from entering the valve and 

destroying the rotor. Over time, it appears that particles from the 

rotor clogged the screen affecting relaxation of the sample-loop 

pressure to ambient. Sample-loop pressure for samples was 

greater than for standards; therefore, measured mole fractions 

were too large. Once the screens were blown out with 2000 psig 

pressure, the system began working properly. All samples with 

analysis dates between November I, 1999, and March 23, 2000, 

were flagged with "A .. ", indicating a problem during analysis. 

The end date was easy to assign; il is the date the screens were 

blown out and the system reassembled and tested. The exact 

start dale of the problem is unknown. November I is somewhat 

conservative and arbitrary, but all data affected by this subtle 

problem were flagged. Since the magnitude of the error was a 

function of the pressure in the flask al the lime it was analyzed, 

and this pressure is not measured , it was not possible lo apply a 

correction lo the data. 

1l1e N20 and SF6 latitude gradients are presented as lhe mean 

difference in annual means between each site and south pole for 

1998 (Figures 2.20 and 2.21 ). Annual means were determined 

from a smoothed curve filled to all data available through midMay 2000 after outliers had been flagged. The gradients for both 

species are similar; higher values are observed in the northern 

hemisphere than the southern hemisphere, and considerable 

~ 

.D 

a. 

a. 

'-' 

o,,, 

z 

90'5 30'$ EQ 30'N 90'N 

3 • 1998 

• 

• 

2 - • 

• 

• • • •• • 

• • I• •._ 

• 1 - • 

• • 

• 0 f-• ···· • ........ ......... .. --... _ .......... ................... .. 

• 

-1.0 -0.8 -0.6 -0.4 - 0.2 0.0 0.2 0.4 0.6 0.8 1.0 

SINE LATITUDE 

Fig. 2.20. Mean difference in annual mean nitrous oxide mole fractions 

(in ppb, nmol mol. 1

) between each site and south pole for 1998, plotted 

versus sine of latitude. The annual means were calculated from curves 

fitted to the data. 
0. 75 

0.50 

a. 

~ 0. 25 

LL "' (/) 

0.00 

9o·s 30'5 EQ 30'N 90"N 

1998 

• 

•• • • . . . , • ... • • ••• 

• • 

• 

• • ... . # ........ .... .........• .. ······-.. ·-.. ······-·--· . --···· -·-·-···-··-·-·· ···-· ···- ....... 

- 1.0 -0.8 -0.6 - 0.4 - 0.2 0.0 0.2 0 4 0.6 0 8 1.0 

SINE LATITUDE 

Fig. 2.21. Mean difference in annual mean SF6 (in ppt, pmol mol"

1

) 

between each site and south pole for 1998, plotted versus sine of latitude. 

The annual means were calculated from curves fitted to the data. 

differences are observed at Hungary (HUN) and other relatively 

polluted continental sites. These gradients are consistent with 

about two-thirds of total N20 emissions, and all SF~ emissions, 

occurring in the northern hemisphere. 

390 North Carolina 

,.---... 380 

E 

Q_ 370 Q_ 

"---" 

N 360 

0 

u 350 

340 

0 390 Wisconsin 

,.---... 380 

E 

Q_ 370 Q_ 

"---" 

N 360 

0 

u 350 

340 

1993 1994 1995 

2.6. MEASUREMENTS ONT ALL TOWERS 

Measurements of mixing ratios of C02 and other trace species 

were made on a 610-m tall TV transmitter tower in North 

Carolina (NC, site code !TN) from June 1992 until June 1999. 

These measurements were discontinued because the TV 

company required the space occupied by our equipment on the 

tower and in the transmitter building in order to install HDTV as 

mandated by Congress. Measurements began on a 447-m tall 

tower in Wisconsin (WI, station code LEF) in October 1994 and 

are ongoing . 

The C02 mixing ratio data through 1997 were presented in 

Bakwin et al. [ 1998]. Figure 2.22 provides an update of the data 

through 1999. Bakwin et al. [ 1998] discuss a method to account 

for excess fossil fuel C02 at the towers relative to the 

"background" marine boundary layer (MBL). The difference 

between the CO daily means at the towers and a MBL reference 

for CO is divided by an estimated CO/C02 molar emission ratio 

for fossil fuel combustion of 0.023 [Bakivin et al., 1994]. This 

value is subtracted from the C02 mixing ratios at the towers. 

The results provide a means to compare more directly C02 

mixing ratios over the continent with those in the MBL. Table 

2.10 updates these data through 1999. The annual mean C02 

mixing ratios at the towers are generally higher than in the MBL 

at the same latitude [Bakwin et al., 1998]. However, it is 

estimated that excess fossil fuel C02 typically accounts for 

+ 

1996 1997 1998 1999 2000 

Fig. 2.22. Daily mean CO! mixing ratios al 496 m above the ground on the North Carolina tower and 396 m on the Wisconsin tower (points). The data 

are fit with smooth curves (heavy) as described by T/11mi11x et al. [1989]. The thin lines show the t\IBL reference curves [Globalvie1r-C01. 2000] for the 

latitudes of the towers. 

39 
TABLE 2.10. Carbon Dioxide Mixing Ratios (ppm) at Two Tall Towers With and Without the Estimated 

Fossil Fuel Contribution Subtracted as Descri bed in the Text* 

Year NC NC-FF MBLat NC WI WI-FF MBL at WI 

1995 363.1 360.7 360.9 361.9 na 360.7 

1996 364.7 362.4 363.0 363.8 362.4 363. 1 

1997 365.7 363.5 364.0 364.4 363.6 363.9 

1998 368.9 366.8 366.7 367.6 366.6 366.5 

1999 na na 368.8 369.4 368.5 369.0 

*Uncertainty of the annual mean C02 mixing ratios at the towers is roughly 0.2 ppm. 

NC= North Carolina; FF = fossil fuel; MBL =marine boundary layer; WI = Wisconsin 

2.1-2.4 ppm C02 at the NC tower and 0.8-1.5 ppm C02 at the 

WI tower. Subtracting these values gives annual mean values 

for C0 2 at the towers that are a few tenths of a ppm lower than 

in the MBL, suggestive of a biogenic sink for C02 on the 

continent. It is interesting that both towers show a smaller than 

average difference from the MBL in 1998, a year when the 

global atmospheric C0 2 growth rate was exceptionally large. 

This implies that the biogenic sink for C02 in North America 

in 1998 may have been smaller than in other years. An 

alternative explanation could be that interannual changes in 

atmospheri c circulation affect the annual means. However, the 

contribution of recent fossil fuel-derived C02 did not change 

much at either tower. 

A large program has evolved around the WI tower to study 

processes that regulate the carbon balance of the surrounding 

temperate/boreal mixed forest and to understand how the signal 

of C02 exchange at the terrestrial surface propagmes to the 

regional and global atmosphere. The program, known as the 

Chequamegon Ecosystem/Atmosphere Study (ChEAS), includes 

scientists from several universities and government research 

laboratories and is funded mainly by NOAA, U.S. Department of 

Energy (DOE), National Science Foundation (NSF), NASA and 

U.S. Department of Agriculture (USDA). The backbone of the 

project is the CCGG measurements of the exchange of C02 

between the atmosphere and the forest using eddy covariance 

and atmospheric budget methods. Information about the studies 

involved in ChEAS can be found at [http://cheas.umn.edu]. The 

first publications utilizing the CMDL measurements are Yi et al. 

[2000] and Berger et al. (2000). 

During 1998-1999 significant progress was made towards 

quantifying the forest carbon balance and understanding the 

biophysical processes that drive interannual changes in net 

ecosystem exchange of carbon (NEE). Figure 2.23 shows 

cumulative NEE for 1997 and 1998. During the wintertime 

modest net release of C02 by the forest, due to respiration, was 

observed. Since the soils are mostly frozen, the rate of 

respiration is fairly small; the average for January 1997 is 0.3 

μmol m·

2 s· 1

, compared to nighttime respiration of 5.0 μmot m·

2 

s·t in July. The timing of leaf-out is well predicted by degreedays, the integral of temperatures greater than 0°C starting from 

April I. The spring of 1998 was unusually warm, and leaf-out 

occurred about l month earlier than in 1997. During the summer 

rapid photosynthesis by the vegetation leads to net uptake by the 

forest. The rate of uptake in midsummer was similar in 1997 and 

1998. A severe drought occurred in the region du ring mid-tolate summer of 1998, and the moisture content of the surface soil 

dropped to about 25% of that in 1997. The drought suppressed 

both photosynthesis and respiration by the forest, and the daily 

40 

N 

I 

E 

w 

w 

z 

so 0 1997, annual NEE = ·47 

)<( 1998, annual NEE = ·73 

0 

·100 

Jan Feb Mai A.pf May Jun Jul Aug Sep Oc1 Nov Dec 

Fig. 2.23. Cumulative net ecosystem exchange of CQ2 measured at tht: 

Wisconsin tower during 1997 and 1998. Points are measured data and 

lines are cumulative sums of curve fits to the measured daily net 

ecosystem exchange (NEE). 

NEE became approximately zero about l month earlier than in 

1997. The drought reduced annual NEE by about 15 g C nf2 

compared to the well-watered year. However, because of the 

early spring, the forest still took up about 50% more carbon in 

1998 than in 1997. The conclusion is that weather conditions 

during the transition seasons of spri ng and fall are particularly 

important in setting the an nual rate of carbon sequestration by 

the forest. The forest was a net si nk for carbon during both 1997 

and 1998. 

The fi nding that the forest surrounding the WI tower was a 

significantl y larger net sink for C02 in 1998 than in 1997 is 

especially interesti ng in light of the results discussed previously 

that terrestrial systems in North America, as a whole, may have 

been a smaller net sink in 1998. The NEE data (Figure 2.23) are 

representative of a fairly small area, roughly a few km2

• The 

C02 mi xing ratio data obtained at 400-500 m above the ground 

on these towers is representative of a much larger area of the 

order of l x l 06 km2 (M. Gloor et al. , What's the footprint of a 

tall tower?, Journal of Geophysical Research, in review, 2000). 

Linki ng the local-to-regional NEE to the larger scale mixing 

ratios is a topic of current investigation using the WI tower data. 

That is, CCGG is working to understand how the signal of 

surface exchange propagates into the regional and global 

atmosphere. This requires a detailed understanding of the 

dynamics of the planetary boundary layer (PBL) and the 

mechanisms by which the PBL exchanges air with the overlying 
free troposphere. Using data from the tall tower and from a PBL 

sounding radar system, there is a detailed study of seasonal 

changes in PBL mixing (C. Yi et al., Long-term observations of 

the dynamics of the continental planetary boundary layer, 

Jo11mal of Atmospheric Science, in review, 2000). It was found 

that the PBL height is maximum in spring when driven by high 

surface sensible heat fluxes. Later in summer the surface energy 

partition is dominated by turbulent fluxes of latent heat because 

of transpiration by the forest, and sensible heat fluxes are 

reduced. In future work the seasonal covariance between surface 

fluxes of C02 and the depth and venting (exchange with the free 

troposphere) of the PBL, which is critical information for efforts 

to diagnose the global carbon cycle by inverse methods, will be 

determined. 

2.7. AIRCRAFT PROGRAM 

Flights over Carr, Colorado (40.9°N, 104.8°W), to collect 

atmospheric samples as vertical profiles continued on a weekly 

basis as they have for the past few years. The Carr flights have 

also served as a testing faci lity for the initial flights of new 

sampling instruments after their construction at CMDL. The 

Carr vertical profiles were also integrated into the NASA Earth 

Observing System (EOS) validation experiments of the CCGG 

where the in situ data from those flights are used to validate the 

remote sensing data retrievals. 

With funding from the NASA Earth Science Enterprise 

Experiment, CO and CH4 in the lower and middle troposphere 

were measured. In collaboration with the Measurement Of 

Pollution In The Troposphere (MOP!TT) science team, four 

locations were chosen for study. These sites, their three-letter site 

codes and locations are: Poker Flats, Alaska (PFA, 65.1°N 

147.5°W), Harvard Forest, Massachusetts (HFM, 42.5°N 71.2°W), 

and Molokai, Hawaii (HAA, 2 l.4°N 157.2°W). Using portable 

automated sampling equipment, measurements from chartered, 

turboprop aircraft began at these sites during 1999. Original plans 

called for flights above SMO, but problems with the charter 

service required that the program be moved to Rarotonga in the 

Cook Islands (RTA, 21.2°S 159.8°W), and the first flights were 

made in April 2000. Sampling typically extends to an altitude of 

about 8 km (25,000 ft), except for RTA (7 km). 

The equipment consists of two suitcases, one with 17-20 

sampling flasks and a controller, and one with batteries and 

compressors. Only a clean air inlet and a place to stow the 

suitcases on the aircraft are needed. Usually a sampling inlet is 

created on a modified storm window. These samplers are then 

shipped back to NOAA for automated analysis through the flask 

analysis system, in which not only CO and CH4, but also C0 2, 

H2, N20, and SF6 are being measured. Recently isotopic analysis 

of C02 in these samples was started through mass spectrometry 

by INSTAAR. A second analytical system is being readied at 

NOAA to absorb the increase in aircraft profile analysis. 

In addition to these sites CMDL has flown the automated 

sampler at several experimental sites such as the WLEF tower in 

Wisconsin and onboard a Citation aircraft as part of the C02 

Budget and Rectification Airborne (COBRA) campaign. 

Aircraft sites were also prepared at two locations in Brazil for the 

Large Scale Biosphere Atmosphere (LBA) experiment; one site 

is in the Amazon Basin and one is off of the East Brazilian coast. 

Intensive flights will also occur in Southern Africa in 2000 

during the NASA EOS validation flights as part of the Southern 

African Fire-Atmosphere Research Initiative (SAFARI) 2000 

campaign. In addition, NCAR test flights recently used the 

NOAA sampler onboard the DOE Citation aircraft. 

The first attempts at shipping the sampling equipment 

between Boulder and the sites led to considerable damage to the 

units. Over the past 2 years, significant effort has been devoted 

to improving the design for greater ruggedness and a 

corresponding increase in successful analysis. An example of 

mixing ratios determined from these aircraft programs is shown 

in Figure 2.24. 

2.8. AIR-SEA GAS EXCHANGE 

There are several strong incentives to improve the 

understanding of the process of air-sea gas exchange. The 

strongest oceanic data constraint on the uptake of C02 by the 

oceans is a decadal one, namely the rate of increase of the ocean 

inventories as measured by World Ocean Circul ation 

Experiment/Joint Global Ocean Flux Study (WOCEJJGOFS), 

Geochemical Ocean Sections (GEOSECS), etc. [e.g., Gruber e1 

al., 1996]. An independent estimate is obtained from 

measurements of t.pC02 (the difference in partial pressure of 

C02 between the water and the air) at the surface of the oceans, 

as compiled by Takahashi et al. [ 1997]. In order to convert that 

information into a flux, the map of ilpC02 needs to be multiplied 

by the space- and time-dependent air-sea transfer coefficient, 

which has traditionally been modeled as a function of wind 

speed. The currently most-often used relationship is that 

proposed by Wanninkhof [ 1992], in which the transfer velocity 

increases quadratically with wind speed. There is a large amount 

of scatter in the measurements that suggest there are factors other 

than wind speed influencing gas transfer. 

41 

Because there is not a satisfactory physical explanation of the 

gas exchange velocity, we cannot be very sure of fluxes derived 

with this relationship from observed ilpC02 values. The global 

flux estimate is sensitive to the relative rates of gas exchange at 

high and low wind speeds. Low wind speeds are more prevalent 

at low latitudes that tend to have positive ilpC02 (outgassing), 

whereas high wind speeds occur more often at high latitudes that 

tend to take up C02 because of negative ilpC02 values. The net 

global uptake is the balance between these two opposing 

tendencies at low and high latitudes. 

The first combined use of the large scale north-south gradient 

of atmospheric C02 with oceanic <'.lpC02 data led to the 

hypothesis of a large terrestrial sink of C02 at northern 

midlatitudes [Tans el al., 1990]. The north-south gradiem 

determines, with the use of an atmospheric transport model, the 

balance of all sources and sinks of C02 as a function of latitude. 

The partitioning between land and ocean at each latitude zone 

depends on ilpC02 data and the air-sea gas exchange velocity. 

The recent paper by Fan et al. [ 1998] also had to employ 

independent estimates of net air-sea exchange to arrive at its 

conclusion of unexpectedly large C02 uptake in North America. 

The lesson is that atmospheric inverse models, used to derive 

sources and sinks from atmospheric gradients, would gain 

significantly in value and power as our understanding of air-sea 

gas exchange is improved. Not only would terrestrial estimates 

be improved, but regional oceanic uptake or loss would be much 

better quantified based on atmospheric gradients. This is 

especially true over the southern oceans where the atmospheric 

constraint would attain serious weight. 

Furthermore the 13C/12C ratio of C02 provides us with a tool 

to distinguish between terrestrial and oceanic influences on 
HAA 2000_01_31-2145 HAA 2000_01_31-2145 BOOT 

6000 

8000 

E 

~ 

w 

0 4000 I w 1 g 4000 :::> 

It:= 

....J 

4: 

2000 

ol 

50 60 70 80 90 

co (ppb) 

HAA 2000_01_31 _2145 

8000 1 -- ..., ::i 

6000 

I f 

w 

0 4000 :::> 

It:= 

....J 

4: 

2000 

0 ·- I 

740 750 760 770 780 

CH, (ppb) 

100 

.. .., 

790 

It:= 

....J 

4: 

~ 

E 

~ 

w 

0 

:::> 

If:= 

....J 

4: 

2000 

0 

368.0 368.5 369.0 369.5 

C02 (ppm) 

HAA 2000_01_31-2145 8000 ~----

6000 

4000 

2000 

0 

475 480 485 490 

H2 (ppb) 

370.0 

495 

Fig. 2.24. Example or vertical profile results collected as part or the MOPITI calibration program at Molokai, Hawaii, on January 3 1, 2000. CO has 

been correc1ed 10 1he 1999 gravime1ric scale (section 2.4.2). 

atmospheric C02• Unfortunately the largest term in the 13C 

atmospheric budget, fossil fuel emissions, is followed 1101 by the 

net uptake of C02 by terrestrial ecosystems, but by two-way 

"gross" isotopic exchange between the atmosphere and the 

oceans unrelated to net uptake. Also the global effect here is a 

balance between high latitudes that tend to decrease atmospheric 

813C and low latitudes that tend to increase 813C. The functional 

form of the gas exchange parameterization has a major effect on 

the use of 13

C/12C to apportion carbon between the oceans and 

the continents. 

The atmosphere, with its rapid mixing, gives us the best tool 

to keep track of seasonal and interannual variations of the carbon 

cycle on large spatial scales. The relatively large interannual 

variations that are being measured [e.g., Co11way et al., 1994] 

give us an opportunity to validate process models. Once such 

variations are mostly understood, it will be much easier to 

discern underlying trends in the atmospheric C02 burden. At 

present there appears to be a conflict between deductions purely 

from atmospheric data [Fra11cey et al., 1995) about the 

variability of ocean uptake, and an oceanographic approach 

using pC02 data combined with observed wind speed and 

temperature [Lee et al., 1998]. The latter approach depends on 

the gas exchange velocity. 

42 

CCGG participated in a measurement campaign aboard the 

NOAA ship Ronald H. Brown from the late spring to the early 

summer of 1998 to specifically study gas exchange (GASEX98). 

Three different methods were employed to measure the C02 

flux: on leg 2 in a cold core eddy with large nega1ive 6pC02 

values north of the Azores, the small vertical C02 gradient 

created above the water by the flux was measured, and on leg 3 

during the return to Miami, the flux was measured by the eddy 

covariance and eddy accumulation methods. An important zero 

bias of the eddy covariance method that affects, to a greater or 

lesser degree, all other such measurements that have been made 

to date with a rotating optical chopper wheel in the C02 analyzer 

was discovered. The motion of the ship produces a torque on the 

chopper that affects the analyzer response. This false signal 

component of the analyzer is multiplied with the ship-motion 

corrected vertical wind that still has a residual error. The 

residual error is coherent with the false analyzer signal, and 

multiplication leads, therefore, to an apparent C02 flux. 

On leg 2 vertical concentration differences above the water 

that were significantly different from zero were measured. 

Several tests for potential systematic biases gave zero results. 

The observed concentration differences had to be converted into 

fluxes with the help of meteorological data and similarity theory. 
When the derived gas exchange velocities are plotted as a 

function of wind speed, two features stand out. There is a finite 

gas exchange velocity at low wind speeds (U < 6 m s"1

) that 

appears to be independent of wind speed. It is likely that the gas 

exchange in this regime is controlled by thermally driven 

overturning of the thin skin layer of the water. At intermediate 

wind speeds (6 m s·• < U < 11 m s·

1

) the gas exchange velocity 

seems to increase linearly with wind speed. In this range CMDL 

results appear to agree well with the often used relationship 

between gas exchange velocity and the square of the wind speed 

[Wanninkhof. 1992], but our results are significantly higher at the 

lower wind speeds. CMDL data do not extend into the higher 

wind speed range. 

2.9. DATA INTEGRATION (GLOBALVIEW) 

Systematic observations of atmospheric C02 continue to play 

an essential role in advancing our understanding of the global 

carbon cycle. Atmospheric transport models run in the "inverse" 

mode and are used to estimate the magnitude and distribution of 

the sources of C02 by requiring that the modeled spatial and 

temporal patterns are consistent with the observations. Results 

from recent inverse modeling studies debate both the magnitude 

and distribution of the midnorthern latitude terrestrial sink. The 

90°N 

so·N 

• 30°N 0 0 49 •• • 

• 

. . 1\ 0 • 

o· • b 

• 

. ·~ 

3o·s 0 

) . 0 

so·s 

studies agree that the most important limitation to this approach 

is the sparseness of observations. The growing need for greater 

temporal and spatial coverage requires the integration of existing 

observations made by different laboratories into larger merged 

data sets. A major challenge is ensuring that the spatial and 

temporal patterns observed among independent measurement 

records are due to emissions as affected by atmospheric mixing 

and transport and not because of differences in calibration scales 

or experimental methods. 

In 1995 CCGG established the Cooperative Atmospheric 

Data Integration Project for carbon dioxide. Participants from 

18 laboratories in 12 countries contribute their up-to-date highprecision C02 records from land-surface, aircraft, ship, and 

tower sites (Figure 2.25). These data are used to construct 

Globalview-C01 [2000), a globally consistent data product for 

use with carbon cycle mode ling studies (http://www.cmdl. 

noaa.gov/ccgg/global view/default.html). Global view-C0 2 consists of statistical summaries of atmospheric variability, 

average diurnal and seasonal patterns, and smoothed 

representations of the observations. The product, which is 

updated annually, contains no actual data. Since GlobalviewC02 was first introduced in 1996, more than 1200 electronic 

requests (=26 per month) have been made from more than 35 

countries. 

90°N 

... so0

N 

0 

30°N 

o· 

30°5 

0 

60°5 

go·s ~~~~~~~~~~g~~~~~§g;g§~~~Ugo-s 

100°E 1 40°E 180° 1 40"W 1 OO"W 60"W 20"W 20°E 60°E 100°E 

Fig. 2.25. The Cooperative Atmospheric Data Integration Project for C02 includes observations from land-surface discrete (0) and continuous sites (a), 

ships (o), aircraft ( ~ ), and towers (Li). Laboratories contributing fou r or more measurement records are identified by color. Active participan!S include 

CMDL (red); CSIRO, Australia (blue); LSCE, France (green); AES, Canada (orange); !OS, Canada; CAMS. China; UBA/IUP-HD, Germany; HMS, 

Hungary; CESI, IMS, and ENEA, Italy; JMA and NIPR, Japan; METRVSNU, Republic of Korea; NIWA, New '.Zealand; !NM, Spain; MISU, Sweden. Colocated independent sampling programs are critical for assessing comparability among atmospheric records. 

43 
A major focus of the integration project is to assess the level 

of comparability among observations produced by different 

laboratories. Nearly 2 decades ago, the C02 community stated 

that interpreting spatial and temporal gradients of C02 would 

require a level of agreement among laboratories to within 0.1 

ppm [World Meteorological Organization (WMO), 1981). To 

assess consistency among independent measurement programs, 

CMDL conducted periodic intercomparison experiments (round 

robins) whereby more than 20 laboratories measured air from a 

set of traveling high-pressure cylinders. Results from the 1995-

1996 intercomparison experiment show that all laboratories 

contributing to Globalview-C02 are consistent to within 0.2 ppm 

[Peterson et al., 1999]. These experiments are critical for 

assessing each laboratory's ability to make high-precision C02 

measurements and maintain a calibration scale. However, they 

are not designed to compare different sample collection, storage, 

and extraction methods that are potential sources of uncertainty 

when making atmospheric measurements. Thus agreement 

among laboratories based on comparisons of high-pressure 

cylinders does not necessarily imply comparability among their 

atmospheric C02 records. To complement the round-robin 

experiments, ongoing lnterComParison (ICP) experiments were 

established whereby participating laboratories compare more 

directly the atmospheric measurements themselves. CCGG has 

ongoing ICP programs with the Commonwealth Scientific and 

Industrial Research Organization (CSIRO), Australia; 

Atmospheric Environment Service (AES), Canada; National 

Institute for Water and Atmospheric Research (NJW A), New 

Zealand; and HATS (U.S.). For the moment, only the ICP 

program with CSIRO is providing enough detail to properly 

assess comparability. 

The effectiveness or an ICP program depends on several 

essential features. First, participants must view lCP activity as 

an additional level of quality control whereby measurements are 

routinely scrutinized. Potential problems identified by the 

collaborating laboratory should not be viewed as an 

embarrassment but as proof that the JCP is working effectively. 

Second, the ICP acti vity is an ongoing long-term program of 

routine (at least weekly) comparisons of atmospheric samples. 

Third, the ICP program must include supporting measurements 

(e.g., control samples) that can be used to narrow possible causes 

when differences are observed. Fourth, the ICP program should 

have minimal impact on daily operations. This is accomplished 

only if participating laboratories have advanced data management tools in place. Analysis of ICP samples and processing and 

data exchange between laboratories must be automatic and 

routine. ICP results must be summarized automatically and 

made readily available to participants. Timely feedback 

improves the likelihood that potential problems are detected 

early. 

The CSIRO and NOAA Oask air lCP program began in 1992 

and has served as a model for subsequent ICP programs 

[Hofma1111 et al., 1996). The program includes the essential 

features described previously and demonstrates the difficulties in 

establishing and mainta111111g measurement comparability 

between independent laboratori es. Figure 2.26 shows the level 

of agreement between NOAA and CSIRO measurements of the 

same air in a glass nask for C02, 8nc (C02), ~. and CO. The 

observed variability in the differences demonstrates the need for 

ongoing and frequent intercomparisons. The level of agreement 

among C02 measurements combined with supporting evidence 

(e.g., round-robin results and pair agreement) suggests that 

e o.5 a. 

~ 0 

0 

u 

44 

......... 

L> 

a. 

~ 

.. J: 

u 

0 

u 

1992 1993 1994 1995 1996 1997 1998 1999 

YEAR 

Fig. 2.26. (a-d) Differences (CSlRO minus NOAA) between 

independent measurements of 1he same air in ICP Oasks for 1he period 

1992-1999 (open circles). The mean differences (CSlRO minus NOAA) 

detem1ined from mulliple in1ercalibra1ions of air in high-pressure 

cylinders are shown as solid green hourglass symbols and ploued a1 !he 

middle of 1he year in which !he analyses 1ook place. The doued lines 

abou1 1he zero difference line represent 1he 67% confidence limi1s abou1 

1he mean NOAA Oask pair difference (excluding lCP nasks and males) 

al Cape Grim. The band defined by solid lines represents 2 srnndard 

errors (95% confidence limil) from the mean of 1he residuals de1crmined 

from a smoo1h curve fined 10 !he distribu1ion. A 6-mon1h window 

centered a1 each difference value is used 10 compute !he s1andard error 

for 1ha1 value. 

NOAA and CS I RO network measurements of C02 are comparable 

to within 0.2 ppm (0.06%). Differences in the independent 

measurements of 813C show significant variability with time and 

are not yet fully understood. Methane measurements from NOAA 

and CSIRO network samples are comparable to within 1 ppb 

(0.04%) and have been integrated with observations from other 

laboratories to produce Globalview-CH4 [ 1999]. Differences in 

the independent measurements of CO show a systematic offset of 

about 5 ppb from 1992 to 1994. The difference increases at a rate 

of about I ppb y( t from 1995 to 1998 and appears to stabili ze 

again in 1999. Results from high pressure cylinder 

intercomparison experiments are consistent with the ICP results 

suggesting that the problem is likely related to the maintenance of 

the internal CO calibration scale in one or both laboratories. Both 

NOAA and CSIRO are working to understand the causes of these 

differences. 
2.10. INVERSE M ODELING 

Efforts to quantify the possible responses of the climate 

system to anthropogenic emissions of radi atively active trace 

species such as C0 2 and CH4 are complicated by the significant 

contributions of terrestrial biospheric and oceanic sources to the 

budgets of these gases. Future attempts to manage carbon 

reservoirs depend critically on the ability to understand and 

quantify the distributions of carbon sources in the atmosphere 

and oceans. Inverse modeling techniques, which have long been 

applied lo geophysical problems such as seismology, satellite 

data retrieval, and acoustic tomography, have over the past 

decade been applied to the problem of determini ng the source 

and sink distributions of atmospheric trace species, especially 

CO}. Early attempts were aimed at obtaining the 

interhemispheric gradient of the C0 2 sources and sinks [Tans et 

al., 1990; E111i11g and Mansbridge, 199 1; Ciais et al., I 995a,b; 

8011sq11e1 et al., 1996; Law and Si111111011ds, 1996]. However, 

with the expansion of the C0 2 observational network, attempts 

have been made over recent years to obtain source and sink 

distributions over cominental scales. 

Currently it seems that the observational network is too sparse 

to allow accurate estimates of trace gas budgets on continental 

scales, though it is likely that reasonable estimates over large 

latitude zones may be made. A further complication is that the 

current network is designed to sample mostly marine boundary 

layer air so that information from the terrestrial biosphere at 

regional scales is lost by mixing over large distances. In addition 

it is clear that even if more observations over continental regions 

were obtained, the current generation of models would likely not 

represent atmospheric boundary processes adequately, leading to 

; ignificant uncertainly [e.g., Den11 i11 g et al. , 1995]. Despite these 

daunting difficulties, efforts to estimate the carbon budget at 

continental scales with reduced uncertainty arc underway. It is 

hoped that the observational network will be expanded and that 

models \\ill improve significantly in the near future. 

Ongoing work by the CCGG group is focused on development 

of an operational inverse calculation at continental scales. The 

mass balance and a;similation technique employed has been 

described in detail by Bmhwiler et al. [2000]. The global 

transport model to be used for operational source calculations is 

the NCAR MATCH model with the National Center for 

Environmental Predictions (NCEP) winds. Since this model 

requires large amounts of computational resources. development 

and evaluation of the inverse technique has taken place using a 

much simpler and faster low resolution version of TM2ffM3 

[Heima1111 , 1995) with I year of European Center for McdiumRangc Weather Forecasts (ECMWF) winds that arc repeated for 

multi-year calculations (although multiple year wind fields and I 

year of TM2 vertical diffusion may be used with TM3 for a 

rough idea of the effects of interannual variability). The 

inversion uses the Globalview-C0 2 data set and 14 basis 

functions for comincntal and oceanic regions. 

The sensitivity of source regions 10 a variety of conditions has 

been tested. Examples of these conditions include use of radon 

(Rn) to filter out simulated C02 values of recent conti nental 

origin and applying a smoothing procedure to calculated time 

series rather than using instantaneous values. Estimates of the 

long-term average ( 1979-1998) C02 sources range from about -I 

to+ I Gt C yr" 1 for the terrestrial biosphere and from 0.0 to -2.75 

Gt C yr" 1 for the oceans. In each case, the esti mate is for 

nonrcpeating meteorology. Although the estimates seem to be 

45 

rather insensiti ve to smoothing and Rn fi ltering, use of 

nonrepeating meteorology appears to have a large impact, at 

least in the present configuration ofTM3. 

Current estimates of the North American carbon sink are -I to 

-1.75 Gt C yr" 1

, while Eurasia appears to be a carbon source on 

the average (about 1 Gt C yr" 1

). The high-latitude northern 

hemispheric oceans are estimated to take up carbon at the rate of 

about 1.5 Gt C yr" 1

(larger than suggested by ~pC 2 data), while 

the equatori al oceans, especially the equatori al Pacific, release 

carbon at approximately the same rate. Time series of monthly 

estimates of carbon sources are rather noisy, and time series of 

annual averages exhi bit significant variability, which is due to 

both uncertainty in the inversion and real vari ability in sources 

and sinks. During El Nino years, for example, the emissions 

from the equatorial Pacific are estimated lo decrease, and the 

total terrestrial sink appears to decrease, possibly to the point at 

which the terrestrial biosphere becomes a net source of C02• 

Recent developments were aimed at reducing noise and 

uncertainty in the inverse calculation. The ability to retain basis 

function (the C0 2 pattern resulting from a well-defined source) 

transport information for an arbitrary length of time previous to 

the time of the inverse calculation was added. Tests suggest that 

basis functions may need to be carried for periods of half year or 

longer. In addition the inverse technique was modified to allow 

simultaneous inversion of multiple trace species. This allows the 

possibility that constraints relating the budgets of two or more 

trace species may be used to reduce noise and uncertainty. Test 

calculations suggest that uncertainty could be significantly 

reduced if the uncertainty in the constraints employed is 1101 too 

large. 

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carbon dioxide on \t:ry tall towers: Results of the NOANCMDL 

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monoxide abundance: A three di mensional sensitivity study, Atmm. 

E11 l'iro11., 30, 1673- 1692, 1996. 

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Kasischke, E.S., K. Bergen, R. Fenimore, F. Sotelo, G. Stephe ns, A. 

Janetos, and H. H. Shugart, Satellite imagery gives clear picture of 

Russia's boreal fo rest fires, Eos, Trn11s. Am. Geophys. U11io11, 

80(1 3), 14 1- 152, 1999. 

Kitzis, D .. and C. Zhao, CMDUCarbon Cycle Gases Group Standards 

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Environ. Res. Labs., Boulder, CO, 1999. 

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and sinks to variations in transport and imposed surface 

concentrations. Tel/us, 488 , 6 13, 1996. 

Lee, K., R. Wanninkhof, T. Takahashi, S.C. Doney, and R.A. Feely, 

Low interannual variability in recent oceanic uptake of atmospheric 

carbon dioxide, Nature, 396, 155- 159, 1998. 

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and the environment: A global synthesis, UNEPIDEJAE\V!TR.99-1, 

UNEP (WMO), Geneva, 1999. 

Masarie, K.A., Steele, L.P., 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 TM ERL CMDL-3, 37 

pp., Boulder, CO, 1991. 

Novelli, P.C., J.W. Elkins, and L.P. Steele, The development and evaluation of a gravimetric reference scale for measurements of 

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

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and comparisons with reference scales al NASA-Langley and at the 

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46 

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3. Aerosols and Radiation 

3.1. AEROSOL MONITORING 

D . DELENE(EDITOR), E. ANDREWS, D. JACKSON. A. JEFFERSON, 

J. OGREN. P. SHERIDAN, 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 knowledge of regional and global-scale 

chemical processes, physical transformation, and transport 

models for calculating the spati al distributions of the major 

chemical species that control the optical and cloud-nucleating 

properties of the particles. Developing and validating these 

various models require 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 

observatori es in the nud-I 970s as part of the Geophysical 

Monitoring for Climatic 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 of the lessons learned 

is that residence times of tropospheric aerosols are generally less 

than I week, and another is that human activities primarily 

influence aerosols on regional and 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 

Co1111cil, 1996], CMDL expanded its aerosol research program to 

include regional aerosol monitoring stations. The goals of this 

regional-scale monitoring program are: (I) to characterize 

means, variabilities, and trends of climate-forcing properties of 

different types of aerosols and (2) 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 involving modeling, 

monitoring, process, and closure studies. This report describes 

the observations that CMDL is conducting towards this goal. 

No single approach to observing the atmospheric aerosol can 

provide the necessary data for monitoring all the relevant 

47 

dimensions and spatial/temporal scales necessary to evaluate 

climate forcing by anthropogenic aerosols. In situ observations 

from surface sites, ships, balloons, and aircraft can provide very 

detailed characterizations of the atmospheric aerosol but on 

li mited spatial scales. Remote sensing methods from satellites, 

aircraft, or the surface can determine a limited set of aerosol 

properties from local to global spatial scales, but they cannot 

provide the chemical information needed for linkage with global 

chemical models. Fixed ground stations are suitable for 

continuous observations over extended time periods but lack 

vertical resolution. Aircraft and balloons can provide the vertical 

dimension but not continuously. Only when systematically 

combined can these various types of observations produce a data 

set where point measurements can be extrapolated with models 

to large geographical scales, where satellite measurements can be 

compared to the results of large-scale models, and where process 

studies have a context for drawing general conclusions from 

experiments conducted under specific conditions. 

Measurements of atmospheric aerosols arc used in three 

fundamentally different ways for aerosol/climate research: 

algorithm development for models and remote-sensing retrievals, 

parameter characterization, and model validation. Laboratory 

and field process studies guide the development of 

parameterization schemes and the choice of parameter values for 

chemical transport models that describe the relationship between 

emissions and concentration fields of aerosol species. 

Systematic surveys and monitoring programs provide 

characteristic values of aerosol properties that are used in 

radiative transfer models for calculating the radiative effects of 

the aerosols and for retrieving aerosol properties from satellites 

and other remote sensing platforms. And finally, monitoring 

programs provide spatial and temporal distributions of aerosol 

properties that are compared to model results to validate the 

models. Each of these three modes of interaction between 

applications and measurements requires different types of data 

and entail different measurement strategies. • Ogren [ 1995] 

applied the thermodynamic concept of "intensive" and 

"extensive" properties of a system to emphasize the relationship 

between measurement approach and applications of aerosol 

observations. 

Intensive properties do not depend on the amount of aerosol 

present and are used as parameters in chemical transport and 

radiative transfer models (e.g., atmospheric residence time, 

single-scattering albedo). Extensive properties vary strongly in 

response to mixing and removal processes and are most 

commonly used for model validation (e.g., mass concentration, 

optical depth). Intensive properties are more difficult and 

expensive to measure than extensive properties because they 

generally are defined as the ratio of two extensive properties. As 

a result, different measurement strategies are needed for meeting 

the data needs of the various applications. Measurements of a 

few carefull y chosen extensive properties, of which aerosol 

optical depth and species mass concentrations are prime 

candidates, are needed in many locations to test the ability of the 

models to predict spatial and temporal variations on regional to 

global scales and to detect changes in aerosol concentrations 

resulting from changes in aerosol sources. The higher cost of 

determining intensive properties suggests a strategy of using a 

limited number of highl y instrumented sites to characterize 

means and variabilities of intensive properties for different 

regions or aerosol types, supplemented with surveys by aircraft 
and ships to characterize the spatial variability of these parameters. CMDL's regional aerosol monitoring program is 

primarily focused on characterizing intensive properties. 

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 

and 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 that 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 

condensation nuclei (CN) concentration, aerosol optical depth 

(8), and components of the aerosol extinction coefficient at one 

or more wavelengths (total scattering cr,r• backwards hemispheric scattering <1tisr• and absorption cr,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 because of 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 wi nd 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. Since 1995 

an automatic editing algorithm has been applied to the baseline 

data in addition to manual editing of local contamination spikes. 

For the baseline stations (Barrow, Alaska (BRW); Mauna Loa, 

Hawaii (MLO); American Samoa (SMO); and South Pole, 

Antarctica (SPO). as well as Sable Island (WSA)), 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 m s·

1

) . 

In addition, at MLO, data for upslope conditions ( 1800-1000 

UTC) are excluded since the air masses 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 three 

or four wavelengths 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 fi lter is inserted periodically into the sample 

stream to measure the light scattered by gas molecules. This is 

then subtracted from the total scattered signal to determine the 

contribution from the particles alone. The instruments are 

48 

TABLE 3. 1. Data Editing Summary for NOAA 

Baseline and Regional Stations 

Station Editing Clean Sector 

South Pole a,b,c 0°< WD< 11 0°, 

330°<WD <360° 

Samoa a,b,c 0° < WD < 165°, 285°<WD < 360° 

Mauna Loa a,b,c,d 90° < WD < 270° 

Barrow a,b,c 0°<WD< 130° 

Sable Island a,b,c 0° < WD < 35°, 85° < WD < 360° 

Southern Great Plains a 

Bondville a 

a: Manual removal of local contamination spikes 

b: Automatic removal of data not in clean sector 

c: Automatic removal of data fo r low wind speeds 

d: Removal of data for upslope wind conditions 

WD: Wind direction 

calibrated by filling the sample volume with C02 gas that has a 

known scattering coefficient. 

The aerosol light absorption coefficient is determined with a 

continuous light absorption photometer. This instrument 

continuously measures the amount of light transmitted through a 

quartz filter while particles are being deposited on 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 were 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, Magee Scientific, Berkeley, 

California) were calibrated by the manufacturer in terms of the 

equivalent amount of black carbon (BC) from which the light 

abso~ption coefficient is_ calculated, assumi nf a mass absvrption 

efficiency of the calibration aerosols of 10 m g· 1

• 

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 optically detected and counted. The instruments in use have 

lower particle-size detection limits of 10-20 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 extensi ve properties. These properties are used in 

chemical transport models to determine the radiative effects of the 

aerosol concentrations calculated by the models. Inversely, these 

properties are used by algorithms for interpreting satellite remotesensing data to determine aerosol amounts based on measurements 

of the radiative effects of the aerosol. 

3.1.3. ANNUAL CYCLES 

The annual cycles of aerosol optical properties for the four 

baseline and three regional stations are illustrated in Figures 3.1 

and 3.2. The data are presented in the form of box and whisker 

plots that summarize the distribution of values. Each 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, also shown are the annual statistics for the 

entire period of record. A horizontal line is given that intersects 

the annual median so measurements above and below the median 

can be easily discerned. 
TABLE 3.2. CMDL Baseline Aerosol Monitoring Stations (Status as of December 1999) 

Category Baseline Arctic Baseline Free Troposphere Baseline Marine Baseline Antarctic 

Location Point Barrow Mauna Loa American Samoa South Pole 

Designator BRW MLO SMO SPO 

Latitude 7 l .323°N 19.539°N 14.232•s 89.991°s 

Longitude 156.609°\V 155.578°\V 170.563°\V 102.G°E 

Elevation (m) 8 3397 77 2838 

Responsible institute CMDL CMDL CMDL CMDL 

Starns Operational, 1976 Operational, 1974 Operational, 1977 Operational, 1974 

Major upgrade, 1997 

Sample RH RH <40% Uncontrolled Uncontrolled Uncontrolled 

Sample size fractions D<l μm Uncontrolled Uncontrolled Uncontrolled 

D<IO μm 

Optical measurements cr..,(31..). cr....,(31..). cr,r( I A.) cr,.,(31..). cr"'( I A.). B(6A.) none cr'{>(4A.) 

M icrophysical CN concentration CN concentration CN concentration CN concentration 

measurements 

Chemical measurements Major ions, mass None None None 

TABLE 3.3. CMDL Regional Aerosol Monitoring Sites (Status as of December 1999) 

Category Perturbed Marine Perturbed Continental Perturbed Continental 

Location Sable Island, Nova Scotia, Canada Bondville, Illinois Lamont, Oklahoma 

Designator WSA BND SGP 

Latitude 43.933°N 40.053°N 36.605°N 

Longitude 60.001·w 88.372°\V 97.489°\V 

EleYation (m) 5 230 315 

Responsible mstitute CM DL CMDL CMDL 

Collaborating institute AES Canada, NOAAJPMEL Univ. of Illinois, IL State Water Survey DOE/ARM 

Status Operational. August 1992 Operational, July 199.t Operational, July 1996 

Sample RH RH <40'k RH <40% RH <40% 

Sample size fractions D<l μm, D< IO μm D<l μm, D< IO μm D<I μm, 0<10 μm 

Optical measurements cr'f>(3A.). cr.,_,,(31..). cr,r( I A.) cr'f>(3A.). cr....,(31..). cr,r< I!..) cr,r(3A.), cr....,(31..). cr,r( I!..), 0{7A) 

M icrophysical CN concentration CN concentration CN, n(D) concentration 

measurements 

Chemical measurements Major ions, mass Major ions, mass None 

TABLE 3.4. Intensive Aerosol Properties Deri ved From CMDL Network 

Properties Description 

a The Angstrom exponent, defined by the power-law (J ocA.'

1

, describes the wavelength-dependence of scattered light. In the figures 

below, <i 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. 

co., The aerosol single-scattering albedo, defined as cr_J(cr..p + cr'f>). 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 cosine-weighted 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 defined as cri.rfcr,r. 

a, The mass scattering efficiency for species i, defi ned as the slope of the linear regression line relating cr,r and the mass concentration of the 

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

modeled. This parameter has typical units of m2 g·

1

• 

49 
JAN MAR MAY JUL SEP NOV ANN JAN MAR MAY JUL SEP NOV ANN 

Fig. 3.1. Annual cycles for baseline stations at BRW, MLO, SMO, and SPO showing statistics for condensation nuclei (CN) concentration, total 

scattering coefficient (cr,p). Angstrom exponent (11), absorption coefficient (crlll') and single-scattering albedo (w0 ). Statistics representing the entire 

period are given in the last column (ANN). with the horizontal line intersecting the median value. 

50 
I 

E 

:l 

..._, 

t 

b 

,..... 

I 

E 

:l 

..._, 

t 

b 

BNO: 1996-1999 

WSA: 1995-1999 

JAN MAR MAY JUL SEP NOV ANN 

BNO: 1994-1999 250.--....---.---.--.--....---.---.--.--....---.---.--.--....-~ 

,..... 200 1

E 150 

:l 

..._, 100 

:t 

b 

,..... 

150 

I 100 

E 

:l 

..._, 

:t 50 b 

0 

200 

~ 150 I 

i 100 ..._, 

._ 

.. 

.. 

... 

,_ 

I-

,_ 

,_ 

,_ 

.__ 

._ 

.. .. -! 50 

0 

,_ 

,_ 

i:-

.. .. 

WSA: 1992-1999 

-

. 

. 

-. 

. 

I - J 

SGP: 1996-1999 . 

. 

. 

...: . 

. 

...: . 

. 

. 

. 

-

JAN MAR MAY JUL SEP NOV ANN 

BNO: 1996-1999 3.0 r--r--r--.....---.-...-~-.-"""'T'"---r-r---r---r-"""'T'"---i 

2.5 

WSA: 1995-1999 

SGP: 1996-1999 3.0 .--....---.----..-..--....--r--..--ir--..---r---....--.r--..--. 

2.5 

2.0 ~-A-~-M-~l--l~+.1--~-i.--+1--1=:i.-~+1-~..! 

JAN MAR MAY JUL SEP NOV ANN 

BNO: 1996-1999 1.00 ,...-.,--r--..-..--.,--r---..--ir--..---.---r---..--..---. _ 

0.90 _ 

-... ~ 0.80~ ... 

... 0.70 ::-

-

-

- 0.60 ,_t__,___.L--....__.___,___.L--...___.___.___,_...___,___.___, 

WSA: 1995-1999 

SGP: 1996-1999 

JAN MAR MAY JUL SEP NOV ANN 

Fig. 3.2. Annual cycles for regional stations at Bondville, Illinois (BND), Sable Island, Nova Scotia (WSA), and Lamont, Oklahoma (SGP) showing 

statistics of absorption coeffi cient (Oap). total scanering coefficient (o..,), Angstrom exponent (A), and single-scattering albedo (Wo). Statistics 

representing the entire period are given in the last column (ANN). with the horizontal line intersecting the median value. 

51 
In general, changes in long-range transport patterns dominate 

the annual cycles of the baseline stations. For BRW, the highest 

values of CN, <lsp• and <lop are observed during the spring Arctic 

haze period when anticyclonic activity transports pollution from 

the lower latitudes of Central Europe and Russia. A more stable 

polar front characterizes the summertime meteorology. High 

cloud coverage and precipitation scavenging of accumulation 

mode (0.1-1 .0 μm diameter) aerosols account for the annual 

minima in a,P and a.P from June to September. In contrast, CN 

values have a secondary maximum in the late summer that is 

thought to be the result of sulfate aerosol production from gas to 

particle conversion of DMS oxidation products from local 

oceanic emissions [Radke et al., 1990]. The aerosol singlescatlering albedo displays little annual variability, which is 

indicative of highly scattering sulfate and seasalt aerosol. A 

September minimum is observed in 11 when a,P and accumulation 

mode aerosols are also low but when primary production of 

coarse mode seasalt aerosols from open water is high. 

For MLO, the highest a,P and a.P values occur in the springtime and result from the long-range transport of pollution and 

mineral dust from Asia. However, little seasonality is seen in CN 

concentrations at MLO, indicating that the smallest particles 

(<0. I μm diameter), which usually dominate CN concentration, 

are not enriched during these long-range transport events. Both 

the aerosol a,P and Angstrom exponent display seasonal cycles at 

SPO, with a a,P maximum and an 11 minimum in winter 

associated with the transport of coarse mode seasalt from the 

Antarctic coast to the interior of the continent. The summertime 

peaks in CN and 11 arc associated with fine mode sulfate aerosol 

and correlate with a seasonal sulfate peak fou nd in the ice core, 

presumably from coastal biogenic sources [Bergin et al., 1998]. 

The aerosol extensive properties at SMO display no distinct 

seasonal variation. Instrument noise at low aerosol concentration 

is responsible for albedo values at BRW and MLO above I. 

These high albedo values are not present in daily averaged data. 

Furthermore, these high albedo values are removed if you 

exclude data where a,P is below 1 Mm·

1

. Hence, the high albedo 

values result from an instrument detection limitation problem. 

Based on only 4-7 years of measurements, the annual cycles 

for the regional stations are less certain than those of the baseline 

stations. The proximity of the regional sites to North American 

pollution sources is apparent in the results, with a monthly 

median value of <lsp at the Bondville site (BND) that is nearly 

two orders of magnitude higher than the a,P al SPO. BND is 

situated in a rural agricultural region and displays an autumn 

high in a,P and low in w,, that coincides with the autumn harvest. 

As evident in the lower a,P and <lap values, the Southern Great 

Plains site (SOP) is more remote than BND. SOP has a similar, 

but less pronounced, annual cycle with late summer highs in a,P 

and <lap and a corresponding minimum in w,,. Little seasonal 

variability is observed in aerosol properties at WSA. Values of 11 

tend to be higher in the summer and likely result from transport 

of fine mode sulfate aerosol from the continent and lower coarsemode production of particles with lower summer wind speeds. 

3.1.4. LONG-TERM TRENDS 

Long-term trends in CN concentration, <lsp• <l•p• w,., and 11 are 

plotted in Figures 3.3 and 3.4 for the baseline observatories. The 

monthly means are plotted along with a linear trend line fitted to 

the data. The aerosol properties at BRW exhibit an annual 

decrease in a,P of about 2% per year since 1980. This reduction 

in aerosol scattering has been attributed to decreased 

anthropogenic emissions from Europe and Russia [Bodliaine, 

1989) and is most apparent during March when the Arctic haze 

effect is largest. The corresponding decrease in the Angstrom 

exponent over the same time period points to a shift in the 

aerosol size distribution lo a larger fraction of coarse mode 

seasalt aerosol. Stone [ 1997] noted a long-term increase in 

surface temperatures and cloud coverage at BRW from 1965-

1995 that derives from changing circulation patterns and may 

account for the reduction in <lsp by enhanced scavenging of 

accumulation mode aerosols. 

52 

Long-term trends in CN concentrations are difficult to 

determine at this time since the data record contains measurements 

from two different instruments, a GE water-based CN counter and 

a TS! butanol-based CN counter. New TS! butanol-based CN 

counters were installed in January 1989 at SPO, January 1993 al 

SMO, January 1991 at MLO, and January 1991 at BRW. The TSI 

butanol-based CN counter concentrations are 1.5-2 times higher 

than the old GE water-based CN counter. The reason for this 

difference is not known. Before any long-term trend analysis can 

be conducted, this difference needs to be resolved, and the data 

sets need to be put on the same scale. 

Previous reports describing the aerosol data sets include: 

BRW: Bod/wine [1989, 1995); Q11akenb11sh and Bod/wine 

[1986); Bodliaine and D1111011 [1993); Barrie [1996); MLO: 

Bodhaine [1995]; SMO: Bod/wine and DeLuisi [1985]; SPO: 

Bodlraine et al. [1986, 1987, 1992); Bergin et al. [1998); WSA: 

Mcinnes et al. [ 1998]. 

3.1.5. SPECIAL STUDIES 

Comparison of Aerosol Ugllt Scattering and Absorption 

Measurements 

CMDL has measured both aerosol light scattering (since 1976) 

and aerosol light absorption (since 1988) at BRW. To obtain 

data representative of clean baseline conditions, measurements 

from the polluted sector, defined by wind speed and direction, 

are automatically removed from the data set. Table 3.5 lists the 

instruments and their period of operation at Barrow. Initially, 

light scattering was measured using a 4-wavelength nephelometer, and light absorption was measured using an aethalometer. 

This original sampling system did not include size or relative 

humidity control of the aerosol sample. New light scanering and 

absorption instruments were installed at BRW (within 2 meters 

of the old instruments) in October 1997. The new instruments 

are designated for North Slope, Alaska (NSA) to distinguish 

them from the co-located BRW instruments. The new system 

obtains measurements at two size cuts by using a valve to switch 

between a 10 μm and I μm impactor. Relative humidity is 

maintained at or below 40% by heating the air sample. The 

BRW and NSA systems were operated simultaneously for 

approximately I year (fall 1997-fall 1998). One year of 

simultaneous light scattering measurements and 2 years of light 

absorption measurements from the co-located instruments were 

compared. It is important to understand how measurements from 

these instruments compare in order to maintain data consistency 

for the entire measurement period. 

The comparison procedure was: 

• Select data for the overlap period October 1997 to October 

1998 for <lsp• and October 1997 to October 1999 for <lop 

• Estimate the absorption coefficient for the aethalometer 

using: a,P = 10 m2

/g *[BC] 
BRW Condensotion Nuclei cm -

3 

400 

200 

MLO 

1000 

800 

600 

~ 400 

200 

SMO 

500 

400 

~ ~I~ 300 

200 

SPO Condensotion Nuclei cm-3 

300 

200 

1992 1995 1996 

BRW 

MLO 

SMO 

SPO 

25 

20 

15 

10 

5 

6 

5 

,_ 

~ 

,_ 

JO 

25 

2.0 

1.5 

1.0 

0.5 

0.0 

1974 

Totol Scattering Coefficient (1/Mm) 

-

-

I 

J v J u 

Total Scotterin Coefficient 1 Mm 

1977 

Fig. 3.3. Long-tenn trends for baseline stations of monthly averaged condcnsa1ion nuclei concentralion and tolal scattering coefficient at 550 nm. A 

simple linear fit is given for the scattering coefficient but is omitted for the condensation nuclei concen1ration since instrument changes make a trend 

line inappropriate. 

• Apply quality control edit corrections to data sets (e.g., 

remove spikes and contaminated data) 

• For the NSA data set, use only I 0 μm size cut data 

• Correct the NSA particle soot absorption photometer 

(PSAP) data for: (a) scattering by particles within the 

filter and (b) spot size. Also, remove low transmittance 

data (e.g., transmittance <0.5 as per Bond er al. [ 1999)) 

• Calculate hourly averages of scattering and absorption 

coefficients 

• Calculate daily averages of absorption for the aethalometer 

and PSAP 

• Remove obvious outliers (four points for the o,P data) 

• Determine the least squares linear fit and correlation 

coefficient for the data sets. Perform the regression for both 

a calculated and forced-to-zero y-intercept 

Figure 3.5 shows that, for the 2 years, there is a relatively low 

53 

correlation between the hourl y averaged PSAP and aethalometer 

measurements (R2 = 0.70), although the instruments agree fairly 

well (the slope is 0.94). Looking at the data on a year-by-year 

basis, the two instruments demonstrated better agreement with 

each other for the second-year period than for the first year 

(slope = 0. 99, R2 = 0.77 and slope = 0.92, R2 = 0.66, 

respectively). This difference is statistically significant, but it is 

unclear what caused this difference. 

For daily averaged data (Figure 3.6) there is a stronger 

relationship between the two instruments' measurements than for 

hourly averaged data and, again, good agreement for the two 

measurements of absorption coefficient. Because particle concentrations and hence, light absorption, are low at the site, often 

near the detection limits of the two instruments, there is considerable noise in the measurements. The improvement in fit for 

the daily averaged values with respect to the hourly averaged 

values is most likely a resu lt of averaging noise in the data over a 

longer time period. 
BRW An strOm Ex onent 550 700 nm BRW Absor lion Coefficient 1 Mm 

2.0 

1.5 

1.0 

0 0.5 

-1 

MLO An strOm Ex onent 550 700 nm MLO 

0 

SMO An strOm Ex onent 550 700 nm 

0 ~& \ 

-10......~.w..~ ....... ~~w.u.~ ....... ~ ...... ~~w...~..w..~ ................ 

0.85 

SPO MLO 1.00 

3 0.95 

0.90 

0 0.85 

-10......~..w..~ ....... ~~w.u.~..w..~ ...... ~~w.u.~ ...... ~ ................ 0.80 

1974 1977 1960 1963 1966 1969 1992 1995 1996 1966 1990 1992 1994 1996 1998 

Fig. 3.4. Long-term trends for baseline stations of monthly averaged Angstrom exponent (550nOO nm), absorp1ion coefficient, and singlc-scauering 

albedo. A simple linear fit to the data is shown. 

TABLE 3.5. Description of Instrumentation at Barrow, Alaska 

lns1rumen1 

MRI nephelometer 

Magee Scientific aethalometer 

TS! nephelometer (model no. 3563) 

Radiance Research 

particle soot absorption photometer (PSAP) 

Period of Operation 

1976-fall 1998 

1988-present 

Fall 1997-present 

Fall 1997-present 

Figure 3.7 shows the hourly variability in the ratio of the two 

instrument measurements as a function of absorption coefficient. 

The relationship between the two instruments appears less variable 

at higher absorption coefficients (cr"" > I Mm-t) but only about 

10% of the data are in this range. At low absorption values (cr.r < 

I Mm' 1

) there is considerable variability due to instrument noise. 

Interestingly, while the aethalometer data are lower than PSAP 

data for high absorption coefficients (consistent with the linear lit 

S1a1ion Comments 

BRW 4 wavelength, no size cut 

BRW Broadband, no size cut 

Specific absorption of IO m2/g used to convert [BC] too"' 

NSA 3 wavelength, I and 10 μm size cut 

NSA 565 nm wavelength, I and 10 μm size cut 

54 

results}, the aethalometer measurements tend to be lower than the 

PSAP's at low Ow 

Table 3.6 summarizes the fit parameters for the absorption 

coefficient. Overall, the linear fits suggest that the BRW 

measurements were consistently lower than the NSA 

measurements. There are other questions that need to be 

addressed in the future with respect to measurements of cr,P at 

Barrow. These include: How much do the differences in 
"e 

~ 

t 2 

3: " 

cc 

c:o 

0 

0 

y = 0 .8 1Ix +0.129 

R2 = 0.744 

. . ·· 

2 

NSA a,. (Mm"') 

y = 0.942x 

A' = 0.701 

3 4 

Fig. 3.5. Comparison of hourly averaged absorption data from NSA and 

BRW, October 1997-0ctober 1999. 

e 

~ 

3 

t 2 

3: " 

cc 

"' 

y = 0.842x + 0.111 

R2 = 0 .925 

y = 0.962x 

A'= 0.883 

-1-=~--~~---~~~~~-~~--~~~ 

0 2 3 

NSA a.,, (Mm"1

) 

Fig. 3.6. Comparison of daily averaged absorption data from NSA and 

BRW. October 1997-0ctober 1999. 

10 

t 

c( " 

(/) 

z 

- 1 t 

t> 

3: 

cc 

"' 0.1 

. . . . ''

1

't .. ~ ... ·:. i .·:: .... : ,_.: 

-~·· 

... 0 .01 +-~~-~~~-~~~-~~~-~~~-~4 

0 2 3 4 

NSA a,, (Mm"1

) 

Fig. 3.7. Variation in the ratio of absorption measured at BRW to that 

measured at NSA as a function of hourly averaged absorption coefficient. 

wavelength of the two instruments influence cr,P? Are there 

corrections that should be applied to the aethalometer: for 

example some sort of spot size correction? How appropriate is 

the arbitrarily chosen I 0 m2

/g used to convert from mass 

55 

TABLE 3.6. Results From Linear Fits of Data 10 Equation: 

BRW = m*NSA for Absorption Coefficient 

Number of 

Parameter Slope (m) R2 Points 

cr'I' (hourly) year I 0.92 ± 0.01 0.66± 0.01 3456 

cr,P (hourly) year 2 0.99 ± 0.01 0.77 ± 0.01 3562 

cr (hourly) both years 0.94 ±0.01 0.70± 0.01 7018 

cr 'I' (daily) year I 0.94 ± 0.03 0.88± 0.02 223 

cr 'I' (daily) year 2 1.03 ± 0.03 0.87 ± 0.02 226 ap 

cr'I' (daily) both years 0.96 ± 0.02 0.89 ± 0.01 449 

concentrations measured by the aethalomeler into scauering 

coefficients? 

In addition lo comparing absorption coefficient measurements, 

comparisons of scallering coefficient as a function of wavelength 

for the BRW and NSA nephelometers were also made for l year 

starting October 1997 (Table 3.7). For the two nephelometers 

there is high correlation despite low particle concentrations and 

hence low scattering measurements. The blue scallering coefficients (cr,p8) have the weakest agreement (slope = 0.92). This 

may be because of problems with the blue photomultiplier in the 

BRW nephelometer. The blue scattering measurement al BRW 

was often similar to or even lower than the green scallering 

measurement, while at NSA the cr,P8/cr,pG ratio was typically 

greater than I as expected. 

Differences between the two instruments may be attributable 

lo several factors. Opticall y, the two ncphelometers are (almost) 

identical, so it was assumed that correcting for the truncation 

angle would not improve the comparison. Thus for this 

comparison no corrections for truncation were applied lo either 

instrument. Changes in filler bandpass and calibration error may 

also play a role. 

Optical Property of Indian Ocean Aerosols 

During February and March 1999 the CMDL aerosol group 

participated in the Indian Ocean Experiment (INDOEX), a multiplatform field campaign that took place over the Indian Ocean. 

A central focus of the campaign was to assess the role of 

aerosols from the Indian subcontinent on direct and indirect 

radiative forcing, as well as the role of convecti ve cirrus in 

aerosol transport and photochemical processing. 

This region of the world has a fast growing population that is 

becoming more industrialized with emissions of C02, aerosols, 

and sulfates expected soon lo surpass those of North America 

and Europe. Because of these potentiall y high future emissions, 

an understanding of climate forci ng and transport of trace gases 

and aerosols in this region is critical to being able to predict 

global climate forcing. 

TABLE 3.7. Results From Linear Fils of Data to Equation: 

BRW = m*NSA for Scallering Coefficient 

Parameter Slope (m) Ri Number of Points 

<J"'e 0.92 ± 0.00 0.95± 0.01 3456 

<J..,a 1.00± 0.00 0.94± 0.01 3456 

(J'i'R 0.97 ± 0.00 0.94 ± 0.01 3456 
The INDOEX campaign was based at the Maldive Islands, 

about 700 km southwest of India. As part of the campaign, 

CMDL performed in situ measurements of aerosol optical 

properties on two separate platforms: the Scripps Institution of 

Oceanography (SIO) climate observatory on the island of 

Kaashidhoo (KCO) and onboard the NCAR C- 130 aircraft. 

These measurements included the aerosol total and hemispheric 

backscattering coefficients, the aerosol hygroscopic growth 

factor (f(RH)), and the aerosol absorption coefficient. Here the 

aerosol hygroscopic growth factor is defined to be the ratio of the 

aerosol scatteri ng coefficient at 85% relative humidity to the 

aerosol scattering coefficient at 40% relati ve humidity. 

During the northeast monsoon season (January-April) the 

lntertropical Convergence Zone is south of the island and air 

circulation is from the Indian subcontinent. Thus aerosols 

measured at KCO during this time represent polluted continental 

air masses. Figure 3.8 shows a time series of the measured 

aerosol optical properties at KCO. 

Back trajectory calculations show a change in the air mass 

origi n on March 7 (Day 66) from the east Bay of Bengal region to 

the west Arabian Sea. Evidence of this change is apparent in a 

decreased aerosol loading and accompanied by lower cr,P and <J,p 

values. Despite this difference in aerosol loading, the aerosol 

intensive properties of single-scattering albedo, backscatter 

fraction, and hygroscopic growth are simil ar between the two 

regions. The lower aerosol loading in the Arabian Sea air masses 

t60 

140 

120 

100 

80 

60 

40 

20 

Jt: 

·r! 

a) Scattering Coefficient (Mm.

1

) 

- Total Subrricron 

o+-----...-----.----.,-----...----... 

50 

45 

40 

35 

30 

25 

20 

15 

10 

5 

40 50 60 70 80 90 

Day of Year 

b) Absorption Coefficient (Mm.

1

) 

-Total - Submicron 

+-----.------,.-----.,------,----~ 

40 50 60 70 80 90 

Day of Year 

likely resulted in a larger contribution to the total scattering from 

supermicron seasalt particles as evident in the smaller fractions 

of submicron aerosol scattering and absorption from the Arabian 

Sea. 

In addition to surface-based measurements at KCO, aerosol 

optical properties were measured in situ from the NCAR C-130 

research aircraft using an aircraft version of the ground-based 

CMDL aerosol measurement system. Aircraft measurements 

were necessary for information on spatial (i.e., horizontal and 

vertical) and temporal variability of aerosol optical properties. 

Vertical profiles and horizontal legs at altitude were conducted to 

characterize aerosol variability in the region with coverage of 

much of the Indi an Ocean Basin between 8°S and l 7°N. 

The measured aerosol light scattering coefficients over the 

northern Indian O cean were typically several times those 

observed at perturbed continental sites in the United States. 

The highest aerosol concentrations were observed in the 

northern Indian Ocean (north of the Maldives). The aerosol 

was substantially darker than U.S. sites with an average 

single-scatte ring albedo for all flights near 0.85. The o ptical 

depths in the region, calculated using aircraft aerosol optical 

propert y data, were in the 0.15-0.35 range for most days. 

Elevated aerosol layers, decoupled from the surface, were 

observed in over one-third of the verti cal profiles. Figure 3.9 

shows two vertical profiles, with one profile s howing an 

e levated aerosol layer. 

0.90 

0.85 

0.80 

0.75 

0.70 

0.65 -1-----...-----.----,...----.,-------. 

40 50 60 70 80 90 

Day of Year 

d) f(RH) 

2.4 - TOUll Submicron 

40 50 60 70 80 90 

Day of Year 

Fig. 3.8. Time series of measurements from KCO in 1999: (a) aerosol total and submicron scaueri ng coefficient, (b) aerosol total and submicron 

absorption coefficient, (c) aerosol total and submicron single scattering albedo, (d) aerosol total and submicron hygroscopic growth. All values are 

reported for 550 nm wavelengths. 

56 
Single-Scattering Albedo 

0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 

7 

6 

2 

' L 

Ascent Profile NNW of Male 

5.7 N, 73.3 E, 16 February 1999 

I 

I 

, 

·20 ·10 0 10 20 30 40 50 60 70 80 90 100 

Reference Oap, 550 nm• ap, 1)65 nm (Mm"1

) 

Single-Scattering Albedo 

0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 

7 

6 

5 

4 

I 

L 

r 

Ascent Profile From Male 

4.2 N, 73.5 E, 25 March 1999 

I I 

.. ._ - -1- --·- ---- ·- -' .. _, _ 1 I I 

3 . 

2 

I 

I - - - -,-

·10 0 10 20 30 40 50 60 70 80 90 100 110 

Reference <Jsp, 550 nm• (! >. 560 111 (Mm"

1

) 

Fig. 3.9. Two vertical profiles of total scattering coefficienl (CJ,.,. red). absorption coefficient (CJ,"' blue), and single-scattering albedo (green) obtaim:d 

by CMDL instruments onboard the NCAR C-130 aircraft. The profile on the left shows a thick aerosol layer from the surface lo -2 km. The profile 

on the right shows an elevated aerosol layer with a peak at -3 km altitude. 

Table 3.8 lists the mean values of the measured parameters 

and compares them to those from other CMDL surface sites. In 

comparison to aerosol properties measured at Bondville (a U.S. 

continental site) and Sable Island (a Canadian marine site) the 

aerosol from the Indi an subcontinent has a far greater 

absorption coefficient. Unlike aerosols from U.S. continental 

sites, the single scattering albedo at KCO declines with an 

increase in aerosol loading (Figure 3. 10). Apparently under 

highly polluted conditions the aerosol soot fraction relative to 

sulfate is higher than that from U.S. sites. This difference could 

reflect the regional sources of sulfate and carbon as well as rates 

of in-cloud sulfate oxidation. Although the Indian subcontinent 

aerosol has a large absorbing fraction, its mean hygroscopic 

growth is similar to that from regions with less absorbing 

aerosol. This difference points to either a significantly different 

composition or morphology for the absorbing components of 

aerosols from the Indian subconti nent with respect to North 

America. 

TABLE 3.8. Means and Variabilities of Pollution Aerosols 

Aerosol Property Bay of Bengal Arabian Sea Sable Island Bondville 

Osp 95±20 54±9 42±35 60±49 

(J.,, 25 ±7 10±3 2±2 5±4 

F Osp 0.70 ±0.06 0.62±0.05 0.26 ±0.10 0.86±0.07 

F o.,, 0.85 ±0.04 0.80±0.07 0.81 ±0.10 0.82±0.10 

j{RH) 1.65 ±0.10 1.67 ±0.14 1.7 ±2.7* 1.5 ± 0.4t 

* Mcf1111es et al. [ 1998] 

tS. Koloutsou-Vakakis, et al., Aerosol properties at a midlatitude northern hemisphere continental site, submitted to J. Geophys. Res., 1999 

Scattering coefficients, CJ"', are measured at L = 550 nm. Absorption coefficients are measured at O = 565 nm. FCJ'fl and FCJ"" are the subrnicron 

fractions of aerosol scattering and absorption, respectively.j{RH) is given for a relative humidity of 85% relative to 40%. Variabilities are reported as 

±I standard deviation. Sable Island, Nova Scotia, and Bondville, Illinois, are anthropogenically perturbed marine and continental sites, respectively. 

The range ofjlRH) at Sable Island is between polluted and clean air masses observed over a -10-day period. Time periods of 4 hours before and after 

rain events were excluded from the KCO data. 

57 
550 nm Wavelength, Aerosol Diameter< 10 um 

1.00 

.g 0.95 0 

.0 

~ 

bl) 

c: ·5 0.90 ...... 

~ (.) 

(/) 

I 

0 

~ 0.85 Cl) 

c: 

<:I 

:0 

0 

~ 0.80 

0.75 

arrow 

~Sable Island 

-+-Southern Great Plain 

..,._Bondville 

-

1 - ---+---• -o Kaashidhoo 

a a 

a \ I 

o ·-

a 

0 25 50 75 100 125 150 

Scattering Coefficient [Mm1

] 

Fig. 3.10. Aerosol single-scattering albedo plotted against scattering 

coefficient (hourly average data). Data are from the four CMDL North 

American monitoring stations (entire period of record) and the 

Kaashidhoo Island station in the Indian Ocean (February and March 

1999). 

3.2. SOLAR AND THERMAL ATMOSPHERIC RADIATION 

B. BODHAINE (EDITOR), G. ANDERSON, G. CARBAUGH, 

E. DUTTON, B. HALTER, D. JACKSON, D . LoNGENECKER, 

D. NELSON, R. STONE, R. TATUSKO, AND N. Wooo 

3.2.1. RADIATION MEASUREMENTS 

Introd11ctio11 

The CMDL Solar and Thermal Atmospheric Radiation 

(STAR) group provides supporting radiation information for 

baseline climate monitoring activities and investigates trends and 

variations in the observed surface radiation budget. Energy 

derived from the earth's radiation budget is responsible for not 

only maintaining the temperature of the planet but for 

atmospheric and oceanic motions. Predicted anthropogenic 

trends in surface radiation quantities at globally remote sites are 

near or below the level of detectability, on the decadal time 

scale, for the currently available instrumentation. However, 

fundamental climatological variability in the global surface 

radiation budget is not adequately understood. Therefore, STAR 

measurements contribute to this basic knowledge. These 

contributions include the definition of diurnal and annual cycles, 

effects of cloudiness, variations 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 

UY changes), and possible anthropogenic modification to 

cloudiness. The STAR group also makes remote sensing 

measurements of various atmospheric constituents that are 

potentially responsible for variations in surface radiative 

quantities. In addition to the research conducted by CMDL, 

STAR measurements contribute to several international 

databases. International databases are needed to evaluate the 

radiation and energy budget necessary to diagnose the climatic 

time scale general circulation of the atmosphere. These 

observations also contribute to satellite-based projects by helping 

verify spot estimates and to allow features of the intervening 

atmosphere tO be deduced. Still, a major goal of the monitoring 

program is to obtain as long and as complete a record as possible 

of surface radiation parameters that 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 STAR group maintains complete and 

continuous surface radiation budget observations at several 

globally diverse sites with various ancillary observations. The 

following describes those projects and recent changes. 

58 

Baseline Monitoring 

Surface radiation measurements have been made at the four 

principal CMDL baseline observatories (BRW, MLO, SMO, and 

SPO) since the mid-I 970s. The different environments and 

conditions at the various sites resulted in somewhat different 

programs evolving at each site. The basic measurements made at 

;ill sites include the downward components of solar radiation: 

global, diffuse, and direct. Broadband thermal infrared 

irradiance measurements were added over the past I 5 years. 

Upward solar and thermal infrared irradiances are measured at 

sites where the surrounding terrain is representative of a larger 

regional area, as at SPO and BRW, for at least part of the year. 

The records acquired at these sites constitute some of the longest 

known in the U.S. for solar radiation research. The raw data are 

routinely transmitted over telephone lines or the Internet to the 

central data processing facility in Boulder, where data editing, 

final calibrations, graphical inspection, and archiving, are 

performed, as discussed in section 3.2. 11 . 

Other Measurement Sites 

Boulder Atmospheric Observatory (BAO tower). Observations of upwelling and downwelling solar and thermal 

irradiances began in 1985 at the top of a 300-m tower, known as 

the Boulder Atmospheric Observatory (BAO) located near Erie, 

Colorado. Nearly continuous observations of all quantities have 

been made with hourly resolution until 1992, 3-min resolution 

until 1998, and I-min resolution thereafter. The upwelling 

radiation data provide a unique view of surrounding agricultural 

land making the data more representati ve than typical surface 

based solar radiation budget observations. The data from the site 

are being used by the National Aeronautics and Space 

Administration/Clouds and Earth's Radiant Energy System 

(NASNCERES) and NOAA Geophysical Fluid Dynamics 

Laboratory (GFDL)/General Circulation Model (GCM) 

programs and have been used by Nemesttre et al. [ 1994], Cess et 

al. [1995), D1111011 and Cox [1995), Garrell and Prata [1996), 

and several earlier papers. Since 1990 observations of direct 

solar and downwelling solar irradiances have also 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). 

Kwajalei11. Observations of direct solar and downwelling 

solar and thermal IR irradiance began at Kwajalein in 1989. 

Kwajalein is a small , <4 km2

, island in the tropi cal west 

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 have been used as oceanic representati ve by Dutton 

[ 1993), Whitlock et al. ( 1995]. and Bishop et al. [ 1997]. and are 

currently being used by CERES and the European Center for 

Medium-Range Weather Forecasts (ECMWF) GCMs. 

Substantial upgrades to the Kwaj alein radiation measurements 

were carried out in recent years, including the addition of 

spectral total and diffuse, broadband diffuse, UY-B, and PAR 

instruments, as well as improved solar tracking capability, 

including a shade disk pyrgeometer. Data from K wajale in 

have been submitted to the BSRN data archi ve. 

Bermuda. Observations of downwelling solar and thermal IR 

began at the NASA Bermuda Tracking Station al the eastern end 

of Bermuda in 1990. The rather small size and low relief of the 

island in the lower midl atitude westerlies has 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 have been submitted to the BSRN data archi ve and 

have been used by Whitlock et al. [ 1995]. Bishop et al. [ 1997), 

and currently by the CERES program in satellite comparison and 

Daily Average 

(24-Hour) 

OayolYear 

Monthly Average Time Serles 

400 --

350 +-------------------~ 

E 250+-Hll--t--.-IH- lr-ollf---+-,,--Ll--.,.......f--~~-+-M-~Hf-il~ 

~ 

8 200t-1'lHt'ffHt-ttTHtt-\r<!14"~-tt-H-11~'ttt-Hl"tt'tMll-'l Htllft-~ 

e 

.. 

~ 150 +----.__--~-t-...._ ____ _,.__._ __ +--~ 

i loo +--~.---on-g---er-m-...., ___________ __, 

variations 5o r--~'--~~--.,..__-----------~ 

1975 1980 1985 1990 1995 2000 

Year 

validation studies and by ECMWF and GFDL in their GCM 

testing. On December 8, 1998, the monitoring site was moved 

from the NASA tracking station (32.2670°N, 64.6670°W) near 

the east end of the island to the top of Prospect Hill near the 

center of the island (32.3009°N, 64.7659°W). This move was 

necessitated by the imminent closing of the tracking station and 

by the desirability of operating further from the influence of 

occasional island-induced clouds that are generated at, and 

dynamically attached to, the east end of the island. The new site 

is ably tended by the Bermuda Biological Station for Research. 

Basic Measurements 

Broadband irradiance. The basic measurements currently 

conducted at each of the four baseline observatories for the past 

24 years include normal direct and downward broadband solar 

irradiance, downward solar irradiance in the 0.695-2.8 μm band, 

and wideband spectral direct solar irradiance. Downward broadband thermal irradiance measurements were added at all sites in 

more recent years, as well as upwelling irradiance measurements 

at SPO and BRW. The wideband spectral direct observations are 

obtained manually with a filter wheel pyrheliometer under clearsky conditions while the others are sampled at 1 Hz with I -min 

averages recorded on computer media. Preliminary data from all 

CMDL radiation sites are generally available graphically within 

a couple of days of acquisition in the radiation section of the 

CMDL Web home page and subsequently as described in 

Section 3.2. 11. Figure 3. 11 shows different summaries of the 

24-yr record of total solar irradiance collected at Samoa using 

the single pyranometer technique. 

400 

Annual Cycle 

(monthly averages) 

;;-- 300 

E 250 +-~-~~--------~~~----< 

~ B 200 +--1- ....___.. ....._~-----+- >---'----'-~ 

e 

.. i 150 

100 

10 11 12 

Month 

Annual Average 

1975 1980 1985 1990 1995 2000 

Year 

Fig. 3. 11 . Total solar irradiance record for American Samoa obtained from a pyranometer ( 1975-2000}, summarized for four different presentation 

methods. The comments in the ovals in each figure section point out some of the highlights of that panicular presentation. 

59 
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 is intended for use at the surface only. 

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 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 opti cal 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 sunphotometry. The data record from this observation is 

shown in Figure 3. 12 through 1999. The accuracy of the data is 

no better than 0.03 optical depth units and should only be used 

accordingly when sunphotometer-derived data are not available. 

0.30 

0.25 +--------; 

.&: 0.20 

1S. 

~ 'Bo.15 

a 

00.10 

0 .05 

- Bam>W 

- Am. Samoa 

S. Polo 

0.00 t=~~::::::~~~~~~~:.:!--,--._::~_:;::~';_.,~ 

n 82 87 92 97 

Year (-1900) 

Fig. 3. 12. Aerosol optical depth (monthly averages from wideband 

estimates) at the four CMDL baseline observatories. The values arc 

derived from fihcr-wheel pyrheliometers that produce lower accuracy 

and precision measurements than sunphotometers but have proven to be 

more stable and viable than sunphotometers in the CMDL monitoring 

program. Seasonal, volcanic , and inter-site variations are seen in the 

figure. The recent spike at Barrow is believed to be caused by smoke 

evenls originaling in Russia. 

MLO appare11t tra11smissio11. The transm1 ss1on for direct 

broadband solar irradiance through the atmosphere above MLO 

is monitored using a quantity known as the apparent 

transmission. The 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 airmass divided by the 

irradiance at the next smaller integer air mass as first defined by 

Ellis a11d P11esc/1el [ 1971 ]. The apparent transmission measurement is inherently stable over time because it is independent of a 

radiometer calibration value and also, therefore, quite sensitive 

to small changes in transmission that can be due to aerosols, 

ozone, or water vapor. Previous studies [Bodhai11e et al., 198 1; 

D1111on et al .. 1985] have shown that aerosols tend to dominate 

observed changes in the monthly averages of 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, and 

0.94 

0.92 

0.90 I 0.88 l 0.86 

I- 0.84 

0.82 

0.80 

0.78 

57 61 ~ ~ n n ~ ~ ~ ~ ~ 

YEAR (·1900) 

Fig. 3.13. Monthly means of apparent solar transmission for clear skies 

at Mauna Loa. Data are updated through the end of 1999 and show 

continued recovery towards the baseline conditions last established in 1.he 

late 1950s. Another few years of data will be required to de termine if 1he 

earlier baseline level will once again be auained or if a different 

background level exists. 

60 

Pinatubo in 1991 and an annual oscillation caused primarily by 

the springtime transport of Asian aerosol over the site [Bodlrai11 e 

er al., 1981]. Figure 3. 13 is complete through 1999 and most 

recently shows that recovery from the eruption of Mt. Pinatubo 

required several years. The fact that the Mauna Loa apparent 

transmission record took several years to recover from Pinatubo 

is evidence of the sensitivity of the measurement since it is 

known from other measurements by CMDL and others that the 

optical depth of Pinatubo in 1995 was already very low, on the 

order of 0.005 at 500 nm. 

Optimal Total Solar Irradia11ce Meas11reme11ts 

Total downwelling solar irradiance is the primary input 

component of the earth's energy budget. Instruments for 

measuring this quantity at the earth 's surface first appeared in the 

19th century with current single-instrument technology for 

routine observations maturing in the 1950s and 1960s. Many of 

the current commercially available instruments meet the highest 

standards of the World Meteorological Organi zation (WMO) for 

such measurements, but only specimen instruments are typically 

well characterized. The uncertainties in the measurements using 

these instruments are often given for extended averaging, days to 

months, which reduces the uncertainties inherent in instantaneous measurements. In recent years there has been increased 

interest in near-instantaneous solar irradiance observations for 

various research applications. These applications include 

comparisons to values derived from satellite overpasses and 

radiati ve transfer model calculations using a nearly instantaneous 

quantification of the atmospheric state. For these comparisons 

the full extent of the uncertainty of the irradiance measurement is 

important and needs to be low enough to be useful in improving 

the satellite algorithms and radiative transfer models, particularly 

when there are significant parameterizations used. While 

different individuals had ideas about improving surface solar 

irradiance observations, the first internationally organized effort 

to make improved irradiance measurements (solar and thermal 

IR) a primary goal was the BSRN (http://bsrn.ethz.ch/) project of 

the WCRP (http://www.wmo.ch/web/wcrp/wcrp-home.html). 
The first step in the improvement of the instantaneous surfacebased solar irradiance measurements was the recommendation 

for the use of the combination of separately measured direct and 

diffuse irradiance, which incorporates the highly accurate direct 

beam measurement capabilities developed over the past 4 

decades with the greatly reduced cosine response error inherent 

in the single-instrument Oat-plate receiver of the pyranomcter. 

This method of measuring total solar irradiance led to 

improvements discussed by Olwwra el al. [ 1998], Micha/sky el 

al. [ 1999]. and Bush e1 al. [ 1999]. As a result this measurement 

method has made a large amount of direct and diffuse solar 

irradiance data available to the research community, which was 

useful because the most sophisticated and physically complete 

radiative transfer models also separately calcul ate these 

quantities. The easiest to calculate and also easiest to measure is 

the direct component, and most significant problems in measurements and models have been solved so that the agreements 

between the two are very good, typically less than 3 W m-2

• if 

there are no blatant errors in either. Such is not the case for the 

diffuse component. For the diffuse, there are difficulties in 

specifying correct modeling procedures, specifying correct 

model input values, and knowing the measurement truth since no 

standards exist. From the instrument perspective, not only can 

signal strengths be low, but also there are no reference standards 

that exist to which the measurement can be compared to 

absolutely determine measurement error. This has resulted in 

some recent modifications in the way in which STAR is making 

diffuse irradiance measurements, both in the type of instruments 

used and the adjustments for thermal offsets induced in the 

certain diffuse pyranometers. The specifics of the new 

measurements and adjustments to older data are given by D11110 11 

et al. [2000]. With these changes it is estimated that diffuse 

irradiance is currently measured to within about 5 W m2

. This 

results in accuracies to within about 8 W m-2 for total solar 

irradiance when determi ned from the combined diffuse and 

direct measurements. 

Improved Tlzen11al IR Irradiance Measurements 

Although there has been a substantial reduction in the 

uncertainty of thermal infrared irradiance measurements in the 

last 10 years, from nearly 30 W m2 in the late 1980s to about 5 

W m-2 now, there still appears to be room for further 

improvements and the potential for the establishment of a 

measurement reference standard for these measurements. Over 

the past 2 years, STAR has become involved in the efforts of 

BSRN and the World Radiation Center (WRC) in Davos, 

Switzerland, to work towards these potential improvements. 

This work is conducted through the recent establishment of new 

radiance measurement capabilities that rely on absolute, selfcalibrating, sky-scanning instruments. CMDL, working with 

BSRN, organized and participated in the first International 

Pyrgeometer and All-sky Scanning Radiometer Comparison 

(IPASRC-1) in September 1998 where this process to establish 

such capabilities and reference standards was begun [Philipona 

et al., 1998]. 

3.2.2. SOLAR RADIATION CALIBRATION FACILITY 

Solar Radiation Monitoring Support 

CMDL baseline observatories. Support for monitoring 

surface radiation budget components at the four CMDL baseline 

observatories (BRW, MLO, SMO and SPO) was maintained 

61 

during 1998 and 1999. Routine instrument exchanges and 

recalibrations were completed as required, and modifications and 

enhancements were incorporated as necessary. 

CMDL BSRN monitoring sites. At the three CMDL BSRN 

sites located at Bermuda, BAO, and Kwajalein, measurements 

continued and operational additions and improvements were 

completed. The Bermuda site was relocated during 1998, and a 

new instrument platform was designed, purchased, and deployed. 

Additional measurements were also added to the relocated 

Bermuda BSRN site with the installation of meteorological 

sensors. Wind speed, direction, pressure, temperature, and 

relative humidity are now being monitored at all three sites. The 

Bermuda meteorology sensors were installed in late 1998, and 

Kwajalein meteorology sensors were installed in late 1999. 

Collaborative activities. Post mission performance checks of 

sensors used during the Study of the Heat Budget in the Arctic 

(SHEBA) project were completed and provided to the 

institutions involved (NOAA Air Resources Laboratory, 

National Center for Atmospheric Research (NCAR), United 

States Navy/Post Graduate School, and University of Washington). Other checks were performed on sensors used by the 

NOAA Environmental Technology Laboratory, Indi an Ocean 

Experiment (INDOEX), NOAA aircraft facility, University of 

Utah, and NCAR. 

SRF Reference Radiometers 

All CMDL solar radiation measurements are referenced to the 

World Radiometric Reference (WRR) as defined using the 

absolute scale. Comparison of the Boulder, Colorado, Solar 

Radiation Facility (SRF) reference radiometers to peer radiometer!: is the accepted method of ensuring long-term stability of 

their performance. The SRF has been comparing its re ference 

radiometers an nuall y with radiometers at the National 

Renewable Energy Laboratory (NREL) located in Golden, 

Colorado. At these comparisons, NPCs (NREL pyrheliometer 

comparisons), a WRR is constructed by forming an average 

irradiance with a group of radiometers that participated in the 

latest International Pyrheliometer Comparisons (!PC) in Davos. 

Typically this group consists of at least fi ve radiometers. 

Additionally, the SRF reference radiometers are compared 

every 5 years with the World Standard Group of radiometers 

maintained at the World Radiation Center in Davos. These 

comparisons are referred to as IPC. Regular checks of reference 

radiometer performance are also performed using groups of SRF 

sensors and checking their performance against each other. 

Table 3.9 illustrates the results of comparisons of SRF 

references and their variability with respect to the WRR over 

time periods on the order of years. 

TABLE 3.9. Comparisons of SRF References 

Pyrheliometer AHF28553 TMI 67502 

Comparison WRR Factor WRR Factor 

IPC VIII (1995) 0.99756 0.99869 

NPC 1998 0.99783 

NPC 1999 0.99741 

SRF Windowed Reference Radiometer Development 

The reference radiometers used by the SRF have cavity-type 

receivers that are open to the environment, which makes them 
unsuitable for continuous deployment at a moni toring site in an 

unmanned mode since dust, dirt, rain, insects, and other debris 

can enter the cavity receiver. Typicall y, reference cavity 

radiometer measurements arc limited to fair weather, clear days, 

and manned operation. Testing of unmanned, all-weather cavity 

radiometers equipped with windows was begun by the SRF 

during 1998. Initial results using a cavity equipped with a quartz 

window material were compromised by the sprectral limitations 

of the quartz window. The longwave cutoff of the quartz 

window material blocked solar radiation in the region above 4 

microns. During atmospheric conditions when water vapor 

concentration is low, there is solar energy present beyond 4 

microns. These conditions can occur in Colorado. Calcium 

nuoride window material with a longwavc cutoff beyond 4 

microns was selected as a possible replacement for the quartz. 

Comparisons between windowed and unwindowed cavity 

radiometers were conducted during 1999 using quartz and 

calcium Ouoride windows as presented in Figure 3. 14. 

The data in Figure 3.14 ill ustrate the differences that are 

potentially present between windowed and unwinclowed cavity 

radiometers under various atmospheric conditions. One cannot 

assign a unique window transmission factor, because each day 

generates a different factor depending upon the transmission of 

the atmosphere with the apparent dominant factor being the 

water vapor concentration. 111is presence of the water vapor 

effect is also suggested by results obtained using conventional 

pyrheliometers. Special calcium nuoridc windows were 

fabricated to replace the usual quartz windows on SRF 

pyrhcliometers. The pyrheliometers were calibrated with an 

unwindowecl reference cavity and then operated side by side at 

the SRF, and the data show an apparent water vapor effect when 

pyrheliometers with calcium Ouoride windows were compared 

with pyrheliometers "ith quartz windows. Some results of these 

comparisons are presented in Figure 3. 15. 

Cavity radiometers and conventional pyrheliometers equipped 

with calcium nuoride wi ndows were deployed at the SRF roof 

facility in early 1999, and the long-term feasibility of using 

calcium nuoride windows is being investigated. Deployment of 

the first all-weather cavity radiometer will be lo the BAO BSRN 

site in late 2000. Results of the SRF all-weather windowed 

cavity work were presented at the 1998 BSRN meeting, the 

CMDL annual meeting in 1999, and the American 

Meteorological Society Tenth Conference on Radiation in June 

1999. 

SRF Relocation 

During March 1999 the SRF was relocated to the new David 

Skaggs Research Center (DSRC) on the National Institute of 

Standard Technology (NIST) campus at 325 South Broadway in 

Boulder from its prior site at 3 100 Marine Street site where it 

operaced for for 24 years. Measurements were begun at the new 

location during April 1999, and the facility was fully operational 

by mid-summer 1999. 

SRF /11ternatio11al Activities 

Global Ah11osphere Watch (GAW). Visitors from GAW 

baseline stations at Ushuaia, Tierra del Fuego, Argentina; West 

Sumatra, Indonesia; Tamanrasset, Indonesia; and the Chinese 

station at Waliguan sent personnel to Boulder for training and 

site upgrade activity in 1998 and 1999. Contacts were also 

maintained with the Brazil GAW station at Arembepe. 

0.97 ...----------------------. 

.... 

~ 0 

.... 

c 

~ 

-0 

0 

·::: 

0.96 

0.95 

...... ' .. ::: :::: :· ....... . 

0.94 . .............. : ~ ·. ~: : ·:.:: ·::.: ·:::::::::::::::: . 

i:z: "0.93 .._ __ _._ __ _._ __ __.. __ __. ___ .._ _ ___. 

JO 40 so 60 70 80 90 

Sola r u nith Angle 

Fig. 3. t4. Examples of clear-sky window transmissions for windowed 

cavity radiometers used for measurements at the CMDL facility in 

Boulder, Colorado. The calcium fluoride (solid line) window resuhs in 

less day-to-day variability compared with the Suprasil 300 (do11ed line) 

that is a 1ype of quanz. 

62 

20~-------- --------~ 

1 

- 10 ! 

o lrradia nce Differences (CaF2 "indo,.s) 

a lrradiancc Differences (Qlz Windows) 

M Irradiance Differences ((Qtz and CaF2 Windo\\S) 

0 

~ 0 0 0 

~ Ot---=--=;;-:i!io:.::"o<~P-....rr.---<>------.,.- -_-_-_-_-_-__-_o_-t 

~ ····~ ··· ···IJ~"''D•••••• .. •·"··············a"·• ··· ~··· ·"··· ········ .. ~ Q " t3 Q M 

~ - (0 '::" M" 

:g .. " -;;ttw"M .r M M 

f M .M4M 

~ -20"---------------------' 0 2 3 4 

IPW Path in cm (from FSUGPS-IPW) 

Fig. 3.15. Examples of measured irradiance differences between two 

pyrheliometers equipped with quanz windows, two pyrheliome1ers 

equipped with CAF2 wi nds, or 1wo pyrheliometers equipped with the 

quani:. and CAF2 windows. Measurements were made on clear sky days 

at the DSRC in Boulder. 

Collaboration with NREL personnel regarding data archiving 

procedures was begun, with NREL also hosting personnel from 

GAW stations and conducting site visits to Arembepe and 

Ushuaia for the purpose of installing data processing software 

and training site personnel in data editing, analysis, and 

archiving procedures. 

Baseline Surf ace Radiatio11 Network (BSRN) activities. The 

SRF coordinated the process of upgrading the Algeri an GAW 

site to BSRN status. This involved purchase of a dual tracking 

disk shading system, pyrgeometer, pyranometer, new data 

logger, and desktop computer as well as training of the Algerian 

site personnel in the install ation and use of the new items. 

3.2.3. AEROSOL OPTICAL DEPTH REMOTE SENSING 

Aerosol optical depth measurements with the FWNIP 

continued at the CMDL baseline stations at BRW, MLO, SMO, 
and SPO. The Physikalish-Meteorologisches Observatorium 

Davos (PMOD) tracking sunphotometer continues to collect data 

in the Mauna Loa dome, as it has for the past 17 years. In 

addition a new precision filter radiometer (PFR) was installed in 

the MLO tracking dome at the end of 1999. This PFR has four 

channels (367.6, 412.0, 501.2, and 862.4 nm) and is the next 

generation tracking sunphotometer from PMOD in Switzerland. 

A small group of handheld instruments is still used for special 

projects, and instrument calibrations have been maintained at 

MLO. These handheld instruments were used in the Aerosol 

Characterization Experiment (ACE-I) and ACE-II field 

programs, as well as in the arctic and antarctic. 

A group of multifilter rotating shadowband radiometers 

(MFRSR) were deployed at BAO, Boulder, Bermuda, and 

Kwajalein. These MFRSRs were installed at Bermuda (February 

1996), K wajalein (April 1996), Boulder Atmospheric 

Observatory (November 1996), and Boulder (July 1999) in 

conjunction with the BSRN program. The main goal of this 

program is to obtain a spectral optical-depth time seri es and to 

maintain calibrations using Langley analysis. Data are currently 

downloaded from the sites automatically and archived on the 

STAR computer. 

A four-channel (368, 412, 500, and 865 nm) tracking 

sunphotometer (SPO 1-A) manufactured by Carter-Scott Design 

was purchased for operation at BRW during the northern 

summer and at SPO during the austral summer. This instrument 

travels from pole to pole every year and is installed temporarily 

in the MLO tracking dome after every move for comparison with 

the MLO optical depth instruments, particularly the PFR because 

of the similar wavelengths. 

3.2.4. MLO AND BOULDER UV SPECTRORADIOMETERS 

!11troduction . 

UV spectroradiometcrs were installed at MLO in July 1995 

and at the Boulder DSRC in June 1998. The first instrument 

(UVL) operated at MLO until June 1997. The next instrument 

(UV3) was installed at MLO in November 1997 and is still in 

operation. After remo,al from MLO, the UVL instrument was 

installed in Boulder and then replaced by a new instrument 

(UV4) in September 1999. UV data from MLO were described 

by Bod/wine er al. [ 1996, 1997], and briefly in CMDL Sw11111a1)' 

Reports No. 23 and 2.J [Hofman11 er al., 1996, 1998]. The UV 

irradiances measured at MLO arc much larger than at lowaltitude midlatitude locations, primarily because of less Rayleigh 

scattering, but also because of lower column ozone in the 

subtropics. The complete data set selected for clear mornings at 

MLO and clear mornings and afternoons at Boulder is presented 

in this report. Clear mornings occur at MLO approximately 60% 

of the time providing an excellent site for solar radiation 

measurements. All processed spectral data are available from 

the solar radiation division of the CMDL program. 

Jnstrum en tatio11 

The UVL spectroradiometer was described by McKe11 zie er al. 

[ 1992] and Bod/wine et al. [ 1997]. Briefly, a diffuser designed 

to minimize cosine error and machined from Teflon is mounted 

as a horizontal incidence receptor to view the whole sky. For 

UVL, stepper-motor driven gratings cover the spectral range of 

290-450 nm in a single scan with a bandpass of about l nm. The 

newer instruments (UV3 and UV4) cover the range 285-450 nm 

with a bandpass of about 0.8 nm and use fiber optic cables to 

transmit the light from the sensor to the spectrometer. A 

complete forward scan for UVL requires about 3 minutes. The 

UV3 and UV4 instruments do a backward scan and then a 

forward scan centered at the desired solar zenith angle (SZA) 

and, therefore, require about 6 minutes for a complete 

measurement. All instruments are programmed to perform scans 

every 5 degrees of SZA during daytime hours. 

63 

Absolute calibrations of the spectroradiometers are performed 

at approximately 6-mo intervals using 1000-W FEL lamps 

traceable to NIST standards. Weekly stability calibrations are 

performed using mercury lamps and 45-W standard lamps as 

long-term stability checks. The expected long-term accuracy of 

the spectroradiometer systems is expected to be better than ±5%. 

Data Analysis 

For the following analyses, UV spectroradiometer data for 45° 

SZA were chosen for clear mornings at MLO during the July 

1995-December 1999 time period. This gives approximately 4.5 

years data and includes ozone values in the range of 212-330 

Dobson units (DU). For Boulder data, 70° SZA and the period 

July 1998-December 1999 were used, covering an ozone range 

of 230-390 DU. Clear mornings at MLO and Boulder were 

determined in the same manner as in previous studies; that is, a 

day was accepted as a clear day at MLO if the sky was cloudless 

from dawn through the time of the desired scan and if Dobson 

ozone data were available for that morning. At Boulder, 

generally speaking, the sky had to be clear at the time of the 

scan. Figure 3.16 shows MLO ozone and UV erythema data for 

July 1995-December 1999. Figure 3.17 shows similar data for 

Boulder for July 1998-December 1999. Erythemal radiation data 

were obtained from the spectroradiometer data for both sites by 

applying the erythemal weighting function of McKinlay and 

Diffey [ 1987) and integrating over wavelength for each scan, as 

discussed by Bod/wine et al. [ 1997). Figures 3.16 and 3.17 also 

show the time series of ozone at the two sites. The inverse 

relationship of UV erythema and ozone is apparent. 

Figures 3.18 and 3.19 show the relationships between UV 

erythema and ozone at MLO and Boulder, respectively, for the 

time period July 1998-December 1999. The radiative 

amplification factor (RAF), defined as the percent change of UV 

(erythemal) irradiance divided by the percent change of total 

350 40 

. 

: 300 35 

~ 250 

.. 30 E 

u 

~ 200 

3: 

::1. 

25 ~ 

.. g ~ 

~ 150 20 ~ w 

100 15 

SZA = 45° 

50 10 

1995.5 1996.0 19965 1997.0 19975 1998.0 1998.5 1999.0 1999.5 2000.0 

Year 

Fig. 3.16. Erythemal irradiance al SZA 45° (bottom, squares) and total 

ozone (top. circles) for clear-sky mornings at MLO from July 1995-

Deccmber 1999. 
5.0 

+-'"a...--.-~ =------;,..o.-:--'-~'l-1~J-r.o.__ -+ 4.o -I 

Ii r----------------~--+3.5 ;:: 

1 

+------~--~--~--- -~ 1.5 

1999.5 2000.0 

Year 

Fig. 3. 17. Ery1hemal irradiancc at SZA 70° (bouom, squares) and 1otal 

ozone (lop, circles) for clear-sky mornings and afternoons at Boulder 

from July 1998-December 1999. 

4.0 

RAF= 1.12 

SZA = 70° 

y = 1586.3x' 11 02 

R2 = 0.908 

2.0 +-------.------- -----~ 

200 250 300 350 

Dobson Ozone (DU) 

Fig. 3.18. Power law regression between erylhemal irradiancc at SZA 

70° and Dobson Iota! ozone at MLO from July 1998-December 1999. 

The graph is ploucd on a linear scale to facili1a1e reading 1he unils. The 

coefficienl of the power law func1ion ( 1.12) gives the RAF. 

3.5 ,-- ------------------~ 

3.0 i----~--- ------- -----l 

.-

E 

u 

;:: 2.5 t----~-~ta'±-7----i--------{ 

"' 

~ 2.0 t-----------c=-=,..__._~~---- -f .c 

~ w 

AAF=l.12 

SZA = 70' 

y:; 1304X·1 UIS 

R2 = 0.4236 

1.0 +----- ----~---- -----< 

200 250 300 350 400 

Dobson Ozone (DU) 

Fig. 3.19. Power law regression between erythemal irradiance at SZA 

70° and Dobson Iota! ozone at Boulder from July 1998-December 1999. 

The graph is plotled on a linear scale to facililate reading lhe units. The 

coefficienl of the power law funclion ( 1.12) gives 1he RAF. 

64 

ozone, was calculated for both sites for 70° SZA using the 

power-law formulation of Madro11ich (1993): RAF 

-t.ln(l)/t.ln(03), where I is UV irradiance. The RAF is simply 

the slope of a straight-line fit on a log-log plot. The data for 

Boulder are subject to more scatter because of less pristine clear 

sky conditions than for MLO. 

Co11clusio11s 

1. Erythema irradiance calculated from UV spectra at MLO 

and Boulder is inversely correlated with Dobson total ozone. 

2. The erythema RAF measured at MLO and Boulder for the 

1.5-yr period is about 1.12 for both sites, in reasonable 

agreement with current modeling efforts. 

3. No significant trend in UV irradiance may be inferred 

because of the limited time period. 

3.2.5. BROADBAND UV 

lntroductio11 

Broadband UV instruments (Yankee UVB- 1) were operational 

at MLO, BRW, BAO, Bermuda, Kwajalei n, and Boulder as pan 

of the various programs being operated by the STAR group. 

These instruments were all compared at various times with the 

MLO instrument and with the MLO UV spectroradiometer 

installed at MLO in July 1995 [Bodhaine et al., 1998). Because 

the erythemal response defined for human skin is significantly 

different than that of the broadband instrument, the calibration of 

the broadband instrument reporting in erythemal units is strongly 

dependent on total ozone [Bod/wine et al., 1998). When a 

broadband instrument is placed in the field, it is necessary to 

know the calibration as a function of ozone to determine accurate 

erythemal irradiance. However. the manufacturers of broadband 

instruments do not generally provide information on the ozone 

dependence of the calibration. 

lnstrume11tatio11 

The UVB-1 instrument uses a UV-sensitive phosphor that 

absorbs radiation in the UV-B region and re-emits in the green 

region. A photodiode that has its peak response in the green pan 

of the spectrum is used to measure the green light emitted by the 

phosphor. The UYB-1 is temperature stabili zed at 45°C. The 

manu facturer provides conversion factors for estimating various 

portions or weighted integrals of the UY spectrum, such as total 

UY-B (280-3 15 nm or 280-320 nm), Diffey Action Spectrum, 

Parrish Action Spectrum, or the DNA-weighted spectrum. 

However, these estimates can be significantl y in error because of 

the fac t that the actual spectral response of the instrument can be 

significantly different than the portion of the spectrum being 

estimated, which in turn causes strong ozone dependence of the 

measurements. Because of these uncertainties the broadband 

measurement program is currently being reviewed. 

3.2.6. BASELINE SURFACE RADIATION NETWORK 

The STAR group has the leadership role in the BSRN having 

fulfilled the duties of International Project Manager for the past 5 

years. The BSRN is intended to not only supply the international 

climate research community with the highest-quality surface 

irradiancc data from a globall y and climatologically diverse 

long-term net work, but also to keep advancing the state of the art 

in improving those measurements so that research uses of the 

data can continue to be challenged. Support of the U.S. BSRN 
program comes from several agencies (NOAA National Weather 

Service, NOAA Oceanic and Atmospheric Research, NASA, and 

the Department of Energy) and is funded internationally by the 

participating countries that operate surface BSRN stations and 

contribute technical experts. The BSRN data are being utilized 

in major satellite and GCM research programs mentioned 

previously. The program was conceived in 1988, began 

operations in 1992, and is intended to operate indefinitely until 

there are no further extensive research needs for such data. 

Current acti vities of the BSRN are further summari zed by 

O h11111ra et al. [ 1998). 

3.2.7. BARROW SNOW MELT DATE 

Snow Melt Analysis 

An important process that occurs every spring over continental 

regions of the arctic is the melting of the snow pack. Variability 

in the date when the tundra becomes snow free is expected to 

affect the annual net energy budget of the region. As the global 

mean temperature continues to increase, the arctic is predicted to 

experience enhanced warming because of a positive radiati ve 

feedback caused by decreasing surface albedo in response to 

accelerated melting of ice and snow. Albedo is derived from the 

ratio of reflected to downwelling, shortwave, broadband 

irradiances. Of particular interest to CMDL has been the timing 

of the spring snowmelt at BRW that has historically been 

designated as the day "hen albedo drops below 0.30 [Duuon and 

Endres, 1991). Fresh snow has an albedo exceeding 0.85, 

"hereas dry tu ndra has a value of about 0.17 [Stone er al., 1996]. 

Once the daily average albedo drops below 0.3, it seldom 

increases again until snow accumulates the following autumn. 

This fact makes monitoring the melt relatively straightforward 

and provides an important record for evaluating regional climate 

change. Figure 3.20 shows daily average albedos spanning the 

period of melting for 1998 and 1999. Although the final melt 

typically occurs in a matter of a few days as shown in the figure, 

the actual timing of this event is highly variable from year to 

year at any particular location, depending on many fac tors. 

Temperature is usually presumed to be a primary factor; 

however, changes in cloud cover that affect solar intensity or 

thermal emissions, the stability of the atmosphere, and boundary 

layer turbulence (winds) are also factors. Another important 

variable is the amount of snow that accumulates during the 

preceding months. Any long-term variation in these or other 

factors may affect the spatial or temporal distribution of snow 

and lead to a perturbation in the regional energy balance. It is 

essential that these processes be understood and be parameterized correctly in models to improve climate simulations. 

Foster [ 1989] found that the disappearance of snow in spring 

at Barrow has occurred progressively earlier since the 1950s and 

has speculated that this was a manifestation of global warming. 

His analysis was based on observations of snow cover made at 

the Barrow NWS station. D11110 11 and Endres [ 1991] argued that 

the apparent trend was attributable to local urbani zation effects, 

basing their analysis on the more objective, radiometric 

determination of melt made at BRW (e.g., Figure 3.20). Because 

BRW is located on open tundra several kilometers upwind of 

town, it has not been affected by such development. Foster er al. 

[ 1992] expanded on these earlier studies using satellite data to 

show that the earlier melt was regional in scale. In this report, 

the record from BRW is updated in an attempt to explain the 

trend and variability of the annual melt there. 

65 

1 

0.9 

0.8 

0 0.7 

c 0.6 

~ 0.5 

cl 0.4 

0.3 

0.2 

0.1 

0 

145 150 155 160 165 170 175 

DAY OF YEAR 

Fig. 3.20. Time series of daily average surface albedo for 1998 and 

1999 at BRW. The snowmelt date is determined radiometrically as the 

date when the surface albedo drops below 0.30 (30% ). 

Updated time series for NWS and BRW indicate a further 

divergence as shown in Figure 3.21. It is now known for certain 

that the NWS record was contaminated because of new 

construction and a dramatic increase in traffic directly upwind of 

that site. The development began in the late 1960s in 

anticipation of developing the North Slope oil reserves. Thus the 

NWS data subsequent to this time are progressively more 

suspect. To construct a valid, long-term time series of melt dates 

for Barrow, the BRW radiometric record was appended onto the 

early NWS record, bridging the gap of 1966-1985 using proxy 

> 0 

Q 

-

175 

170 

165 

160 

155 

150 

145 

140 

135 

130 

1940 1960 1980 

YEAR 

2000 

Jun 24 

Jun 19 

Jun 14 

Jun 09 

Jun 04 

May 30 

May 25 

May 20 

May 15 

May 10 

Fig. 3.21. The date of snowmelt in the vicinity of Barrow shows a 

trend. Al the NWS site in town the disappearance of snow is occurring 

much earlier than al BRW because of local urbanization effects. The 

linear trend for BRW is given in the legend and is based on a 95% 

confidence level. 
data. The proxy data were derived from careful examinations of 

temperature records that show a distinct seasonal signature 

related to the melting process. This repeatable feature appears as 

a period of about 8 days running of near-freezing air 

temperatures, followed by an abrupt and sustained warming 

caused when solar radiation is absorbed by the exposed tund ra 

that then releases heat to warm the overlying air. 

Regression analyses were used to evaluate the time series 

shown in Figure 3.21. The downturn (quadratic) indicated for 

the NWS record is now attributed to contamination of that site by 

nearby development, but the composite BRW time series shows 

a trend that is statistically significant (-8. l ±4.6 days over 60 

years at the 95% confidence level). It is hypothesized that the 

earlier melting of the snow pack in the vicinity of Barrow results 

from less than normal accumulation of snow throughout the 

winter and/or warmer spring temperatures possibly associated 

with enhanced thermal emissions from clouds as described by 

Stone [ 1997]. To explore these possibilities, meteorological 

records were analyzed dating from the mid- l 960s, the period 

showi ng the most pronounced trend. Integrated water equivalent 

precipitation (WEPC) from October through February is used to 

quantify seasonal snow accumulation because this measure is 

less prone to error than actual snow depth data. In addition, the 

temperature (T) and total sky cover (SC) averages for March and 

April were examined. Although the final phase of melting is 

obviously dependent on concurrent weather conditions, the 

analysis suggests that the factors mentioned previously probably 

condition or "ripen" the snow pack prior to the onset of melt by 

establishing its maximum depth and its microphysical 

characteristics. Figure 3.22 displays time series for each of these 

factors compared with the record of melt. Each time senes was 

analyzed for a trend and was cross-correlated with melt date. 

The coefficients correlating melt with WEPC, T, and SC are, 

respectively, +0.39, -0.47, and -0.30. As expected, melt date is 

positively correlated with snowfall (represented by WEPC) and 

anti-correlated with temperature, but no one factor explains a 

significant portion of the variance. However, an empirical model 

based on a multiple regression using a nonlinear combination of 

these factors was found to explain > 70% of the variance [R. 

Stone, unpublished results, 2000]. It is concluded that 

decreasing snowfall during winter, combined with warmer, 

cloudier spring conditions are primary factors that have led to an 

earlier melt at BRW. 

Overall the melt has advanced by more than a week since the 

mid-60s but is characterized by significant interannual 

variability. The most pronounced change occurred during the 

last decade, with the melt dates of 1990, 1996, and 1998 being 

particularly early. Figure 3.22 shows that during each of these 

years little snow accumulated through the winter (minimal 

WEPC) and the following March and April periods were 

relatively warm. In colllrast, the 1999 melt occurred late because 

WEPC was much higher and spring temperatures were much 

colder. Because the melt occurs during the peak of the annual 

solar cycle [Stone er al., 1996]. there is a dramatic increase in net 

surface radiation when the tundra becomes snow free. It is 

estimated that the trend indicated in Figure 3.21 represents an 

increase in the annual net radiation balance at BRW of about 

I 0%. Analyses of melt dates for other North Slope sites (not 

presented here) show a similar tendency toward an earlier melt 

suggesting that the region as a whole has experienced an increase 

in net radiation in recent years. If the area affected covers a 

66 

e 

_.. u 

() 

c.. 

w 

:: 

§: 

... 

·ca 

I-

> 0 

_.. 

c 

·1 

·1 

A _/'\ MELT DATE 

::::> 0-~~ 

~ v ---+-,t,..._,j.~-.::j 

-7.4d/30yr (+/- 5.1 d) v 

1970 1975 1980 1985 1990 1995 2000 

YEAR 

Fig. 3.22. Time series of factors that are believed to affect spring 

snowmelt a1 BRW compared with dates of mel1. As labeled, 1op 10 

bottom: integrated water equivalent precipitation for October through 

February, average March/April 2-meter air temperature, average total sky 

cover for March/ April, and melt date determined from prox) 

(temperature) data and albedo measurements as described in the 1ex1. 

Each time series has a linear fit to determine trends based on the 95% 

confidence level given in the lower legends. Also, cross-correlation 

coefficients relating melt date with each variable are given (upper, left). 

large enough region of the artic and this trend is sustained, then 

the implications of these 

significance in the context 

important to understand 

observations. 

Trajectory Analysis 

findings will have even greater 

of global climate change. It is 

what processes underlie these 

A previous study showed that shifts in circulation panerns 

influence northern Alaska climate [Stone, 1997). It is very likely 

that similar changes underlie the variations in the annual melt at 

BRW through perturbations in the precipitation and temperature 

patterns of the region. To a large extent the climate of northern 

Alaska is influenced by the relative positions and intensities of 

two dominant pressure systems, the Aleutian Low and the 

Beaufort Sea anti cyclone. This is revealed th rough analyses of 

back-trajectories similar to those of Harris and Kahl [ 1994] 

made in conjunction with an examination of geopotential height 

fields that highlight these synoptic patterns. Enhanced precipitation during winter was found to occur often when warm moist 

air reaches northern Alaska from the North Pacific as a result of 

circulation around the Aleutian Low. Drier conditions prevail 

there when upper-level winds are generated over the Beaufort 

Sea and effectively block the southerly flow. Year-to-year 
variability of these features appears to be associated with natural 

shifts in planetary wave patterns rather than a response to a 

general warming of the arctic. It is speculated that these 

variations are correlated with the phase of the arctic oscillation 

[e.g., Thompson and Wallace, 1998]. This possible connection 

is a focus of continuing research. Eventuall y it is hoped to 

determine to what extent the annual cycle of snow cover over 

northern Alaska is affected by natural versus anthropogenic 

factors. 

3.2.8. ARCTIC UV MONITORING 

Introd11ctio11 

In June 1998, with conti nued support from the NOAA Arctic 

Research Initiative (ARI), CMDL deployed two additional 

Biospherical Instruments, Inc. (BS!), fi ve-channel UV filte rbased radiometers at the NWS facilities at Nome (64°N, l 65°W) 

and St. Paul Island (57°N, l 70°W). The three Alaska UV 

monitoring sites are identified in Figure 3.23. The instruments at 

Nome and St. Paul are identical to the one deployed at BRW in 

September 1997 except that the 340-nm channel was replaced by 

a wide-band channel that measures across the 400-700 nm part 

of the spectrum (known as photosyntheticall y acti ve radiation or 

PAR). Thus these instruments have three channels in the UV-B 

region (305 nm, 313 nm, and 320 nm) and one channel in the 

UY-A region (380 nm). All three UV instruments produced 

excellent data in 1998 and 1999, other than a temporary 

malfunction in the 380-nm channel at St. Paul in 1999. All three 

instruments continue to operate within normal parameters with 

the exception of I week of downtime at Nome in July 2000 

because of a bruwnuul requiring the return of the data acquisition 

computer for repair. 

The three instruments conti nue to undergo regular annual 

calibration by the manufactu rer during the winter period 

(November-January). The calibration of the BS! instrument is 

tied to a spectroradiometer used in the National Science 

Fig. 3.23. CMDL arctic UV Network. 

Foundation's Polar UV Monitoring Network. This high 

resolution scanning spectroradiometer (the BS! model SUV- I 00) 

has a well-documented calibration history. In addition to the 

SUY-100, BS! has a series of multi-channel reference 

instruments (RGUVs) installed at their San Diego facility, 

similar to those installed at the three CMDL sites. These 

RGUYs have been operated next to the spectroradiometer since 

1995, allowing for intercomparison on a continuous basis. Thus 

far solar calibrations of the RGUVs relative to the SUV have 

indicated the stability of the RGUVs to be about ±3% across all 

channels. These RGUY instruments are then used as the basis 

for cali bration of other BS! multi-channel UV instruments. The 

process generates a calibration scale factor for each optical 

channel that is used to determine any changes in instrument 

sensitivity. Analysis of the cali brations for all three instruments 

has shown changes in sensitivity of 2- 11 %. 

Data Analysis 

One year of data ( 1998) was analyzed for all three sites. For 

Barrow, the observation period was May 18-0ctober 26; for 

Nome, June 12-0ctober 22; and for St. Paul, June 8-0ctober 23. 

Figure 3.24 shows the daily total energy for each site at the 

individual UV wavelengths for the period during which the 

instruments were taking observations in 1998. The 400-700 nm 

measurements from the Nome and St. Paul instruments are not 

presented here, although they show the same vari abi lity as the 

other four channels. The 305-nm channel is multiplied by ten so 

that it can be more easily seen on the charts. Because of missing 

data during the integration process (integrated for the entire 24-

hr day), Barrow is missing 2 days; Nome is missing 7 days; and 

St. Paul is missing 4 days. Nonetheless, the figure hu w~ large 

day-to-day variations for all three sites and a decrease in UV at 

all wavelengths over the observation periods. 

67 

A regression analysis was conducted to investigate the 

correlation of ozone with each of the UV wavelengths at the 

three sites. This was done by first removing the variability in 

UV because of SZA by filtering the daily I-min values between 

69.5° and 70.5°. This yielded two reduced sets of data for each 

day (AM and PM values), whi ch were then combined into one 

dataset, effectively yielding two data points for each day. 

Unfortunately this also resulted in a loss of about I month's data 

for Barrow (because of a rapidly setting sun) but captured nearly 

all of the observational period at Nome and St. Paul. In addition, 

because of limited clear-sky data at all three sites, ratios were 

taken to reduce the effects of clouds at the shorter wavelengths 

of 305 nm, 3 13 nm, and 320 nm. At Nome and St. Paul there are 

no 340-nm channels, so the ratios used the 380-nm wavelengths. 

Total column ozone values were obtained from the Dobson 

spectrophotometer at the Barrow Observatory and from the 

NASA Total Ozone Mapping Spectrometer (TOMS) at all three 

sites for the same periods as the UV observations. During the 

observation period in Barrow there were 62 days without Dobson 

observations. Only 5 days of TOMS ozone data were missing 

for Barrow. Therefore, a combined Dobson!fOMS ozone 

dataset was used for the regression. Three Dobson observation 

sets are usually obtained for each day: in the morning, near local 

noon, and in the afternoon. Where available, the Dobson value 

most closely matching the UV measurement time was used. 

When this was not possible, the single dail y representative value 

from TOMS was used. At the other two sites, only the TOMS 

ozone data are available, and there were 26 days missing for 
2 .5E+04 

1.SE+04 

1.0E·04 

5.0E•03 

Daily Total Energy for 1998 

- 3 13 nm 

l20nm 

340nm 

1._ 380 nm 

- 30S nm • 10 

O.OE •00 -1----.---....---r--=-.:....::=::c:sc::~-"T"~-i--

5/17 6 /6 6126 7/ 16 8/5 8/25 9/14 10/4 10/24 

2.3E+04 

1.8E+04 

1.4E+04 

9.2E+03 

4 .6E+03 

O.OE+OO 

Nome - )l)l'W"'I 

- 320nm 

360MI 

- 30$ nm .. 10 

6/12 6126 7110 1124 sn B121 91• a11s 1012 10116 

2.20E+O. 

6/6 6126 7116 815 8125 9114 10/4 10/24 

Date 

Fig. 3.24. The 1998 daily total energy for Barrow, Nome, and St. Paul, 

Alaska. 

Nome and 11 days missing for St. Paul. However, this allowed a 

sufficient sample size to obtain significant correlations. Figure 

3.25 shows the time series of the ratio of irradiances and ozone at 

the three sites using the shortest wavelength of 305 nm, to 

illustrate the direct correspondence between these two variables. 

Figure 3.26 shows three regressions demonstrating the 

correlation between ozone and the 305-nm/380-nm wavelengths 

(305-nm/340-nm for BRW). As expected there is a strong 

negative correlation between ozone and UV at the 305 nm 

wavelength at both Barrow and St. Paul. However, there is only 

a weak negative correlation at Nome. It is not clear why Nome 

would have such a significant difference from the other two sites. 

It is possible that the Nome UV instrument is being affected by 

pollutants emitted from aircraft, since the installation is on the 

roof of the NWS office right next to the airport. This will 

necessitate further investigation. 

A multiple linear regression analysis was conducted using UV 

(the ratio of the irradiances for the 305-, 313-, and 320-nm 

wavelengths, but individually for 340 and 380 nm, and PAR), 

ozone, and cloud cover. Cloud cover data were obtained from 

68 

Ratio of 305/340 nm vs. Combined Dobson & TOMS Ozone 

0.009 460 

0.000 - - - - - - - -

0.007 

0.006 

0.005 

0.004 

0.003 

Barrow 

400 

340 

&16 6'1 6'15 6'29 7/13 7/27 8110 8124 917 9"21 

0.012 Ratio of 305/380 IVll vs. TOMS Orone 415 

Nome 

--------------- 395 0.010 

\~~~ = 

0.000 

0.006 

0.004 

0.002 -+-- -.---.---.----,.--------.- 295 

6'12 6126 7110 7/24 817 8121 9'4 9118 l<Y.! 

Ratio of 305/380 nm vs. TOMS Orone 

0.012 440 

0.010 .m 

0.003 

I :B) 

O.<nl 

0.004 

I~ ~ 

O.ro! :Bl 

6'6 6'Z3 7110 7/ZJ 8'13 83) 9'16 10'3 1<Ya'.> 

Date 

c 

Q 

,,, 

,Q 

Q 

Q 

Fig. 3.25. The 1998 time series of ozone and UV for Barrow, Nome, 

and St. Paul, Alaska. 

the NOAA National Climatic Data Center. The cloud cover is a 

fraction of the total celestial dome in tenths. In order to ensure 

equality across all three variables, the cloud cover value most 

closely matching the period of time for the AM and PM values 

of UV observations was used. The relative strengths of the 

individual predictors (ozone and clouds) with the five 

wavelengths are shown in Table 3.10 for Nome and St. Paul and 

in Table 3.11 for Barrow. As expected the bivariate correlations 

between ozone and the shorter wavelengths (305, 313, and 320 

nm) are negative at all three sites with the strongest relationship 

seen for Barrow and St. Paul. There is no relationship between 

ozone and UV at the 380-nm and PAR (400-700 nm) 

wavelengths, as expected. On the basis of the correlation 

analyses with ozone and clouds, ozone alone contributed most of 

the variance in UV at 305, 313, and 320 nm. The cloud cover 

fraction offers little additional predictive power in the regression 

model summary, although the correlations (Tables 3. 10 and 3.11) 

at the longer wavelengths at St. Paul and Barrow (380 nm) and at 

all five wavelengths at Nome are significant. For St. Paul and 

Barrow this would be expected, given that the 380-nm 
Ratio of 305/340 nm vs. Combined Dobson & TOMS Ozone 

I . • 

. 0.009 1 

0.0075 - - t. - -.- - - - - - - - - - - - - - - - - - - - - - - - - -

0.0015 - Ba~; - - - - - - - - - - - - - - - - - -

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

280 310 340 370 400 430 

l/l Ratio of 305/380 nm vs. TOMS Ozone Q) 

~ :·::: l ~ --~ --------------------------- • "'C 

~ 0.008 + 

lo.. 

-0 

0 

~ 0.002 .;.----- --~--~--~--~--''----, 

ex: 295 315 335 355 375 415 

Ratio of 305/380 nm vs. TOMS Ozone 

0.012 1 • 

0 010 + .- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - . 

. . . ' . • • 0. (X)8 .. __._ .... -e- - - - - - - - - - - - - - - - - - - - - - . 

. . •. . i •. 0.006 r:---~ -• - •• ,. 0.004 T - - - - - .. ' - •- - -

St. Paul 0.002 +---- --,---r-- --r---,c----=-~- llL--, 

~ D B ~ B B ~ ~ ~ 

Ozone (DU) 

Fig. 3.'.!6. The 1998 linear regressions of UV and ozone a! Barrow, 

Nom.:. and St. Paul. Alaska. For all !hrec si!es, !he regression equation 1s 

) = ( . .J x 1 o·i) x ... 0.02 The Pearson produc1-momem correla1ion 

coeffi ciem (r) for Barro\\. Nome, and St. Paul was 0.88 (n = 248), 0.58 

(n = 178), and 0.87 (n = 254), respecti,ely. 

wavelength and PAR are more inOuenced by clouds instead of 

ozone. It is not en1irely clear why there arc signilica111 

correlations between clouds and all live wave ength ~ al Nome. 

TABLE 3.10. The 1998 Nome and S1. Paul Pearson 

Correlations (r) Between Each Predictor 

(Ozone and Clouds) and UV 

Nome (64°N, 165°\V) St Paul (57°N, 170"\V) 

TOMS Clouds TOMS Clouds 

\Vaveleng!h (n = 178) (n = 225) (n = 254) (n = 26 1) 

305 nm/380 nm -0.58* 0.26* -0.87* -0.01 

3 13 nmf380 nm -0 . .J3" -0.26* -0.79 ' O.Q3 

320 nm/380 nm -0.27* 0.27" -0.59• 0.09 

380 nm 0.10 -0.28• 0.0 1 -0.29* 

400-700 nm (PAR) 0.06 -0.27* -0.0 1 -0.30* 

·Correlation is significant at the 0.01 level (2 tailed). 

TABLE 3. 11. The 1998 Barrow Pearson Correlations (r) 

Between Each Predictor (Ozone and Clouds) and UV 

Dobson TOMS Combined 

Wavelength (n = 115) (n = 246) (n = 248) Clouds 

305 nm/340 nm -0.90* -0.9 1 * -0.88* -0.06 

3 13 nm/340 nm -0.83* -0.87* -0.83* -0.03 

320 nm/340 nm -0.62* -0.70* -0.65* 0.01 

340 nm 0.39• 0.4 1* 0.49* -0.12 

380 nm 0.34* 0.36* 0.34* -0.lSt 

*Corre laiion is significant at the 0.0 1 level. 

tCorrelation is signifi can! a11he 0.05 level. 

Co11cl11sio11s 

The existence of these three new sites in Alaska greatly 

enhances the capability of monitoring UV in the arctic. The data 

are currently being archived at CMDL and are available to any 

user upon request. As shown in this preliminary analysis, the 

data can be used to investigate the relationship between changes 

in ozone and changes in UY. With a continued decrease in 

ozone in the arctic (as demonstrated by the SAGE III Ozone 

Loss and Validation Experiment), these three sites provide an 

excellent opportunity to establish baseline values of UV in the 

Alaskan arctic. The data can be used lo determine column ozone 

amounts (for comparison with the Dobson spectrophotometer at 

Barrow). UV doses, and cloud effects. The data can be used to 

test and validate algorithms aimed at determining surface UY 

exposure in the arctic from satellite data. Finally, the data can be 

used by ecologists who are interested in studying the potential 

effects of increasing UV on arctic marine and terrestrial 

ecosystems, as well as on human health. 

69 

3.2.9. PYRGEOMETER COMPARISON 

llltrod11ctio11 

The broadband hemispheric downwelling longwave irradiance 

at the earth's surface (F1Rt) is a significant component of the 

surface energy budget. It is a function of both the thermal 

structure and the optical structure of the atmosphere and, 

therefore, includes radiation because of the greenhouse 

properties of atmospheric constituents. Measurements of F1Rt 

typically made by pyrgeometers, have uncertainties thought to be 

of the same magnitude or larger than the potential change in F1Rt 

because of anthropogenic greenhouse forcing. Several fac tors 

con1ribute to the uncertainties in these measurements: lack of an 

adequate traceable, absolute calibration standard; variations in 

calibration techniques; and uncertainties in the thermal balance 

within the instruments. 

A recent inlercomparison conducted with a suite of pyrgeometers, a new scanning absolute IR radiometer (sky-scanner) (R. 

Philipona, personal communication, 1999), and radiative transfer 

model calculations suggests that significant reductions in the 

uncertainty of pyrgeometer measurements may be achieved. A 

comparison of averaged nighttime measurements shows 

excellent agreement between pyrgeometer and sk}-scanner 

measurements (within - 0.1 ± 0.2 W m-2 out of 280 W m2

) (R. 

Philipona, personal communication, 1999) when all 

pyrgeometers are calibrated using a common technique. The 

development of the sky-scanner, which utilizes a cavil} detector 
referenced in near-real time to a blackbody calibration target, 

suggests that a stable reference standard radiometric scale for JR 

(similar to the World Radiometric Reference scale for 

shortwave) is achievable and transferable to pyrgeometers for 

field use. The modeled irradiances (calculated using 

MODTRAN4 [Anderson et al., 1999] with radiosonde data as 

input) exhibit a positive mean bias of 1.0 W m2 versus the 

measurements. The radiative impacts of other model 

components unspecified by the sonde data (CFCs and aerosols, 

for example) are being evaluated. 

l11str11111e11tatio11 a11d Models 

The first International Pyrgeometer and Absolute Scanning 

Radiometer Comparison (IPASRC-1) was held at the Department 

of Energy Atmospheric Radiation Measurement (ARM) 

program's Southern Great Plains Cloud and Radiation Testbed 

(CART) site at Lamont, Oklahoma, during September 20-

0 ctober I, 1999. A suite of 15 pyrgeometers and the skyscanner were deployed at the site's Radiometer Calibration 

Facility (RCF). The pyrgeometers measure the spectrally 

integrated (e.g., approximately 3.5-50 μm for Eppley model PIR 

pyrgeometers), horizontally incident longwave irradiance. All 

pyrgeometers had user-supplied calibrations. In addition, all 

pyrgeometers were calibrated by CMDL and seven pyrgeometers 

were calibrated by Physikalish-Meteorologisches Observatorium 

Davos (PMOD) prior to the field experiment. The CMDL 

calibrations were performed using a method similar to that 

described by Albrecht and Cox [ 1977]. The PMOD calibration 

technique is described by Philipona et al. [ 1995]. 

The sky-scanner is a directional instrument that measures the 

normal, unfiltered, spectrally integrated atmospheric longwave 

irradiance. This irradiance is measured at multiple directions, 

and then the measurements are cosine-weighted and integrated 

over the solid angle to produce the horizontally incident 

irradiance. The sky-scanner periodicall y measures a 

temperature-controlled blackbody target, which allows for 

absolute calibration. ARM performs periodic radiosonde 

launches from a site located near the RCF. These nearl y coJocated sonde data can be applied in radiative transfer models to 

simulate the downwelling irradiances observed by the 

instruments and help account for instrumental differences in 

spectral range and implementation. MODTRAN4, an Air Force 

radiative transfer algorithm with flexible simulation capabilities, 

was chosen for this use. 

Data A11alysis 

Measurements were taken at 1-s intervals for half-hour periods 

during the day and night over the course of 5 clear days. 

Pyrgeometer measurements were converted to irradiance using 

first the user-supplied calibrations, then the CMDL calibrations, 

and finally (for seven of the pyrgeometers) the PMOD 

calibrations. The measurements were averaged over each half 

hour for each instrument, and then the pyrgeometers were further 

averaged by cali bration grouping. Sonde data (temperature, 

pressure, relative humidity) were obtained for the launch nearest 

in time to the observations. The vertical resolution of the sonde 

data was reduced to levels appropriate to MODTRAN4; these 

reduced-resolution data were validated by running several test 

cases with a version of MODTRAN4 specially modified at 

CMDL to accept the full 2000+ layers of sonde data. Model 

calculations were performed to match the spectral range of the 

sky-scanner. Because the calculations were not completely 

defined by the sonde data, other input parameters (specifically 

CFCs and aerosols) were set at realistic default values. 

70 

Under the four nighttime comparisons, the agreement between 

the averaged user-calibrated pyrgeometers and the sky-scanner is 

within 1.6 ± 0.4 W m-2 out of 280 W m-2

, while for PMODcalibrated pyrgeometers the agreement is within -0.7 ± 0.4 W 

m-2 (Figure 3.27). If the CMDL calibrations are employed, the 

agreement is exceptional, within -0. l ± 0.2 W m-2

. However, 

significant differences exist among the 15 pyrgeometers. The 

spread, averaged over all nighttime measurements, is 8.4 W m2 

with CMDL calibrations, 3.4 W m-2 with PMOD calibrations, 

and 11.9 W m-2 with user calibrations. These results are 

consistent with prior estimates of the uncertainty associated with 

single measurements (±10 W m-2 [Philipona et al., 1995] or 

about ±5% [D1111011, 1993]). Future intercomparisons are being 

planned that will incorporate other absolute scanning radiometer 

instruments, as available, and additional sites. 

The MODTRAN4-modeled irradiances exhibit a somewhat 

consistent positive mean bias of 1.0 W m-2 relative to the skyscanner measurements. Potential sources of the bias include the 

use of default values for CFCs and aerosols, as mentioned 

previously, and the treatment of the water vapor continuum 

within the model. An investigation into the magnitude of the 

influence of CFCs and aerosols on F1R-L suggests that the effect 

of aerosols is significant compared to the size of the bias (Figure 

3.28), while that of CFCs is not. Further work is being done to 

evaluate the influence of the water vapor continuum treatment. 

3.2.10. RAYLEIGH OPTICAL DEPTH CALCULATIONS 

llltrod11ctio11 

A variety of different techniques are used for the calculation 

of Rayleigh optical depth in the atmosphere. In some cases, 

differences among these techniques can be important, especially 

in the UV region of the spectrum and under clean atmospheric 

conditions. It is recommended that Rayleigh optical depth be 

calculated from first principles of Rayleigh scattering theory 

rather than the variety of curve fitting techniques currently in 

use. This approach requires the accurate calculation of the 

refractive index of air based on the latest published 

measurements. Small inaccuracies in Rayleigh optical depth 

~ 320 < 

E 300 

== 4i 280 <.> 

c; 

<II 260 '6 

<II 

~ 240 

22·Sep·99 24·Sep·99 29-Sep·99 :JO.Sep·99 

Case 

D Pyrg. W/ user 

cals. 

• Pyrg. W/ CMDL 

cats. 

• Pyrg. W/PMOD 

cals. 

•Sky-scanner 

DModtran4 

Fig. 3.27. IR irradiances from user-calibrated pyrgeometers, CMDLcalibrated pyrgeometers, PMOD-calibrated pyrgeometers, the skyscanner instrument and MODTRAN4 model results for four nighttime 

comparisons. 
~ 

e 

u 

";:: 

Q) 

iii 

C\J 

E 

~ 

~ Q) 

u 

c 

'5 "' 

a: "' 

2.00E-05 

1.50E·05 

1.00E-05 

5.00E-06 

-Total spectral 

radiance 

-(Aerosol 

contribution)*10 

0.00E+OO .1---.._.l-....,.....~--,,.....-....,...--,.....--! 

0 500 1000 1500 2000 2500 3000 

Frequency (cm-1) 

Fig. 3.28. Down welling spec1ral irradiance (offsel by +2.5 x IO"") and 

1he con1ribu1ion by aerosols (scaled up by a fac1or of 10). The aerosol 

spec1rum accounis for 2 \V 111·

2

. 

calculations can equal or even exceed other quantities being 

estimated, such as aerosol optical depth, particularly in the UV 

region of the spectrum. The procedure described here was 

presented by Bod/wine et al. [ 1999). 

Rayleigh scattering calculations for air have traditionally been 

made using the method of Pe1111do1f [I 957) where the refractive 

index was calculated for "'standard" air (760 mm I lg, 15° C) 

using the equation of Ed/en [I 953), and the scattering cross 

section per molecule was calculated using the classical equation 

presented in many textbooks [e.g., va11 de Hulst, 1957; 

McCart11ey, I 976). This calculation includes the depolarization 

term, or the King factor, which describes the effect of molecular 

anisotropy and is the least well known for these purposes. 

Results of such calculations were presented by Penndo1f [ 1957). 

It is this table of values that has been used by many workers in 

the field to estimate Rayleigh optical depths, usually by some 

curve fitting routine over a particular wavelength range of 

interest. 

Possible errors in the depolarization term were considered by 

Hoyt [I 977], Frohlich and Shaw [I 980], and Young [I 980, 

1981]. The correction proposed by You11g [1981] had been 

accepted for modern Rayleigh scattering calculations in 

atmospheric applications. However, Bates [ 1984) and Bucholtz 

[ J 995) discussed the depolarization in detail as a function of the 

individual constituents, and as a function of wavelength, and 

presented new values. 

Optical Depth 

A quantity of fundamental importance in atmospheric studies 

is the optical depth (or optical thickness). This quantity has been 

discussed by numerous authors [e.g., Dutton et al., 1994; 

Stephens, I 994) and is derived from the exponential law of 

attenuation variously known as Bouguer's law, Lambert's law, or 

Beer's Jaw. For purposes of illustration only, Bouguer's law may 

be simply written as: 

l(A.) = J0(A.)exp(-1:(A.)/cos0) ( I) 

where 111(;\.) is the extraterrestrial flux at wavelength A., !(A.) is the 

flux reaching the ground, 0 is the solar zenith angle, and 't(A) is 

the optical depth. Clear-sky measurements of l(A) as a function 

of 0, and plotted as In I(A.) against sec0, should yield a straight 

line with slope -'t(A) and intercept 111 (ex1rapolated back to sec0 

= 0). An important point is that 't(A), may be composed of 

several components given by: 

(2) 

where 'tR(A.) is the Rayleigh optical depth, 't,(A.) is aerosol optical 

depth, and 'tg(A) is the optical depth due to absorption by gases 

such as 0 3, N02, and H20. In principle it is possible to measure 

't(A) and then derive aerosol optical depth by subtracting 

estimates of 'tR(A) and 'tg(A). In practice, however, arriving at 

reasonable estimates of these quantities can be difficult, 

particularly during fairly clean atmospheric conditions such as 

those found at Mauna Loa, Hawaii. To isolate the individual 

components of optical depth it is necessary to provide accurate 

estimates of Rayleigh optical depth. 

Rayleigh optical depth is relatively easy to calculate once the 

scattering cross section per molecule has been determined for a 

given wavelength and composition because it depends only on 

the atmospheric pressure at the site. That is, it is only necessary 

to calculate the total number of molecules per unit area in the 

column above the site, and this depends only on the pressure, as 

shown in the formula: 

71 

(3) 

where cr is scattering cross section per molecule, P is the 

pressure, A is Avogadro's number, m, is the mean molecular 

weight of the air, and g is the acceleration due to gravity. Note 

that m. depends on the composition of the air, whereas A is a 

constant of nature. Although g may be considered a constant of 

nature, it does vary significantly with height and location on the 

earth's surface and may be calculated according to the formulas 

of List [I 968). 

Rayleigh Optical Depth of Air 

Bod/wine et al. [I 999) outlined a method for the calculation of 

Rayleigh optical depth that goes back to first principles as 

suggested by Penndorf [I 957] rather than using curve fitting 

techniques, although the refractive index of air is still derived 

from a curve fit to experimental data. All of the latest values of 

the physical constants of nature were used, and the effects of 

C02 on the refractive index and the mean molecular weight of air 

were included, even though these effects are in the range of 0.1 · 

0.0 I%. It should be noted that aerosol optical depths are often as 

low as 0.0 I al Mauna Loa. Since Rayleigh optical depth is of the 

order of I al 300 nm, it is seen that a 0. 1 % error in Rayleigh 

optical depth translates into a 10% error in aerosol optical depth. 

The effects of high concentrations of water vapor on the 

refractive index of air may be of the same order as for C02 

[Edle11, 1953, I 966]. However, for practical atmospheric 

situations the total water vapor in the vertical column is small 

and does not significantly affect the calculations. Furthermore, 

the water vapor in the atmosphere is usually confined to a thin 

layer near the surface, which significantly complicates the 
calculation, whereas C02 is generall y well mixed throughout the 

atmosphere. 

It is recommended that Peck and Reeder's [ 1972) formula for 

the refractive index of dry air with 300 ppm C02 be used after 

corrections have been applied for the actual C02 concentration of 

the air. Next the scattering cross section per molecule of air 

should be calculated from the classical equation using the same 

temperature and pressure as were used for refractive index 

(10 13.25 mb and 288.15 K). Note that the scattering cross 

section per molecule is independent of pressure and temperature. 

The depolarization should be calculated taking into account the 

C02 concentration. Finally the Rayleigh optical depth can be 

calculated using Equation (3), taking into account the effect of 

C02 concentration on the average density of air, the surface 

pressure, and the effective value of gravitational acceleration 

using the correct latitude and the correct mass-weighted mean 

altitude of the column of air above sea level. By following these 

guidelines it is possible to calculate the Rayleigh optical depth as 

a function of wavelength for any point at ground level or in the 

atmosphere at any location on the earth. 

Some Example Ca/c11/atio11s 

Using the previous equations Bod/wine et al. [ 1999) presented 

a table of values of Rayleigh scattering cross section, and of 

Rayleigh optical depth for dry air containing 360 ppm C02 at sea 

level, 10 13.25 mb, and at latitude 45°; and at MLO (altitude 

3400 m, pressure 680 mb, and latitude 19.533°). For those 

readers who wish to use curve-fitting techniques, Bodlraine et al. 

[ 1999) investigated several different equations similar to those 

currently in use by other authors. TI1ey found that the accuracies 

of those equations were not sufficient and therefore looked for a 

better approach. They found that the equation 

(4) 

gives excellent accuracy. This five-parameter equation falls in 

the class of "ratio of polynomials" commonly used in curvefitting applications. It gives an excellent fit in this case because 

the general form of the data being fit by the equation is also a 

ratio of polynomials. For the scattering cross section data the 

best fit equation is: 

o{x I 0-2scm2 )= 1.0455996- 341.2906 IA.-2 -0.90230850A.2 (

5 

I +0.0027059889A-2 -85.968563A.2 ) 

Equation (5) is accurate to better than 0.01 % over the 250-850 

nm range, and still better than 0.05% out to I 000 nm. In fact, 

this equation is accurate to better than 0.002% over the range 

250-550 nm. Best fits for sea level at 45°N, and for MLO are: 

<R (sea level, 45°N) = 

0.0021520. 1.0455996- 341.2906 IA.-2 -0.90230850A.2 

I +0.0027059889A.- 2 -85.968563A.2 

and: 

1R (M LO, 3.4 km, 680 mb) = 

(6) 

72 

0.00 14484 .1.0455996-341.29061A.-

2 -0.90230850A.2 

I +0.0027059889A.-2 -85.968563A.2 (7) 

It should be noted that the leading coefficients in Equations (6) 

and (7) are the only difference from Equation (5). These 

numerical values represent the columnar density for the two 

cases. 

Conc/11sio11 

For the most accurate calculation of Rayleigh optical depth it 

is recommended that users employ fi rst principles and that Peck 

and Reeder's (1972) formula be used to estimate the refracti ve 

index of standard air. Next, Pem1dorfs [ 1957] method should be 

used to calculate the scattering cross section per molecule of air, 

taking into account the concentration of C02• In most cases the 

effects of water vapor may be neglected. The recommendations 

of Bates [ 1984] were used for the depolarization of air as a 

function of wavelength. Finally the Rayleigh optical depth 

should be calculated using the atmospheric pressure at the site of 

interest. Note the importance of taking into account variations of 

g. Curve fitting techniques are not necessarily recommended for 

estimating Rayleigh optical depth because the inaccuracies that 

arise can equal or even exceed other quantities being estimated, 

such as aerosol optical depth. However, for those who wish to 

use a simple equation and are satisfied with less accuracy, the 

techniques used to produce Equations (5)-(7) may be of interest. 

In some calculations of optical depth it may be desired to take 

into account the vertical distribution of the composition of air, 

particularly C02 and H20. In this case a layer-by-layer 

calculation may be done using the estimated composition for 

each layer, and then the total optical depth may be estimated by 

summing the optical depths for all of the layers. 

3.2.11. DATA PROCESSING 

Shortwave and longwave radiation are monitored at the four 

CMDL baseline stations (BRW, SPO, MLO, SMO) and three 

other stations (Bermuda, Kwajalein , and BAO). Data are 

collected using Campbell Scientific data loggers. Meteorology 

data from the last three stations are also collected. Standard 

telephone lines are used to download the data from all stations 

except SPO, where the Internet is used. The telephone download 

intervals vary from station to station, but are typically 4 hours. 

The Internet transfer of data takes place once a day. 

The Mauna Loa Automated Solar Dome data are collected on 

a PC by a custom program. These data are downloaded once a 

day to Boulder via the Internet. Multifilter, rotating shadowband 

radiometers (MFRSR) arc operated at four sites: Bermuda, 

Kwajalein, BAO. and Boulder. Data from these stations are 

downloaded locally to a PC system and transferred over the 

Internet once a day to the Boulder server. UV radiation is 

monitored at three sites in Alaska: Nome, St. Paul, and Barrow. 

BS! instruments are used to gather data, and the data are stored 

on an on-site PC. These data are transferred to Boulder once a 

day over the Internet. In addition, a Norwegian Institute for Air 

Research instrument is also used to monitor UV at Barrow. Data 

from this instrument are stored locally on a PC and transferred to 

Boulder over the Internet. It should be noted that this transfer 

has to be initiated manually. 

All data mentioned are permanently archived on a server in 

Boulder. Each morning plots of the previous day's data are 
created and made available on local-access-o nl y Web pages. 

Data listings are also available. With this informatio n, scientists 

in the Boulder laboratory can review the data collection 

performance and make changes if problems occur. 

The radiatio n data are edited using q ualitati ve and quantitative 

methods developed in the laboratory. These data are available to 

researchers through the CMDL web pages. CMDL is a 

contributing member to the BSRN. Mo nthly files are made from 

Barrow, South Pole, Bermuda, Kwaj alein and BAO data and sent 

to the BSRN archi ve in Zurich, Switzerl and. 

All-sky photographs are collected at three sites: Barrow, BAO, 

and Boulder. Images are taken at I-min intervals and analyzed 

on a dedicated PC. Once every 15 minutes an image and a 

calculated cloud-cover image are transferred to one of the 

laboratory servers and made available o n the Web. 

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Harris. J.M .. and J.D.W. Kahl. Analysis of 10-day isentropic no" 

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25,855, 1994. 

Hofmann, D.J .. J.T. Peterson, and R.M. Rosson (Eds.). Chmnte 

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co. 161 pp .• 1996. 
Hofmann, D.J., J.T. Pe1crson, and R.M. Rosson (Eds.), Climate 

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co. 166 pp., 1998. 

Hoy1, D.V., A redetcnnination of the Rayleigh optical dep1h and its 

application to selected solar radiation problems, J. Appl. Meteoml., 

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List, R.J .• S111ithsonian Mete"rologiwl Tables. Smithsonian. Washingion, 

D.C., 527 pp., 1968. 

Madronich, S., The aimosphere and UV-B radiaiion ai ground level, in 

£111·11·on111emal UV P/111tobio/11gy, edi1ed by A. R. Young el al., 

Plenum Press. New York. 1-39, 1993. 

McCanney, E.J .. 0 11tics ".f the At111osphere, Wiley. New York, 408 pp .. 

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Mc innes. L.M., M.H. Bergin. J.A. Ogren, and S.E. Schwartz, Differences 

in hygroscopic grow1h betl\cen marine and anthropogenic aerosols, 

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McKenzie, R.L.. P.V. Johns1on, M. Kotkamp, A. Biuar, and J.D. Hamlin, 

Solar uhraviole1 spcctroradiome1ry in Ne\\ Zealand: lnsirumentation 

and sample results from 1990, Appl. Opt., 31. 6501-6509, 1992. 

McKinlay, A.F., and B.L. Diffey, A reference aciion spec1rum for 

uhraviole1 induced erythcma in human skin, J. 1111 . C"mm. 11/11111 •• 6, 

17-22, 1987. 

Michalsky, J., E. Duuon, D. Ncl~on, M. Rubes, T. S1offd, M. Wesley, 

M. Splitt, and J. DeLuis1. Optimal measurement of surface shonwa\e 

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16. 55-69, 1999 

Naiional Research Council (NRC), Aero.wt Radtmi1·e Forcing and 

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Leighton , lmpacl of 1he shonwave radiation budge! of 1he surfaceaunosphere sys1em for snow-covered surfaces, J. Cli111 .. 7, 579-585. 

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Ohmura, A .. el al.. Baseline Surface Radiation Network (BSRNIWCRP): 

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Penndorf, R .. Tables of 1he re frac1ive index fo r s1andard air and 1he 

Rayle igh scattering coeffi cient for 1hc speciral region bc1ween 0.2 

a nd 20.0 μ and their application to aunospheric optics, J. Opt. Soc. 

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1998. 

Quakenbush, T.K., and B.A. Bodhaine, Su rface aerosols ai 1hc Barro\\ 

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74 

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4. Ozone and Water Vapor 

S. 0LTMANS, J. BARNES, M. CLARK, R. EVANS, J. HARRIS (EDITOR}, B. JOHNSON, G. CARBAUGH, 

M. O'NEILL, D. QUINCY, D. SHERMAN, H. VOMEL, AND E. RICE 

4.1. CONTINUING PROGRAMS 

4.1.1. TOTAL OZONE OBSERVATIONS 

Total ozone observations continued throughout 1998 and 1999 

at 15 of the 16 stations that comprise the U.S. Dobson 

spectrophotometer net work (Table 4. 1 ). Of the 16 stations, 

CMDL personnel operated 5, NOAA National Weather Service 

(NWS) operated 5, 2 arc university 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 Peru\ ian station became operational in the middle of 1999 

when the instrument was installed at the new Global Atmospheric 

Watch station at Marcapomacocha (I I .401°S, 76.324°\V, 4513 m 

above sea level). 111e sne does not have reliable power, and few 

observations were made. The instrument was sent to Buenos Aires 

in December 1999 for a calibration check against the Dobson 

secondary standard D065. The shelter for the Dobson instrument 

at the CMDL Samoa ObserYatory, American Samoa (SMO) was 

replaced in December 1998. Observations at Tallahassee are 

continuing at Florida State University until the new NWS office is 

completed in January 2002. The station in Haute Provence, 

France, was struck by hghtni ng in October 1999 and was not 

operational by the end ot the year. 

Provisional daily total ozone amounts applicable to local 

apparent noon for the St<llions listed in Table 4.1 were archived 

at the World Ozone and Ultraviolet Data Center (WOUDC}, 

4905 Dufferin Street, Ontario M3H 5T4, Canada, in Ozone Data 

for the World. Table 4.2 lists the monthly mean total ozone 

amounts measured at the various stations for 1998 and 1999. 

4.1.2. UMKEHR OBSERVATIONS 

Umkchr observations made with the Automated Dobson 

Network instruments continued in 1998 and 1999 at Boulder, 

Colorado; Haute Provence, France; Lauder, New Zealand; 

CMDL Mauna Loa Observatory, Hawaii (MLO); Perth, Western 

Australia; and at the Geophysical Institute, University of Alaska. 

Data processing has been completed for all stations through 

December 1998, and the vertical profiles are available from 

WOUDC. Processing has also been completed through 

November 1999 for Boulder, Lauder, Perth, and the Geophysical 

Institute. Problems at MLO and Haute Provence have yet to be 

resolved. 

Preliminary results from a number of Umkehr "intercomparisons" were presented at the Meteorological Service of 

Canada (MSC)-WOUDC Umkehr Meeting, November 17-18, 

1999, in Toronto, Canada. The results showed that, 111 general, 

instruments well calibrated in total ozone mode agreed to within 

3-5% of the standard in Umkehr layers 4, 5, and 6 and to within 

10% in layers 3, 7, 8, and 9. However, there appeared to be 

systematic differences between some of the instruments. Further 

investigation will to be done in an attempt to determine the 

possible causes of these differences. 

4.1.3. CALIBRATION OF DOBSON SPECTROPHOTO· 

METERS 

Seven Dobson ozone spectrophotometers in the Cf\IDL 

network, as well as 20 others (Table 4.3), were calibrated during 

1998 and 1999. Table 4.3 lists the cali bration difference 

expressed as a percent ozone difference. This percent difference 

TABLE 4.1. U.S. Dobson Ozone Spectrophotometer Station Network for 1998-1999 

Station Period of Record Instrument No. Agency 

Bismarck. North Dakota Jan. I. 1963-present 33 NOAA 

Caribou, Maine Jan. I, 1963-present 34 NOAA 

Wallops ls., Virginia July I, 1967-prcscnt 38 NOAA; NASA 

SMO Dec. 19, 1975-pn:sent 42 NOAA 

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

Nov. I, 1992-present 

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

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

Lauder, New Zealand Jan. 29, 1987-prcsent 72 NOAA; NIWA 

MLO Jan. 2. 1964-prescnt 76 NOAA 

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

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

SPO Nov. 17, 196 1-present 82 NOAA 

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

Huancayo, Peru Feb. 14, 1964-Dcc.3 1, 1992 87 NOAA; IGP 

BRW June 6, 1986-present 91 NOAA 

Fresno, California June 22, 1983-March 13, 1995 94 NOAA 

Hanford, California March 15, 1995-present 94 NOAA 

75 
TABLE 4.2. Provisional 1998 and 1999 Monthly Mean Total Ozone Amounts (DU) 

S1ation Jan. Feb. March April May June July Aug. Sept Oct Nov. Dec. 

Bismarck, North Dakoia 

Caribou, Mame 

Wallops ls .. Virginia 

SMO 

Tallahassee, Florida 

Boulder. Colorado 

Fairbanks, Alaska 

Lauder, New Zealand 

MLO 

Nash' ille, Tennessee 

Perth, Auslraha 

SPO 

Hau1e Provence, France 

Huanca)'O. Peru 

340 355 

361 360 

313 318 

233 234 

[283] [263] 

326 346 

[423] 

275 263 

229 245 

317 314 

265 263 

267 264 

321 314 

343 

(390] 

359 

235 

312 

349 

421 

268 

265 

336 

266 

[338] 

363 

408 

357 

246 

311 

372 

430 

267 

276 

340 

271 

393 

1998 

347 

(374) 

361 

247 

290 

328 

(387) 

283 

282 

337 

263 

(266) 

363 

334 

[362) 

332 

247 

321 

363 

312 

281 

308 

289 

(260) 

335 

300 

339 

314 

256 

302 

339 

341 

271 

303 

292 

(262) 

320 

288 

329 

309 

258 

294 

(324) 

342 

263 

301 

296 

[243] 

316 

297 

318 

295 

262 

279 

351 

266 

284 

320 

311 

283 

300 

267 

[26 1) 

280 

367 

255 

268 

321 

122 

298 

276 

310 

270 

262 

270 

264 

320 

246 

263 

302 

162 

292 

328 

334 

291 

[268] 

(255] 

286 

290 

236 

271 

284 

252 

293 

BRW 

Hanford. Cahfom1a 

Bismarck. North Dakola 

Caribou, Mame 

Wallops ls .. Virginia 

SMO 

Tallahassee, Florida 

Boulder, Colorado 

Fairbanks. Alaska 

Lauder. New Zealand 

MLO 

Nash' 1lle. Tennessee 

Perth. Aus1ralia 

SPO 

Hau1e Pro' ence, France 

Huancayo. Peru 

BRW 

Hanford, California 

Nol in operalion 

303 332 

340 355 

[344) 341 

299 306 

257 254 

[264] (264) 

291 313 

264 253 

235 232 

292 307 

263 263 

257 253 

276 327 

Nol in opera1ion 

273 291 

446 

327 

343 

376 

330 

244 

[298) 

313 

257 

261 

312 

263 

360 

(451] 

327 

444 

355 

363 

386 

341 

240 

(271) 

332 

(433) 

274 

287 

306 

262 

(278] 

371 

420 

355 

409 

356 

1999 

347 

354 

351 

245 

335 

376 

266 

278 

265 

[261] 

340 

365 

322 

357 

333 

334 

342 

324 

242 

[306) 

317 

[337) 

292 

272 

322 

276 

[246] 

332 

319 

317 

325 

322 

300 

312 

248 

(288) 

301 

317 

312 

267 

305 

273 

[248] 

325 

311 

297 

321 

288 

(360) 

311 

249 

287 

296 

293 

332 

264 

301 

290 

1221 I 

302 

277 

297 

323 

297 

[284) 

[278) 

(257) 

296 

316 

325 

265 

296 

318 

294 

292 

291 

(316] 

286 

283 

285 

26 1 

281 

[326) 

340 

258 

279 

319 

122 

(294) 

273 

268 

276 

(271] 

286 

257 

266 

[336] 

327 

257 

264 

311 

164 

259 

280 

328 

[331) 

299 

244 

309 

295 

250 

290 

283 

258 

295 

l\lon1hly mean ozone values in square brackels are derived from obscrva1ions made on fewer lhan I 0 days per rnonlh 

1~ between ozone calculated from the test and the standard 

instrument measurements with the most common observation 

type averaged from μ (optical path length through the 

atmosphere calculated from solar zenith angle) values of I, 2, 

and 3, 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. 

CMDL participated in international Dobson spectrophotometer calibrations at the WMO Region VI (Europe) Regional 

Dobson Calibration Center at Hohenpeissenberg, Germany, and 

the Swiss i\leteorological Institute (SM!) Lichklimatisches 

Observatorium (LKO) at Arosa, Switzerland, in July-August 

1999, and the Argentine Servicio Meteorol6gico Nacional 

(SMN) Buenos Aires Observatory in November-December 1999 

as part of its role as the World Center for Dobson Calibrations. 

Instruments for Lerwick, Scotland, Buenos Aires, Argentina, and 

the Japanese regional standard Dobson instrument were 

calibrated in Boulder during this period. 

4.1.4. SURFACE OZONE 

Observations of surface ozone continued at each of the four 

baseline observatories, as well as Niwot Ridge, Colorado; 

76 

Westman Islands. Iceland; and Arrival Heights, Antarctica. In 

November 1999 a TEI Model 49C owne analyzer was added at 

the CMDL South Pole Observatory, Antarctica (SPO), and it will 

operate alongside the Dasi bi I 003AH analyzer. In mid-1999 the 

Dasibi 1003AH analyzer at SMO malfunctioned and could not 

be repaired. It ran alongside the TEI Model 49 for nearly 2 

years. The operation of the Dasibi was discontinued temporarily 

but will be resumed when the instrument is repaired. Data from 

the CMDL Barrow, Alaska, Observatory (BRW), MLO, and 

SPO have been processed through 1999. The monthly mean data 

for the three sites are given for 1998 and 1999 (Table 4.4). For 

MLO the average is based on downslope (10-18 Universal Time 

Coordinated (UTC)) data. The data system at SMO experienced 

a number of outages after the measurements were restarted in 

1997 following about a I-yr gap. Although the data were 

recorded on a backup chart recorder, resources have not been 

available to process these data and bring the record up to date. 

At Arrival Heights, Antarctica (near McMurdo Station), a 

surface ozone analyzer was installed near the end of 1996. This 

instrument is operated in cooperation with the National Institute 

for Water and Atmospheric Research, New Zealand (NIWA). 

The data for 1996-1999 for this site are included in Table 4.4. In 

Figure 4.1 the seasonal behavior for 1997-1999 is compared to 
TABLE 4.3. Dobson Ozone Spectrophotometers Calibrated in 1998-1999 

lnstrumeni Previous Calibration Calibration Standard 

Station Number Date Correction ('k) Number Place 

1998 

Tallahassee, Florida 58 Sept. 23, 1994 +1.2 65 Boulder, Colorado 

Fairbanks. Alaska 63 May 29, 1992 +0.4 65 Boulder. Colorado 

Hanford, California 94 Sept. 15, 1994 +0.6 65 Boulder, Colorado 

Buenos Aires, Argentina 97 June 1994 NIA* 83 Boulder, Colorado 

Tsukuba, Japan 116 July 1995 -2.0 65 Boulder, Colorado 

1999 

Wallops Island, Virginia 38 April 27, 1995 0.0 83 Boulder, Colorado 

Barrow, Alaska 9 1 Sept. 15, 1994 +0.5 83 Boulder, Colorado 

Armenia (Proposed) 44 NIA NIA 65 Hohenpeissenberg, Germany 

Cambome, United Kingdom 41 July 30, 1995 +0.6 65 LKO Arosa 

Sestola, Italy 48 July 25. 1995 -0.5 65 LKO Arosa 

Bordeaux. France 49 July 30, 1995 +0.2 65 LKO Arosa 

Oslo. Norway 56 J unc 22, 1994 -0.9 65 LKO Arosa 

Arosa, Switzerland 62 1995 +0.9 65 LKO Arosa 

Hohenpeissenberg. Germany 64 July 22, 1997 +0.4 65 LKO Arosa 

Aswan, Egypt 69 May 25, 1993 +2.5 65 LKO Arnsa 

Hradec Kralove, Czech Republic 74 July 22. 1997 -0.3 65 LKO Arosa 

L'OHP, France 85 July 10, 1992 + 1.5 65 LKO Arosa 

Arosa. Switzerland 101 1995 +1.3 65 LKO Arosa 

l\loscO\\ , Russia 107 July 30. 1995 -0.3 65 LKO Arosa 

El Arenosillo, Spain 120 June 22, 1994 +1.6 65 LKO Arosa 

l\larcapomacocha. Peru 87 June 22. 1994 +0.7 65 Buenos Aires. Argenuna 

Buenos Aires. Argentina 97 June ? . 1998 0.0 65 Buenos Aires. Argentina 

f\larambio. Antan;tica (Argentina) 99 Aug. 3 1, 1992 +2.5 65 Buenos Aires, Argentina 

Cachoeira Paulista. Brazil 114 Nov. 24. 1980 +0.1 65 Buenos Aires. Argentina 

referenced to 1995 

Ushuaia, Argentina 13 1 June 22. 1994 +0.2 65 Buenos Aires, Argentina 

Co111uduw Rivadavia, Argentina 133 April 12, 1995 -U.5 65 Buenos Aires. Argentina 

Saito, Uruguay 134 April 12, 1995 ·0.8 65 Buenos Aires, Argentina 

*Instrument damaged 

TABLE 4.4. Monthl y Mean Surface Ozone Mixing Ratios (ppbv) 

Year Jan. Feb. March April May June July Aug. Sept. Oct. Nov. Dec. 

BR\V 

1998 333 28.9 22.7 25.3 21.6 19.2 21.6 18.8 2 1.2 25.1 27.5 24.8 

1999 23.4 21.9 9.3 6.3 

MLO (11il{hlli111e 011/y) 

1998 49.0 47.S 55.4 57.7 57.0 45.3 46.4 39.7 46.7 37.1 35.9 43.2 

1999 

SPO 

1998 23.5 23.7 22.2 25.5 28.7 32.4 33.3 33.6 33.0 3 1.4 32.6 29.5 

1999 26.9 20.I 21. l 25.I 29.3 32.9 36.3 37.0 35.2 31.3 32.3 29.6 

Arriml Heil{hts. A11111rctic:a 

1996 15.5 

1997 13.7 17.1 21.9 26.4 30.3 33.0 34.4 32.6 30.4 28.0 23.5 14.5 

1998 9.2 14.5 17.9 22.2 26.0 29.1 30.5 31.2 29. 1 25.6 18.0 17.4 

1999 15.9 16.5 19.3 24.7 27.7 32.5 33.6 32.6 30.0 27.6 20.9 15.7 

77 
0 0 I/) I/) 

,---., a ,.--... b 

> > (I) 0 (I) 0 Cl.. ... Cl.. ... Cl.. Cl.. 

~ ~~~8~~~~ '--' -.__,. 

0 

~fiJBEii~~ 0 

i== 0 i== 

<( 0 r') <( r') 

a::: a::: 

Cl 

~~~~ ~~ Cl 

~ Ei3 ~ z z x 0 x 0 N N 

::!E ::!E 

w w z 0 z 0 0 0 N N 

0 0 

0 0 I 

J F M A M J J A s 0 N D J F M A M J J A s 0 N D 

MONTH MONTH 

Fig. -l. l. Seasonal variation of surface ozone m1:-.111g ra1io at (a) Arrival Heights. Antarctica. and (b) SPO. The solid dot is the mean: the horizontal bar 

1s the median. the box is the inner 50 .. percentile: and the "whiskers" are the inner 90"' percentile of the data. The data arc for the period 1997-1999 

that for SPO. 111e winter maximum in ozone at each site is almost 

identical in magnitude, but the summer minimum at Arrival 

Heights 1s much deeper. At Arrival Heights the minimum 1s 

reached in January, while at SPO it is in Feb111ary. The depth and 

timing of the minimum at these antarctic sites likely reflects the 

photochemical loss mechanism in the southern hemisphere in 

which ozone 1s lost in the formation of the hydroxyl radical where 

nitrogen oxide (NO,) concen1rations are low 

4.1.5. 0ZONESONDES 

Table 4.5 summarizes the 1998-1999 CM DL ozonesonde 

projects. Nine sites, supplied by CMDL, launched one ozonesondc per week. The longest continuous ozonesonde records 

(> 12 years data) arc from Boulder, Colorado; MLO; and SPO. 

One United States site at Trinidad Head, Califorrna (August 

1997), and the newest site at the University of AlabamaHuntsville (April 1999) are part of the NOAA ''Health of the 

Atmosphere" Air Quality Research Program. These two sites 

and the Boulder site, represent a broad longitudinal transect 

across the United States that can be helpful in identifying the 

impact of anthropogenic emissions on tropospheric ozone lcveb 

during the general west-to-east flow across the cont111ental 

United States. 

SMO began launching weekly ozonesondes again in August 

1995 as part of the Pacific Exploratory Mission in the Tropics 

TABLE4.5. Summary of 1998-1999 Ozonesonde Projects 

1998 1999 

Ozonesonde Sites Totals Dates Totals Dates 

511111011 (\\'eekly) 

Boulder, Colorado 60 Full year 51 Full year 

MLO 44 Full year 47 Full year 

SPO 65 Full year 78 Full year 

Tahiti 33 Jan. 15-Nov. 24 54 Full year 

Fiji 42 Full year 53 Full year 

SMO 43 Full year 53 Full year 

Trinidad Head, California 47 Full year 44 Full year 

Hun1sville, Alabama 0 30 April 20-Dec. 31 

Galapagos 19 l\tan;h 25-Dec. 31 58 Full year 

Jn1e11s11·es (-daily) 

Old Hickory, Tennessee 0 30 June 14-July 15 

Kaashidhoo. Maldives 0 57 Jan. 27-March 28 

Ship Cmise 

Atlan1ic Ocean 0 35 Jan. 15-May 10 

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

SHA DOZ - Southern Hemisphere Additional Ozonesondes 

SOWER - Soundings of Ozone and Water in the Equatorial Region 

78 

PrOJect 

NOAA long term 

NOAA long 1erm 

NOAA long 1erm 

PEM Tropics/SHA DOZ 

PEM Tropics/SHADOZ 

PE1\I Tropics/SHADOZ 

NOAA "Heallh of the Atmosphere" 

NOAA "Heallh of 1he Atmosphere" 

SOWERJSHADOZ 

Soulhern Oxidanl Study 

CMDUNASA/SCRIPPS 

SHADOZ NOAA ship Rmwld H. 8rull'11 
(PEM Tropics). The PEM Tropics sites also included Papeete, 

Tahiti (July 1995) and Suva, Fiji (February 1997). The PEM 

Tropics A and B missions were designed 10 collect baseline data 

from aircraft platforms and ozonesondes in the South Pacific 

Basin 10 aid in the determination of the controlling factors 

related 10 the oxidizing power of the troposphere. The PEM 

Tropics missions ended in late 1999. However, Fiji and SMO 

continued operation under the Southern Hemisphere Additional 

Ozonesondcs (SHADOZ) campaign. This project uses 

ozonesonde profile data to validate tropospheric ozone derived 

from satellite measurements in the tropics and subtropics 

[H11dso11 and Tho111pso11 , 1998]. Additional SHADOZ 

ozonesondes were launched at San Crist6bal, Galapagos, an 

island in the eastern equatorial Pacific (0.9°N, l I0.0°W), for 

Special Observations of Ozone and Water in the Equatorial 

Region (SOWER), and on the NOAA ship Ronald H. Brown. 

The ship cruise went from Norfolk, Virgina, to Capetown, South 

Africa, and finally to Mauritius (east of Madagascar). 

The third intensive field campaign for the Southern Oxidants 

Stud) (SOS) was conducted in the Nashville, Tennessee, area 

from June 15 10 July 15, 1999. Daily ozonesondes were 

launched from Old Hickory, Tennessee. The SOS project 

included several research groups studying the formation of ozone 

in the troposphere and evaluating strategics to reduce pollution 

precursors leading to the high ozone levels often observed in the 

southern United States in the spring and summer months. 

40 

-29 JULY, 1998 254DU 

35 -05 OCTOBER, 1998 95 DU 

30 

-

~ 25 

-

w 

0 

:J 

20 

II-

...J 15 

<( 

10 

5 

a 

0 

0 5 10 15 20 

OZONE (mPa) 

Daily ozonesonde measurements were flown at Kaashidhoo 

Observatory in the Maldives during early 1999 in a joint project 

with CMDL, National Aeronautics and Space Administration 

(NASA) Goddard, and the Center for Clouds, Chemistry and 

Climate, Scri pps Institution of Oceanography (SIO) as part of the 

Indian Ocean Experiment (INDOEX). And finally, daily 

ozonesondes were flown in Boulder for 5 days in June of 1998 to 

provide ozone profiles for the International Photolysis Frequency 

Measurement and Modeling Intercomparison. 

SPO is a key CMDL ozonesonde site. The continuous data 

set, beginning in 1986, characterizes the typical development of 

the yearly ozone hole over Antarctica. First signs of the ozone 

hole recovery will be observed by comparing future ozonesonde 

data to the long-term south pole record [Hofmann et. al., 1997]. 

Figure 4.2 shows the severe depletion that occurred in both 1998 

and 1999, especially in the 14 to 21-km layer. Total ozone 

dropped by 64%, reaching 95 DU in 1998 and 90 DU in 1999. 

Table 4.6 lists the minimum total ozone values and the date on 

which they occurred since 1986. 

4.1.6. ATMOSPHERlC WATER VAPOR 

Water vapor measurements using balloonborne, frostpoint 

hygrometers continued in Boulder, Colorado. In addition, water 

vapor soundings were done from Kiruna, Sweden, during 

November 1999 as pan of the NASA Stratospheric Aerosol and 

40 

-28 JULY, 1999 255DU 

35 -29 SEPTEMBER, 1999 90 DU 

30 

-

~ 25 

-

w 

0 20 

:J 

II-

_J 15 

<( 

10 

5 

b 

0 

0 5 10 15 20 

OZONE (mPa) 

Fig. 4.2. Venical profiles of ozone panial pressure in millipascals (mPa) at the South Pole Observatory during (a) 1998 and (b) 1999. The thin line 

represents the pre-depletion profile. The thick line is the profile observed during the minimum in total ozone. 

79 
TABLE4.6. Summary of the Minimum Total Ozone Measured at SPO* and the Date of the Ozonesonde Flight 

Year Date Total Ozone 

1986 Oct. 7 140 

1987 Oct. 9 115 

1988 Oct. 10 185 

1989 Oct. 9 131 

1990 Oct. 7 130 

1991 Oct. 7 128 

1992 Oct. II 100 

*The uncertainty is ±5 Dobson Units. 

Gas Experiment (SAGE) llI Ozone Loss and Validation 

Experiment (SOL VE) campaign. The long-term record of 

stratospheric water vapor measurements at Boulder continues to 

show an increase of about I% yr" 1 as illustrated in the time series 

for the 20 to 22-km layer (Figure 4.3). This layer is typical of 

the increase seen at all altitudes above about 16 km over 

Boulder. An earlier set of water vapor soundings made in 

Washington, D.C., from 1964-1977 (Figure 4.4) also shows an 

increase of about the same magnitude as seen at Boulder, 

suggesting that the increase in stratospheric water vapor has been 

occurring for several decades. 

4.1.7. ATMOSPHERIC TRANSPORT 

The CMDL isentropi c trajectory model continues to be a 

valuable tool for diagnosis of the origins of air parcels measured 

at the CMDL observatories, as well as those measured on ships, 

aircraft, and at miscellaneous experimental sites. The 

atmospheric transport project in CMDL is designed for a high 

\'Olume of output. Improvements made over 1998 and 1999 

enhanced this capability. The standard gridded meteorological 

data used as input to the CMDL trajectory model come from the 

European Centre for Medium Range Weather Forecasts 

(ECMWF) through the U.S. National Center for Atmospheric 

Research (NCAR). These data have become available in a more 

6 

0 7 ..:; 

.,, 

..... 

bl) 6 c: 

>< 

2[ , , ..l, J, •I I 

1980 1982 1984 1966 1988 1990 1992 1994 1096 1098 2000 2002 

Year 

Fag. -U. Water \apor mixing ratios (ppmv) for the 20-22 km layer over 

Boulder. Colorado. The solid line is a linear fit to the individual 

sounding layer average mixing ratios. The trend value is 1.0 ± 0.2% > ( 1

, 

and the error is for the 95% significance level. 

Year Date Total Ozone 

1993 Oct. 6 89 

1994 Oct. 5 102 

1995 Oct. 5 93 

1996 Oct. 6 114 

1997 Oct. 8 117 

1998 Oct. 5 95 

1999 Sept. 29 90 

timely fashion, reducing the lag time of the data to about I 

month. Another factor that has greatly improved the speed at 

which trajectories can be produced is accessing the input data in 

direct access mode on disk rather than accessing these data 

sequentially from magnetic tape. Fifteen years of meteorological 

data ( 1985- 1999) are now readily available on disk, eliminating 

the need for magnetic tapes. The trajectory program is 

automated so that obtaining large volumes of trajectories (e.g., 

for a site climatology) is straightforward. 

80 

The trajectory input data are fairl y coarse because of storage 

and processing constraints. The data have a horizontal resolution 

of 2.5 degrees latitude x 2.5 degrees longitude, a verti cal 

resolution of 14 levels (from surface to I 0 hPa) and a temporal 

30 

28 

:: ~-

E 22l 

=. t ~ 20 ::l 

,.j 

:.::; 

< 18 

16 

14 

12 

Water Vapor 

1964-19?7 

IO LLI.-'--'-L.LJ...u...u.......u...LJ....L...1....1...!.'"-'...w...LJ....L...w...LJ....L...w...LJ....L...w...LJ....L...w..._...--= 

-5 - 4 - 3 -2 - 1 0 l 2 

Trend [%/year J 

3 4 5 

Fig. 4.4. The linear trend in percent per year as a function of altitude for 

the water vapor mixing ratio over Washington, D.C., during I 96.t-1977. 

The shaded area represents the 95'7c significance level (i.e., if the shaded 

area intersects the zero line, the trend is not significantly different from 

zero). 
resolution of 12 hours. Trajectories produced with these data are 

not suitable for diagnosis of mesoscale transport, but rather they 

track large-scale regional air flow. The gridded winds are 

interpolated kinematically to isentropic surfaces with the 

specification of arrival height, arrival pressure, or potential 

temperature. The method of wind interpolation to the isentropic 

surface is detailed in section 3. 13.4 of Summary Report No. I I 

[Harris and Bodlrai11e, I 983] 

Aside from the standard ECMWF trajectories, trajectories are 

provided in real-time on the trajectory web site 

(http://www.cmdl.noaa.gov/ozwv/traj). These trajectories are 

made with meteorological data downloaded twice daily from the 

National Centers for Environmental Prediction (NCEP). The 

differences between the ECMWF and NCEP data sets are usually 

slight, but to avoid confusion, it is recommended that the realtime trajectories be used only as a first look. Trajectories for 

publication should be based on the ECMWF data. 

Trajectories have been used to investigate the relationships of 

trace gas and aerosol measurements to their sources and sinks. 

Published transport studies .for each of the four CMDL 

observatories arc cited in section 4. I .7 of CMDL Summary 

Report No. 24 [Hof111a1111 et al., 1998). A special project, in 

section 4.2.3 of this report, presents some highlights of a new 

transport study for BRW that was recently completed. Section 

4.2.4 presents an analysis of 0 3 and CO at Cape Point 

Observatory that also uses trajectories. 

4.1.8. STRATOSPHERIC AEROSOLS 

At MLO in early I 998, both the ruby and Nd:YAG (neodymium doped yurium aluminum garnet type laser) lidars were 

moved into the new Network for the Detection of Stratospheric 

Change (NDSC) building. The NDSC has three rooms devoted 

to the CMDL lidar program that are used as a control room, a 

laser room, and a telescope room. The entire optical structure 

was redesigned to house the lasers and the telescopes more 

compactly. The optical rails extend through the wall to rigidly 

tie the telescopes and lasers together. Separating the telescopes 

from the lasers reduced the signal-i nduced noise on some of the 

detectors. The new facilities are far better fo r maintaining the 

equipment and developing new measurements. The move was 

accomplished in about 2 weeks because the hatches were 

installed previously. The Nd:YAG laser required a service call 

to get the power back to specification. 

The ruby lidar signal strength was severely reduced in the new 

conliguration. After exchanging several of the components, the 

signal was still too weak for reasonable data. Since the 

backscatter at 694 nm can be interpolated from the Nd:YAG 

backscatter measured at 532 nm and 1064 nm more accurately 

then the actual ruby lidar measurement, it was decided to end the 

ruby lidar measurement. Over I year (44 measurements) of 

overlapping data showed the interpolated and measured 694 nm 

backscatter agreed to a few percent, well within the 20% error of 

the ruby lidar data. 

A grant from the NOAA National Environmental Satellite, 

Data, and Information Service (NESDIS) was received for the 

rescue of the ruby lidar database. Although the integrated aerosol 

data were available, the individual profiles (over 700 

measurements) were in various formats and could not be analyzed 

consistently. The database will be standardi zed and errors will be 

estimated. The data can then be submitted to the NDSC archive 

for use by other researchers. Interactive Data Language (IDL) 

software was acquired under the grant to use for the lidar 

temperature analysis. A temperature analysis by the Jet Propulsion 

Laboratory (JPL) lidar group, written in IDL and well researched, 

will be used for the reanalysis of the temperature record. 

81 

The background conditions in the stratospheric aerosol 

[Barnes and Hoft11a1111, 1997) that began in 1996 at MLO 

contioued through I 999. Figure 4.5 shows (a) the quasi-biennial 

oscillation (QBO) winds, (b) the backscatter from the upper part 

of the stratospheric aerosol layer (25-33 km), and (c) the 

backscatter from the total stratospheric layer (I S.8-33 km). The 

total layer is dominated by the I 6 to 22-km region. 

40 ~~~~~~~~~~~~~~~~~~~~ 

~ 20 

E 

:; OP-~....,..;....~......,-+-~~-+~~_....,i--~~-+<-~~~ 

c 

~ ·20 

~o ~~~~~~~~~~~~~~~~~~~ 

~ 2 .., 

(") 

' 

I 

I 

I I I I 

I I I I --,---,---,--1--

1 I I I 

I I I 

I I --1 

b 1.-.~~-'--~~--'-~~-'-~~~'--~~..L-~~~ 

1994 1995 1996 1997 1998 1999 2000 

~\..30 ., 

~ 

0 

~ 

E 

.>< 20 

~ 

(/)-

al 10 ~ 

I 

I 

I I I I I 

l __ J_ _ _ _J __ _ L _ _ _L_ __ 

I I I I 

I I I I 

I I I I 

I I I I --1--1---1--

I 

I 

I --+--

1 

I 

I 

c o~~~~~~~~~~~~~~~~~~~~ 

1994 1995 1996 1997 1998 1999 2000 

Fig. 4.5. (a) Quasi-biennial oscillation (QBO) winds (30 hPa at 

Singapore). and Integrated Aerosol Backscatter (IABS) from (b) the 

upper part of the stratospheric aerosol layer (25 to 33 km), and from (c) 

the total stratospheric layer ( 15.8 to 33 km) observed over M LO. 
The 4 years ( 1996-1999) show a clear annual cycle in the total 

layer, peaking in the winter. The winter peak coincides with the 

doubling of the vertical transport of air through the tropical 

tropopause [Rosenlof and Holton, 1993) during the winter 

compared to the summer months. It is not clear if the winter 

peak in the aerosols is consistent with the stronger verti cal 

transport. Although this would mean that more sulfur-rich air 

would enter the stratosphere during the winter, the residence 

time necessary for aerosol formation would be shorter. 

There is no clear QBO effect in the total aerosol layer. Both 

the easterly and westerl y phases have about the same yearly 

averages, I.I x I0"

4 per steridian (sr"\ However, a QBO effect 

is discernable in the upper part of the layer. During the westerly 

phase, the aerosol loading is a factor of two less than during the 

easterly phase. This is consistent with the lofting of the aerosol 

layer during the easterly phase when the tropical stratospheric 

reservoir is sequestered from mixing with midlatitude air. 

In Boulder a new stratospheric aerosol lidar was built and 

111stalled 111 one of CMDL's rooftop domes in August 1999. The 

lidar uses a single, electronically gated photomultiplier tube and 

a 61 cm telescope (I S2 cm focal length), similar to the ones at 

f\ILO. A much smaller Nd:YAG, frequency doubled laser (Big 

Sky Lasers) is used for the 532 nm source. A multi-channel 

scaler data acquisition board is used, and the MLO software was 

modi lied for the Boulder configuration. The lower tropopause at 

Boulder increases the dynamic range needed to profile the entire 

stratospheric layer on one channel. Preliminary measurements at 

Boulder show that there is often no clear lower boundary of the 

layer in contrast to the case at MLO. This makes the 

interpretation of the data more difficult. 

4.2. SPECIAL PROJECTS 

4.2.1. EVIDENCE FOR THE INFLUENCE OF BIOMASS 

B URNING ON TROPOSPHERIC OZONE IN BOTH THE 

EASTERN AND WESTERN TROPICAL PACIFIC 

Beg1 nn111g in August I 99S, as part of the Pacific Exploratory 

Mission (PEM) Tropics A. ozone vertical profile measurements 

were started at the airport in Pago Pago, American Samoa 

( 14.S S, I 70.S0 W) and Papeete, Tahiti (14.S0 S, I SO.S0 W). 

Profile measurements were continued at Tahiti and Samoa 

through PEl\1 Tropics B v. ith the program at Tahiti completed in 

December 1999. At Samoa weekly soundings continue as part of 

the SHADOZ project. During most of the measurement period, 

soundings were done weekly. During two aircraft field 

campaigns in September-October 1996 (PEM Tropics A) and 

March-April 1999 (PEM Tropics B), soundings were done twice 

a week. In January 1997 weekly soundings were begun at Suva, 

Fiji (I 8.0°S, I 70.0°W). As part of the SOWER project, ozone 

profile measurements were started on a campaign basis in March 

1998 at San Crist6bal, Galapagos, and were upgraded to 

biweekly soundings in September 1998, and to weekly soundings 

as part of SHADOZ early in 1999. The ozone vertical profiles 

were obtained using the electrochemical concentration cell 

(ECC) ozonesonde [Komhyr et al., I 99S]. This has become a 

standard technique for obtaining ozone profiles with high 

vertical resolution in both the troposphere and stratosphere to 

altitudes of approximately 3S km. For the purpose of 

characteri zing the tropospheric airflow patterns influencing 

transport to the tropical sites, isentropic trajectories were 

calculated. The trajectories are computed from the ECMWF 

analysis using the model described in Harris and Kahl [ 1994]. 

Variations on the order of several days and the seasonal cycle 

are the two largest sources of the variability seen in tropospheric 

ozone at the Pacific tropical sites studied here. These variations 

were studied from surface observations at Samoa [Harris and 

Oltmans, 1998) and were found to result from changes in airflow 

to the site that tapped different sources and sinks. In the middle 

troposphere (2-10 km) both the shorter term and seasonal 

variability are primarily associated with the appearance of layers 

with enhanced (>70 ppbv) ozone mixing ratios (Figures 4.6 and 

4.7). These peaks occur primarily during the August-October 

time period. This leads to a seasonal maximum in this layer 

during the austral spring at both the western and eastern Pacific 

sites. At the western Pacific sites there is prominent westerly 

flow during all times of the year, but it is more frequent and 

more vigorous during the austral spring. At the Galapagos, on 

the other hand, easterly flow dominates in the midtroposphere 

82 

18 

16 

" 

12 

e 

~ 10 

"' 0 § • c 

TE.MPERATl.RE I FROST P<JKT CC\ 

·100 ... ., 

I k . I I I I I I I I I I 

\ ' I fr: I I I 

\ I - "!--- ', 

', If 

~ !""':, 

"'"i\.. ' ', '• i 

~ ''\ - ~ 

<: I .- ;-..., I\ 

~ I -... 

' 1\1'. j 

IJ - I . I K\ ,o 20 JO «> 50 ea 10 eo go 100 nl 120 1:x> 140 1s.:t 

OZOtE(ppl>v) 

Fig. -1.6. Ozone mixing ratio (thick line). temperature (dashed line), and 

frost-point temperature (thin line) profiles at Pago Pago. American 

Samoa. for October 30. 1998. 

·100 ... . ., •• ~r - <, ' 

•• 

" I\.' ~ 

;;;;::: t 

' .....- t'-, 12 

-...... -.... 

c. r-t'• ', ,, 

\. ' '· ~ ., 

~ I'--... 1, I 

-.... "-

y -- ........... 

~ i'_ 

" I 

I 

10 4D 3'.J «> 50 8J 70 llO 90 10> HO 120 lXI 1-0 \SO 

OZOtE(l'!ll>Y) 

Fig. 4.7. Ozone mixing ratio (thick line). temperature (dashed line), and 

frost-point temperature (thin line) profiles at San Crist6bal, Galapagos, 

for October 9, 1999. 
and is particularly pronounced in the austral spring. An 

important difference between the western and eastern Pacific is 

the very low ozone amounts throughout the troposphere during 

the summer and early autumn (December-April) in the western 

Pacific. Although this is also the time of the seasonal minimum 

in the troposphere at the Galapagos, mixing ratios do not get 

nearl y as low above the boundary layer as in the western Pacific. 

This reflects the greater influence of convection in the west in 

mixing boundary layer ozone throughout the troposphere. 

The tropics are known to be a significant area of biomass 

burning (see TRACE A and SAFARI, Special Issue of the 

Joumal of Geophysical Research, IOI, 1996). An ozone profile 

with an enhanced midtropospheric layer, often seen during the 

September and October period, is shown in Figure 4.6 for a 

sounding done at SMO. The peak ozone mixing ratio of 105 

ppbv at -6 km for the October 30, 1998, profile at SMO has a 

trajectory that reaches back to southern Africa 10 days prior to 

the sounding. Biomass burning heavily influences ozone in this 

region (Fishman et al., 1996]. Traj ectories identified with peaks 

greater than about 70 ppbv do not always reach back to Africa in 

I 0 days, but they always have paths that have a strong westerly 

component that goes to the west of Australia into the Indian 

Ocean. On many occasions the trajectories pass over Australia 

but usually through the middle or southern part of the continent. 

In the Galapagos the profiles also show a similar 

midtropospheric peak, e.g., October 9, 1999 (Figure 4.7). The 

trajectory for this event crosses Brazil in less than I 0 days over a 

region that is also heavily impacted by biomass burning 

[Fishman et al., 1996]. Investigation of each profile with an 

enhanced ozone layer in the midtroposphere during this time of 

the year showed a trajectory that passed over Brazil. 

In 1997 extensive burning took place in Indonesia associated 

with drought conditions that were a consequence of the strong El 

Nii\o. Several studies have shown high ozone amounts in 

Indonesia and Malaysia in connection with the burning in the 

region [e.g., Fujiwara et al., 1999]. At the western Pacific sites, 

the incidences of elevated midtropsopheric ozone begin to 

decline in most years by mid-November. On November 19 and 

20 at Fiji and Samoa, some of the highest tropospheric ozone 

amounts were seen for any event recorded at these sites, and they 

extended from above the boundary layer to the tropopause. 

These enhancements increased the total tropospheric column by 

about 20 DU or more than 70% over average values for the 

month. The trajectories show that at both sites the air was 

coming from Indonesia. Although these profiles were the only 

ones measured during the event, the trajectories show that the 

flow persisted for about 5 days around the time that the profiles 

were obtained. 

4.2.2. WATER VAPOR AND OZONE OBSERVATIONS AT 

SAN CRISTOBAL, GALAPAGOS 

In March 1998 profile measurements of ozone and water 

vapor were started at San Crist6bal. This project is conducted in 

cooperation with the University of lbaraki, Japan, the University 

of Hokkaido, Japan, and the SHADOZ proj ect. Water vapor 

profiles were measured in four campaigns duri ng the spring and 

fall seasons of 1998 and 1999 and are scheduled to continue in 

the fall of 2000. The main instrument is a balloonborne frostpoint hygrometer, and in th ree cases a new commercial frostpoint hygrometer was tested that could extend the altitude range 

83 

of upper tropospheric humidity measurements for smaller 

radiosonde-type soundings. Regular ozone soundings have been 

launched biweekly since September 1998 and weekly since 

March 1999. The excellent location and the outstanding data 

quality received from this site will hopefully allow continued 

soundings. Despite the political and economic problems of 

Ecuador, which continue to impact the operation of this project, 

it was undertaken successfully. 

San Cristobal is strongly influenced by El Nii\o/La Nii\a 

events and is, therefore, a natural laboratory for atmospheric 

processes controlled by the upwelling and the downwelling part 

of the Walker circulation. It is one of the few tropical regions 

that has significant periods of clear sky and is highly suitable for 

remote sensing studies and radiometry as well. It is currently the 

only tropical site where water vapor near the tropopause is 

measured and is the only site adding to the database for water 

vapor entering the stratosphere through the tropical tropopause. 

Its remoteness from industrial pollution sources allows for the 

study of long-range transport of pollutants across the tropical 

Pacific region. 

Water Vap or Crossing the Tropical Tropop ause 

Since the discovery of the stratospheric dryness [Brewer, 

1949], it is generally accepted that air enters the stratosphere 

predominantly in the tropics because only the tropical tropopause 

is cold enough to explain the low water vapor content of the 

stratosphere. Early investigations based on radiosonde and in 

situ measurements [Newell and Gould-Stewart, 198 1; Kley et al. , 

1982] indicated that there is a regional and temporal preference 

for air entering the stratosphere. A strong focus of the early 

investigations has been deep convecti ve systems and their cirrus 

an vils [Danielsen, 1982, 1993). These systems can achieve 

water vapor mixing ratios at the tropopause well below the mean 

stratospheric water vapor concentration [ Vomel et al., 1995]. 

Yulaeva et al. ( 1994] have shown that the mean tropical 

tropopause temperature is mostly controlled by the seasonal 

cycle of the mean residual vertical velocity in the stratosphere, 

which implies that tropical tropopause regions not influenced by 

tropical deep convection might still become sufficiently cold to 

dry slow rising air. Several studies [Dess/er, 1998; Sherwood, 

2000; Ge/le/man et al., 2000] indicate that a regional preference 

for air crossing the tropical tropopause may not be necessary to 

explain the stratospheric dryness. 

Our first campaign took place in March 1998 at the end of the 

very strong El Nii\o event of 1997/1998. During this campaign 

the average minimum temperature near the tropopause was 

around -83°C with a saturation mixing ratio of about 3.6 ppmv 

(Figure 4.8a). While the atmosphere was convectively more 

active during this campaign because of the El Nii\o event, there 

is no indication that the deep convection reached the local 

tropopause. Therefore, the tropopause temperature did not 

appear to be directly controlled by the deep convection. This is 

in strong contrast to our results from the Central Equatorial 

Pacific Experiment (CEPEX) in 1993, where deep convection 

reached the tropopause and directly caused extremely low 

tropopause temperatures and water vapor mixing ratios. 

Nevertheless, the first frost-point sounding at San Cristobal 

showed a saturated layer between 13 km and the tropopause at 

17 km above a very dry layer between 6 and 12 km with 

humidity values between 10 and 20%. The later soundings of 

this campaign showed a warmer tropopause and only up to 90% 
~ 

E 

.=.. 

QI 

"O 

.3 

:;::; 

< 

~ 

E 

.Y. 

QI 

"O 

.3 

:;:; 

< 

25[ 

201 

t 

t 

I 

15!· 

I 

f 

I 

I 

r 

!O r 

I 

I 

51 

t 

I 

0 l - -.... .ul 

100 lO I 

~o· 

~ 

15j 

r 

I 

f 

I 10' 

~ 

(a ) 

i\ t',. \ . t \I tr I 1 1 • 

lin.lt"r Vapor. MarC'h 10\l9 

r• V ""t.l I 

SaturaUon. March I G9ll 

,,_ ... ~,., ..... J _,j,.__.l....~~~~__u.,.l _~_ 

102 103 104 105 

Mixing Ratio (ppmv) 

r rr-'1 

(b) 

... • • li • 1. 

Wnlrr Vopor, 5f"p lrmhrr lOll~ 

ur .>n " 1 -4 

Saturallon, Septombe. 11100 ~ 

] 

1 

1 

0 ..__ - ..... ~ _ ........... ,..!---.._ ... ...... .!~-~"""""- J 

100 10 1 102 103 10'1 105 

Mixing Ratio (ppmv J 

Fig. 4.8. San Cris16bal, Galapagos, average waler vapor (blue) and 

sa1u ra1ion (red) mixing ra1ios for (a) March 1998 and March 1999, (b) 

Sep1ember 1998 and Sep1ember 1999. The dolled line shows 1he heigh1 

of 1he 1ropopause in 1998 (ligh1 blue) and 1999 (dark blue). 

saturation of water vapor over ice with a more moist middle 

troposphere. These soundings indicale local drying at the 

tropopause may occur but is not necessarily related to deep 

convection. The campaign in March 1999 confirmed this result 

clearly without the innucnce of deep conveclion. The soundings 

typically showed a dry layer be1wcen 11 km and 16 km and a 

considerable increase in ozone above 11 km. This indicates 

downward transport in the upper 1roposphere corresponding to 

the descending part of the Walker circulation. 

In both fall campaigns (Figure 4.8b) the tropopause was 

significan1ly warmer, around -78°C, with a saturation mixing 

ratio between S and 12 ppmv. The water vapor soundings 

showed a dry layer below and up to the tropopause except for the 

actual temperature minimum, which in some cases could reach 

up to 90% rel ative humidity (ice). The measured water vapor 

mixing ratio at the temperature minimum of the tropopause 

ranged between S.S and 7.S ppmv. Local drying at the 

tropopausc level was not observed; however, relatively higher 

water vapor mixing ratios at the tropopause indicate air may 

en1er the tropical lower stratosphere without being dried locally 

at the temperature minimum. 

CMDL observations at San Cristobal indicate there is a region 

below the local tropopause that is not directly innuenced by deep 

convection. This region constitutes a barrier to vertical mixing 

below the local tropopause. This result has been found for other 

tropical sites [Folkins et al., 1999] and is indicated here in terms 

of ozone and water vapor. 

The results during CEPEX in the western Pacific showed that 

deep convection can reach the local tropopause causing 

extremely low temperatures and drying air to extremely low 

water vapor mixing ratios. Jn contrast to these observations, our 

results at San Cristobal indicate that in !he eastern Pacific region 

deep convection does not reach as high, and that cold tropopause 

temperatures are achieved by stratospheric processes rather than 

by tropospheric deep convection. Local drying docs occur 

during the northern spring seasons, but not during the northern 

fall seasons. Furthermore, air that is unsatura1cd a1 1hi:: loi.:al 

temperature minimum near the tropopause may enter the tropical 

lower stratosphere during these months. 

84 

Tropospheric Ozone Observations 

Extremely low ozone values observed in the middle and upper 

troposphere in the western Pacific [ Vomel et al., 1995] have not 

been observed in the eastern Pacific (Figure 4.9). This indicates 

that deep convection, which can transport ozone-poor air rapidly 

from !he boundary layer to the upper troposphere, is not as 

vigorous in the eastern Pacific as it can be in the western Pacific. 

However, there is a significant difference in the upper tropospheric 

ozone observed during the March 1998 campaign compared to the 

March 1999 campaign (Figure 4.9a). The first campaign in March 

1998 was still under the innuencc of the El Nino of 199711998 that 

moved the typical upwelling region of the Walker circulation 

towards the central and eastern Pacific. The upper 1ropospheric 

ozone during this campaign shows lower values compared to the 

campaign of the following year, indicating that the El Nino even! 

caused increased transport of boundary layer ozone into the upper 

troposphere. In the fall campaigns (Figure 4.9b) ozone concentrations in the upper troposphere are significan1ly higher than 

for March 1999. In both years the average ozone profiles during 

the fa ll campaigns do not show the difference that was seen in the 

two March profiles, possibly because both campaigns were under 

similar La Nina conditions. 

San Cristobal is considered a remote marine site, far from 

industrial sources of pollution. However, it is often innuenced 

by long-range transport from biomass burning regions and other 

pollution sources of South America. Figure 4.10 shows a 

time/height cross section of the ozone mixing ratio for 1999 over 
25 25 

(a) 

March 1998 

(b) 

September 1998 

- March 1999 - September 1999 

20 20 

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

15 ~ 15 E E .:.: .:.: ~ 

l!J l!J "O "O 

_, 

;:J ;:J 

_, :;:; :;:; ...; 10 < 10 

5 5 

O~~~~~~~~_.___._......__,._._._._....~ ~'-'--'-'-'-'-'-' ._~.__..___.__._._,_....._~_.___._......__,._._._._....~~~'-'--'-'-'-L.U 

0.01 0. 10 1.00 10.00 0.01 0 . 10 1.00 10.00 

Ozone Mixing Ralio [ppmv) Ozone Mixing Ralio [ppmv) 

Fig. 4.9. San Crist6bal, Galapagos, average ozone mixing ratios for (a) March 1998 and March 1999, (b) September 1998 and September 1999. The 

height of the tropopause is shown for 1998 (dark dashed line) and 1999 (light dashed line). 

.OE+ OO 

2.0E-01 

l.OE- 02 

Jan Fe b Ma r Apr May Jun Jul Aug Sep Oc t Nov Dec 

[ppmv] 

Fig. 4.10. Time/height climatology of monthly averages of ozone mixing ratio over San Crist6bal, Galapagos, in 1999. The solid line indicates the 

average tropopause height. 

85 
San Crist6bal. The middle troposphere shows a seasonal cycle 

with higher ozone values typically found between August and 

October and lower values between January and May. Trajectory 

analyses show that during most lime periods the air comes 

predominantly from equatorial South Ameri ca. During June 

through August, for example, more than 90% of all trajectories 

arri ving at 6 km over San Crist6bal originate over equatorial 

South America, in particular from the biomass burning regions 

of the Amazon basin and northeastern Brazil. 

The sounding on May 18, 2000, shows some direct evidence 

for long-range transport from the South American continent 

(Figure 4. 11 ). At S km altitude this sounding displays a shallow 

layer apparently devoid of ozone. While ozone is most likely 

undisturbed within this layer, its signal is masked by an artifact 

of the instrument caused by high concentrations of S02• The 

likely source for this layer is an eruption plume of Tungurahua 

volcano (78.44°W, l.74°S) on May 13 transported lo Galapagos 

within S days. 

E 

-" 

::.> 

-0 

:; 

~ 

:;;: 

16 

14 

12 

10 

8 

6 

4 

2 

0 

Ozone 

San Crisloba l, Galapa gos 

1 8 \.\a y 2000 

Lon = 89 62°W 

Lal = o 9°S 

L-~--'~ --'--'--'-' ...... ..,,'----~-'- -'--'---'-.J..--'-'-' 000 

0 001 0.0 10 0. 100 

Ozone Mi xing Ralio (ppm v) 

~ 

E "

x 

e 

Q, 

Q, 

< 

Fig. 4.11. S02 interference layer caused by long range transport of 

volcanic gases emitted by Tungurahua volcano May 13, 2000, and 

observed May 18, 2000, at San Crist6bal, Galapagos. 

Outlook 

The location of this site is very unique and continued 

observations are planned in the near future. These observations 

will be included in satellite validation studies. A new surface 

ozone monitor at this site will give 24-hr observations of 

boundary layer concentrations of ozone that will allow for the 

study of some interesting aspects of the chemistry of the lower 

troposphere. 

4.2.3. EVIDENCE OF 03 TITRATION DURING BRW 

WINTER DARK PERIODS 

Trace gas measurements from BRW during the winter dark 

periods of 1986-1997 were examined. After ensuring that local 

pollution from the Barrow town site was not present in the data 

set, a smooth curve consisting of a function and fi ltered 

residuals was removed from each data record. The smooth 

curve was designed so that its removal leaves residuals 

containing only the highest frequency vari ations on the order of 

synoptic scale changes [Tho11i11g et al., 1989). Variability 

caused by changes in transport can be examined with these 

residuals. 

Figure 4.12 shows a negative correl ation between 0 3 and 

C02 residuals for Siberian transport. C0 2, CO, and CH4 

residuals were positively correlated with one another (e.g., 

Figure 4. 13). On the basis of trajectory analysis, it is 

speculated that the positi ve correlations among C02, CO, and 

CH4 indi cate industrial sources either in Siberia or further 

upwind (e.g., the Ural region). By limiting the data to 

transport from this direction, the slope of the fi ned line did not 

change much in comparison to that derived from all transport 

types, and the correlation of the fit improved slightly. This 

may reflect the fact that winter transport conditions result in 

the Siberian pollution signature becoming regionally 

widespread throughout the Alaskan Arctic. The other transport 

pathways to Barrow yield few or no man-made sources within 

I 0 days. 

86 

The negative correlations between OJ and the other species 

may be caused by chemical removal of 0 3 by NOx (titration) 

that occurs when NOx is plentiful in the absence of sunlight. 

Based on the chemical reactions that likely take place, the 

range of 1.5-2 0 3 molecules destroyed per NO molecule 

emitted was used. There is negligible NOx in the remote 

Arctic near Barrow. However, it is surmised that 0 3 is being 

destroyed within pollution plumes generated in Siberia or 

upwind from there. As a check on this assumption, the molar 

ratio of NOx to C02 was calculated. The delta (L\.) symbol is 

10 n = 320 

slopi; = -2.;3 ± 0.0 

•o 0 r = 0 .7 0 

,,....., 5 > .0 

a. 

a. 

~ 

0 

:; 0 u 

·c;; 

Cl> 

0::: 

.., 0 . -5 0 

0 s 

- 10 

-4 - 2 0 2 4 6 

C02 Residual (ppm) 

Fig. 4. 12. OJ versus C02 residuals for the winter dark periods, 1986-

1997, at BRW. Only data corresponding to transport from the 

direction of Siberia are included. 
,-.._ 

.D 

Q. 

Q. 

'-..' 

0 

::I 

" I/) 

Q) 

a: 

~ 

I 

(.) 

150 

100 

50 

0 

n "' 327 op~ "' 12.23 ± 0.44 r :;: 0.73 

J( 0 

-50~~~~~~~~~~~~~~~~~ 

-4 -2 0 2 4 6 

C02 Residual (ppm) 

Fig. 4.13. CH. versus C02 residuals for the winter dark periods, 

1986-1997, at BRW. Only data corresponding to transport from the 

direction of Siberia are included. 

used to denote a change in concentration over time or an 

emission rate: 6NOx/6C02 = 6NOx/603 x 6 0 3'6C0 2• 

Inverting the titration factor and with the empirical slope of 

603/6C02 determined from the Barrow data (-2.33 x 1 O" \ 

6NOx/6C02 = ( 1.2- 1.6) x I0'

3 is obtained. This is close to, or 

within, the lower end of the range expected from coal-fired 

industrial processes ( 1.39-3.49) x 10"3 (W. Barbour, 

Environmental Protection Agency, personal communication, 

1999). It is possible that the natural gas burned in this region 

causes the 6NOx/6C02 ratio to be lower than that for pure coal 

burning. Likewise, with the empirically deri ved slope for 

603/6CO (-3.45x l0"\ 6NOx/6CO = 0.1 7-0.23 is obtained 

and is consistent with the ratio determined for eastern North 

America of 0.19 [Saeger et al., 1989]. The empirical ratios 

indicate air measured at Barrow during the winter has a 

pollution component and that the negati ve 0 3 correlations 

could be caused by titration that occurs days upwind of 

Barrow. 

4.2.4. ANALYSIS OF C O AND 03 DATA FROM CAPE 

POINT OBSERVATORY (1994-1998) 

Cape Point Observatory (CPT) is located at the southern tip of 

Africa (34°S) on a peninsula (Figure 4.1 4). This figure shows 

the average transport pathways to CPT and their frequency of 

occurrence. The 5-day fetch is often in the. remote South 

Atlantic. Cape Point is one of a few sites measuring trace gases 

transported from the southern oceans. However, Cape Point is 

also located 60 km from Cape Town, a city of more than two 

million people; therefore, pollution from car exhaust and 

industry does at times reach the observatory. In collaboration 

with the two sponsors of the observatory, the Fraunhofer 

Institute in Germany and the South African Weather Bureau, 5 

years ( 1994- 1998) of hourl y CO and 0 3 measurements were 

obtained to develop an automated selection technique that 

87 

0 

- 15 

-45 

-50 

Cope Point 

Observolory 

-20 10 40 

Fig. 4.14. Average transpon pathways to CPT with their frequency of 

occurrence, based on 1994-1998 5-day back isentropic trajectories 

arriving at 500 111. 

removes Cape Town pollution and then analyzes the remaining 

baseline data. 

Figure 4.15 shows the results of the selection procedure. The 

red plus signs are rejected data; the blue dots are selected data. 

Most of the discarded data points occur during austral winter 

when local meteorology makes pollution episodes at CPT more 

likely to occur. The selection procedure is an iterative technique 

that first fits a smooth curve to the hourly data and then removes 

the smooth curve to obtain residuals. The residuals are filtered 

and points above the +I standard deviation (S.D.) limit are 

discarded. The process continues until no points are discarded. 

The 0 3 measurements were selected by pairing them with the 

selected CO data set. To further reduce the data set, 3-hr 

averages were formed about 0000 and 1200 GMT corresponding 

to arrival times for the trajectories. These twice-daily averages 

are shown in Figure 4. 15. 

Figure 4. 16 shows how the distribution of CO is changed by 

selection. For each color/fit, the upper line represents a fit to 

all of the data while the lower line represents a fit to the 

selected data. The blue line is a polynomial representing the 

long-term trend. Although the unedited data appear to have a 

downward trend, the selected data show no linear trend, merely 

a slow oscillation. The red curve is the polynomial combined 

with four harmonics representing the average seasonal cycle. 

The selection shifts the CO average seasonal maximum from 

Jul y to October and the minimum from the end of January to 

the end of February. Finally, the green curve is the red curve 

combined with residuals filtered in the frequency domain. The 

residuals have variations with periods of about 2 months or 

more. 

CO and 0 3 variations on the synoptic time scale attributed to 

changes in transport were not large. Strong southerly flow 

resulted in average CO values up to I ppb lower and 0 3 values 

1 ppbv higher than average values in air transported from the 

latitude of the observatory. These results are consistent with 

the latitudinal gradients of these species. 
400 1 + 

+ 

300 + 

+ ,...._ + • .0 ++ -t .; + a. 'I+ .... + 

-9: 200 ... + .t 

0 .t+ t • 

() .. 

100 

1995 1996 1997 

Year 

Fig. 4.15. Resul!s of the + l S.D. selection process. Red plus signs mark 

rejected data; bl ue dots are the final selected points for CPT CO data. 

0 

90 

80 

70 

60 

- r -~---,-

\Jl_jJ . . J I I , 

. ., I ) '! I I\ it / 'V' ~ I n-- I .\ ·' 

-·t - I ...,_-...l. '( '. _;--- ifr1 ~ I 1• I f i\J '7jI I 

~\ ! . I ' .. I u 50 

\·) .. ,· :, I <'J ~ \~ · ':Y " 40 

30'--~--'~~-'-~~-'--~~-'-~__J 

1994 i995 1 996 1997 1998 1999 

Date 

Fig. 4.16. The change to the CPT CO distribution made by selection: for 

each color, the upper curve is filled to all the daia, and the lower curve is 

filled to the selected data. (See text for description of curves.) 

Diurnal CO variations in the unedited data set can be up to 80 

ppb. The most extreme pollution events occur during winter 

when local meteorological factors allow more stagnant 

conditions and recirculation of polluted air. Inversion 

characteristics and mesoscale winds (land/sea breezes) may 

contri bute to pollution at Cape Point. Figure 4. 17 shows the 

selected CO data set with nighttime values (blue) and daytime 

values (red). A small diurnal cycle persists in the selected CO 

data set of 0.2-0.4 ppb (depending on the grouping of the data). 

This diurnal cycle is statistically significant if all selected data 

are considered. The selected 0 3 data also show small (up to I 

ppbv) diurnal cycles that vary with season. The sources of these 

remaining diurnal cycles will be investigated in the future. 

.6 

.4 

.2 

T -

i .0 

I I I -.2. 

-.4 8 -.o 

-.8 

-1 .0 

3 4 189 10 1 1 12 

Mo~ 

Fig. 4. 17. CPT selected CO data set with nighttime values (blue) and 

daytime values (red). The dots are the monthly average value, and the 

bars show the 95% confidence interval for 1994- 1998. 

88 

4.2.5. LABO RA TORY TESTING OF ECC 0ZONESONDES 

It is important to conduct regular testing to evaluate the 

precision and accuracy of ECC ozonesondes, as the tests provide 

assurance that the best possible data are obtained from 

ozonesondes used in the wide variety of projects. The testing 

conducted in 1998 and 1999 always included ECC sondes from 

Science Pump Corporation and ENSCI Corporation, the two 

manufacturers and suppliers of ECC ozonesondes. Comparisons 

were also done using two different cathode sensing solution 

recipes, I% KI buffered and 2% KI unbuffered. The ingredients 

for these solutions are listed in Table 4.7. CMDL switched from 

the 1 % KI buffered to the 2% KI unbuffered solution after tests 

confirmed that the buffers were producing a side reaction that 

resulted in high ozone measurements [Hofmann et al. , 1998]. 

The dates for the switch to 2% KI unbuffered solutions are given 

in Table 4.8. CMDL testing in 1998 and 1999 included surface 

ozone comparisons in Boulder and triple ozonesonde flights at 

SPO. 

Eleven surface ozone comparisons were done with 

ozonesondes and a TEI model 49C UV ozone analyzer in July 

and August 1999. The sondes were run for 4 to 7 hours. Both 

6A and 2Z models were used in the tests. Figure 4.18 shows a 

typical comparison between the ozonesondes and the TEI ozone 

TABLE 4.7 . Cathode Solution Recipes Used by 

CMDL ECC Ozonesondes* 

Ingredients: 

Kl (potassi um iodide) 

KBr (potassium bromide) 

Sodium phosphate buffers: 

NaH2PO,·H20 

Na2HPO,· l 2H20 

l % Kl Buffered 2% Kl Unbuffered 

10 g 20 g 

25 g 0 g 

1.25 g 0 g 

5.00 g 0 g 

* I L of solution made with distilled, deionized water 
TABLE 4.8. Dates when 2% Kl Unbuffered Solution 

Replaced I% Kl Buffered Solution 

Location Date Flight Number 

Boulder, Colorado Aug. 21. 1997 BLAl3 

MLO April 15, 1998 Hl32 1 

SPO March 4. 1998 AS557 

Tahui May 6, 1998 TAll9 

F1j1 April 30. 1998 FJ045 

SMO April 17, 1998 SAl38 

Tnnidad Head, Aug. 21, 1997 THOO I (TH002 and 

California TH003 used I% bu ffcrcd) 

analyzer. The ozonesonde using a 2% Kl unbuffered cathode 

solution was consistently about I% to 2% higher than the TEI. 

The sonde containing the I% Kl buffered cathode solution was 7 

to 10% higher than the TEI. These results confirmed previous 

laboratory tests showing the better agreement of the 2% Kl 

unbuffered solution with UY instruments at surface pressures. 

4.2.6. SOUTH POLE: TRIPLE 0ZONESONDE FLIGHTS 

All field campaigns and new sites used 2% Kl unbuffered solutions afler 

January I, 1998. 

Special SPO ozonesonde nights were part of the Teachers 

Experiencing Antarctica project sponsored by the National 

Science Foundation. A teacher from the United Nations 

International School in New York was assigned to work with 

CMDL at SPO to participate in the preparation of ozonesondes, 

distribute the ozone profile data to students, including examples 

of ozone hole measurements from ozonesondes, and later to 

present numerous lectures to students on experiences with ozone 

science at the south pole. 

100 

1% Kl BUFFERED CATHODE 

> 

80 SOLUTION\ 

~ 60 

!:. 

w 

z 40 2% Kl UNBUFFERED 

~ CA THODE SOLUTION 

20 

0 +-~~~~~ ~~~~~~~~~~~~ 

Three different models of ECC ozonesondes were nown on 

four triple-ozonesonde nights at the south pole in January 1999. 

The objective of the experiment was to observe any differences 

between the Science pump 4A, 6A, and ENSCI 2Z ECC 

ozonesondes. The 4A model was used in the 1980s. Because the 

4A's used in this test had been stored for more than 8 years, they 

were sent to the manufacturer to be reconditioned. The 6A and 

2Z sondes are the current models manufactured by the two 

different suppliers. The 2Z model uses a molded plastic sensor 

instead of Tenon. The 2Z also has its own interface board that 

transmits data every second. The 4A and 6A sondes use a 

TMAX board that sends data every 7 seconds. The 4A sonde 

pump runs on a 6-V motor versus 12-V for the 6A and 2Z 

models. A secondary objective was to observe the differences in 

the ozone sensor response using I% Kl buffered cathode 

solutions and 2% Kl unbuffered. The first ozonesonde package 

was a dual sonde using 6A sondes, each with a different cathode 

solution. Different solutions were not used in individual sondes 

on the triple nights since the main objecti ve was model 

comparison. However, the four triple-ozonesonde packages 

were nown in pairs (one triple in the morning and one in the 

afternoon) with 2% Kl or I% Kl buffered for each pair of triple 

ozonesondes. Table 4.9 summarizes the results and gives the 

total ozone measured by each ozonesonde and the Dobson 

7:00 8:00 ~:00 10:00 11:00 NOON 13:00 14:00 15:t0 18:00 

LOCAL TIME 

Fig. 4.18. Surface ozone measurements al Boulder. Colorado. using 

ozonesondcs (\\ ith I% Kl buffered and 2% Kl unbuffered solutions) and 

a TEI 49C UV ozone instrument. 

TABLE 4.9. SPO Dual and Triple Ozonesonde Flights: January 1999 

Flight No. TypeE GMT: Day/Time Sonde No. Board Cathode Solution 

AS6 I 7-a Dual Jan. 11 6A6367 TMAX 1% Kl buff. 

AS6 17-b 00:22 6A6368 2%Kl unbuf 

AS6 18-a Tri ple Jan. 14 6A6255 TMAX 1% Kl buff 

AS618-b 23:18 4A I043-r 

AS619 2Z I039 V2C 

AS620-a Triple Jan. 15 6A6247 TMAX 2%Kl unbuf 

AS620-b 04:36 4Al039-r 

AS621 2ZI032 V2C 

AS622-a Triple Jan. 17 6A6292 2%Kl unbuf 

AS622-b 22:04 4A l012-r TMAX 

AS623 2Zl091 V2C 

AS624-a Triple Jan. 18 6A6325 TMAX 1%Kl buff 

AS624-b 03:35 4A l031-r 

AS625 2ZI 100 V2C 

89 

Total Ozone 

Sonde (DU) Dobson (DU) 

305 266 

269 

296 264 

278 

299 

267 265 

255 

276 

255 263 

253 

266 

281 260 

272 

291 
spectrophotometer measured values. The residual ozone for the 

ozonesonde total above balloon burst altitude was computed by 

the constant mixing ratio method at 7 hPa or lower if the balloon 

did not make it to 7 hPa. 

The different ECC models agree very well in the troposphere. 

Even at low concentrations, all of the ozone measurements 

nearly always fall within about ±10%. In the stratosphere the 

ENSCI 2Z tends to give 1-5% higher ozone than the Science 

Pump 6A model. The reconditioned 4A sondes were generally 

about I to 5% lower in ozone that the 6A models. The 

ozonesondes using the I% Kl buffered solutions gave about I 0% 

more ozone than the Dobson spectrophotometer. The 2% Kl 

solution profiles compare much better at 2-3'« greater total 

ozone than the Dobson. 

Ack11owledg111e11ts. The work at San Cristobal was conducted in 

cooperation with the lnstituto Nacion:il de Meteorologfa y Hidrologia 

(INAMHI). Ecuador. We are very grateful for the work done by Mario 

Agama, Francisco Paredes. and Jaime Cornejo at the radiosonde station 

in San Cristobal. 

4.3. REFERENCES 

Barnes. J E .. and D.J Hofmann, L1dar measurements of stratospheric 

aerosol O\'er Mauna Loa Observatory. Geophys. Res. Leu .. 24, 1923-

1926, 1997. 

Brewer. AW.. Evidence for a world circulauon provided b) 

measurements of helium and water vapor distribution in the 

stratosphere, Q. J. R. Me1e11ro/. Soc., 75. 351-363, 1949. 

Danielsen. E.F., A dehydration mechanism for the stratosphere. Geopilys. 

Res. Leu. 9. 605-608. 1982 

Danielsen. EF, In itu l'Vidence of rapid. ven1cal. irrcvcr;ible transpon 

of lo\\er troposphcnc air into the lower tropical stratosphere by 

convective cloud turre1s and by larger-scale upwelling in 1rop1cal 

cyclone:., J Geophy.1 Res .. 98. 8665-8681, 1993. 

Dcssler. A E.. A reexamination or the "stratosphenc fountain" 

h) pothem. Geophy.< Res. Leu .. 25, .t 165-4168, 1998. 

Fishman. J .. J.M. Hoell Jr., R.D. Bendura. R.J. McNeal. V W.J.H. 

Kirchhoff. NASA GTE TRACE A Expenmcnt (September-October 

1992): Overview. J. Geopilys. Res., JOI. 23,865-23.879, 1996. 

Folkins, I., 1\1. Loewenstein, J. Podolske, S.J. Oltmans, and M. Proffitt, A 

barrier to venical mixing at 14 km in the tropics: Evidence from 

ozonesondes and aircraft measurements, J. Ge11p/1ys. Res., JO-I, 

22.095-22.102, 1999. 

Fujiwara. 1\1.. K. Kita, S. Kawakami, T. Ogawa, N. Kamala. S. 

Saraspriya. and A Surip10. Tropospheric ozone enhancements during 

the Indonesian forest fire events in 1994 and 1997 as revealed b) 

ground-based observations, Geophys. Res. Leu., 26, 2417-2420. 1999 

Gettelman, A .. J. R. Holton, and A. R. Douglass, Simulations of water 

vapor in the lower stratosphere and upper troposphere, J. Geopilys. 

Res., 105. 9003-9023, 2000. 

Harris. J.M .. and B.A. Bodhaine (Eds.). Geophysical Mo111wri11g for 

Clrmatic Clumge. No. 11. S11111111ary Reporl 1982, NOAA Environ 

Res. Labs .. Boulder, CO, 160 pp., 1983. 

Harris, J.M .. and J.D. Kahl. Analysis of I 0-day isentropic OO\\ panerns for 

Barro\\ , Alaska: 1985- 1992,J. Geophys. Res., 99, 25,845-25,855, 1994 

Harris. J.M .. and S.J. Oltmans, Variations in tropospheric ozone related to 

trnnspon at American Samoa, J. Geophy.,. Res .. 102, 8781-8791. 1998. 

Hofmann, DJ.. S.J. Oltmans. J.M. Harris, B.J. Johnson. and J.A 

Lathrop. Ten years of ozonesonde measurements at the south pole. 

Implications for recovery of springnmc Antarctic ozone. J Geopl1ys. 

Res., 102, 893 1-8943. 1997. 

Hofmann, D.J .. J.T. Peterson. and R.M Rosson (Eds.), C/111u11e 

M1111itori11x a11d D111x1wstics u1borawry. No. 2-1. S11111111ary Repor1 

1996-1997. NOAA Environ. Res. Labs., Boulder. CO. 166 pp .. 1998. 

Hudson, R.D .. and A.1\1. Thompson. Tropical tropospheric ozone from 

total ozone mapping spectrometer by a modified residual method, J 

Geophys. Res., 103. 22,119-22,145. 1998. 

Kley, D .. A.L Schmeltekopf, K.K Kelly, R.H. Winkler, T.L. Thompson. 

and M. McFarland, Tr:mspon of water vapor through the 1ropical 

tropopause. Geopilys. Res. Leu .. 9. 6 17 -620. 1982. 

Komhyr. W.D .. R.A. Barnes, G.B. Brothers. J.A. Lathrop, and DP 

Opperman. Electrochemical concentration cell ozonesondc 

performance evaluauon during STOIC 1989. J. Geophys. Res., JOO, 

9231-9244. 1995. 

Newell, R.E .. and S. Gould-Ste\\an. A stratospheric fountain·). J. A111111s. 

SCI., 38. 2789-2796, 1981. 

Rosenlof. K.H., and J.R. Holton, Estimates of the stratospheric residual 

circulation using the downward control principle. J. Geophys Res .. 

98, I 0,465-10,479, 1993 

Saeger, M., J. Langstaff, R. Waltc1;., L. Muc.J1ca, and 0. Z1mmennan. 

NAPAP emissions inventory (Version 2): De\elopment of the 

annual da1a and modelers' tapes. Rep. EPA-600/1-89-0l 2A. U.S 

Em iron Protect Agency. Washington.DC .. 693 pp .. 1989. 

Sherwood. SC .. A "stratospheric drain" mer the mant1me continent. 

Geophys Res. Leu .. 27, 677-680. 2000. 

90 

Thomng, K.W .. P.P. Tans. and W.D. Komhyr, Atmo>pheric carbon 

dioxide at Mauna Loa Observatory: 2. Analysis of the NOAA/GM CC 

data. 1974- 1985, J. Geophys. Res .. 9./, 8549-8565, 1989. 

Vomel, H .. S.J. Oltmans, D. Kley, and P.J. Crutzen, New evidence for 

the stratospheric dehydration mechanism in the equatorial Pacific, 

Geophys. Res. Lei/., 22. 3235-3238, 1995. 

Yulaeva, E .. J.R. Holton, and J.M. Wallace, On the cause of the annual 

cycle in tropical lower Mratospheric temperatures, J. A1111os. Sn., 52, 

169-174. 199.t. 
5. Halocarbons and Other Atmospheric Trace Species 

8 .0 . HALL (EDITOR), J.W. ELKINS, J.H. BUTLER, S.A. MONTZKA, T.M. THOMPSON, L. DEL NEGRO, 

G.S. 0 UTION, 0 .F. HURST. 0 .8 . KING, E.S. KLINE, L. LOCK, 0 . MACTAGGART, 0. MONDEEL, 

F.L. MOORE, J.D. NANCE, E.A. RAY, AND P.A. ROMASHKIN 

5.1. CONTINUING PROGRAMS 

5.1.1. INTRODUCTION 

The mission of the Halocarbons and other Atmospheric Trace 

Species (HATS) group. formerly known as the Nitrous Oxide 

and Halocarbons (NOAH) group, is to study trace atmospheric 

species that cause chemical and radiati ve change in the 

atmosphere. The goal of the HATS group is to measure and 

interpret the distributions and trends of many halocarbons, 

nitrous oxide (N20), sulfur hexafluoride (SF6), fluorocarbons, 

pertluorocarbons (PFCs), organic nitrates (e.g., peroxyacetyl 

nitrate (PAN)), organic sulfur gases (e.g., OCS), and 

h)tlrocarbons (HCs) in the 1roposphen.:. '>tratosphere. and oceans 

''1th the best anal)tical toob available. The halocarbons include 

the chlorofluorocarbons (CFCs), ch lorocarbons (CCs like CCI~. 

CH3CCl 3, CHCl.1. CH2Cl 2, ~. etc.), hydrochlorofl uorocarbons (llCFCs), hydrotluorocarbons (HFCs), methyl halides 

(CH3Br. CH3CI, CH1I). bromocarbons CCH2Br2• CHBr.1), and 

halons. 

These trace gases affect the quality of the Eanh's atmosphere. 

All of these trace gases, except the HCs and organic nitrates. 

produce direct climate forcing on the Eart h's atmosphere. Many 

ol these chem1cJls. including the halocarbons and N20, arc 

invol,·ed in stratospheric ozone depletion. The production of 

some of these compounds is currently restricted for the 

tle,cloped countries by the J\1ontrcal Protocol and its 

,unendmcnts [UNEP. 1987]. The hydrocarbons. some sulfur 

gJses. organic nitrates. and CCs play a major role in tropospheric 

air qualit). Recent changes to the U.S. Clean Air Act no11 

restrict the emissions of some CCs antl HCs by certain induqrics 

and manufacturing processes. 

Acti\llies conducted b) HATS 1n 1998 and 1999 included: 

1J1 weekly llasl.. sampling and analysb of air from remote and 

,cm1-remote sites. c 2) operation of llhtrumentatrnn for houri). m 

'>llll me.1surcments of trace gases .u the four Cf\IDL baseline 

observatories and four non-baseline sites. (3) preparation and 

ma111tenanee of trace gas standards. (-1) participation on airborne 

eampa1gm using in situ gas chromatographs (GCs) on aircraft 

and balloon payloads. and (5) investigation of oceanic processes 

influencing trace gas composition of the atmosphere. 

Continuing programs within the group are based upon in situ 

and flask measurements of the atmosphere from the four CMDL 

baseline obscrrntories and ten coopcrati\e stations (Figure 5. I). 

Table 5.1 lists the geographic locations and other useful 

information on all of the sites. There arc currently 13 tlask sites 

antl I 0 in situ sampling sites in the HATS Atmospheric 

Sampling Network. Flask samples and in sttu trace gas 

measurements obtained in cooperation with the CMDL Carbon 

Cycle Greenhouse Gases (CCGG) group were ceased at the 

WITN, Grifton, North Carolina (ITN) tower on June 12. 1999, 

because the laboratory layout was changed to accommodate onl y 

digital tele\ision equipment. A high tower site in Texas is being 

studied as its replacement. A new in situ GC was prepared for 

installation and operation sometime in earl y 2001 at Ushuaia, 

9 1 

Fig. 5.1. Geographic locations of old and ne" stations in 1he HA TS 

flask (gray circles) nnd 111 situ (crosses) networks. The sues for balloon 

launches are noted by .. X"s. The location (small black filled circles) and 

the range of the aircraf1 operations (arcs and ovals) also are indicated. 

Argentina. 11 ith funds from the World Meteorological 

Organization (WMO). 

One of the highlights of this report is that the total Effective 

Equi,alent Chlorine (EECI) continues to decrease at about I '7r 

)r.

1 as a result of the :'\1ontreal Protocol. The main reason for 

this decline is that methyl chloroform (CH!CCl.1) concentrations 

continued to decline to less than half of the peak levels present in 

1992. However. atmospheric concentrations of the halon~ and 

CFC- I~ arc still 111creasing because of allowed production 111 the 

developing countries and the large bank of chemicals present in 

the developed countries. After CH3CCI, concentrations drop to 

near Lero, continuetl production and release of the halons may 

introduce a significant change 1n the trentl of EECI Other 

sig111licant results include the observed global increases in 

atmospheric N20 and SF6 (1dcnlllicd through both tlask and in 

situ moni toring), the continued growth of the CFC replacements 

(HCFCs and HFCs), and the decline in the nonhern hemispheric 

concentrations of CHCl.1. CH~Cl , and C2Cl4 as a result of the U.S. 

Clean Air Act. 

Airborne measurements were conducted in the upper 

troposphere and lower stratosphere in tropical. midlatitude, and 

polar regions during 1998 and 1999 (Figure 5.1 ). The exchange of 

air between the lower stratosphere and the troposphere and 

midlatitude upper stratosphere was quantilicd. The development 

and deployment of the next generation airborne gas chromatograph 

with electron capture and mass selective detection was funded by 

the National Aeronautic and Space Administration's (NASA) 

Instrument Incubation Program to measure trace gases, mcluding 

acetone and PAN that influence atmospheric chemistry in the 

upper troposphere. 
TABLE 5.1. Geographic and Network Information on HATS Network Sites 

Eleva1ion LST-GMT 

Code S1a1ion La1i1ude Longitude (rn) (hr) T)pe 

ALT Alen. Nonhwest Tenitories. Canada (AES)* 82.45°N 62.52°\V 210 -4 F. I 

BRW Point Barro". Alaska 71.J2°N 136.60°\V II -9 F, I 

MHT Mace Head, Ireland (University College) 53.33°N 9.90°\V 42 0 F 

LEF WLEF tower. Wisconsin (CMDL-CCGG) 45.95°N 90.28°W 470 -6 F. I 

HFl\I Harvard Fores!. Massachuselts (Harvard Univcr.i1y) 42.54°N 72.18°\V 340 -5 F. I 

NWR Ni wot Ridge. Colorado (Universi1y of Colorado) 40.04°N 105.54°\V 3013 -7 F. 1 

ITNt WITN 1ower. North Carolina (CMDL-CCGGJ 35.37°N 77.39°\V 9 -5 F. I 

MLO Mauna Loa, Hawaii 19.54°N 155.58°\V 3397 -10 F.1 

KUM Cape Kumukahi, Hawaii I 9.52°N 154.82°\V 3 -IO F 

Sl\10 Tuluila. Arnencan Samoa 14.23 s 170.56°\V 77 -JI F. I 

CGO Cape Gnm. Tasmania, Australia+ 40.41 °S l.W.64°E 94 +IO F 

TDF Ushua1a. Tierra Dd Fuego. Argenuna (\\IMO GAW sta1ion)* 54.82'S 68.32°\V IO -3 

PSA Palmer S1a1ion. An1arctica~· 64.92°S 6Hl0°W IO +12 F 

SPO South Pole. Antarctica 89.98°S Io:2.00°E 2841 +12 F. I 

Cooperative sites CF= nasks, I = in silu) with: 

*In situ GC: Only N20 and SF0: nask sampling for all gases. however. 

t ITN si1e's nask and 1n si1u GC were discontinued on June 12. 1999 (sec IC>.I) 

+Cornrnonweallh Sc1en11fic and lndus1rial Research Organ1za1ion (CSIROl and Bureau of Meteorology. Aus1ralia 

~S tart s collecling clam in March 2001. 

··Only glass nasks used. 

Oceanic measurements of CH.1Br and other gases were obtained 

on l wo research crnises during 1998-1999. !\ lcasuremems in 

marine air and surface seawater showed that the oceans arc still a 

significant sink for atmospheric CH_1Br, but the magnitude of the 

s111k is slightly smaller than pre,iously dctcnrnncd. 

5. 1.2. FLASK SA~IPLf,.S 

01•erriell' 

No new sampling stallons were added in 1998-1999. although 

Mace Head, Ireland (M llS) and Palmer, Antarctica (PSA) were 

added at the end or 1997 (Figure 5.1 ). Sampling at PSA continued 

throughout 1998-1999, but sampling from M HS was discominued 

temporarily because of a high rate of loss of llasks during transit. 

Effons were made during the past 2 years lo impro,·e the sampling 

frequency and precision at all sites with considerable success. 

Progress, howeYer, was delayed some\\ hat by the CMDL mo,·e to 

the NOAA Broadway slle in 1999. One of the analytical 

mstruments (Low J:.lectron Allachment Potential Species <LEAPS) 

gas chromatograph '' llh electron capture detection (GC-ECD)) 

experienced considerable difficulties following the move and 

required the replacement of two electron capture detectors. 

Flasks brought into the laboratory were analyLcd on two to four 

instruments depending on the species being examined and the size 

of the indi"idual sampling flask (Table 5.2). Although all 300-mL 

flasks were retired from the system. there arc still some 850-mL 

flasks that contain a marginal amoum of air for all of the lo\\-le,el 

analyses. ~lost flask analyses were of samples from the network. 

although many were from research cruises, lirn air sampling. and 

other special projects. 

An intercomparison of SF1, and N20 analyses was sta11ed with 

the CCGG group, but it is still in its early stages. Although HATS 

records extend back into the 1970s for N20 and the 1980s for SF~ 

(including archived samples). the CCGG network has the 

adYamage of sampling from many more sites per week, thus 

allowing a belier spatial picture of the distributions of these 

compounds to be obtained. 

92 

TABLE 5.2. lnstrnmentation for HATS Flask Anal)Sls 

lns1ru111en1 

OTTO 

LEAPS 

HCFC·l\IS 

HFC-1\IS 

Type 

GC-l:CtJ. 

3-channd. 

1so1hermal 

GC-ECD. 

1-channd, 

1cmpcra1ure 

programmed 

GC-:--ts. 

I-channel. 

tempera1ure 

programmed 

GC-1\IS. 

1-channd. 

1c111pern1ure 

programmed 

Sampling and Analysis 

Gases 

N~U. 

CFCs (3), 

CCs (2). 

SF,, 

halons (2). 

ClhCI. CH,Br. 

CH Ch 

HCFCs (3). 

HFCs (I). 

CFCs (3). 

halons (I). 

CCs (6). 

BrCs (3) 

HCFCs (5 ). 

IIFCs (2). 

CFCs (2). 

halons (2). 

CCs (6), 

BrCs (3). 

CIBrCs OJ 

Frequenc> of 

Ne1work Da1a 

\\'eek I> 

Se1m-1110111hl) to 

month I> 

Semi mon1hly 

Sen11-1110111hl> 10 

mon1hl) 

In 1996, 269 flasks from the network were tilled and dell\ered 

to the Boulder laboratory for analysis. This number has increased 

each year reaching a total of 399 in 1999 (Figure 5.2). This 

increase is the result of added sites ( 1996-1997) and a more 

cflicient turno,·cr of llasks between Boulder and the field sites. 

This was accomplished through impro\'ed record keepmg of flasks 

coming to Boulder and by adding additional flasks to the network 

in 1996-1997 to accommodate additional sites. Sampling success 
450 

"O 

Q) 399 IJl 

0 400 a. 

x 

LU 350 ~ 

'(ii 

a.. 

~ 3'.Xl IJl 

<1l 

u::: 250 0 

'**' 200 

1996 1997 1998 1999 

Year 

Fig. 5.2. Number of flask pairs filled and returned to Boulder each year 

from the HA TS station network. 

was i "!proved substantially from that for 1996 at nearly all of 

our sites (Table 5.3). This was mainly the result of repairing 

small leaks and replacing valves where necessary on flasks 

following analysis in Boulder. These repairs greatly improved 

the agreement in flask pressure within simultaneously sampled 

pairs (Figure S.3). 

While most of the time the GC-ECD instruments were utilized 

to process flasks from the station network, I 0-20% of the time 

was devoted to calibrating gas standards, and about 5% of the 

instruments' operation was dedicated to other quality-control 

experiments. Special projects involving flask measurements 

over the past few years included primarily firn air analyses and 

analysis of flask samples from research cruises. 

Results 

Results for most of the major ozone-depleting gases are also 

discussed in the subsection "Overall Trends in Ozone-Depleting 

Gases." Many of these gases are analyzed by both GC-ECD and 

gas chromatography with mass selective (GC-MS) detection. 

CFC- 12 continues to increase in the atmosphere while mixing 

ratios of CFC- I I continue to drop slowly at about 1 % 

yr" 1 (F~Fure S.4). CFC- 11 3 ~nd CC14 e also decreasing at about 

1 % yr , and CH3CC13, which has dnven the overall decline in 

TABLE 5.3. Flask Sampling Success at CMDL 

Observatories and Cooperative Sampling Sites 

Sampling Station 1996 1997 1998 1999 

Barrow, Alaska 69% 94% 88% 87% 

Mauna Loa, Hawaii 69% 83% 90% 96% 

American Samoa 54% 67% 73% 87% 

South Pole 77% 69% 77% 88% 

Alen, Canada 52% 46% 67% 67% 

Niwot Ridge, Colorado 63% 92% 87% 77% 

Cape Grim, Australia 60% 69% 85% 85% 

WLEF tower, Wisconsin 12% 35% 69% 92% 

Harvard Forest, Massachusetts 46% 62% 69% 69% 

Kumukahi, Hawaii 50% 54% 67% 69% 

Palmer, Antarctica 8% 65% 81% 

Mace Head, Ireland 8% 15% 

WITN tower, Nonh Carolina 65% 62% 62% 38% 

100% 

90°/o 

80"/o 

7CJ% 

60% 

50% 

1996 1997 1998 

Year 

90°/o 

1999 

Fig. 5.3. The percentage of flask pairs agreeing within I psi in total 

pressure upon arrival in Boulder. 

93 

atmospheric chlorine, continues to drop about 18% yr' 1 (subsection on "Overall Trends"). Gases analyzed only by GC-ECD 

are N20, SFh, and CBrF3 (H-1301 ). Nitrous oxide has been 

monitored by the in situ instruments for the past 12 years. The 

record from flask samples goes back to the mid-I 970s (Figure 

5.5). The global growth rate of N20 from 1978 to 2000 was 0.74 ± 

0.01 (95% confidence level, C.L.) nmol mor 1 yr' 1 (pans-perbillion, or ppb, yr'\ which amounts to a mean of about 0.25% yr' 1

• 

From 1996 to 2000, the global growth rate was 0.85 ± 0.06 ppb 

yr' 1

, which differs significantly at the 95% C.L. from the 20-year 

600 

a 

550 

500 

0 

E 

450 

1) 400 

§_ 350 - NH 

300 --SH 

250 --Global 

200 

300 

275 b 

250 

0 225 E a 200 

K 175 

150 

125 

100 

1975 1960 1985 1990 1995 

Year 

Fig. 5.4. CFC-12 (a) and CFC-I I (b) from flask samples. Data are 

monthly averages. 
320 

315 

0 310 ~ 0 

E 3)5 c 

295 

1976 1980 1984 1988 1992 1996 200) 

Year 

Fig. 5.5. Atmospheric history of N20 deri ved from CMDL nask 

measurements. Data are smoothed with a lowess fit. 

average. This suggests that N20 concentrations were increasing 

more rapidly in the atmosphere near the end of the 20th century. 

Whether this was a temporary or long-term feature will be borne 

out in future data. 

Sulfur hexafluoride still appears to be increasing linearly in 

the atmosphere with a growth rate of about 0.24 ± 0.01 (95% 

C.L.) pmol mor1 (parts per-trillion, or ppt, y( 1

) since 1996 

(Figure 5.6). CMDL measurements of polar firn air confirmed 

the early history of this gas as derived from emission inventories 

[8111ler et al. , 1999], indicating natural sources are absent or 

insignificant in the global SF6 budget. 

CMDL measurements show that halons are still increasing 

slowly in the atmosphere in spite of a ban on their production as 

of 1994. The global growth rate of H- 1301 in 1998-1999, at 0.09 

± 0.04 ppt y( 1

, does not differ significantly at the 95% C.L. from 

the 1995 to 2000 average of 0.06 ± 0.0 I ppt yr" 1

, nor from the 

1995-1 996 average of0.044 ± 0.011 ppt yr" 1 reported in 8111ler et 

al. [I 998a] (Figure 5.7). However, at the 90% confidence level, 

a 30-40% increase in H- 1301 emissions is suggested during the 

past few years. H-1 2 11 is still increasing at a rate of 

5.0 .-----------------~ 

4.6 

~ 4.2 -... 

0 

~ 3.8 

3.4 

3.0 

1995 1996 

EJ SH 

Gobal 

1997 1998 1999 

Year 

Fig. 5.6. Recent history of atmospheric SFo from CMDL nask 

measurements. Data are monthly averages. 

0. 1-0.2 ppt yr" 1

, which means that there has been no curtailment 

of its global emissions since the 1994 ban on its production in 

developed countries. 

Ch/orofl11orocarbo11 Alternatives Measurement Program 

Measurements of chlorofluorocarbon alternatives from flask 

air samples continued during 1998- 1999. On average nearl y 

three flask pairs per month were sampled and analyzed from nine 

remote sampling stations across the globe. Slightly fewer than 

two pairs per month were sampled from the WLEF tower in 

Wisconsin (LEF), ITN, and Harvard Forest, Massachusetts 

(HFM). The main change during this period involved building a 

new inlet isolation box for the instrument and moving the 

instrument and laboratory to the new building site in Boulder, 

Colorado, in early 1999. These improvements allow for more 

precise and reproducible measurements of gases that are present 

at high levels in laboratory air such as HFC-I 34a, HCFC- 142b, 

and CH2Cl2. Moving the instruments does not seem to have 

caused any unexpected shifts in the results from the GC-MS 

flask program. 

94 

Mi xing ratios of HCFCs measured in the flask program 

(HCFC-22, HCFC-14lb, HCFC- 142b) continued to increase in 

the troposphere (Figure 5.8, Table 5.4). Concentrations reported 

2.8 

2.4 

0 2.0 

E 

::::::. 

0 

E 

0.. 1.6 

1.2 

:-:_: <J!!~--- - _ ___ 0 0 t.~ _ __ _ _ __ __ _ oNH 

• • 0 c D SH 

cf •Global 

- _o_ - - - - - - - - - - - - - - - - - - - - - - - - - -

• 

D 

• D 

1990 1994 

Year 

o NH 

c SH 

• Global 

1998 2002 

Fig. 5.7. Halons H-1301 (a) and H-121 l (b) from CMDL nask 

measurements. Data are monthly averages. 
-

160 

140 

120 

100 

2: 80 

60 

40 

20 

0 

HCFC-22 

•• • l . 

1986 1988 1990 1992 1994 1996 1998 2000 

-

16 

14 

12 

10 

2: 8 

-

6 

4 

2 

0 

1986 

16 

14 

12 

10 

2: 8 

6 

4 

2 

0 

HCFC-141b 

1988 1900 

HCFC-142b 

• • • •• 

• • 

1992 1994 1996 1998 2000 

1986 1988 1990 1992 1994 1996 1998 2000 

16 

14 

12 

10 

a. 8 

a. 

6 

4 

2 

0 

HFC-134a 

1986 1988 1990 1992 1994 1996 1998 2000 

Year 

Fig. 5.8. Atmospheric dry mole fractions (ppl) of selected HCFCs and 

HFC-l 34a measured by GC-MS in the CM DL flask program. Each point 

represents the mean of two fl asks from one of eight or nine stations: ALT, 

BRW, NWR, red; KUM and MLO, green; SMO, CGO, PSA, and SPO, 

blue. Also ploned are results from analysis of archived air samples (open 

red circles) filled al NWR or on cruises in both hemispheres. 

TABLE 5.4. Global Burden and Rate of Change for 

HCFCs and HFC-134a 

Mean 1998 Mean 1999 

Compound Mixing Ratio (ppl) Mixing Ratio (ppl) 

Growth Rate 

(ppl yr"') 

95 

HCFC-22 

HCFC-14lb 

HCFC-142b 

HCFC-134a 

131.4 

9.1 

9.7 

7.6 

136.9 

10.9 

10.8 

10.6 

5.1 (1992-1999) 

1.8 (1996- 1999) 

1.0 (1996-1999) 

3. 1 ( 1998-1999) 

Quantities estimated from latitudinally-weighted measurements al 

seven remote stations: SPO, CGO, SMO, MLO, NWR, BRW, and ALT. 

for these gases in past publications have been referenced to a 

constant set of gravimetric standards (section 5. 1.4) [Montz.ka et 

al., 1993, 1994, 1996b, 1999a, 2000]. Fairly linear rates of 

increase were measured for these three HCFCs since the 

beginning of 1996. In mid-1999 these HCFCs accounted for 

about 6%, or 170 ppt, of the atmospheric burden of chlorine 

contained in long-lived anthropogenic halocarbons. When 

combined with an estimate of atmospheric lifetimes, 

measurements of anthropogenic halocarbons can be used to infer 

emission rates. Such an analysis suggests that since 1998, total 

molar emissions of HCFCs surpassed the aggregate moles 

ernined of other ozone-depleting substances (CFCs + CCI~ + 

halons + CH3CC13). 

Continued increases were observed for HFC-1 34a during 

1998-1999 (Figure 5.8, Table 5.4). The observed concentrations 

are in reasonable agreement with the amounts expected based 

upon the available industri al production and emission data and 

an atmospheric lifetime of - 15 years [Mo111zka et al., 2000). 

Continued declines in the concentration of CH3CC13 were 

observed from flask measurements during 1998-1999 (Figure 

5.9). These data are reasonably consistent with the results from 

the in situ Radiatively Important Trace Species (RITS) GC-ECD 

instruments. Accurately describing the atmospheric decline of 

CH3CC13 can provide unique information regarding the 

180 

0. 100 . 

a. 80 . 

60 . 

40 . 

20 

O · 

1992 1994 1996 

Year 

1998 2000 

Fig. 5.9. Atmospheric dry mole fra ctions (ppt) of CHiCCli measured by 

GC-MS in the CMDL flask program. Each point represents the mean of 

two simultaneously filled flasks from one of eight or nine stations 

(symbols the same as in Figure 5.8). 
atmospheric abundance and distribution of the hydroxyl radical. 

an important atmospheric oxidant [Ravisha11kara and Albri11011, 

1995; Mo11t::.ka et al., 2000; Spimko1•sky et al., 2000]. 

Flask Meas11re111e11ts of CH3CC/3 and Their /111plicatio11s for 

Atmospheric Hydroxyl 

The analysis of CH3CC13 in llask air by GC-MS provides 

some unique adva111ages over other techniques, such as linear 

response (Figure 5.10), good chromatographic resolution (Figure 

5.11 ), and the ability to monitor more than one ion. During 

1998-1999 repeat injection precision for GC-MS analysis of 

llasks was typically 0.4% (the median standard deviation from 

repeat injection5 on I 028 llasks during that period); for 95% of 

all analyses the repeat injection precision was <l.3%. A 

disadvantage of llask sampling for measuremellls of CH3CCl3 is 

that degradation of CH.

1CCl3 during the interim between 

sampling and analysis can be observed in llasks filled with 

extremely dry air. This problem is apparent in results from the 

South Pole, Antarctica, CMDL Observatory (SPO), where poor 

flask pair agreement and anomalously low mixing ratios are 

observed from some llask samples. Because the rate of this loss 

is flask-dependent, its occurrence is readily idemifiable by poor 

agreement between simultaneously fi lled fl asks. Samples in 

which degradation is suspected are not considered in further data 

analysis. 

In recem years many unique features have appeared in the 

atmospheric data for CH3CCl3 that confirm a dramatic decline in 

"C 

cu 

1.04 

0 1.02 

cu ·c: 

cu 

0 E 1.00 

Gi 

I/I 

c: 

0 

~ 0.98 - cu 

a: 

0.96 

o ion 97 

--ion 99 

0 50 100 150 200 

Gravimetric mixing ratio (ppt} 

Fig. 5.10. Consistency of gravimetricall y prepared standards containing 

CH1CCIJ as analyzed on the GC-MS during 1997-1999. For well-made 

standards analyzed on an instrument with a linear response. the response 

fac tor should be independent of mixing ratio. Response factors 

(measured response divided by the gravimetrically determined mixing 

ratio) for two different ions are plotted for individual gravimetric 

standards and are normalized to the mean response factor for all 

standards. The error bars are one standard deviation of the measured 

response factor for each tank (from seven to nine measurements of each 

standard during 1997-1999). The results for one standard at 195.7 ppt 

(ALM-64596) do not appear in this figure because its response fac tor 

was much different from the other standards (0.90 in late 1999), and was 

changing over time. presumably from slow degradation of CH1CCh in 

that tank. 

96 

Q) 

(/) 

c 

0 

a. 

(/) 

Q) 

a: 

3000 

2500 

2000 -

--ion97 

----ion99 

n ----·Ion 11 7 II 1500 II · · · · · · baseline 11 

I 

1000 

500 

• I 

"""-~-~-----~········~ ..... -··-··-··-··-··- 0 -1-~-+-~~1--~-+-~--1~~-+-~-+~~+-~-i 

12.8 12.9 13.0 13.1 13.2 13.3 13.4 13.5 13.6 

Retention time (min) 

Fig. 5. 11 . A portion of a chromatogram from the GC-MS nask 

instrument showing the signals observed for CH,CCh (ions 97 and 99) 

and CCL. (ion 117: peak maximum not shown) in ambient air collected at 

Samoa. Concentrations were determined to be 47 ppt CH3CCh and 100 

ppt CCl4 . The peak height relative to the standard deviation of the 

baseline was 800 and 600 for CH1CCh at m/z = 97 and mil = 99 and 

-2000 for CCI, at 111/z = I 17 in this air sample. Also shown are baselines drawn from our custom automatic integration routine (shon-dashed linef 

emissions. Not only has the mixing ratio decreased 

exponenti ally recently (Figure 5.9), but the difference observed 

between the hemispheres (Figure 5.12) has declined substantially 

as the emissions, which emanated predominantly from the 

northern hemisphere, have declined. Furthermore, the gradient 

observed within each hemisphere is now very similar, suggesting 

that the atmospheric distribution of CH3CCl3 in 1998-1999 was 

controlled by the distribution of loss processes rather than the 

distribution of sources during this period (Figure 5.13). 

The measured rate of decay during 1998-1999 at nine remote 

stations and LEF allows us to estimate an upper limit to the 

global lifeti me of CH3CC13 of 5.5 (±0.1) years [Mo111zka et al., 

2000]. Because the decay observed for CH3CCl3 arises 

predominantly from OH oxidation (Table 5.5), this lifetime limit 

allows estimation of upper limits to the lifetime of other 

chemically reduced gases that degrade predominantly by OH 

oxidation in the atmosphere (Table 5.5). This lifetime limit is 

completely independent of calibration standard accuracy and 

emission estimates, but depends upon a consistent calibration 

reference over time. An uncertainty of ±0. 1 year is estimated on 

the measured e-fold time from potential drift of 0.3% yr' 1 based 

on comparisons between a reference air sample and ten 

gravimetric standards (Figure 5. 14). 

When the magnitude of emissions of CH3CCl3 during 1998-

1999 are considered (A. McCulloch, personal communication, 

2000), lhe rate of decay measured implies that the true global 

lifetime of CH3CCl3 is 5.2 (+0.2, -0.3) years [Montzka et al., 

2000). Unlike previous estimates of global lifetime, this estimate 

is insensitive to calibration standard accuracy and includes a 

factor of two uncertainty in the magnitude of emissions. 
25% 

20% Q) 

.0 

0 

a 15% 

x 

--

I 10% 

U) 

x 

I 5% 

z 

~ 0% 

-5% 

1992 

• 

~ 

1994 1996 

Year 

1998 2000 

Fig 5.12. The hemispheric mixing ratio difference for CH,CCI, in 

recent years. The difference was inferred from weighted, monthly mean 

mixing ratios at three to six sampling stations in each hemisphere. 1\lonthly differences (solid diamonds) are connected '' ith a thin line; the 

heavy line represents a 12-month runnmg mean difference. The results 

suggest that northern hemisphere emissions have declined substantially 

m recent )Cars [M11111:.ka el al . 2000]. 

rhe recent measurements also provide a unique opportunity to 

discern hemispheric loss rates for CH3CC13. The rate of change 

observed in the southern hemisphere is determined by emissions 

within the southern hemisphere, chemical loss in the southern 

hemisphere, and the CH3CC1 3 delivered from the northern 

hemisphere through net hemispheric exchange. Because 

emissions in the southern hemisphere ha\e always been <10% of 

the total emissions. this term is insignificam compared to the 

others. From the observed difference m the hemispheric 

concentratton or CH3CCI3, the net exchange of this gas between 

the hemispheres can be estimated. By also including the 

observed decline of CH3CC13 in the southern hemisphere, the 

lifetime or CH3CC1 3 111 the southern hemisphere is estimated to 

be 4.9 ( +0.2, -0.3) years [Mo111::.ka er al., 2000]. This estimate is 

also insensnive to calibration standard accuracy and emission 

estimate figures. 

These results suggest that the mean hemispheric loss 

frequency for CH3CCI 3 and the mean hemispheric concentration 

of OH are slightly larger (by 15 ± I 0%) in the southern 

hemisphere than in the northern hemisphere despite the higher 

levels of precursors for OH such as NO, and 0 3 found in the 

northern hemisphere. This conclusion hinges on emission 

figures for 1998-1999 being reasonably accurate; higher mean 

concentrations of OH in the northern hemisphere could be 

reconciled with the observations only if emissions were 

substantially underestimated in 1998-1999 (by about a factor of 3 

or more). Higher mean concentrations of OH in the southern 

hemisphere may result because certain OH sinks, such as CO, 

are greater in the northern hemisphere, and because the southern 

hemisphere contains more of the OH-rich tropics compared to 

the northern hemisphere (given that the intertropical convergence 

zone (ITCZ) is on average a few degrees north of the equator). 

97 

1.06 

1.04 

~ Q) 

.r::; 

g.1.02 

.E 

Q) 

.r::; 

x 1.00 ..._ 

x 

0.98 

0.96 

1.06 

1.04 

Q) 

(i) 

.r::; 1.02 a. 

(/) .E 

~ 1.00 

x 

..._ 

x 0.98 

0.96 

A) 1998-1999 

on 

B) 1994-1995 

0 

0 Q 

0 30 60 90 

Latitude 

Fig. 5.13 Measur.:d intrahcmispheric gradients in annual mean mixing ratios of CH,CCh [M111111.ka et al., 2000]. (A) Annual means for 

mdi,idual sites (X,) are shown normalized to respective hemispheric 

annual means for the 2 years 1998-1999. Nonhem hemisphcnc data 

from low altitude sites (<IOOOm) (triangles) arc connected wi th lines to 

allow for appropriate comparisons to similar sites m the southern 

hemisphere (circles). High altitude sues (MLO and NWR) are sho\\ n (crosses) bul are nol connected with lines because there is a clear 

difference in the in1rahcmispheric gradient bel\\een lO\\ and high alti1ude 

sites dunng this period. (8) Same as (A) but for the 2 years 1994-1995 

when nonhem hemispheric emissions were substantial. Because of a 

lack of measurc111cn1s from all sites in 1his earlier period, data from bo1h 

low and high allltude locations are shown with similar S)mbols m this 

panel. Error bars m bolh panels represenl one slandard de\ iation of the 

annual mean ra1101> estimated for 1he 2 years. 

Overall Trends i11 Ozo11e-Depleti11g Gases 

Emissions of most ozone-depleting gases decreased during the 

1990s. The atmospheric response to reduced emissions was 

most pronounced for the industrial gas CH3CCl3 (Figure 5.9). 

The global concentration of this gas decreased at an exponential 

rate of -18% yr'1 during 1998-1999. Such a rapid decline is 

observed for this gas because it has a fairly short atmospheric 

lifetime, and its past use as a solvent caused changes in 

emissions to be closely linked to changes in production. This 

link is not as strong for CFCs and other gases because their 

emissions can be sustained from devices and foams for years 

after production has ceased. For example, although similar 

declines in emissions are inferred for CFC- I I and CFC-12 in the 
TABLE S.S. Lifetimes of Chemically Reduced Gases (in Years) for 1998-1999 

Panial lifetime with respect to: 

Total Lifetimet 

OH Loss• Stratospheric Loss Total Lifetimet Upper Limit 

CH., 10.5 (+0.5, -0.6) 110 9.0 (+0.4, -0.6) 9.5 (±0.2) 

HCFC-22 13.6 ( + 0.6, -0.8) 306 13.0 ( +0.6, -0.8) 13.8 (±0.3) 

HCFC-1.tlb 11 .5 (+0.5, -0.7) 81 I 0.1 ( +0.4. -0.6) 10.6 (±0.2) 

HCFC-l.t2b 21.8 (+1.0, -1.3) 372 20.6 (+0.9, -1.3) 21.8 (±0.4) 

HFC-134a 15.7(+0.7,-l.0) 377 IS.I (+0.7,-0.9) 16.0(±0.3) 

CH,CCh 6.3 (+0.3, -0.4) 45 S.2 (+0.2, -0.3) 5.5 (±0.1) 

•Panial lifetimes with respect to oxidation by OH are derived from the estimate of the total lifetime for CH,CCh of 5.2 (+0.2, -0.3) years. a panial 

lifetime with respect to oceanic loss of 94 years. and with respect to stratospheric loss of 45 years, and from rate constant ratios evaluated at 272 K 

(Spirnkm·sky el al .. 2000; Pra1'1er and Spirnkm·sky. 1990). Quoted uncenainties in these lifetime limits do not include uncenainties in rate constants. 

t Total lifetimes were calculated as the inverse of summed rate constants. The lifetime quoted for CH, also includes a panial lifetime with respect to 

soil loss of about 145 years. 

+Upper limits to trace gas lifetimes were derived in the same way as the best estimates. except that the upper limit for the total atmospheric lifetime 

of CH,CCh of 5.5 ± 0.1 years is considered. Note that these limits are entirely independent of calibration accuracy and emissions figures. 

1990s compared to the 1980s on a relative basis. the atmospheric 

conce111ration of CFC- I I is now decreasing but CFC-12 

co111inues to increase. This difference arises because the lifetime 

of CFC-12 is approximately I 00 years or about twice that of 

CFC-I I. 

While the tropospheric concentration of some ozone-depleting 

gases decreased and some increased during 1998-1999, the 

overall ozone-depleting capacity of the atmosphere has 

1.0% 

0) 

O> 

O> 

,.... 

,..:.. 

O> 

O> 0.5% 

>-

~ 

~ 0.0% 'O 

c 

~ 

! 

! 1----- Q) 

en 

c 8.. -0.5% en 

Q) 

a: 

-1.0% 

0 50 100 150 200 

Prepared mixing ratio (ppt) 

Fig. 5.14. The stability of calibration for CH,CCh during 1997-1999. 

From multiple (7-9) comparisons of 10 gravimetric standards 10 a single 

high-pressure sample of ambient air during 1997-1999, trends in the 

response ratio (ratio of the response for CH ,CCI, in the standard to that 

observed in the high-pressure real-air sample) were calculated and are 

expressed as linear regression slopes. Error bars represent the range in 

linear regression slopes calculated when any singk response ratio 

determination was remo,•ed from the slope calculation. Drift in the 

response ratio for ALl'-1·64596 was so large that it does not appear on 

this figure (the standard at 195.7 pp! drifted at -3.2 (±0.1 )~ yr' 1). 

98 

decreased since 1993-1994. Estimates of Effective Equivalent 

Chlorine (EEC!) and Equivalent Chlorine (ECI) [Daniel el al., 

199S; Mo111zka el al., 1996a) from tropospheric measurements 

provide a very rough estimate of ozone-depleting halogen 

concentrations in the future stratosphere (once a 3-S year time 

lag associated with mixing processes is considered). The EECI 

and ECI burdens of the troposphere have decreased since 1993-

1994 primarily because of the rapid decline in the trace gas 

methyl chloroform. By the end of 1999, tropospheric EECI was 

-S% below its peak and was decreasing at - I% yr' 1 (Figure 

5.15). 

As the influence of methyl chloroform on EECI and EC! 

diminishes, co111inued declines in EECI and ECI will be realized 

only if emissions of CFCs and related ozone-depleting gases 

become smaller than estimated for 1997 [Mo111::.ka el al., l 999a]. 

An update of the Mo111::.ka el al. [I 999a] analysis suggests that 

overall emissions of ozone-depleting gases have decreased only 

slightly since 1997 (Figure S. l S). 

Emissions of halon-12 11 have not decreased significantly 

during the 1990s despite stringent restrictions on production in 

developed countries since 1994 [8111/er e1 al., J 998a; Fraser el 

al., 1999; Mo111::.ka el al., J 999a). The lack of a decline in 

emissions of this gas likely Mems from the large reservoir of this 

chemical that currently exists in portable fire extinguishers in 

developed countries. Furthermore, production of halon-1211 in 

developing nations continued to increase in the 1990s each year 

through 1998 (the latest year for which production data are 

available). Production in developing countries is slated for 

reduction during 2002-20 I 0. Continued emissions from the 

large amount of halon in existing fire extinguishers, and from 

new production, have resuhed in a steady increase in the 

atmospheric concentration of halon-1211 through the end of 

1999 (Figure S.7b). This increase continues to retard the decline 

in EECI and ECI more than other gases. Unless further efforts 

are made to restrict continued production and emission of this 

halon, its concentration will likely increase for a number or years 

into the fu ture because of the substantial reservoir of halon 

produced but not yet released to the atmosphere. 

Emissions of the CFC-substitutes, known as the HCFCs and 

HFCs, also increased through the 1990s as use of CFCs and 

related ozone-depleting substances declined. These gases 

contribute Jess to reacti ve halogen in the stratosphere because a 
3.2 T 

3.1 T 

3.0 -

A :Q' 

8: 2.9 1 

§ 2.8 , 

2 .7 - B 

2.5 . --- ·-~- -

1990 1995 2000 2005 2010 2015 

4.6 -

4.5 -

4.4 -

4.3 -

-g_ 4.2 -

E: C3 4 .1 -

w 4 .0 -

3.9 . 

3.8 -

:!:'-ff!. 

~-~ 

. ·:~ · .... '• .. 

"····· ... 

3.7 -------~-~ 

1990 1995 2000 2005 2010 

Year 

A 

B 

2015 

Fig. 5. 15. The measured and potential future burden of ozone-depleting 

halogen in the lower atmosphere. Ozone-depleting halogen is estimated 

from tropospheric measurements of halocarbons by appropriate 

weighting factors to calculate Effective Equi valent Chlorine (EECI) for 

midlatitudes and Equi valent Chlorine (ECI) as an upper limit for polar 

latitudes [Daniel et al., 1995; Montl.kn et a/_, I 996a, I 999a]. Projections 

into the future are based on two scenarios: (A) emissions of all longlived halogenated gases (CFCs, HCFCs, CHJCC13, CCI;, and halons) 

remain constant at 1999 levels, (B) scenario A with the exceptions that 

emissions of CFCs, CH1CCli, and CCl4 continue decreasing at - 10% yf 1

• 

Future scenarios indicated with dashed lines were formulated with 

ambient air measurements through 1997 [M1mtz/w et al., 1999a); 

scenarios indicated with solid lines incorporated CMDL halocarbon 

measurements through the end of 1999. 

large percentage of these gases is re moved from the a tmosphe re 

in the troposphere, and certain HCFCs (HCFC-22 and HCFC142b) degrade slowl y in the stratosphe re. 

Measurements of Shorter-Lived Halogenated Gases 

Measure ments from flasks of shorter-li ved gases continued 

d uring 1998- 1999 (Figure 5. 16). Both C H3Cl and CH3Br 

contribute significantly to the halogen b urden of the stratos phere. 

Significant interannual variability was measured for both gases 

during 1995- 1999 [Montzka et al., l 999b]. For CH2Cl2 and 

C2Cl4 a trend towards lower mixing ratios is evident, particularly 

in the northe rn hemisphe re. These d ecreases may result from 

efforts to reduce emissio ns of toxic organic compounds in some 

nations. Although such gases (CH2Cl2, C2Cl4, CHC13) contribute 

some to the halogen burden of the stratosphere, global 

measurements of them a lso provide an improved understanding 

99 

700 

600 

500 

- 400 a. 

a.300 

200 

100 

a 

.. 

CH3CI 

--+-~...-~-+ ---.-~+-~~ --j 

1992 1994 

20 

15 

~ 10 

5 

CH3Br 

• .t 

a 

1996 1998 2000 

-l- -.---.---+-~~~--1-~,.-~-+-~-.---.---l 

1992 

50 

45 

40 

35 

30 

a. 25 a. 20 

15 

10 

5 

1994 1996 1998 2000 

CH2Cl2 

a 

a 

-1-~ ........ ....,....-+-~~~--;-~,.-~-+-~-.--....,....-i 

1992 1994 1996 1998 2000 

25 

20 CHCl3 

15 

a. 

a. 10 

5 

0 

1992 1994 1996 1998 2000 

16 C2Cl4 14 

12 

10 ·" .ft a. 8 a. 6 

4 

2 

0 

1992 1994 1996 1998 2000 

Year 

Fig. 5. 16. Atmospheric dry-air mole fractions (ppt) determined for 

selected chlorinated trace gases and CHJBr by GC-MS in the CMDL 

flask program_ Each point represents the mean of two simultaneously 

filled flasks from one of e ight or nine stations (symbols the same as in 

Figure 5.8). Results shown for all compounds except C2CL. are from 

2.4-L flasks only. 
of atmospheric processes such as !race-gas oxidation by OH and 

Cl atoms and atmospheri c transport rates. 

CMDL results for CH2Cl2 and C2Cl4 from GC-MS flask 

measurements were compared lo mixing ratios calculated in a 

three-dimensional model [Spivakovsky et al., 2000]. The 

comparison revealed that industrial emissions of CH2Cl2 are 

sufficient 10 account for the amount observed in the atmosphere; 

the addition of a relatively small oceanic source would cause the 

model to over-predict the observations in both hemispheres. The 

data also suggest that the actual loss rate of C2Cl4 is somewhat 

greater than can be accounted for by reaction with OH. This 

additional loss suggests either the bimolecular rate constant for the 

reaction OH + C2Cl4 is underestimated by -30%, or additional 

atmospheric loss arises from significant Cl atom oxidation. The 

results for CH2Cl2 also provide unique constraints to the 

distribution of OH on hemispheric scales provided that air 

transport rates are well known. Concentrations of shorter-lived 

gases such as CH2Cl2 and C2Cl4 are more sensitive to rates of 

inlerhemispheric mixing than longer-lived gases such as CFCs and 85Kr [Spi11ako11sky er al., 2000]. Further improvement in our 

unders1anding of OH and Cl concentrations on smaller spatial 

scales from measurements of these gases will require a better 

understanding of air exchange rates. Measurements of long-lived 

gases that are increasing rapidly (such as HCFCs and HFCs) may 

provide !his additional constraint. 

5.1.3. IN SITU GAS CHROMATOGRAPH MEASUREf\.lENTS 

Operations Update 

Four-channel GC-ECD instruments, developed 10 replace the 

aging RlTS instruments and add new measurement capabilities, 

were installed at the CMDL field sites (Barrow Observatory, 

Alaska (HK W); Mauna Loa Observatory, Hawaii (MLO); Samoa 

Observatory, American Samoa (SMO); and SPO). 111is new 

instrument is called Chromatograph for Atmospheric Trace 

Species (CATS). Three of the channels have packed gas 

chromatographic columns and the fourth contains a capillary 

column. 111e three packed-column channels are similar to those 

used in the RITS in situ GCs. They are used 10 measure three 

chlorofluorocarbons (CFC- I I, CFC-1 2, and CFC-1 13), chlorinated 

solvents (CH3CCl3, CHCl3, and CCl4}, N20, SFfo and halon-1211. 

The capill ary column is used to measure three new compounds for 

the HATS in situ program: HCFC-22 (CHCIF2) and two methyl 

halides (CH3CI and CH3Br). The CATS GCs analyze an air 

sample once every hour. 

New techniques were developed by !he HATS group to 

measure HCFC-22 and the methyl halides with an ECO. An 

ECO is less sensitive to methyl halides than 10 the CFCs. To 

enhance the methyl halide response a larger air sample is 

required. An 80 cm3 air sample is pre-concentrated on a 

cold 1rap held at about -60°C. The !rap is subsequently healed 

10 release and inject the sample onto the capillary column 

for separation. More detailed information on the chromatography of this channel can be found on a Web page at 

http://stndstealth.cmdl.noaa.gov/channel4.html. 

The CATS GCs are controlled by a PC-based data acquisition 

system using the QNX operating system (QNX Software 

Systems Ltd., Kanata, Ontario). QNX is a multi-tasking UNIX 

operating system for PC that allows for simultaneous control of 

the GC, preliminary data processing, data backup and storage, 

and World Wide Web access. Each CATS GC is accessible via 

the Internet. System status and preliminary data can be accessed 

on-li ne. 

The first CATS instrument was installed at SPO in late 

January 1998. A CATS instrument was installed at BRW in 

mid-June I 998. After 8 months the data comparison was 

deemed sufficient, and the RITS instrument was shut off 

(February I 7, 1999). The MLO equipment was deployed in late 

September 1998, and the SMO instrument was deployed in 

December 1998. Comparisons of RITS and CATS instruments 

continue at SMO, SPO, and MLO. It is expected that these RITS 

instruments will soon be shut down. 

Data A11alysis - RITS 

Trace gas mixing ratios measured by ground-based in situ 

instruments have shown marked changes over the I 0-13 year 

record (Figure 5.17). These trends reflect changes in chemical 

usage, atmospheric lifetimes, and mandated world-wide 

termination of production and consumption of some chemicals. 

The RITS data sets, which include individual measurements, 

daily, monthly, hemispheric and global averages, are available 

on the Internet at ftp.cmdl.noaa.gov/hats. 

Mixing ratios of CFC- I I leveled off in late 1993 indicating a 

temporary balance between source and sink strengths. The 

average global rate of decrease for the past few years is 1.6 ppt 

y( 1

• With an estimated atmospheric lifetime of 45 years, a 

global mean mixing ratio of 267 ppt at the beginning of I 999, 

and assuming negligible sources, the expected decrease in 1999 

should have been 5.9 ppt y( 1

• Tiius CFC- I I continues to be 

emitted to the atmosphere, albeit at rates that are less than those 

of the previous decade. 

The average global concentration of CFC-1 2 reached 537 ppt 

at the end of 1999 and continues to grow in the troposphere at a 

reduced rate of 2 ppt y( 1

• From the average rate of decrease in 

the growth rate since 1995, it is projected that CFC-12 will peak 

in the atmosphere in the next 3-4 years (Figure 5.18). 

Methyl chloroform emissions have decreased dramatically 

since earl y 1993. The effects of reduced emissions can be seen 

as a decrease in atmospheric mixing ratio (Figure 5. I 7). The 

global rate of decrease reached a maximum of 13.5 ppt y( 1 in 

1996-1 997. The interhemispheric difference is now very small 

(Figure 5.12), indicative of similar emissions in both 

hemispheres (near zero in 1his case). As emissions become 

negligibly small, the atmospheric lifetime can be estimated 

solely from the trend in atmospheric mixing ratio (Figure 5.19) 

[Mo111zka er al., 2000]. Based on in situ measurements from 

1998-1999, the globally averaged lifetime is estimated to be 

5.6 years. This result is consistent with that obtained from 

fl ask-air measurements over the same time period (section 

5. 1.2). It is encouraging that the flask and in situ programs, 

employing different sampling methods, diffe rent detection 

methods, and slightly different calibration methods, can 

provide the same result over this period. 

100 

Mixing ratios of carbon tetrachloride have been decreasing 

globally si nce 1990 at an average rate near -0.8 ppt y( 1

• The 

interhemispheric difference indicates that sources are located 

primarily in the northern hemisphere. Because CCl4 is used 

mainly as feedstock for the production of CFCs, which were 

banned in the industrialized nations, developing nations may be 

responsible for current emissions of CCl4. 

The tropospheric mixing ratio of N20 continues to grow at a 

steady rate near 0.7 ppb y( 1 and has reached a global mean of 

3 15.5 ppb at the end of 1999. A north-to-south gradient of 1.2 

ppb persists over the period of record because of differences in 

the balance of sources and sinks in the northern and southern 

hemispheres. 
320 

:0- 315 

0. 

s 310 

305-r~~~~~~~~~~~~~~~~~~-t 

500 

450 

~ 400 

a. 

a. :Q 350 

(ii 

;;, 300 c 

:8 E 250 

c 

m 200 

E 

(ij 150 .0 

0 °' 100 

50 

CFC-11 

CCl4 

O-i-~.---r---,~-r---,-~...--.....,...~.---r---,~-r---,-~...---1 

1987 1989 1991 1993 1995 1997 1999 2001 

Year 

Fig. 5.17. Global monthly mean mixing ratios fo r (a) N20 and (b) CFC12. CFC-I I, CH3CC'1. and CCI, from the in situ gas chromatographs. 

25-.-~~~~~~~~~~~~~~~~~---. 

-;:- 20 

5 

a. 

s 

Q) 15 

~ 

..c 

~ 10 

e 

Ol 

C\J 

~ 

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u.. 

0 

5 

0 

measured 

estimated 

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

.5-r--..--.--.~.--,---r--...---.--.--r--.--.---..--..--,--,'""""".....-i 

1987 1990 1993 1996 1999 2002 2005 

Year 

Fig. 5.18. Growth rate of CFC-12 as detennined from in situ 

measurements. The growth rate is projected to reach zero in the next 3-4 

years based on the average rate of decrease since 1995. 

Vi" 

tu 20 Q) 

Z: 

Q) 

:§ 15 "O 

s 

Q, 

<"'> 10 

0 

0 

<"'> 

I 

0 5 

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

: : : . . . . . . . . . . . . . . . . . . . . . 

..•..•..•• ~ ••...•.••. ·:- .•••...... !' .•.•.• . . . . . . . . . . . . 

: : : : : ; . . . . . . ·· ··~r~ ........ ~~-~1),__ i ~-(x .......... ;~;-x....,.....;") ····· ···· · ············ ···· ······ 

o-+~.--........ --..~..---.---<1----r--+~,------.~...--.---1 

1987 1989 1991 1993 1995 1997 1999 2001 

Year 

Fig. S.19. Using a single box model for the atmosphere with emissions 

assumed to be negligible, thee-fold time ("r.) is estimated using measured 

global mean methyl chloroform mixing ratios one year apart. X1 is the 

monthly mean global mixing ratio for the first month and X11 is the 

mixing ratio I year later ( 1311> month). Calculated values approach a limit as the emissions truly become negligible. 

Data Analysis - CA TS 

Over the pasts 5 years the HATS instruments have monitored 

the decrease of several important ozone-depleting gases [Elkins 

et al., 1993; Mo11tzk.a et al. , 1996a, 1999a). The new CATS GCs 

provide insight i1110 addilional ozone-depleting gases while still 

monitoring the trends of the CFCs and chlorinated solvents. 

HCFC-22 is a refrigerant compound that is replacing some of the 

phased-out CFCs. The CATS in situ measuremems, in 

corroboration with the HATS nask program, have monitored the 

global atmospheric increase of HCFC-22 (Figure 5.20a). 

Emissions of HCFC-22 are solely anthropogenic, dominated by 

the industrial northern hemisphere. This can be seen as a mixing 

ratio gradient from north to south. 

In situ measurements obtained by the HATS group have 

traditionally focused on long-lived compounds that have 

predominately anthropogenic sources. Recent measurements of 

the methyl halides have added importalll natural halocarbons to 

the suite of ozone-depicting gases measured by the HATS group . 

As the CFCs and other chlorinated compounds arc phased out, 

the natural sources of methyl halides will become more 

important sources of atmospheric chlorine and bromine. 

Moreover, the sources of these compounds are not well 

understood [8111/er, 2000). Monthly mean trends of the CATS in 

situ data for CH3CI and CH3Br show strong seasonal cycles in 

the northern hemisphere (Figures 5.20b and 5.20c). The 

seasonal cycle is at its minimum during the summer in both 

hemispheres when the dominant sink, hydroxyl radical (OH), is 

at its maximum. 

IOI 

With the addition of the CATS in situ methyl halide 

measurements at the CMDL observatories, there is the ability 

to not only monitor these compounds, but also help locate and 

quantify their sources. A recent study points to coastal 

vegetation as a source of CH3CI [ Yokouchi et al., 2000). 
a. 140 

.9: 

~ 130 

u 

LL 120 u 

I 

14 

13 

a. 12 .9: 

cD 11 C') 

I 10 u 9 

8 

a 

b 

c 

~~ 

~ ~ / 

580 

560 

540 0 

520.l 

- 500 Q 

480'0 

460 :g, 

440 

420 

1/1/98 7/1/98 1/1/99 

Date 

7/1/99 1/1/00 

Fig. 5.20. Monthly mean mixing ratios of (a) HCFC-22, (b) methyl 

chloride, and (c) methyl bromide measured by the CA TS in situ gas 

chromatographs deployed a1 the CMDL observatories (8RW, 1riangle; 

t\ILO, open circle: SMO. square: SPO, invencd triangle). The solid 

circles are global averages of !he four si1es caleula1ed by cosine 

la1i1udinal weigh1ing. 

Measurements of CH.,Cl at our two tropical coastal sites, MLO 

and SMO, also point to a coastal terrestrial source. Figure 5.21 

shows rapid changes in the CH3Cl mi xing ratio at Mauna Loa 

(Figure 5.21 a) and corresponding changes in wind direction 

(Figure 5.21 b). High concentrations of CH3CI are associated 

- S6S ... 8: S60 

SSS .-< 

u 

n 550 :c 

u 

S45 

S4 0 

a 

3/Si OO 3f7 /00 3/9/00 3 / 11/ 00 Date 

1. 0 ~. 

0. s g, 0. 0 tl 

-o. s~· 

-1. o~ n 

,... 

0 

~ 

Fig. 5.21. Houri} mcasuremen!s of CH,CI in air a1 MLO (a) show rapid 

variabili1y in the CH1Cl mixing ra1io. indicating local sources. The 

cosine of 1he wind direc1ion (values near I correspond 10 northerly 

winds. values near-I correspond to southerly winds) (b) and wind speed 

(c) are ploued fo r comparison. 

with periods of northerl y winds (daytime up-slope conditions) 

that bring CH3Cl-rich air from the vegetated northern section of 

the island of Hawaii up to MLO. 

5.1.4. GRAVIMETRIC STANDARDS 

Calibration of Working Standards 

In May 1999 the three-channel gas chromatograph system 

used to calibrate standards fo r the in situ monitoring program 

was replaced by a four-channel, custom-built GC. The fourchannel GC is similar to the four-channel CATS instrumems 

used for in situ monitoring at the observatories. The GC is 

operated under slightly different conditions compared to those at 

the observatories in order to optimize chromatography for 

cylinder calibration (Table 5.6). 

The new four-channel instrument was compared to the old GC 

to ensure that the new GC would provide similar calibration 

results. For calibrations of ambient-level working standards, the 

new GC agreed to within 0.1 % for N20, 0.4% for CFC-1 13, 

0.5% for CH3CCl3, and I% for CFC- I I and CCI~. Initial tests 

revealed a 2-3% discrepancy for CFC-12. This experiment was 

repeated several momhs later, and the discrepancy could not be 

reproduced. Testing in December I 999 showed that the GCs 

agreed to within 0.2% for CFC-12. Following this CFC-1 2 

experiment. the old three-channel GC instrumem was retired. 

The four-channel GC is now used to calibrate working standards. 

Each standard is typically analyzed for 2 full days over a 2-3 

week period (8- 12 injections each day) (Table 5.7). 

Preparation of Working Standards 

Working standards for use with laboratory and in situ GCs 

continue 10 be filled at the C-1 si1e al Niwot Ridge, Colorado 

(40.04°N, 105.54°W. elevation 3013 m). Cylinders are filled 

using a three-stage, SA-68 compressor from Rix Industries 

(Oakland, California). Cylinders have occasionally been 

contaminated with trace amounts of unknown compounds that 

elute near CFC- I 1 and CFC- I I 3 on the columns used in the 

CMDL in situ program. Contaminated standards have 

traditionally been associated with warm temperatures, while 

clean standards have been obtained during winter when ambient 

air temperatures are often below 5°C. The comaminants are 

thought to result from outgassing of material from the piston 

rings of one or more of the compressor stages (Ray Weiss, 

personal communication, 1999). Outgassing may be more 

severe at higher operating temperatures. To reduce the operating 

temperature of the first stage of the compressor, the compressor 

was modified in order to allow a small amount of distilled, degassed water to be injected into the air stream just upstream of 

102 

TABLE 5.6. Configuration of the Four-Channel GC for 

Calibration of Working Standards 

Channel Column Detector Compounds Resolved 

I Porapak Q Valeo ECO N20, SF6 

2 Unibcads Is Shirnadzu ECO CFC-12, CFC-I I. 

halon-1211 

3 OV-101 Valeo ECO CFC-1 2, CFC-I I, 

halon-1211, CFC-113, 

CHCI,, CH1CCh, CCI, 

4 Poraplot Q Shirnadzu ECO HCFC-22, CH)CI, CH1Br 
TABLE 5.7. Analytical Precision Typically Obtained for a 

Complete Calibration of a Working Standard on the 

Four-Channel GC-ECD 

Compound* 

N10 

CFC- 12 

CFC-II 

CFC-l 13 

halon-121 lt 

CH Ch 

CH,CCIJ 

CCI, 

SF6 

Precsion (%) 

0.05 

0.08 

0.10 

O.l 5 

0.2 

1.0 

0.2 

0.1 

0.8 

*Calibration of HCFC-22, CH3Cl and CH3Br is only performed on the 

Oask GC-MS instrument at this time. 

t The calibration scale for halon- 12 11 is determined on the flask GCECD instrument. Halon- 12 11 calibration on the four-channel instrument 

is complicated by a co-eluting peak occurring on both channels 2 and 3. 

the first stage. Injection of water in this manner reduces the 

operating temperature of the first stage cylinder head from 

>100°C to -50°C. Contamination is substantially reduced by 

injecting water at a rate of 10-20 mL min· 1 (Figure 5.22). 

Standards Preparation 

A total of 66 natural-air standards were filled at Ni wot Ridge 

during the 1998-1999 period. Fifty-eight of these were used by 

CMDL or related projects; eight standards were prepared for 

outside laboratories. A total of 10 gravimetric standards were 

prepared. Four were prepared for CMDL use, while 6 were 

prepared for outside laboratories. 

Calibratio11 Scales 

A summary of the calibration scales used in conjunction with 

measurements performed by the HATS group is reported here. 

Table 5.8 lists the year that each calibration scale was 

established. Table 5.9 lists the gravimetric standards and mixing 

ratios used to define each calibration scale. Factors that 

10.0x10' 

9.5 

~ 9.0 

., 

., 

c 

&. 

8.5 

., 

e 8.0 

7.5 

7.0 

200 400 600 800 1000 1200 1400 

time (s) 

Fig. 5.22. Chromatograms of air samples from tanks pumped at Niwot 

Ridge, Colorado, with and without water injection (see text). The 

chromatogram (top) without water injection shows more contamination 

peaks. 

TABLE 5.8. Reference Dates for HATS Calibration Scales 

Compound Year* Reference* 

N20 1993 Swc111st111 et al. [ 1993) 

CFC-12 1997 Butler et al. ( l 998b] 

CFC-I I 1992 Elkins et al. [ 1993) 

CFC-113 1993 Sww1st111 eta/. [1993) 

CHiCCli 1996 8111/er et al. [998b I 

CCL, 1996 Butler et al. [ l 998b I 

HCFC-22 1992 Mt111tzlw et al. [ 1993) 

HCFC- l4 lb 1994 Mt111tzlw et al. [ 1994] 

HCFC-l42b 1994 Mt1111l}w et al. [ l 994] 

HCFC-1 34a 1995 Mt111tzlw et al. [ 1996b] 

CH3CI 1996 Butler et al. [I 998b] 

CH3Br 1996 Butler eta/. [1998b) 

CH2Clit 1992 Spivakovsky et al. (2000] 

C2CL.t 1992 Hurst et al. [ 1997] 

CHCht 1992 Hurst et al. (1997] 

halon-2402t 1992 Butler et al. [I 998b) 

halon-1211 1996 8111/er et al. [I 998a] 

halon-1 30 1 1990 Butler et al. [I 998a] 

SF6 1994 Geller et al. [ 1997) 

Hi 1995 Novelli et al. [ l 999) 

co 1991 N1welli et al. [ l 991) 

•Calibration scales are defined by a particular set of gravimetric 

standards (see Table 5.9). ln some cases only a single standard is used. 

The year shown for each species refers to either the year during which 

the standards were prepared or the year in which a significant change in 

calibration scale occurred. Thus data reported prior to the year listed are 

associated with a different calibration scale than those reported in 

subsequent years. 

tThese species are measured by CMDL. but their calibration is 

defined only by an incomplete set of standards. 

:j:The reference listed for each species refers to a publication that 

describes a calibration change or n publication that includes recent 1e>uli!>. 

influence the number of gravimetric standards used to define a 

particular scale include the time-history of the measurements, the 

range of concentrations investigated, and the linearity of 

response (e.g., CFC-12 measurements were made over more 

extensive spatial and temporal scales than CH3Br, thus a large 

number of CFC-12 standards were prepared over the years). All 

of the standards listed in Table 5.9 were prepared in 5.9-L or 

29.5-L Aculife-treated aluminum cylinders (Scott Specialty 

Gases, Plumsteadville, Pennsylvania). 

103 

Examples of calibration response curves determined on the 

CATS GC instrument are shown in Figure 5.23. The uncertainty 

associated with the calibration curves (expressed as the standard 

error of the residuals) is typically 0.2-0.5%. 

The number of gravimetric standards used to define scales for 

N20 and SF6 will be expanded in the near future. A number of 

standards with N20 and SF6 mixing ratios near ambient levels 

will be prepared. The addition of numerous standards at nearambient concentrations will enable high-precision maintenance 

of the scales over ti me. 

5.2. AIRBORNE PROJECTS 

5.2.1. AIRBORNE CHROMATOGRAPH FOR 

ATMOSPHERIC TRACE SPECIES (A CATS-IV) 

Overview 

Airborne Chromatograph for Atmospheric Trace Species 

(ACATS-IV) is a four-channel gas chromatograph designed to 
TABLE 5.9. Gravimetric Standards Used to Define Calibration Scales for the HATS Group 

Cylinder Prepared Gravimetric Cylinder Prepared Gravimetric 

Compound Number Concentration Compound Number Concentration 

N20 *ALM-38408 96.2 ppb SF6 *CLM-7506 3.1 ppt 

*ALM-26738 172.0 ppb *CLM-75 19 23.2 ppt 

*ALM-26743 331.0 ppb *CLM-7494 60.6 ppt 

*ALM-26737 359.9 ppb *CLM-7503 107.6 pp! 

*CLM-301 35 801.1 ppb CH1Br t CLM-7490 5.3 pp! 

CFC-I I *ALM-38408 25.5 pp! t ALM-62626 5.3 pp! 

*CLM-243 1 49.5 ppt tALM-3977 1 25.6 pp! 

*ALM-384 17 80.9 pp! CH1CI tALM-39971 1024 ppt 

*CLM-2482 69.2 pp! HCFC-22 tALM-26738 105 pp! 

*ALM-26735 75.16ppt tALM-26743 145 pp! 

*CLM-2413 136.3 pp! t ALM-26735 105 ppt 

*ALM-26743 288.2 pp! tALM-384 17 111.6 pp! 

*ALM-26737 313.6 ppt t ALM-26737 158 ppt 

CFC-12 *CLM-2426 77.8 ppt HCFC- 141b t ALM-39758 5.0 ppt 

*CLM-243 1 163.5 pp! t ALM-39744 25.5 pp! 

*CLM-90 15 189.2 ppt tALM-39749 5 1.3 ppt 

*CLM-2482 228.8 pp! HCFC- 142b t ALM-39758 5.0 ppt 

*CLM-904 1 274.4 ppt t ALM-39744 25.4 pp! 

*CLM-9018 370.3 pp! tALM-39749 51.1 pp! 

*CLM-24 13 450.7 ppt HCFC-134a tCLM-8952 5.44 ppt 

*CLM-9038 646.9 ppt tCLM-9036 10.22 ppt 

CFC- 11 3 *CLM-2482 19.I ppt halon-1211 *tCLM-9039 3.02 pp! 

*CLM-24 13 37.5 pp! *tCLM-9024 5.41 pp! 

*tALM-26735 48.0 ppt halon-1301 *tCLM-24 16 95.4 pp! 

t ALM-26738 48.0 ppt *tFF-3007 1 6.08 ppb 

*tALM-26743 82.8 ppt halon-2402 t ALM-26748 47.5 ppt 

*tALM-26737 90.0 ppt CH1Ch tALM-26748 122.0 ppt 

CH1CCl1 *tALM-52792 30.9 ppt C2CI; t ALM-26748 157.0 ppt 

*tALM-52788 70.8 ppt CH Ch t ALM-26748 141.0 ppt 

*tALM-59967 111.0 ppt 

*tALM-528 11 151.4 ppt 

CCl4 *tALM 52792 22. 1 pp! 

*t ALM-52788 50.6 pp! 

*tALM-59967 79.4 ppt 

*tALM-528 11 108.3 ppt 

*These standards are used to define the calibration scales associated with GC-ECD instruments. 

t These standards are used to define the calibration scales associated with GC-MS instruments. 

measure atmospheri c trace gases in the upper troposphe re and 

lower stratosphere onboard the NASA high-altitude ER-2 aircraft 

[Elkins et al., 1996). ACATS-IY measures six chlorinated trace 

gases (CFC- 12 , CFC-I I, CFC- 11 3, C HC13, C H3CC13, CCl4) in 

addi tion to halon- 12 11 , NiO, C H4, Hi, and SFi.. ACATS-IV has 

been part of the ER-2 payload for studies o f stratosphe ric 

transport and ozone depletion si nce 1994, and in 1997 

participated in the Photochemistry o f Ozone Loss in the Arctic 

Region in Summer (POLARIS) study. The principal objecti ve of 

POLARIS was to determine the roles of photochemistry and 

transport in summertime decreases of stratospheric ozone over 

the arctic. Nineteen instruments onboard the NASA highaltitude ER-2 aircraft made in situ measurements o f trace gases, 

radicals, aerosols, radiation, and meteorol ogy in the upper 

troposphere and lower stratosphe re of the northe rn hemisphere 

during spring, earl y summer, and late summer. The edge of the 

arctic polar vortex was penetrated during one night in late April, 

and fragments of the eroding vortex were sampled during several 

other fli ghts in May and June. The observed 35% decrease of 

the ozone column above Fairbanks, Alaska, was largely 

attributed to photochemistry, predominantly catalytic reactions 

between 0 3 and NO in air parcels continuously exposed to 

sunlight for up to I 0 days. A CATS-IV data from POLARIS 

104 

were incorporated in several publications that appeared during 

1999 [e.g., Hurst et al. , 1999; Romashki11 el al., 1999; Sen et al., 

1999; Too11 el al., 1999). 

Hydrogen Budget 

The total hydrogen budget of the northe rn hemisphere lower 

stratosphe re was recently evaluated for closure from in situ 

measure ments of HiO , C H4, and Hi onboard the NASA ER-2 

aircraft during POLARIS and the 1995-1 996 Stratospheric 

Tracers of Atmosphe ric Transport (STRA T) mission [H11rs1 el 

al., 1999). Budget closure requires that measured abundance 

relationships between these principal hydrogen reservoirs 

corroborate theoretical hydrogen partitioning predicted by 

reactions that oxidize C H4 to H20 and Hi. and oxidize Hi to 

HiO. A simple evaluation of these reactions predicts that HiO 

production (AHiO) should equ al two limes C H4 loss (-2•6CH4) 

plus the net change in Hi (AHi). ACATS-IV measurements 

revealed that H2 mi xing ratios are relatively constant in the lower 

stratosphere (Figure 5.24). From the measured 6 Hi/6CH4 = - 0 .027 ± 0 .003 (Figure 5 .24), the ratio of H20 production to C H4 

destruction (6H20 /6CH4) was predicted to b e -1.973 ± 0.003 

[H11rs1 et al., 1999). 
1.2 -..-~~~~~~~~~~~~~~~~~ 

1 .0 

<ll 

~ 0.8 0 

g- 0.6 ~ 

<ll 0.4 -~ 

co 

~ 0.2 . 

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

3.0 

e: 2.5 c 

g_ 2.0 VJ 

~ Q) 1 . 5 

.~ 

co 1 .0 

~ 0.5 

0.0 

1 .2 

Q) 1. 0 VJ 

c 

g_ 0.8 VJ 

~ 0.6 Q) 

-~ co 0.4 

~ 0.2 

0 200 400 600 

0 25 50 75 100 125 150 175 

0.0 

0 50 100 15 0 

prepared mixing ratio (ppt) 

Fig. 5.23. Sample calibration curves for CFC-12 (a). CH,CCl 1 (b), and 

CCI, (c). Each filled circle represents the response or a gra' imetric 

standard relati,·e to a working standard. Sohd lines are second-order 

polynomial fits to response data. 

This predicted relationship was compared to the slope of the 

alllicorrelation between H20 and CH4 mixing ratios measured in 

the lower stratosphere during STRAT and POLARIS. H20 was 

measured during both campaigns by the Harvard University 

Lyman-a hygrometer [Hi11tsa et al., 1999] and also by the Jet 

Propulsion Laboratory (JPL) tunable diode laser (TDL) 

hygrometer during POLARIS. CH4 was measured by ACATSIY and a JPL TDL spectrometer. The anticorrelation between 

H20 and CH4 in the lower stratosphere was found to be tight and 

linear for air masses with mean ages greater than 3.8 years 

(Figure 5.25). ln younger air masses large variations in H20 

mixing ratios degrade the compactness of the anticorrelation. 

These variations result from the seasonal cycle of temperature 

near the tropical tropopause, the elllry point for most 

stratospheric air masses. Air masses passing through the tropical 

tropopause are regularly imprinted with an H20 mixing ratio 

dictated by the lowest temperature they encounter [e.g., 

600 

J:j' 

Q. 560 .9: 

N 

:r: 

CJ) 

~ 520 

(.) 

<( 

480 

800 1000 1200 1400 1600 1800 

ACATS CH4 (ppb) 

Fig. 5.24. H2 and CH, measured by ACATS-IY in the lower stratosphere 

between 3°S and 60°N latitude during STRAT (1995-1996). The solid 

line is an ODR fit to the data with a slope or -0.027 ± 0.003, indicating 

that H2 production slightly exceeds H2 destruction in the strtosphere. The 

crossed error bars represent the average random errors (I cr) of the 

measurements. 

Mote et al., 1996]. As young air masses age in the stratosphere, 

they gradually lose their H20 imprilll as they mix with air masses 

of different H20 content. 

Data from each unique combination of H20 and CH4 

instruments were fit with an orthogonal distance regression 

(ODR). Data for air masses with mean ages <3.8 year (or 

alternately CH4 >1450 ppb) were excluded from the fits. For all 

instrument combinations the mean slope (t.H20/t.CH4) was 

-2.15 ± 0.18 (lcr). The mean slope using only ACATS-IY CH4 

data, -2.02 ± 0.17, is in excellent agreement with the predicted 

t.H20/t.CH4 = -1.973. The annual mean mixing ratio of H20 in 

air masses elllering the stratosphere was estimated from the slope 

and illlercept values from each ODR and a CH4 mixing ratio of 

1.7 ppm (the annual mean CH, mixing ratio entering the 

stratosphere). The result. 4.0 ± 0.4 ppm H20, agrees well with 

the 3.8 ± 0.3 ppm H20 deduced from a recent re-evaluation of 

radiosonde temperature data near the tropical tropopause 

[ Dessler, 1998]. 

105 

Tracer Correlatio11s 

Measurements of CH3CCl 3 and CFC- I I in the lower 

stratosphere during POLARIS revealed significalll differences in 

the CH3CCl3-CFC-I I correlation between spring and summer, 

1997 [Ro111ashki11 et al., 1999]. These differences were 

associated with the rapid decrease of tropospheric CH3CCl3 that 

began in 1992 (see sections 5. 1.2, 5.1.3) and the fact that the 

mean ages of the air masses observed during spring and summer 

differed by up to I year. 

Before the CH3CCl3-CFC-I 1 correlations could be used to gain 

insight into stratospheric transport, the influences of the large 

tropospheric CH.,CCl3 trend on the lower stratospheric CH3CCl3 

distribution had to be minimized. Initiall y, the CH3CCl3 mixing 

ratio in each air mass sampled by ACATS-IY was normalized to 

the CH3CCl3 mixing ratio in air masses that entered the 

stratosphere on January I, 1997. The normalization was based on 

the well-documented trend of tropospheric CH3CCl3 (Figure 
7.0 

E 6.0 a. 

.e, 

0 

"' 5.0 I 

'E 

Cl! 

~ 

Cl! 4.0 ................ I 

3.0 

600 800 1000 1200 1400 

ACATS CH4 (ppb) 

Fig. 5.25. A tight, linear anlicorrelation between Harvard H10 and 

ACATS-IV CH, was observed in the lower stratosphere during STRAT 

(1995-1996) and POLARIS (1997). The solid line is an ODR fit to the data with a slope of - 2.01 ± 0.16. Data for air masses with mean ages 

<3.8 years were omiued from this analysis. 

5.9) and the mean ages of stratospheric air masses calculated 

from ACATS-IV measurements of SF6. 

This normalization procedure, based solely on mean age, is 

inexact because an air mass is better characterized by a spectrum 

of ages [Hall a11d Plumb, 1994]. Two methods were used to 

quantify the effect of age spectra width on the initial 

normalization. In the first method, the stratospheric entry mixing 

ratio of CH3CCl3 was expressed as the mean tropospheric mixing 

ratio of CH3CCl3 over ±1.25-year intervals, the estimated width 

of the age spectrum [Volk et al. , 1997]. For the second method, a 

10-year-wide age spectrum (Green's) function based on a onedimensional diffusive model (equation 2 1 of Hall a11d Plumb 

[ 1994] with diffusion coefficient K = 1.5 m2 s'1

) was used to 

weight the CH.1CCl3 tropospheric trend. The model-derived, 

weighted trend was used in combination with mean ages from 

ACATS-IV because the model underpredicts mean ages by a 

factor of two or more. The two normalization methods were 

similar in their influences on lower stratospheric CH3CCl_1 

mixing ratios. 

Correlations between normalized CH3CCJ_, and CFC- I I 

mixing ratios (Figure 5.26c) exhibit greater curvature than the 

raw correlations (Figure 5.26b). The induced curvature reveals 

straight lines of data between different parts of the correlation, 

evidence that air has mixed between the polar vortex and the 

midlatitudes (lines a and ~on Figure 5.26c). These mixing lines 

were not visible in the linear, un-normalized correlations (Figure 

S.26b). The study confirms that stratospheric correlations 

between trace gases can be significantly altered by a strong 

tropospheric trend in one of the gases. 

Total Inorganic Clzlori11e 

Se11 et al. [ 1999] compared two methods of determining the 

total inorganic chlorine content (Cly) of air masses sampled in 

the arctic stratosphere during POLARIS. In the first method, Cl> 

was calculated as the difference between the total chlorine 

content (Cli.ul of an air mass when it entered the stratosphere and 

the total organi c chlorine content (CCly) of the same air mass at 

the time it was sampled by the ER-2. CCly was determined from 

ACATS-IV in situ measurements of chlorinated source gases 

1.2 i:::::::=::::-r---r--,-----,r---r--:i 

~0.9 

;o.6 

0 0.3 QJ 

~ 0.0 r------;---;---~:.......::::::::::::;:::::::::==--~--:j 

80 

60 

b Raw 

obseNations 

a 

li 

.,9, 

"' 0 40 

0 

I "' 

0 

106 

20 O Spring 1997 

Summer 1997 

OIL..I:=--~+-~~+-~~-+-~~-+-~~-+-~ 

a_ 

.,9, 

"' 

80 

60 

0 40 (_) 

I "' 

(_) 

20 

c Normalized 

to 1997.0 

o=-=~_,,__._~~---1.~~~...__~~-'--~~---''----' 

0 50 100 150 200 250 

CFC-11 (ppt) 

Fig. 5.26. Results from CH3CCh and CFC-I I measurements made 

during the POLAR IS campaign ( 1997): (a) differences between the SF6-

based mean ages of air masses sampled by ACATS-IV (summer-spring). (b) corrdations between CH1CCh and CFC-I I during spring and summer, and (c) same correlations as (b) with the effects of the 

tropospheric CH1CCl1 trend removed using I 0-year-wide age spectrum, 

normalized lo January I, 1997. Solid lines in (b) and (c) are least squares 

fits to the following data subsets: a , I 00 ppl<CFC-11 <225 ppl measured 

on June 26, 1997: ~. 0 ppt<CFC- 11 <125 ppt measured on June 29, 1997. 

near 20 km altitude (lower stratosphere) during the ER-2 flight 

of April 26, 1997. Cl,.,, values for the sampled air masses were 

compiled from time series of source gas mixing ratios measured 

at the Earth's surface in flasks and at NOAA observatories 

[Woodbridge et al., 1995; Montzka et al., 1996a]. The date of 

stratospheric entry of each sampled air mass was determined 

from its mean age calculated from ACATS-IV SFfi data. Cly 

was also calculated as the sum of remotely sensed solar 

occultation Fourier transform infrared (FTIR) measurements 
of HCI, CION02, and HOCI by the JPL Mk lV interferometer 

and estimates of CIO from a photochemical model. The MklV 

observations were made during a balloon flight on May 8, 

1997. These two methods of estimating Cl> agree to within 

I 0% (Figure 5.27), adding confidence to both the in situ and 

remotely sensed data and suggesting that the photochemical 

model estimates of CIO are realistic for the sunlit lower 

stratosphere. 

luterco111pariso11 of Trace Gas Meamrements 

ACATS-IV measurements of CFC-I I, CFC-12, CFC-113 , 

CCl4 , and SF6 during POLARIS were compared to remotely 

sensed solar occultation FTIR measurements by the JPL Mk!V 

interferometer on a balloon floating at 38 km altilllde [Toon et 

al., 1999]. Both sets of tracer data were correlated with N20 to 

account for the different dynamical histories of air masses 

sampled several days apart by the two instruments. Differences 

were less than 2% for both CFC- I I and CFC- 12, well within the 

experimental uncertainties of the MklV measurements. CFC11 3 and CCl4 data agreed to within experimental uncertainties 

(1 1-1 5%) between 13 and 21 km altitude, but the MklV mixing 

ratios of both gases increased anomalously below 13 km. The 

anomalous increases were not observed for other long-lived 

tracers and were attributed to interfering absorption lines in the 

spectral regions used to quantify these gases. ACATS-IV SF6 

mixing ratios were on average 0.5 ppt ( 14%) lower than the 

MklV values. This bias is surprising given that there was no 

discernable bias between SF6 data from ACATS-IV and the 

Atmospheric Trace Molecule Spectroscopy (ATMOS) FTIR 

instrument aboard the space shuttle during 1993 and I 994 

[Chang er al., 1996; Michelson er al., 1999). The reason for this 

discrepancy has not yet been determined. 

lllstru111e11t Modificatio11sfor TIES and SOLVE 

ACATS-IV was modified twice during the second half of 

1999 in preparation for the 2000 Stratospheric Aerosol and Gas 

Experiment-Ill (SAGE) Ozone Loss and Validation Experiment 

3 '-~ l~ .. ~ .. I ~ ... I ..... ~··· ·· ··· ·· 1·············-'····················· l l j . I ! j j 

i I ~~~~ 1 Y I 

0 ~· ............. ; ............. -~ ............ i• ............ -~ ............. ·; ............ . 

0 100 200 300 

ACATS N20 (ppb) 

Fig. 5.27. Two independent methods were used to detcnnine the total 

inorganic chlorine content (Cl,) of stratospheric air masses during 

POLARIS (1997). One method (solid line) utilized CMDL surface 

measurements of chlorinated source gases and ACATS-IV ( 1997) 

measurements of organic chlorine compounds in the lower stratosphere. The other method (open circles) combined MklV measurements of HCI, 

CION02. and HOC! and modeled estimates of CIO. The two methods agree to within 10%. 

(SOLVE) in Kiruna, Sweden. The fi rst modifications were made 

for the 1999 Tracer lntercomparison Experiment for SOLVE 

(TIES) mission, a side-by-side intercomparison of coincident 

measurements by the three in situ N20 and CH4 instruments 

selected for the SOLVE ER-2 payload. TIES was conducted at 

NASA Dryden, Edwards Air Force Base, California, during 

September-October 1999. The mission was a critical evaluation 

of N20 and CH4 measurements by the JPL TDL spectrometer 

and a new, lightweight, compact TDL spectrometer that will 

replace a heavy, large TDL spectrometer that provided high 

quality N20 data aboard the ER-2 for many years. ACATS-IV 

was modified to include a new, rapid chromatography channel to 

measure N20 and SF6 every 70 seconds. The new channel was 

operated in parallel with the "old" 250-s N20 and SF6 channel 

during TIES, and the coincident data were in excellent 

agreement. ACATS-IV measurements of N20 and CH4 were 

used to assess the reliability of higher-frequency measurements 

by the TDL instruments. The assessment demonstrated that the 

quality of TDL N20 data was, at times, inadequate for the 

upcoming SOLVE mission, and that further refinements of the 

spectrometers and their retrieval algorithms were necessary. 

ACATS-IV was again modified after the TIES mission by 

replacing the "old" N20 and SF6 channel with a new, rapid 

chromatographic channel to measure CFC-12 and halon-1 21 1 

every 70 seconds. This channel was thoroughly tested in the 

laboratory for artifacts, flown during SOLVE test flights in 

December I 999 and then adopted as part of the final instrument 

configuration for SOLVE. The two modifications to ACATSIV enabled 70-s measurements of N20, SF~. CFC-12, and 

halon-121 I, 140-s measurements of CFC- I I, CFC- 11 3, 

CHCl.i. CH3CCl_1, CCl4 , CH4, and H2, and improved the 

precision of SF6 and halon-1211 measurements to about ±1% 

during SOL VE. 

107 

5.2.2. LIGHTWEIGHT A IRBORNE CHROMATOGRAPH 

EXPERIMENT (LACE) 

LACE is a three-channel gas chromatograph that operates on 

the NASA-sponsored Observations in the Middle Stratosphere 

(OMS) gondola and the NASA WB-57F aircraft. The OMS 

platform represents a collaboration with scientists from CMDL, 

Cooperative Institute for Research in Environmental Sciences 

(CIRES), NOAA Aeronomy Laboratory (AL}, JPL, NASA 

Ames Research Center, Harvard University, and Penn State 

Uni versity. The WB-57F platform represents collaboration with 

scientists from CMDL, CIRES, AL, National Center for 

Atmospheric Research (NCAR), Uni versi ty of Denver, JPL, 

NASA, and California Institute of Technology. 

OMS deployments at Fairbanks, Alaska, and Brazil were 

reported in Ray et al. [ 1999]. On May 18, 1998, CMDL 

participated in a midlatitude OMS balloon flight out of Fon 

Sumner, New Mexico, as a follow-up to the STRAT and 

POLARIS campaigns. After finali zing the data from this flight, 

the LACE instrument was modified for the Atmospheric 

Chemistry and Combustion Effects Near the Tropopause 

(ACCENT) campaign designed to investigate the effects of 

rocket and aircraft combustion in the upper troposphere and 

lower stratosphere and the SOL VE campaign designed to 

examine the processes controlling ozone levels at mid- to high 

latitudes. 

A new chromatography channel was developed that proved 

advantageous for both campaigns. This channel measures 

molecular hydrogen, methane, and carbon monoxide once every 
140 seconds. Carbon monoxide was included on the ACCENT 

mission to help identify rapid convection in the troposphere. 

Molecular hydrogen and carbon monoxide were included on the 

SOLVE campaign because of their strong mesospheric sources, 

and methane was included to help close the hydrogen budget 

[Hurst et al., 1999]. 

The ACCENT campaign in Houston, Texas, (September 1999) 

utilized an unpressurized chamber in a WB-57F aircraft. 

Substantial thermodynamic, mechanical, and electrical 

modifications of the LACE instrument were required in order to 

participate in the ACCENT mission. LACE operated successfully 

on all eight ACCENT science nights, including a tropical night, a 

night over the eye of hurricane Floyd, a night within the 

commercial airline !light corridor, and a rocket plume intercept. 

The ACCENT data were finalized and submitted to the NASA 

archi ve. Following the ACCENT campaign, LACE was 

reconfigured to fly on the balloon platform as part of the OMS 

SOL VE campaign in Kiruna, Sweden. 

The SOL VE campaign began with a balloon flight well inside 

the northern vortex just days after the vortex had formed 

(November 19, 1999). Preliminary analysis of these data revealed 

man) interesting features of atmospheric transport such as the rate 

of descent of air "ithin the \Ort ex, the degree of entrainment of 

m1dlalltude air into the ,·ortex. and mixing characteristics within 

the vortex. 

Tracers such as CO, H2, and SF,, that have large vertical 

gradients in the mesosphere can also provide an estimate of the 

distribution of alti tudes from which air originated before 

descending into the vortex. Estimates of the mesospheric 

sources and sinks for these molecules can also be made. After 

quantifying the mesospheric losses of SF0 and C02• limits on the 

corrections to the age profiles calculated from these molecules 

can be quantified. In addition to proYiding information on vortex 

air descent, thc~e measurements contributed to ongoing studies 

of transport in the lowermost stratosphere [Ray et al., 1999). 

5.2.3. PAN AND OTHER TRACE HYDROHALOCOl\IPOUNDS EXPERll\IENT (PANTHER) 

The next step in evolution for the HATS airborne gas 

chromatographs is the development of the PANTHER 

instrument. ACATS-IV and LACE instruments use packed 

columns and electron capture detectors. In addition to these 

technologies, PANTHER "ill incorporate cryogenic trapping to 

collect larger samples, capillary columns to increase separation 

and signal-to-noise. and a Hewlett Packard (HP, no'' Agi lent 

Technologies) model 5973 quadrupole mass selecti\ e detector 

(MSO). These added technologies \\ill enable PANTHER to 

make in situ measurements of the CFC replacement molecules, 

methyl halides. peroxyacctyl nitrate (PAN. CH.1C(0)00N02). 

and one of PAN·s precursors, acetone. 

Initial acthities focused on proof of concept studies. Three 

basic concepts (chromatography, calibration, and data 

acquisition) had to be addressed before design and construction 

of the flight instrument could begin. 

The first objective was to shm' that adequate chromatography 

could be achie,·cd. Reliable chromatography of the CFC 

replacements and the methyl halides has already been 

demonstrated within the HATS group by the flask, ocean, and in 

situ projects. Chromatograph) for PAN and acetone arc new 

concepts for the HATS group. This year, in collaboration with 

NOAA Aeronomy Laboratory, PAN was successfully separated 

from the air peak using a 5-m, 0.53-mm inside di ameter, megabore column with a 1-μm thick RTX 200 coating, cooled to 15°C. 

Output from this column was directed into the HP-GI 533A anodepurged ECO and the MSO. A detection limit of better than 3 ppt 

was demonstrated for the ECO, and an impressive detection limit 

or better than 0.8 ppt was demonstrated for the MSO using the 

chemical ionization source, with a flo" of 1 seem CHJ. 

Peroxypropionyl nitrate (PPN, CH3CH2C(0)-00N02) was also 

detected. 

A modest sensitivity to acetone was detected on the MSO; the 

ECO has no sensitivity to acetone. However, large (100 cm\ 

cryo-focuscd samples arc needed. A 30-m, 0.25-mm inside 

diameter HP-5MS capillary column was used with a 0.25-μm thick 

5% PH ME siloxane film to separate acetone and many of the 

HCFCs from the air peak. Using an electron ionization source and 

running the quadrupole in single ion mode, tuned to mass/charge 

(m/z) ratios of 58 and 43, a detection limit of I ppt was obtained 

for acetone. A detection limit of0.3 ppt for HCFC-141 bat m/z of 

81 was verified. No chromatographic interference was found 

when 50 ppm of O_, was dynamically mixed with the inlet stream. 

For ease, this work was done with a liquid N2 cryogen. Thermal 

electric coolers will be employed in the flight instrument. 

Calibration of ACATS-IV and LACE systems was achieved by 

in situ analysis of gas mixtures stored in Aculife-treated aluminum 

cylinders. ll1is method \\ill not work for PAN because it cannot 

be reliably stored as a gas mixture. An in-llight PAN source \\Ill 

be required for calibration. The generation or PAN from a 

calibrated NO source dynamically diluted to the ppt level was 

studied. PAN was produced by photolyzing acetone at 285 nm 111 

the presence of NO. Carbon monoxide was added to quench 

competing reactions. 

The third proof of concept area was to resolve incompatibilities 

between the HP MSO instrument control, data acquisition 

mvoh ing Chemstation on a Windows NT operating system 

utilizing an HPIB bus, and the airborne HATS approach usmg 

DOS "ith a metrobitc bus. The most recent GCs built within the 

HATS group arc the CATS GCs with QNX. Substantial 

development of reliable GC control and data acquisition was 

invested in this operating system. QNX requires a relatively small 

memory overhead compared to the NT operatmg system and is 

less prone to system crashes prevalent with the Windows NT 

environmc111. Both 1 IP-IB (IEEE) and RS-485 drivers for the 

QNX operating system cxis1. Usmg these dri,·crs the HP l\1SO 

runs entirely from QNX. ll1c new sman electrometers. gassamplc Ya!Yes. and the strcam-selccuon ,·ahc were moYed off ot 

the stack built b) Tommy Thompson and onto RS-232 and RS-485 

serial communication lines. reducing wiring and power 

requirements. This should result in an instrument that is lighter. 

easier to work with, and more dependable. 

108 

With these three issues resolved, the design and construction 

phase of the project will proceed in 2000. Validation fli ghts 

onboard the ER-2. WB-57F, or both will take place in 200 I. 

5.3. OCEAN P ROJECTS 

Observations 

The oceans play an important role in the atmospheri c budgets 

or halogenated, organic gases, both as sources and sinks. Natural 

halocarbons contribute a substantial amount of chlorine and 

bromine to the troposphere and, in some cases, the stratosphere. 

Methyl bromide (CH1Br) and methyl chloride <CH3CI) together 

contribute about one quarter of the total equiYalcnt chlorine to 

the atmosphere [Butler, 2000]. As the production and use or the 

anthropogenic, halogenated gases are phased out, methyl halides, 

which are primarily natural in origin. will play an increasingly 

important role in regulating stratospheric ozone. 
Other halogenated compounds, such as dibromomethane 

(CH2Br2) and bromoform (CHBr3), could be important sources 

of bromine to the stratosphere. While these compounds are 

generally present at low concentrations in the atmosphere and 

have short lifetimes, rapid vertical transport, particularly in the 

tropics, could provide a mechanism by which they could 

participate in stratospheric ozone depletion. An understanding 

of the sources and sinks of these compounds is needed to 

predict recovery of stratospheric ozone in the event of climate 

change. 

The HATS group participated in two research cruises during 

1998-1999 with the goal of quantifying the fluxes that constitute 

the oceanic cycle of CH3Br. On both cruises, conducted aboard 

the NOAA ship Ronald H. Brown, the group made saturation 

measurements in conjunction with CH3Br production and 

degradation measurements made by other groups. The first 

cruise, RB-98-02, Gas Exchange Experiment (GasEx 98), 

focused on the North Atlantic and coastal northeastern Pacific 

Oceans during May-July 1998 [King et al., 2000]. The cruise 

departed from Miami, Florida, and ended in Newport, Oregon, 

with port stops in Lisbon, Portugal, Ponta Delgada, Azores, and 

Miami, Florida (Figure 5.28). The focal point of this cruise was 

a month-long air-sea exchange experiment in a cold-core eddy 

northeast of the Azores. The second cruise, RB-99-06, Bromine 

Air-Sea Cruise Pacific (BACPAC 99), was conducted in the 

North Pacific during September-October 1999, departing from 

Kwajalein, Marshall Islands, and ending in Seattle, Washington, 

with port stops in Oahu, Hawaii, and Dutch Harbor. Alaska 

(Figure 5.28). 

During GasEx 98 CH3Br was supersaturated in temperate 

waters and undersaturated in tropical and subtropical waters 

(Table 5.10). Supersaturation implies a net flux from the ocean 

tu the atmosphere, while undersaturation implies the reverse. 

These trends were particularly evident during the third leg of the 

cruise from the Azores to Miami, as the saturation anomaly 

became more pronounced with decreasing latitude (Figure 5.29). 

The CH3Br supersaturations in the temperate northeastern 

90N 

GON 

30N 

Q) 

"Cl 

:J ON ....... 

~ _J 

30S 

GOS 

Atlantic Ocean during GasEx 98 differed from previous 

observations [Lobert er al., 1996; Groszko and Moore , 1998). 

Direct comparison of springtime supersaturations (23 ± 8%, 

standard error of the mean, s.e., King et al. (2000]) and fall 

undersaturations (-15 ± 4%, s.e., Lobert et al. [1996]) in the 

same region of the North Atlantic (37-45°N, 17-26°\V) suggests 

that there may be a seasonal cycle in temperate North Atlantic 

waters. When seasonal cycling in temperate waters is 

incorporated into global flux calculations, estimates of the net, 

global, air-sea flux ofCH3Br range from -11 to -20 Gg yr" 1 [King 

et al., 2000). This net CH3Br sink is not as strong as previously 

reported [Lober/ et al. , 1997), but the oceans are still estimated 

to provide an overall net sink for atmospheric methyl bromide. 

Methyl bromide was undersaturated throughout most of the 

BACPAC 99 cruise with supersaturations observed primarily in 

coastal regions (Table 5.10, Figure 5.29c). In general CH3Br 

was more undersaturated in the subtropics and closer to 

equilibrium in the temperate waters. The undersaturations in the 

temperate North Pacific during fall arc consistent with the 

existence of a seasonal cycle in temperate waters as suggested by 

observations in the temperate North Atlantic. The data from 

BACPAC 99 showed less variability than that from GasEx 98. 

While the precision during BACPAC 99 was significantly better 

than during GasEx 98 (2.6% versus 5.8%, I cr), this difference 

cannot completely explain the increased variability in the GasEx 

98 data. h is likely that the remaining variability was a result of 

natural processes in the North Atlantic at that time of year. 

Mean saturation anomalies for Cl-13Cl, methyl iodide (CH31), 

CH2Br2, and CHBr3 are provided from both GasEx 98 and 

BACPAC 99 on a regional basis (Table 5.10). In contrast to 

CH3Br, these trace gases were generally more supersaturated in 

the subtropics and tropics than in the temperate waters. Higher 

supersaturations of these compounds in the tropics are 

particularly important as tropical deep convection could 

transport these short-l ived compounds to the upper troposphere 

and lower stratosphere, where they could participate in 

stratospheric ozone depletion. 

90N 

GON 

30N 

r 

~ 

ON -;:::;.: 

c: 

a. 

(1) 

30S 

GOS 

90S .. 1.J...J...1 •• 1 • .l.1 .. 1.J..1 •. 1 • .l.1..l.J..1..1 . .l.1 .. 1.J .. 1 .. <.l..1 • .1.1 •• 1 •• 1.J •• 1 .• 1.1 •• 1.J..l •• 1.J..1.1 •• 1 •• 1 .. 1.J.. 1 .. 1 • .l.1 •• 1.J...1 •• 1.J •• 1 •• 1.1 .. 1 .. 1.J..1 .. 1.1 •• 1 .• 1.J •• 1 •• 1.1 •• 1.J 90S 

0 30 GO 90 120 150 180 210 240 270 300 330 3GO 

Longitude 

Fig. 5.28. Cruise tracks from RB-98-02 (GasEx 98) and RB-99-06 (BACPAC 99) and previous cruises (light gray) by the HATS group bemeen 1987 

and 1996. 

109 
TABLE 5.10. Average Measured Saturation Anomalies and Associated Standard Errors for Two Oceanic Regions From CMDL 

Cruises in 1998 (GasEx 98) and 1999 (BACPAC 99) 

Saturation Anomaly(%) Saturation Anomaly(?<) 

S(!rinpSummer 1998 Fall 1999 

Compound Subtropicsrrropics* Temperate• Subtropicsffropics* Temperate• 

CH,Br -12±2 37 ± 3 -35 ± I -19± I 

CH1CI 122 ± 3 37 ± I 7 1±3 2± I 

CH1l 5067 ± 11 0 :n51 ±65 2603 ± 78 111 3±37 

CH1Br1 334 ± 75 76 ± 3 33± 3 37 ± 2 

CH Br, 173 ± II 69 ± 3 230± 17 69±6 

~s ubtrop cs and tropics are defined as the region between 0° and 30°N, and temperate regions arc defined to be between 30° and 60°N. 

... 

- 20 

8: 15 

... 

:.;: 10 ... 

al 

:t 5 

u 

0 

60 

--. 

~ 40 ~ 

< 20 

20 25 30 

c 

c GasEx98 

a BACPAC99 

35 40 45 50 55 

~ I o GasEx98 I r, v a BACPAC99 

o~ C/) 

... 0 '--- . ~ ~~ 'o - a f 

:c 

M 

al -20 o~~o~J ~~ u -40 - ~v~ ~ 

-60 

20 25 30 35 40 45 50 55 

Latitude 

Fig. S 29. f\lelh) I bromide measurements in air (a) and air equilibrated 

with surface seawater (b). Saturation anomaly (c) is the percent difference 

between the panial pressure in water and air. Data from GasEx 98 are only 

shown from the third leg. between the Azores and Miami, Florida. Data 

from BACPAC 99 are only shown from the second leg, bemeen Hawaii 

and Dutch Harbor, Alaska. 

Temperature D ependence 

Gros:ko and Moore [ 1998] suggested that there is a 

relationship between methyl bromide concentrations in the 

surface water and sea surface temperature. CH3Br saturation 

anomalies were used from five CMDL research cruises to test 

this relationship for a wider range of waters (Figure 5.30a). 

The correlation observed from the CMDL data is similar to 

that reported by Gros:ko a11d Moo re [1998] with CH3Br 

supersaturated in ocean waters bet ween I I 0 and 21 °C. Based 

on this relationship, sea surface temperature can account for 

40-70% of the variability in CH.1Br satu ration anomaly on a 

global basis. Howeve r, only a small fraction of the observed 

seasonal cycle in temperate waters can be accounted for by 

the change in sea surface temperatu re f King et al. , 2000]. 

A global oceanic net flux of methyl bromide of - 14 Gg yr' 1 

can be calculated with the temperature relationship shown in 

Figure 5.30a and a global map of sea surface temperature, 

wind speed, solubility from De Bruy11 a11d Sal1:111a11 [1997], 

and a gas exchange coefficient based on the equation from 

Wanninklwf [ 1992]. This estimate falls within the range 

predicted by other methods [Lober/ et al .. 1997; King et al., 

2000]. However. it does not accurately describe the temporal 

and spati al distribution of dissolved CH3Br, especiall y in 

temperate waters, where widespread supersaturations are 

predicted year-round. Predicted supersaturations in 

temperate waters are not supported by data obtained from 

several field campaigns [lobert et al., 1995, 1996: Gros:ko 

and Moore, 1998], which indicates temperature is not the 

only variable controlling the concentration of CH3Br in 

surface waters. 

110 

Methyl chloride and methyl iodide have a different 

relationship to sea surface temperature than that of methyl 

bromide (Figures 5.30b and 5.30c). For both of these 

compounds, this relationship is best described with a linear 

regression. About three-quarters of the variability in the 

saturation anomaly of CH3CI can be explained by the 

variability in sea surface temperature. For CH31, only about 

one-half of the variabil ity in the saturation anomaly can be 

explained by the variability in sea surface temperature. Global 

maps of both CH3CI and CH31 will be created in the near future 

to estimate global air-sea fluxes for these compounds. 
300 

250 

~ ~ 200 

ct 150 

I/') 100 ... 

m 

M 50 

:x: 0 u 

~ 

~ 

~ 

~ 

I/') 

;:;; 

:x: 

(.) 

-50 

-100 

300 

250 

c 200 

~ 150 

u 100 M 

:x: 50 

u 

0 

-50 

12000 

10000 

8000 

6000 

4000 

2000 

0 

-2000 

a 

-5 0 5 10 15 20 25 30 35 

Sea Surface Temperature (C) 

b 

-5 0 5 10 15 20 25 30 35 

Sea Surface Temperature (C) 

,-, ----

c 

~~-~ ---

-5 0 5 10 15 20 25 30 35 

Sea Surface Temperature (C) 

Fig. 5.30 Corrdations bcl\\een the saturation anomalies of the meth)I 

halide' (methyl bromide (a). 111e1hyl chloride (b). and meth)I iodide (c)) 

and sea surface temperature based on data from li ve CMDL research 

cn11ses between 199.J and 1999. 

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Butler. J.H .. et al., 5. Nitrous Oxide and Halocompounds, in Climate 

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Cummings, Global tropospheric distribution and calibration scale of 

HCFC-22, Geoplrys Res. le11 .. 20, 703-706. 1993. 

Montzka. S.A .. R.C. Myers, J.H. Butler. and J.\V. Elkins, Early trends in 

the global tropospheric abundance of hydrochloronuorocarbon-141 b 

and -I 42b, Geoplrys. Res. Lett., 21, 2483-2486. 1994. 

Montzka. S.A., J.H. Butler, R.C. Myers, T.M. Thompson, T.H. Swanson, 

A.O. Clarke, L.T. Lock, and J.W. Elkins, Decline in the tropospheric 

abundance of halogen from halocarbons: Implications for 

stratospheric ozone depiction, Science. 272. 13 18-1 322, I 996a. 
Monti:ka, S.A., R.C. Meyers, J.H. Butler, J.W. Elkins, L.T. Lock, A.O. 

Clarke, and A.H. Goldstein, Observations of HCFC-134a in the 

remote troposphere, Geophys. Res. Leif .. 23, 169-172. I 996b. 

Montzka. S.A., J.H. Butler, J.W. Elkins, T.M. Thompson. A.D. Clarke. 

and L.T. Lock, Present and future trends in the atmospheric burden of 

ozone-depleting halogens, Nature, 398, 690-694, I 999a. 

Montzka, S.A .. J.H. Butler, J.W. Elkins, L. Lock, and D. Mondecl, 

Seasonal and inter-annual variability of methyl bromide and methyl 

chlonde from a global flask sampling network. Eos Tm11s. AGU, 

80(46), Fl.t9, 1999b. 

Montzka. S.A., C. M . Spivakovsky. J. H. Butler. J.W. Elkins. L.T. Lock, 

and D.J. Mondeel. New observational constraints for atmospheric 

hydroxyl on global and hemispheric scales, Sne11ce. 288, 500-503, 

2000. 

Mote. P.W .. K.H. Rosenlof, M.E. Mcintyre, E.S. Carr, J.C. Gille. J.R. 

Holton. J.S. Kinnersley, H.C. Pumphrey, J.M. Russell Ill. and J.W. 

Waters, An atmospheric tape recorder: The imprint of tropical 

tropopause temperatures on stratospheric water ''apor. J. Geophys. 

Res .. JOI, 3989-4006. 1996. 

l\ovelli. P.C., J.W. Elkins. and L.P. Steele. The development and 

evaluation of a gravimetric reference scale for measurements of 

atmospheric carbon monoxide, J. Geophys. Res .. 96, 13.109- 13, I 2 I. 

1991. 

Novelli. P.C., P.M. Lang, K.A. Masarie, D.F. Hurst, R. Meyers, and J.W. 

Elkins. Molecular hydrogen in the troposphere: Global distribution 

and budget, J. Geophys. Res., 104, 30,427-30 . .\44, 1999. 

Prather. M.J., and C.M. Spivakovsky, Tropospheric OH and the lifetimes of 

hydrochlorofluorocarbons, J. Geophys. Res .. 95, 18.723-18.729. 1990. 

Ravishankara, A.R., and D.L. Albritton. Methyl chlorofor111 and the 

atmosphere. Science. 269. 183- 184, 1995. 

Ray. E.A., F.L. Moore. J.W. Elkins. G.S. Dutton. D.W. Fahey. H. 

Yti111el. S.J. Oltmans, and K.H. Rosenlof. Transpon into the nonhem 

he111isphere lowermost stratosphere revealed by in situ tracer 

111easure111cnts. J. Geophys. Res.. 104, 26.565-26580. 1999. 

Romashkin, P.A .. D.F. Hurst. J.W. Elkins. G.S. Dutton, and P.R. 

Wamsley. Effect of the tropospheric trend on the stratospheric tracertracer correlallons: l\lethyl chlorolor111 , J. (;eophrs. Res., 104. 26,643-

26,652, 1999. 

Sen. B .. G.B. Osterman. R.J. Salawitch, G.C. Toon. J.J. Margitan, J.-F. 

Blavicr, A.Y. Chang. R.D. May. C. R. Webster, R.M. Sti111pflc. G.P. 

Bonne, P.B. Yoss, K.K. Perkins. J.G. Anderson, R.C. Cohen, J.\Y. 

Elkins. G.S. Dutton, D.F. Hurst. P.A. Romashkin, E.L. Atlas. S.M. 

Schaufner, and M. Loewenstein. The budget and partitioning of 

stratospheric chlorine during the 1997 Arctic summer, J. Geophys. 

Res., 104, 26,653-26,665, 1999. 

Spivakovsky, C.M., J.A. Logan, S.A. Montzka, Y.J. Balkanski, M. 

Foreman-Fowler, D.B.A. Jones, L.W. Horowitz, A.C. Fusco, C.A.M. 

Brenninkmeijer, M.J. Prather, S.C. \Yofsy, and M.B. McElroy. Threedimensional climatological distribution of tropospheric OH: Update 

and evaluation, J. Geophys. Res., 105. 8931-8980, 2000. 

Swanson. T. H. et al., 5. Nitrous Oxide and Halocarbons Division, in 

C/i111111e Mm1itori11g a11d Diagnostics Laboratory S11111mary Report No. 

21. 1992, J.T. Petersen and R.M. Rosson (eds.). 59-75. NOAA 

Environ. Res. Labs., Boulder, CO, 1993. 

Toon. G.C .. J.-F. Blavier. B. Sen, J.J. Margitan, C.R. Webster, R.D. May. 

D. Fahey. R. Gao. L. Del Negro. M. Proffitt. J. Elkins, P.A. 

Romashkin. D.F. Hu rst. S. Olunans. E. Atlas. S. Schaufner, F. Flocke. 

T.P. Bui, R.M. Stimpfle. G.P. Bonne, P.B. Yoss, and R.C. Cohen, 

Comparison of MklY balloon and ER-2 aircraft measurements of 

atmospheric trace gases, J. Geophys. Res .. 104. 26,779-26,790, 1999. 

United Nations Environmental Programme (UNEP), Montreal Pm111wl 

111 Reduce Substances that Deplere the O~o11e Layer Report, IS pp., 

UN, New York, 1987. 

Yolk. C.M., J.\Y. Elkins, D.\Y. Fahe}. G.S. Dutton, J.M. Gilligan, t\I. 

Loewenstein, J.R. Podolske, K.R. Chan. and M.R. Gunson, Evaluation 

of source gas lifetimes from stratospheric observations. J. Geophn. 

Res., 102, 25,543-25,564. 1997 . 

\Yanninkhof. R .. Relationship between wind speed and gas exchange 

O\'er the ocean, J. Geophys. Res .. 97. 7373-7382, 1992. 

Woodbridge. E.L.. J.W. Elkins, D.W. Fahey, L.E. Heidt. S. Solomon. 

11 2 

T.J. Baring. T.M. Gilpin. \Y.H. Pollock. S.1\1. Schaufner, E.L. Atlas. 

M. Loewenstein. J.R. Podolske, C.R. Webster. R.D. May. J.M. 

Gilligan. S.A. Montzka, K.A. Bocring. and R.J. Salawitch. Estimates 

of total organic and inorganic chlorine in the lower stratosphere from 

in situ and flask measurements during AASE II, J. Geophys. Re.\., 

JOO, 3057-306.t, 1995. 

Yokouchi, Y., Y. Noijiri. L.A. Barrie. D. Toorn-Sauntry. T. Machida, Y. 

lnuzuka. H.-J. Akimoto. Y. Fujinuma. and S. Aoki, A strong source of 

methyl chloride lo the aunosphere from tropical coasrnl land. Nm11re. 

403. 295-298. 2000. 
6. Cooperative Programs 

UV Spectroradiometer Monitoring Program: Influence of Total Ozone, 

Cloud Cover and Surface Albedo on UV Doses in Barrow, Alaska 

G. B ERNHARD, C.R. B OOTH, J.C. E HRAMJIAN, S.A. LYNCH, AND Y.V. QUANG 

Biospherical ln.11r11111e1J1s Inc., San Diego, Califomi11 92110-2621 

INTRODUCTION 

The United States National Science Foundation's (NSF) 

Ultraviolet Spectroradiometer Monitoring Network for Polar 

Regions was established in 1988 to collect data on the 

consequences of ozone depletion. The network cu rrently 

consists of several automated, high-resolution spectroradiometers (Table 1 ). Three network stations are located in 

Antarctica, including the CMDL site at the South Pole 

Station (SPO). Another instrument is deployed close to the 

CMDL facility in Barrow, Alaska (BRW). Additional 

instruments are located in Ushuaia, Argentina, and San 

Diego, California; the latter serves as a training and testing 

facilit). Finally, a portable system is available for instrument intercompansons. Now in its thirteenth year of 

operation, the net work continues to make measurements of 

ultraviolet (UV) spectral irradiance and provides a variety of 

data products to quantify biologically relevant UV exposures. 

Biospherical Instruments Inc. is responsible for operating and 

maintaining the network and distributing data to the scientific 

community. 

The network is equipped with Biospherical Instruments 

Inc. Model SUV- I 00 spcctroradiometers. Each instrument 

contains a double monochromator with holographic gratings 

and a photomultiplier tube detector. A vacuum-formed 

Teflon diffuser serves as an all-weather irradiance cosine 

collector. All systems are temperature stabilized for optimum 

radiometric stability. Spectra are sampled automatically 

every IS minutes between 280 and 600 nm with a spectral 

bandwidth of 1.0 nm full width at half maximum. Tungstenhalogen and mercury vapor calibration lamps are used for 

daily automatic internal calibrations of both responsivity and 

wavelength registration. All instrument functions, calibration 

activities, and solar data acquisition are computer controlled. 

Further details on the spectroradiometers are described by 

Booth er al. [ 199-t, 2000 ]. 

UV RADIATION CLIMATEATTHESPO AND BRW 

NETWORK INSTALLATIONS 

This report focuses on data from the CMDL facil ities at the SPO 

and BRW network installations. 111e SPO site is characterized by 

very high surface albedo throughout the year. Clouds are usually 

thin and clear sky days are relatively frequent. Because of the stable 

weather conditions, the high air purity, and high latitude, SPO is an 

ideal place to study the influence of variations in total column 

ozone on UV irradiance [Boorli a11d Madronich, 1994]. 

The conditions at BRW are quite different from SPO. Cloud 

cover is highly variable, and significant changes in surface albedo 

occur because of both the springtime snowmelt [D111ro11 and 

Endres, 1991] and changes in sea ice coverage. Also, Barrow 

experiences significant changes in incident irradiance because of 

Arctic storms. 

Figure I contrasts the radiation pattern of both sites. Timcseries of integrated spectral irradiance at local solar noon arc 

rlepicted for t\\O wavelength bands covering 1991-1999. One 

spectral band (Figure I a) represents DNA-weighted irradiance 

calculated from measured solar spectra and the action spectrum 

for DNA damage suggested by Ser/ow [ 1974]. DNA-weighted 

irradiance has a high contribution from wavelengths in the UV-B 

and is, therefore, very sensitive to changes in atmospheric ozone 

concentrations. The other band (Figure I b) is spectral irradiance 

in the visible part of the spectrum, integrated between -tOO and 

600 nm. From Figure I b it is evident that visible radiation at 

SPO shows little variation from year to year. Moreover, 

irradiances in this wavelength band arc usually close to the 

envelope formed by the clear-sky level, confirming that cloud 

influence at SPO is small. In contrast, irradiances in the -t00-

600 nm band at BRW show a high variability because of day-today changes in cloud cover. The cloud influence is clearly more 

pronounced in the second part of the year. Because of the 

diffe rence in latitude, radiation levels in the visible part or the 

spectrum are usually lower at SPO than at BRW. 

TABLE I. Installation Si tes 

Site 

South Pole 

McMurdo Station 

Palmer Station 

Ushuaia. Argentina 

Barrow, Alaska 

San Diego, California 

Latitude 

90°00'S 

77•51 ·s 

64°46'5 

54°49'5 

71°18'N 

32"45'N 

Longit ude 

l66°40'E 

64"03'\V 

68°19'\V 

156°47'\V 

117°11'\V 

Establish.:d 

February 1988 

March 1988 

May 1988 

November 1988 

December 1990 

October 1992 

•ARO: Atmospheric Research Observatory, system relocated to this new, joint NSF/CMDL facility in January 1997. 

tCADIC: Centro Austral de lnvestigaciones Cicn1ificas, Argentina. 

:j: UIC-NARL: Ukpeagvik lnupiat Corporation-Naval Arctic Research Laboratory. 

11 3 

Location 

ARO• 

Arrival Heights 

T-5 Building 

CAD IC' 

C-NARL~ 

Biospherical lnstrumen1s Inc. 
(a) 

DNA Weighted lrradiance 

'E 0.2 0 

~ 0.18 

.: 0.16 

- -1- South Pole 

Barrow 0 

0 0.14 c 

~ 

~ 0.12 ~ 

... 0.1 .!:: 

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

-

"ti 

0 0.08 - ~-

~ OI 0.06 

·o 

~ 0.04 

< 0.02 z 

0 0 

i ...., l I 

I I 

~ , I 

~ 'V r J ~ ' I t ~11 t II \ 

01 -Jan-91 01-Jan-93 01 -Jan-95 01-Jan-97 01-Jan-99 

Date 

(b) 

400 - 600 nm Integrated Spectral lrradiance 

"e 

.!:! 30000 ~ 

.: 

0 25000 0 

-south Polel -- c 

~ 

~ 20000 

~ 

.!:: 

l 

~ 

' 

Barrow I 

- I 

I 

' 

I 1 .. 

01-Jan-91 01-Jan-93 01-Jan-95 01 -Jan-97 01-Jan-99 

Date 

I 

i 

Ftg I Local solar noonurnc integrated spectral 1rrad1ancc at South Pole and Barrow for 1991 -1 999· (a ) DNA-weighted irrad1ancc and (b) visible 

1rradmnce (400-600 nm integral). Note that 1999 data arc preliminary and subject to re\ision 

In contrast to v1~ible radiation, DNA-weighted 1rradiance at 

SPO <Figure I a) shows high day-to-day fluctuations because of 

the ozone influence. For example, the peak in DNA-weighted 

irrad1ancc obser,ed at SPO in late November 1998 is due to 

extraordinarily low total column ozone values and the 

comparative!) high solar elevations prevailing duri ng this part of 

the year. 

I NFLUENCE OF OZONE, C LOUD COVER, AND A LBEDO ON 

RADIATION DOSES IN BARROW 

Figure 2 shows daily doses calculated from both DNA-weighted 

irradiance data and irradiance measurements in the 400-600 nm 

band. In order to remove year-to-year variability, both doses were 

averaged over 1991- 1997. 

The average daily DNA-weighted dose is qune symmetrical with 

respect to the solstice (June 2 1) (Figure 2). The average daily 

"E Daily Doses Barrow ::; 

~ 8000 0.03 

c Average of years • · - Daily 400·600 nm "E .2 7000 1991-1997 Dose ;; - Daily DNA Dose 0.025 ::; 

:;; :!!. 

~ 6000 0 

0.02 .. ~ 0 5000 / c 

e "ti 

r 4000 O.Q15 ! 

&. J ti .E 3000 i 0 E I 0.01 il c 

0 2000 I < 0 - z 

" 0.005 c 0 1000 0 .?- .. ii ~ 0 0 c .. 

0 !-Jan 2·Mar 2-M ay !-Jul 31 ·Aug 30-0ct JO.Dec 

Date 

Fig. 2. Daily doses at BR W averaged from 199 1-1997. The dashed line 

(left axis) is the average daily dose in the 400-600 nm band; the solid line 

(right axis) is average daily DNA-weighted dose. 

114 

dose in the visible band, however. appears to be shifted b) 

approximately 14 days towards spring. Figure 3 shows this 

asymmetry more clearly. Herc, both doses of Figure 2 were 

mirrored at the solstice. and the ratio of spri ng-to-fall values was 

calculated. The resulting ratios depicted in Figure 3 arc, therefore, 

independent from solar Lcnith-anglc dependence and normalized to 

I at the solstice. Average closes rn the -l00-600 nm band appear to 

be a factor of 2 higher in spring than in fall. DNA-weighted doses, 

on the other hand, do not show a clear spring-fall asymmetry. 

The spring-fall ratio for the DNA-weighted dose derived from 

the measurements was compared with analogous ratios that were 

computed from the expected in fl uence of ozone, cloud cover, and 

surface albedo on the DNA-weighted dose (Figure 4). Li ne I in 

Figure 4 is identical to the measured DNA ratio in Figure 3. Line 2 

rellects the spring-fall DNA ratio that would be expected if the 

seasonal cycle in total column ozone was the only parameter affecting 

the DNA dose. This curve was calculated with Total Ozone 

2.5 c 

:::> 

7 

~ 

2 ----- --~ N 

/, : :I \ I ;', 

.g ;\, ·. 1" \ 11 1.5 ~-----~-...-~,....-

0:: 

Spring I Fall 

0 50 100 150 

· · · Asymmetry 400·600·nm 

dose 

- Asymmetry DNA·dose 

Fall I Spring 

200 250 300 350 

Julian Day 

Fig. 3. Spring-fall asymmetry o f the radiation doses in BRW. The 

dashed line is the spring-fall ratio for the 400-600 nm dose; the sohd line 

is the analogous ratio for DNA-weighted dose. 
4 

-(!)-Measured asymmetry DNA-dose 

3.5 0 Ozone effect 

3 -@ Cloud effect 

-@Albedo effect 

2.5 ©ozone x Cloud x Albedo 

~ I "•.J; 0 

2 "' ~: ~ 0:: 

1.5 

0.5 

0 

0 50 100 150 200 250 300 350 

Julian Day 

Fig. 4 . Explanation of spring-fall differences in the average daily DNAdose at BRW Line I: Measured spring-fall ratio of 1he DNA-dose Line 

2: Expec1ed spring-fall ra1io from 1hc annual cycle in total column ozone. 

Linc 3: Expected ratio from the seasonal cycle in cloud cover. Line 4: 

Expected ratio from the seasonal differences in albedo. Linc 5: Product 

of ozone. cloud, and albedo innuenccs. Linc 5 is similar to line I. 

indicating that the measurements can be well explained by the innucnce 

of the three fac tors. 

Mapping Spectrometer (TOMS) total ozone data and a 

parameterization of the anti-correlation of ozone and UV suggested by 

Boo1h and Madronich (1994] with a radiation amplification factor of 

2.2. With the presumption that all atmospheric parameters, except 

ozone. were constam throughout the year. line 2 indicates the DNAwetghted dose is a factor of 2.'i higher in fall than in spring. TI1is 

large difference can be explained by the fact that total column ozone at 

Barrow is about I SO DU lower in fall than in spring. 

Line 3 in Figure 4 shows the spring-fall DNA ratio that would be 

expected from the annual cycle in cloud cover if clouds were the only 

parameter affecting UY. Cloud cover data provided by the National 

Climatic Data Center ows the relationship between cloud cover and 

attenuation of DNA-weighted irradiance, and was paramete1ized 

according to Thiel e1 al. [ 1997], assummg stratocumulus clouds are 

prevailing. Line 3 indicates that DNA do~es can be expected to be 

higher in spring by about a factor of 2 because of tewer clouds in the 

first pan of the year. Thus the annual cycle in cloud co\'er panly 

cancels out the innuence of the ozone cycle. 

Variability in ~urface albedo is another imponam parameter 

affecting DNA irradiance at BRW. Albedo measurements from BRW 

indicate that the ground is completely covered by snow between the 

beginning of November and the end of May (D1111on and Endres, 

1991 ]. According to data from the National Ice Center the adjoining 

ocean is covered by sea ice during approximately the same period, 

thus causing high albedo beyond the immediate vicinity of the 

measurement site. Comparisons of SUV- I 00 spectral measuremems 

to radiative transfer model calculations show that the effective UV 

albedo is 0.85 during this period. This causes an increase of DNAweighted irradiancc of about 52% compared to snow-free conditions 

that prevail in Barrow between the beginning of July and midSeptember. Finally, line 4 in Figure 4 indicates the spring-fall ratio of 

the DNA dose that can be expected from the albedo variability. 

By multiplying the spring-fall ratios that were calculated previously 

for the effects of ozone. clouds, and albedo on the DNA dose, 

the combined innuence of all three paran1eters was determined. The 

resulting product is line S in Figure 4. The curve is very similar to the 

measured spring-fall asymmetry in the DNA dose (line I), indicating 

that the measurement can be well explained by the seasonal cycles of 

the three factors. Remaining deviations arc pa11ly due to the simple 

parameterizations applied. For example, nonlinear interference of 

albedo and cloud renections were not taken into account. In addition 

not all time-series were complete for the 1991-1997 period; for 

example, no TOMS data exist for 1995. 

SUMMARY 

High spectral resolution scanning UV spectroradiometers have 

been established at six sites, including SPO and BRW, and are 

successfully providing multi-year data sets. The database is now 

sufficiently large to investigate the UV climatology at all sites beyond 

year-to-year variability. This has been demonstrated for Barrow, 

where data from 1991-1997 were used to analyze the impact of ozone. 

cloud, and albedo variations on biologically relevant levels of DNAweighted daily doses. 

Data from the network are distributed by Biospherical Instruments 

Inc. via CD-ROMs and the lmemet to interested researchers. 

Investigations based on this dataset were published or referenced by 

scientists from around the world in more than I 00 peer-reviewed 

publications. TI1e Data and Network Operation Repon ordering, more 

detailed information on the deployed instrumemation, and an 

extensive list of references are available on the website 

(hllp://www.biospherical.com). 

115 

Ack11owledg111e11ts This research and monitoring activity was established 

under the guidance of P. W1tkniss. fonncr Directo1 of the NSF Office of Polar 

Programs. The network is operated and maintained under the contract OPP89-22832 of NSF-OPP (Contracting Officer P. Penhalc) wllh subcontracts to 

Anlarcllc Suppon Associates (ASA) and Ra)1hcon Polar Services. Cordial 

thanks 10 the curn:nt Barrow operators D. Endres and M. Gaylord (CMDL). 

The Ukpeagvik lnupiat Corporation of Barrow provided assistance in the 

original installation. Operators at Palmer, South Pole and McMurdo ''en.: 

pro\ided by ASA. Albedo data from Barrow were provided by E. Dutton and 

D. Longenecker (CMDL). 

REFERENCES 

Boo1h. C.R.. and S. Madronich. Radiation amplification factors: 

Improved formulation accounts for large increases in ultraviolet 

radiation associated with Antarctic ozone depletton. edited b) C.S. 

Weiler and P.A. Penhale. A111arc1. ReJ. Ser .. 62, 39-42, 1994. 

Booth. C.R .. T.B. Lucas. J.H. Morrow, C.S. Weiler. and P.A. Penhale, 

The United States Na1ional Science Foundation's polar network for 

monitoring ultra\ iole1 radiation. edited by C.S. Weiler and P.A. 

Penhale, A111am. ReJ. Ser., 62, 17-37, 1994. 

Booth, C.R .. G. Bernhard, J.C. Ehramjian. L.W. Cabasug, V.V. Quang. 

and S.A. Lynch. NSF Polar Pm1v11111J UV Spec1mradi11111e1er Ne11rnrk 

1997-1998 Opermi1111J Report, 233 pp., Biospherical Instruments Inc .. 

San Diego, 2000. 

Dutton, E.G .. and D.J. Endres, Date of snowmelt at Barro\\, Alaska. 

U.S.A .. Arctic Alpine ReJ., 23( I). 115-119, 1991. 

Se1low. R.B., The wavelength in sunlight effective in producing skin 

cancer· A theoretical analysis. Proc. Nwl. Arnd. Sci .. 71(9), 3363-

3366. 1974. 

Thiel. S .. K. Steiner. and H.K. Seidlitz. Modification of global cry1hemal 

effective irradiance by clouds, Pho1oche111. Plw111bi11l .. 65(6). 969-973, 

1997. 
Whole Air Sampling at Barrow, Alaska 

DONALD R . BLAKE AND F. SHERWOOD ROWLAND 

U11i1-ersity oJCalifomia. ln·i11e 92697-2025 

The University of California-Irvine (UCI) has been collecting 

whole air samples at the NOAA Climate Monitoring and 

Diagnostics Laboratory (CM DL) station at Barrow, Alaska, since 

April 1983. The Barrow measurements are the northernmost 

sampling site of the UCI global CH4 monitoring network that 

extends from 7 1°N to 47°S. The UCI and CMDL CH4 networks 

have a second co-located sampling site in Samoa. 

In the UCI sampling strategy, approximately 60-80 whole air 

samples are collected over a 3-wk period in 40-45 locations four 

times a year (usually March, June, September, and December). 

Of these samples, four or live are collected in Barrow, usually 

over a 2-3 day period. The air samples are collected in 

conditioned, evacuated 2-L stainless steel canisters equipped 

with a single stainless steel bellows valve. During sampling, the 

canister is filled to ambient pressure over a period of about I 

minute. At the end of the collection period the sampling 

canisters arc returned to the UCI laboratory for analysis. 

The CH4 mixing ratio within an air sample is determined by 

gas chromatography (HP-5890A) with !lame ionization 

detection. The CH4 mixing ratios are reported for dry air relative 

to primary standards purchased in 1977 and a National Institute 

of Standards and Technology (NIST) (formerly known as the 

National Bureau of Standards (NBS)) standard purchased in 

August 1982. The uncertainty in the NIST standard is ±I%. The 

analytical precision is determined from intersample comparisons 

that are obtained by alternating measurements of secondary 

standards with aliquots from an individual air sample. The UC! 

analytical precision was 3 ppbv in the 1980s and is currently 

better than 2 ppbv. Data points are individually inspected, and 

points that do not represent remote values arc removed from 

further analysis. 

The UCI global CH4 monitoring program complements the 

fixed station network of the CMDL program. The UCI sampling 

strategy emphasizes intense latitudinal sampling over a short (3-

wk) period while sacriticing the knowledge and statistical 

confidence gained from multiple or continual measurements at 

individual sites. The UCI sampling locations are not fixed, and 

sampling personnel scout out the best location and time for a 

remote air sample according to the prevailing physical and 

meteorological conditions. As a result, the method has the 

llexibility to easily switch sampling sites if local contamination 

is suspected. 

Individual CH4 mixing ratios measured at Barrow by UCI 

over the 2-yr period from March 1998 to December 1999 are 

shown in Figure I. Unlike the other sites in the UCI monitoring 

network, the Barrow and Samoa sampling locations are tixed at 

the CMDL stations. As a result, the CH4 mixing ratios measured 

at these sites arc sometimes elevated as a result of local 

contamination. At Barrow local contamination can occur when 

the prevailing wind is from the direction of town rather than 

from the ocean or tundra. During 1998-1999 the measurements 

collected in September 1998 and March 1999 were elevated as a 

result of local contamination and have not been included in 

Figure I. Indeed, the CH4 mixing ratio exceeded 2 ppmv in two 

of the UCI samples collected in September 1998. The CMDL 

measurements were similarly elevated at this time, confirming 

that the enhancements were real and not a result of measurement 

error. 

The remaining six sets of seasonal data generally show very 

low variability within a given season (Figure 1 ). The 

measurement precision (2 ppbv) is roughly the same size as the 

data points that have been plotted, and the difference among the 

data points within a given season represents real variability, 

rather than measurement error. The mixing ratios over the 2-yr 

period show a characteristic seasonal pattern with a summertime 

minimum and a winter maximum (Figure I). 

The CMDL and UCI networks are two of just three global 

monitoring networks for tropospheric CH4 . The overlapping 

sampling at Barrow provides a valuable opportunity for 

measurement intercomparison. Over the years we have found 

that the UC! CH4 mixing ratios typically exceed those of the 

CMDL network by -20 ppbv. The difference is caused by an 

offset in the calibration scales used by the two groups. A 

scaling factor of 0.989 would make the UCI measurements 

agree with the CMDL values. Many other groups require 

similar scaling factors, again as a result of different calibration 

scales that are used (e.g., Atmospheric Environment Service 

(AES) Canada, Institute of Atmospheric Chemistry (IAC) 

China, Ente per le Nuove Tecnologie, !'Energia e l'Ambiente 

(ENEA) Italy, National Institute for Water and Atmospheric 

Research (NIWA) New Zealand; see http://www.cmdl. 

noaa.gov/ccgg/global view/ch4/methods. html). 

11 6 

1.89 

1.88 

1.87 ' 

> 

E 1.86 • a. 

a. • 

"" 1.85 • 

I 

u • 

1.84 • • • • • 1.83 • • 

1.82 

1998 1998.5 1999 1999.5 2000 

Date 

Fig. I. Methane mixing ratios (ppnw) measured by !he University of 

California- Irvine (UCI) at the NOAA Cl\IDL station in Barrow, Alaska, 

between March 1998 and December 1999. Mixing ratios measured in 

September 1998 and March 1999 were enhanced by local contaminaiion 

and have not been included in !he graph. 
Correlation Between Anthropogenic Aerosols and Gases at MLO 

THOMAS A. CAHILL, STEVENS. CUFF, THOMAS M. CAHILL 

DELTA Group. University o/Califomia, Dm•is 95616-8569 

KEVIN D. PERRY 

Depar1111e111 o/Meteomlogy. San Jose Swre U11frersi1y, Ca/ifomia 95192 

The recent availability of size- and time-resolved aerosol data 

at the CMDL Mauna Loa Observatory (MLO) [Pen)' er al., 

1999) allows for comparison with gas and aerosol measurements 

made routinely at MLO. The three-drum DELTA IMPACTOR 

instrument is the prototype of the unit being proposed for many 

Pacific sites for the Aerosol Characterization Experiment (ACE)-

Asia study in spri ng 2001. Fine mass was established both 

gravimetrically and as a sum of all measured species, and was 

highly correlated with aerosol scattering coefficients (O,r). 

Using NOAA trajectory analysis and trace element analysis, the 

period of May 8-22, 1996, was divided into five classifications: 

(I) oceanic, in which the trajectory remains over the ocean for at 

least 12 days, (2) North Asia, including Japan, (3) Central Asia 

I (north of the Yangtze Ri ver), (4) Central Asia 2 (south of the 

Yangtze Ri,er), and (5) Central America. All data. gas, and 

aerosol were averaged in these categories, and a ratio to 

i 

~ tfBllttl.t J.ll______,__ tigtN sp •9N AP CN · :ZSO Rn 2U CH4 · t110 CO tulitd COZ ucus 

Gu •ndAero•ofCompon.nt.s 

•North Asia = Cttntral Asl1. ( 1) • Central Aaia (2) Central America 

Fig. I. Air mass trajectory analysis combined with aerosol and gaseous 

data. Ratio of ga\ and aerosol components to oceanic periods at M LO, 

May 1996 (nighuime winds only). 

the values in oceani c periods was calculated (Figure I). The 

C02 excess value was the C02 data with the average annual rate 

of rise over I 0 years removed, leaving the strong annual cycle. 

The CO and methane data have a constant value removed to 

emphasize the vari ability over the 2-wk period. With the 

availability of high time resolution data, we can now attempt to 

combine the aerosol data, trajectory analysis, optical parameters 

for scattering (O,r) and absorption (o,r), gases such as C02, 

methane, and CO, and tracers such as Radon 222 into a single 

statistical package. 

Trajectory analysis s hows increased values for all parameters 

when compared to oceanic periods, with particularly large ratios 

for C02 from North and North-Central Asia and optical 

scattering from Central America. Central American transport 

coincided with large peaks of sulfates and biomass smoke. The 

satellite imagery of the May 1996 dust event is convincing proof 

of the impact of these major dust events on the Earth's albedo. 

Additional data are required, however, to ascertain if the lower 

free tropospheric sulfates, organics, and soot particles have an 

impact. 

An absolute principal components analysis (PCA) was 

performed on the data. Two trajectories both anchored in the 

"'Oceanic"' conditions summarize the entire 2-wk period. 

Surprisingly, the midlatitude transport from middle and southern 

China has almost the same statistical signature as that from 

Central America. In general, trace element analysis "ill aid in 

source identification as trace elements are highly indicative of 

particular sources. Thus it appears that MLO is heavily 

inOuenced by anthropogenic sources around the Pacific Rim, 

making MLO a unique and valuable diagnostic site for future 

changes in Asian and American air pollutants. 

11 7 

R EFERENCE 

Perry. K.D., T.A. Cahill. R.C. Schnell. and J.1\1 Harns. Long-range 

transport of anthropogenic aerosols to the NOAA Baseline Station at 

/\fauna Loa Observatory. Hawaii. J. Geophys. Res.. JO./, 18.521-

18,53:\. 1999. 
NIWA Lauder NDSC UV /Visible Measurements at the Mauna Loa Observatory 

PAUL JOHNSTON 

Nmio11al /11s1i1111efor \Vatera11d Atmospheric Research (Nl\VA), Lauder, New Zealand 9182 

The National Institute of Water and Atmospheric Research 

(N l\V A) started Network for the Detection of Stratospheric 

Change (NDSC) certified ultraviolet (UV)/visible spectroscopic 

measurements of stratospheric nitrogen dioxide (N02) in July 

1996 at the NOAA Mauna Loa Observatory (MLO). These 

measurements continued with the same instrument through 1999. 

Some degradation of data quality occurred between February and 

October because of the failure of a mechanical coupling in the 

wavelength drive rotator mechanism. This was rectified in 

October when a NIWA scientist visited MLO to help diagnose 

radio interference in the NIWA UV spectroradiometer operating 

there. On subsequent examination of the coupl ing at Lauder, it 

ll'as determined that the failure was caused by volcanic dust that 

had penetrated the spectrometer box. Although the presence of a 

problem was diagnosed in March using standard quality-control 

procedures, it was not possible to implement repairs earlier than 

October. Fortunately the fa ilure did not significantly compromise the value of the N02 measurements over this period 

with the measurement random errors increasing by less than a 

factor of 2 over those normally expected. 

In December 1999 a new UV /visible spectrometer was 

installed to measure stratospheric bromine monoxide, an 

important species in current attempts to model future nonpolar 

ozone trends. In addition to this new instrument, a second N02 

measuring spectrometer was also installed in the NDSC 

building. It is planned to operate both N0 2 spectrometers for 

several months to provide a good overl ap for intercalibration. 

The two new spectrometers are monitored and controlled over 

the Internet from Lauder, minimizing the work of MLO staff. 

The only routine task required is the cleaning of the two 

viewing windows. 

Archiving of UV/visible data measured at MLO in the NDSC 

database has continued as required. 

No publications have used just the MLO UV/visible data to 

date. However, global ground-based and satellite-derived N02 

climatological studies are using the NDSC archive data sets. 

11 8 
Operation of Brewer Instruments at Mauna Loa Observatory 

J.B. KERR 

Meteomloi.:ical Sen•ice o[Cwwdo. E111'ir1111111ent Cwwd11. Dm1·11wiell'. 0111ari11. Ca11ada MJH 5T./ 

Two Brewer instruments continue to make measurements at 

the Mauna Loa Observatory (M LO) in support of the Brewer 

Instrument World Calibration Centre at the Meteorological 

Service of Canada (MSC) site in Downsview, Ontario [Kerr el 

al., 2000). A single monochromator (instrument no. 9) and a 

double monochromator (instrument no. 119) have been 

measuri ng direct solar, zenith sky and global ultraviolet radiation 

on most days during 1998 and 1999. The instruments are 

programmed and controlled from Downsview. where the data are 

sent automatically on a daily basis, and routine maintenance and 

calibrations are carried out by staff on site. One of the Brewer 

reference triad 111struments (instrument no. 8) was brought to 

l\ILO for calibration in March-April 1999, and comparison with 

the onsite instruments simplilied the calibration process. 

The instruments routinely measure total ozone, ozone profile 

(Umkehr measurements). sulfur dioxide. aerosol optical depth, 

the extraterrestrial solar spectrum (\ ia dail y airmass 

extrapolations of direct solar spectra) and global UV 1rradiance 

spectra. In addition, a new scanning technique was developed to 

determine the temperature of atmospheric ozone. Some 

preliminary resulls of these measurements were reported at the 

Quadrennial Ozone Symposium in Sapporo [Kerr, 2000). 

Brewer instrument no. 9 includes an all-sky camera that records 

and stores images of the sky every I 0 minutes. These images are 

displayed on the MLO Web site and are useful for obtaining real 

time information regarding the sky conditions at MLO. ll1ey are 

also valuable for reviewing sky conditions at times when unusual 

events are noticed in the data set. For example. large ''alues of 

sulfur dioxide have been observed (particul arl y between Januar) 

and March) on several occasions. and the sky images assist in 

determining the cause of these e\'ents. 

REFERENCES 

Kerr. J. 8 ., Measur.:mcnl of 101al ozone and ozone 1.:mperaturi: from 

spectral direct sun mi:asuremcnts. Proc. Quad 0:1111e SymJI .. 

Sapporo. Japan. 473--n-I. :WOO. 

Kerr. J.8. C.T. l\.kElroy. D. I. Wardle, and T.S. GraJnar. The Brc,,cr 

ins1n11ncnt calibration cen1rc 1984-2000. PmL . Quad O:m1t' Sy111J1 .. 

Sapporo. Japan. 177-1 78. :woo. 

11 9 
Isotopic Studies of Carbon Monoxide at Manna Loa 

John E. Mak 

Marine Sciences Research Cemer, State Uni1·ersity of Neu· York. Swny Brook, Ne u· York 1179-1-5000 

As part of an ongoing program to characterize the chemistry, 

sources, and seasonality of carbon monoxide in the tropics the 

Marine Sciences Research Center, State Uni versity of New York 

(SUNY), has been analyzing air samples for CO concentration, 

8 13C, 8 180 , and 14CO from the Mauna Loa Observatory since 

October 1998. During the fi rst year CO concentrations (Figure 

I a) at Mau na Loa ranged from a minimum of SO ppb on August 

11 , 1999, to a maximum of 198 ppb on March 17, 1999, with a 

yearly averaged concentration of 86 ppb. CO concentration data 

reveal an asymmetric seasonal cycle with maximum 

concentrations in the spring and minimum concentrations in the 

summer. The seasonality of 51.'c of CO (Figure I b) generally 

follows that of CO concentration. Val ues of 8 13C peaked during 

the spring followed by an abrupt decrease in the early summer. 

Through the late summer, fall and winter. 81.1C increased 

200 

:0 

a. 150 

~ 

. . 

gradually. Comparisons of 8 180 (Figure I c) and CO 

concentrations sho w a c lose correlation during al l times of 

the year. Again. 0 va lues increase duri ng the spri ng and 

decrease abru ptl y in the ea rl y summer. 

The stable isotope data we re used along with the isotopic 

signatures of the major sources to constrain the relative 

source strengths over ti me. The model results combined 

with back traj ectori es show the predominant sources arc 

from fossi l fuel combustion and biomass burning during the 

spring maximum, which is in agreement with other studi es. 14CO is used separately as a tracer of OH abundance. 

This is based on the fact that the dominant loss rate of 14CO 

is via reaction with O H, and its primary source is 

cosmogcnic. 1'1auna Loa is only the second tropical site for 

routine 14CO measurements in the northern hemisphere. 

0 

~ 100 . •·· ... -·--.·----.. ~·..---------.-_. _ __, .. . . . . . . 50 

.. . .. · ·. .· ....... . .. 

0 '--- ~----~--------.,.----' 

rV°''O ,f>'O cy.°'°' f>°' ~°'°' f;°' ~°'°' 'If>°' 0°'°' ~°'°' ,<§ ,,{I- "'" " ~rr; r,}Oj ,,_{C OJ." ,~ ,'Vrr; 

(b) 

·24 +-----------

=-E- -26 ,----.•. 

. 

--..!...__• ... ·-..~ ------ -l .. .... . . ... . . E: -28 --. - · - -------.. -----. .. _. _ 

u • • • • • • •• ~~ -30+----------- --t~ .-.-- .~ -----l • • ·32 +---------- - --·-'·"-------- ! 

-34 .1-.---------------------" 

rV°''O ,f>'O ~°'°' f>°' ~°'°' ~°'°' ciJ.°'°' 'If>°' ~°'°' i7°'°' 

,c§ <'-"' "-" ~" ~re ~ 'I'(_[; ~" .._.~ ... ~ 

(c) 

8 1---------------------

6 +---------

.. • QI • • •• i 2 +--._.----.--... ·•:.c . 

-~ o+---·~------~-·· ---·-'-·~·-----1 

·2 !--__. _______ __:_ ___ • . ~~ ---

... • ·4 -1----- - - - - - - - - - --------' 

rV°''O ,f>'O ~°'°' .._\°>°' ~°'°' ciJ.°'°' ~°'°' 'If>°' 0°'°' 0°'°' ~ ~ ~ ~ ~ 0 ~ ~ ~ ~ 

Fig. I. Time series of (a) CO. (b) o1'C. and (c) o"O ai Mauna Loa, Hawaii. from Oc1ober 1998 1hrough December 1999. 

120 
Interpreting Seasonal Cycles of Atmospheric Oxygen and Carbon Dioxide 

Concentrations at American Samoa Observatory 

ANDREW C. MANNING, R ALPH F. KEELING, AND LAURA E. KATZ 

Scripps /11stit11tio11 of Ocea11ography. U11i1•ersity of Ca/ifomia, Sa11 Diego, Ln Jolla, California 92093-0244 

INTRODUCTION AND METHODOLOGY 

Precise atmospheric oxygen (0 2) measurements can be used as 

a tool for studying the global carbon cycle. Keeling and Shem. 

[ 1992) calculated global land and ocean carbon sinks from 0 2 

and C02 concentrations measured from flask samples collected 

at three different locations. From an analysis of the seasonal 

cycles of 0 2 and C02 they were also able to provide an estimate 

of net biological productivity in the oceans. Their work has been 

updated with more recent data and findings by Bender et al. 

[ 1996], Keeling et al. [ 1996], and Bau le et al. (2000). 

Atmospheric 0 2 measurements can also be used in a variety of 

other biogeochemical applications such as measuring air-sea gas 

exchange rates [Keeling et al., l 998a], assessing the performance 

of ocean carbon cycle models [Stephens et al., 1998), and 

interpreting and validating satellite ocean color data [Balkanski 

et al., 1999). 

From June 1993 to the present, CMDL staff have collected 

flask samples from Cape Matatula, American Samoa (SMO) as 

part of the Scripps global atmospheric oxygen sampling network. 

These data up to June 2000 are presented in this report. Flask 

sampling protocols are described in detail in Keeling et al. 

[ l 998b]. Briefly, ambient air samples are collected 

approximately biweekly, in triplicate. in 5-L glass flasks 

equipped with two stopcocks that are sealed with Yiton o-rings. 

Air is drawn through a Dekoron intake line mounted ur a tower 

or mast. A small compressor pump maintains an air flow of 

approximately 5 STP L min" 1

, flushing ambient air through each 

flask. Flushing continues until a minimum of 15 flask volumes 

has passed through each flask, and then the sample is sealed off 

at a pressure of about I bar. A cryogenic cold trap at about 

-70°C pre-dries the air to remove water vapor. Flask samples are 

shipped back to the laboratory in La Jolla, California, for 

measurements of both 0 2 and C02 concentrations. 

Flask samples are collected by station personnel during what 

are considered to be "clean, background air" conditions; sample 

air that has not been contaminated by local or regional 

anthropogenic or terrestrial processes is required. In this manner 

seasonal and interannual temporal pallerns in Oi and C02 

concentrations can be observed. The general criteria used to 

determine when these conditions are met are a pre-established 

wind direction and speed and relatively steady, non-fluctuating, 

in situ atmospheric C02 concentrations. At Samoa the criteria 

used are a wind direction between 330° and 160°, a wind speed 

greater than 2 ms· 1

, and 2 consecutive hours of C02 

concentration agreeing to within 0.25 ppm [Waterman et al., 

1989). 

In the Scripps laboratory, flask samples are analyzed 

simultaneously for C02 concentration on a Siemens 

nondispersive infrared analyzer (NDIR) and for Oi/N2 ratio on 

our interferometric analyzer [Keeling, 1988]. Samples are 

analyzed relative to a working gas, which in tum is calibrated 

each day against a pair of secondary reference gases of 

predetermined 0 2/Ni ratios and C02 concentrations. A suite of 

12 primary reference gases are analyzed roughly every 6 months 

as a check on the long-term stability of the secondary reference 

121 

gases. (See Keeling et al. [ l 998b] for a detailed discussion of 

reference gases and calibration procedures.) 

Measurements of Oi/N2 ratios are used to report changes in 0 2 

concentration, relying on the assumption that Ni concentrations 

are constant. Based on the results of other studies [Manning, 

2000), the possibility of Oi fractionation relative to Ni in our 

samples collected at Samoa became a concern. It was discovered 

that under certain flow, pressure, and temperature conditions, 0 2 

will fractionate relative to Ni at "tee" junctions where an 

incoming air stream divides into two. Room temperature 

variability and the ratio of the flow rates at the tee junction 

appear to be the two most crucial parameters [Manning, 2000]. 

At Samoa a tee existed in the intake line because this line is 

shared with the continuous C02 analyzer operated by CMDL 

personnel. Therefore in May 1999 the intake setup was modified 

by installing a dedicated line with no tee junctions. At the same 

time the physical location of the intake line was shifted from the 

top of a mast at 42 m above sea level to the top of a newly 

constructed communications tower located approximately 100 m 

further inland and at a height of 93 m. To assess any potential 

changes in the 0 2/Ni ratios or C02 concentrations of the sampled 

air created by the removal of the tee or shift in physical location 

of the inlet, the old setup was left in place, and a schedule was 

begun alternating the biweekly flask collection hetween the two 

intakes. This schedule was started in May 1999 and plans are to 

continue it for a 2-yr period. There are now 13 months of data 

from this overlapping collection period, and a preliminary 

comparison shows no discernible difference between the two 

intakes. However, further data are needed to validate this 

conclusion. 

LONG-TERM AND SEASONAL TRENDS IN 0i/N2 

RATIOS AND C02 CONCENTRATIONS 

In Figure I the raw 0 2/N2 ratio and C02 concentration data 

collected at Samoa are shown. The differences are expressed in 

Oi/Ni ratios in "per meg" units, where 

where (0i/N2)sam is the ratio of the sample gas and (0 2/Ni)ref is 

the ratio in an arbitrary reference gas cylinder. One per meg is 

equivalent to 0.001 per mil, the unit typically used in stable 

isotope work. By making the assumption that atmospheric N2 

concentrations are constant, this ratio essentially reports 

variations in atmospheric 0 2 concentrations. In these units, 4.8 

per meg are essentially equivalent to I ppm (i.e., I μmole 0 2 per 

mole of dry air). C02 concentrations are expressed in ppm. In 

this figure the y axes have been scaled in such a way that 

changes in 0 2 and C02 are comparable visually on a mole-tomole basis. The curve fits are computed as a least squares fit to 

the sum of a four harmonic annual seasonal cycle and a stiff 

Reinsch spline [Reinsch, 1967) to account for the imerannual 

trend and other nonseasonal variability. 
.:r 

~ -150 [ 

E 

Qi 

~ 

.g -180 ~ 

"' 

~"'-240 f L 

-270 f 

370 

1 .. .. l 

following section. Seasonality in atmospheric O/N2 is generally 

caused by seasonality in photosynthesis and respiration of both 

land and marine biota. There is no corresponding marine biotic 

seasonal component in the atmospheric C02 signal. Biologically 

induced seasonal variability in pC02 in seawater is significantly 

buffered because of both the inverse correlation with seasonal 

solubility changes driven by temperature and the geochemical 

reactions of C02 with water to form carbonic acid and carbonate 

and bicarbonate ions [Keeling et al., 1993). Oxygen, on the 

other hand, is chemicall y neutral in the oceans, and biologically 

induced changes are in phase with temperature-induced 

solubility changes and are, therefore, reinforced in rhe 

atmospheric 0 2/N2 seasonal imprint. 

UNIQUE FEATURES OBSERVED IN ATMOSPHERIC 

DATA COLLECTED AT SAMOA 

When compared to other stations in our flask sampling 

'E 

a. 

~ 

366 

362 -

b. network, data from Samoa are unusual, exhibiting higher shortterm variability and seasonal cycles not in phase with other 

stations. The unusual seasonality is illustrated in Figure 2, whi ch 

0 

(.) 

358 -

354 

1993 1994 1995 1996 1997 1998 1999 2000 

Year 

Fig. I. 01/N1 ratios (a) and C01 concentrations (b) measured from fl ask 

samples collected at Cape Matatula, American Samoa ( 14 °S, 171°W). 

Plots (a) and (b) were scaled so that changes in 0 1 and C01 can be 

compared visually on a mole-to-mole basis. Curve fits are least squares 

fit to the sum of a fo ur harmonic annual seasonal cycle and a stiff spline. 

The OifNi decreasing tu:nd and C01 increasing trend are primarily 

because of fossil fuel combustion. 

The figure shows the well-known increasing trend in C02 

concentrations owing to fossi l fuel combustion and also a 

corresponding decreasing trend in 0 2/N2 ratios. For the 7-yr 

period from June 1993 to June 2000 an average increase in C02 

concentration of 1.9 ppm yr"1 and an average decrease in 0 2/N2 

ratio of 18.8 per meg yr" 1 were observed, or in comparable units, 

C02 increased by 3.3 x I 0 14 mot yr" 1 and 0 2 decreased by 

7.0 x 1014 mol yr" 1

• By contrast, over the same time period, 

fossil fuel combustion released an average of 5.4 x 10 14 mot ·t' 

of C02 into the atmosphere and consumed 7.6 x 1014 mol yr" of 

0 2. The 0 2 consumption by fossil fuel combustion was offset by 

net growth in the land biosphere, producing atmospheric 0 2 and 

consuming a portion of atmospheric C02• The overall decrease 

in atmospheric 0 2 is greater than the increase in C02 because a 

further portion of the C02 emitted by fossi l fuels is taken up by 

the oceans. There is no corresponding flux out of the oceans 

offsetting the 0 2/N2 decrease because 0 2 (and N2) is much less 

soluble in seawater than C02. 

Figure I also shows a small seasonal cycle in C02 and a much 

larger-amplitude cycle in 0 2/N2• Seasonal vari ability in C02 is 

generally attributed to seasonality in photosynthesis and 

respiration processes on land. Because there is relatively little 

land cover in the temperate and high latitudes of the southern 

hemisphere apart from the steril e antarctic continent, and 

because there is little seasonality in the tropics, only a small 

seasonal cycle in atmospheric C02 at Samoa would be expected. 

This is what was observed, but in fact the contributions to the 

seasonal cycle at Samoa are also influenced by long-range 

atmospheric transport as discussed in more detail in the 

122 

70 -~- •• 

50 t 

. a .. 

i 30 · E 

! 

.2 

~ 

~ La Jolra 50~~~~~~~~~~~~~~~~~~~~~ 

5 

-~--~-w~~~-~-~---­ Month 

Fig. 2. Four-harmonic seasonal components of the curve fits in Figure I 

showing 01/N1 ratios (a) and C01 concentrations (b ). Also shown for 

comparison are similar seasonal curve fits calculated from our fl ask 

sampling programs at Cape Grim, Tasmania (41°S, 145°E), and La Jolla, 

California (33°N, 117°\V), representing the midlatitudes of the southern 

and northern hemisphere respectively. To show the seasonal characteristics more clearly, the first 6 months of each cycle are repeated. 

Southern hemisphere and northern hemisphere cycles are roughly 6 

months out of phase with each other, whereas Samoa shows a more 

complicated signal. Plots (a) and (b) have been scaled so that changes in 

0 2 and C02 can be compared visually on a mole-to-mole basis. 
shows the four-harmonic seasonal component of the Oi/N2 and 

C02 curve fits in Figure l . The curves shown are the average 

seasonal cycles calculated from all data over the 7-yr record. 

Also shown are similar curve fits calculated from data collected 

at our sampling stations at Cape Grim, Tasmania, Australia 

(CGO) (4 1°S, 145°E), and La Jolla, California (LJO) (33°N, 

l l 7°W), that are assumed to be broadly representati ve of 

midlatitudes in the southern and northern hemispheres, 

respectively. To illustrate the characteristics of the seasonal 

variability more clearl y, the first 6 months of data are repeated in 

order to generate an 18-month-long record. 

As shown in Figure 2a the maximum 0 2/N2 ratio at Samoa 

occurs in April, approximately 2 months later than the peak at 

Cape Grim occurring in February. The minimum 0 2/N2 ratio at 

Samoa occurs in late August or earl y September, a few weeks 

earlier than Cape Grim. There is some evidence of a weak 

second maximum in late December at Samoa. C02 data in 

Figure 2b show an even larger contrast to typical southern 

hemisphere patterns. Maximum C02 at Samoa occurs in 

February in contrast to September for Cape Grim, whereas the 

minimum occurs in May at Samoa and April at Cape Grim. C02 

also exhibits a clearer second maxima and minima at Samoa as 

seen in the figure. The La Jolla curves show that Samoa 0 2/N2 

ratios and C02 concentrations are also not in phase with northern 

hemisphere trends. In addition at each of the sampling stations 

at La Jolla and Cape Grim, 0 2/N2 and C02 changes are to a good 

approximation anticorrelated with each other, whereas at Samoa 

this is clearly not the case. 

The unique climatological conditions at Samoa and their 

impact on concentrations of atmospheric constituents have been 

noted before. Halter et al. [ 1988) presented 3 years of C02 data 

from 1979- 198 l . They discussed the seasonal dependence of the 

variability observed in their C02 data and related this to air 

masses arriving at Samoa from different source regions. 

Following the wind cl imatology at Samoa presented by Bort11iak 

[ 198 l I and from an analysis of air mass backward trajectories, 

Halter et al. [ 1988) were able to show that the air arrivi ng at 

Samoa came from one of three broadly-defined source regions 

centered on anticyclones named ANP• Asp, and AANZ representing 

the north Pacific tropical anticyclone, the southeast Pacific 

tropical anticyclone, and the Australi a-New Zealand anticyclone, 

respecti vely. 

Halter e1 al. [ 1988] further· demonstrated that the observed 

Samoa C02 seasonal cycle was a superposition of three disti nct 

seasonal cycles originati ng from each of these three air mass 

source regions. Because the seasonal cycles of C02 in the 

northern and southern hemispheres are out of phase , these cancel 

out partially, but not completely, at Samoa resulting in the 

complex seasonal pattern that was also observed as shown in 

Figure 2b. Halter et al. [ 1988) then showed that the seasonal 

dependence of the C02 variability observed at Samoa is a 

function of the seasonally varying interhemispheric gradient in 

C02 concentration and also of the seasonally varying frequency 

of occurrence that air arriving at Samoa originated from the 

northern hemispheri c Arw anticyclone. This frequency of 

occurrence varies because of seasonal vari ations in the position 

and strength of the lntertropical Convergence Zone (ITCZ) and 

the South Pacific Convergence Zone (SPCZ). These two effects 

result in greater C02 vari ability duri ng austral summer and 

autumn. 

Pri11n et al. [1992) and Hartley a11d Black [1 995) found 

relatively high short-term variability in methyl chloroform 

concentrations measured at Samoa during austral summers but 

only in non-El Nino years. Hanley a11d Black [ 1995] showed 

that these observati ons could be explained by changes in largescale atmospheric circulation patterns at Samoa similar to the 

seasonal changes described by Halter et al. [ 1988) and Bortniak 

[ 198 l ]. It was demonstrated that the frequency of occurrence of 

air originating from the ANP anticyclone during El Niiio years 

was signifi cantly reduced, explaining the lack of methyl 

chloroform variability in these years. The C02 data in Figure I b 

support this conclusion where it can be seen that during the 

strong 1997-1998 El Niiio, C02 variability during the austral 

summer is significantly reduced compared to other years. 

Harris a11d Ol1111a11s [ 1997) observed variability in 

tropospheric ozone concentrations at Samoa approximate ly 6 

months out or phase with the variability in C0 2 described by 

Halter e1 al. [ 1988]. They also attributed these observations to 

summer-winter changes in atmospheric transport, in this case 

explaining the high austral winter variability not by variations in 

the latitudinal origin of the air masses arriving at Samoa, but by 

variations in the altitudinal origin that impacts the relative 

strengths of ozone sources and sinks, thus influencing the 

concentration of arriving air masses. 

LAND AND OCEAN PARTITIONING OF AIR 

MASS INFLUENCES AT SAMOA 

With the 0 2/N2 ratio measurements, to a good approximation, 

Scripps is able to distinguish between land and ocean processes 

affecting the air masses arriving at Samoa. This is done by 

defining a tracer, Atmospheric Potential Oxygen (APO), that is 

conservative with respect to 0 2 and C02 exchanges in land biota. 

APO is defined as 

123 

~ RO ,:C ~ APO (per meg) = u(02/N 2) +----uXco2 , 

Xo1 

(2) 

where Ro2:C represents the -02:C exchange ratio for land biotic 

photosynthesis and respiration, Xo2 is the standard mole frac tion 

of 0 2 in dry air, and 8Xco2 is the difference in the C02 mole 

fraction of the sample from an arbitrary reference gas, in ppm. 

This definition is a simplified version of the formula presented in 

Stephens et al. [ 1998) where minor influences from CH4 and CO 

oxidation have been neglected. Ro2:C = I. I based on 

measurements of Severi11gha11s [ 1995] and X02 = 0.20946 from 

Machia a11d Hughes [ 1970] were used. 

To a good approximation APO is not influenced by land biotic 

exchanges, and vari ations in APO can only be caused by air-sea 

exchanges of 0 2, N2, and C02 and by combustion of fossil fuels 

since the - 0 2:C exchange ratio for fossil fuels is approximately 

1.4 higher than the value of I. I for land biotic exchanges 

[Keeling et al., 1998a; Stephe11s et al. , 1998]. In contrast to 

APO, variations in C02 on seasonal and shorter time-scales are 

mainly caused by land biotic exchanges because of the buffering 

of C02 changes in the ocean as mentioned previously. 

Figure 3 shows plots of APO and C02 concentrations 

representing oceanic and land influences, respectively. The 

symbols on each plot show all flask samples collected at Samoa 

from June 1993 to June 2000 where all samples have been 

collapsed into I calendar year. The curves shown are the fourharmonic seasonal component of the curve fits to data from Cape 

Grim and Cape Kumukahi, Hawaii (KUM) (20°N, 155°W), 

representing the nearest sampling stations from which there are 

data in the southern and northern hemispheres, respecti vely. 
40 

30 

20 

Ci 10 .: G> • • ... . • 

E ..,, \ .; • • 

~ 0 ·- •• 

-20 

-30 . 

- - -~ I a. ' l 

l 

.3 .., r•• ....., ~ -,,., J~ ,. -,..,, "'P ~ ,. . '" • .,, " " ,,,,, ""' "'• • "' 

Month 

Fig. 3. Oceanic (a) and land biotic (b) influences on the air masses 

arriving at Samoa are shown. Atmospheric Potential Oxygen (APO}, 

defined in the text, is essentially not influenced by land b1011c processes 

and. therefore, represents oceanic influences. The seasonal component 

of the Samoa flask samples are shown as well as seasonal curve fits from 

Cape Grim, Tasmania, and Cape Kumukahi, Hawaii. representing the 

nearest stations from which we have data in the southern and northern 

hemisphere, respectively. Data were normalized as described in the text. 

As for the previous figure, the first 6 months of each cycle are repeated, 

and the plots were scaled 10 be able to visually compare mole-to-mole 

changes in APO and C0 1 concentrations. 

Typicall y, data that have been interannuall y detrended are 

centered on zero and have no absolute frame of reference. Here, 

in order to compare detrended data across different stations, all 

data have been normalized to the Cape Grim interannual trend. 

In other words, the Samoa flask data shown are the raw data 

points of Figure 1 with the interannual spline component of the 

Cape Grim curve fit subtracted. Because of slight variability 

from year to year in the interannual trends, the Kumukahi fourharmonic curve fit is not shown in the same manner. Instead, the 

average offset between the Kumukahi and Cape Grim spline 

components was calcul ated from 1993 to 2000 (60 2/N2 = -3.6 

per meg; 6C0 2 = 2.8 ppm), and this offset was added to the 

Kumukahi four-harmonic curve fit resulting in the Kumukahi 

curves shown in Figures 3a and 3b. The Cape Grim curves 

shown are simply the Cape Grim four-harmonic components of 

the Cape Grim curve fits. As with Figure 2, the first 6 months 

are repeated to generate 18 months of data, and APO and C0 2 

changes are comparable visually on a mole-to-mole basis. 

There are several prominent features apparent in Figure 3. 

Samoa C02 data in Figure 3b agree very well with the earlier 

data presented by Halrer er al. [1 988), showing greater 

variability in the austral summer and autumn. However, based 

on additional information from our APO data, a slightly different 

hypothesis of source air mass origins is suggested to explain this 

variability. For periods of May, June, and December in the APO 

signal, and from August to October in the C0 2 signal, Samoa 

data exhibit persistently higher concentrations than seen in air 

masses either to the north or to the south. It is believed that these 

data represent recirculated air, perhaps as a component of the 

Pacific Walker cell circulation. In other words, this is air not 

recently originating from the north or the south, but from the 

tropics at some point in the past. 

To further support this hypothesis Figure 4 presents the 

statisti cal variability in the data. The residuals of all flask 

samples shown in Figure 1 were calculated from the curve fits 

also shown in Figure I. The standard deviation of these 

residuals for each month was then calcul ated where, for 

example, all January samples from 1993 to 2000 were binned 

together. These standard deviations for each month are shown 

in the top plots of Figures 4a and 4b for APO and C0 2, 

respecti vely. Thus these plots give a statistical measure of the 

vari ability in APO and C02 at monthly time intervals. To 

provide a comparison, Cape Grim data are calculated in the 

same manner. As for Figures 2 and 3, the first 6 months are 

repeated. Figure 4b shows what was readi ly apparent in Figure 

3b, a clear seasonal pattern to the vari ability in the C0 2 signal, 

and a good correlation of this variability with the north-south 

interhemispheric gradient, shown in the bottom plot of Figure 

4b. In contrast, Figure 4b shows that Cape Grim does not 

exhibit such seasonal vari ability, and that during the austral 

winter and spring, Samoa vari ability is similar to that at Cape 

Grim. Figure 4a shows that there may also be a seasonal 

component to the APO variability. However, such seasonality 

is much less readily apparent than the C02 seasonality, is not 

of the same phasing as C02, and is almost equally apparent in 

Cape Grim APO as it is in Samoa APO. 

124 

Relati vely low monthly standard deviations are observed for 

all of the months described previously in Figure 3 exhibiti ng 

APO or C0 2 concentrations higher than present in the northern 

or southern hemisphere for that month with the exception of 

APO in December (Figure 4). This lower variability also 

suggests that this air has had more time to mix and become 

homogenized and has not been influenced to the same extent by 

air masses from the north or the south, supporting the hypothesis 

of recirculated tropical air. 

Figures 3 and 4 both show a clear difference in the pattern of 

variability in the APO signal compared with the C02 signal. 

APO does not show as clear a seasonal distinction in vari ability 

as C0 2 and does not show significant differences from Cape 

Grim variability (Figure 4). The top plots of Figure 4 have been 

scaled to enable direct comparison of the magnitude of 

vari ability of APO with C02. Thus it is clear that APO exhibits 

about twice the magnitude of variability of C0 2• These 

differences between APO and C0 2 cannot be directly explained 

either by the seasonally varying interhemispheric gradient or by 

the seasonally varyi ng frequency of occurrence of the different 

air masses arri ving at Samoa, both of which can be expected to 

affect APO in a similar manner as C02. There is, however, a 

difference in the southern hemisphere with respect to APO and 

C0 2. Regional sources and sinks for C0 2 are relatively small, 

whereas sources and si nks for APO are comparable to those in 

the northern hemisphere. 

Therefore, from July to November C0 2 vari ability is lowest 

both because of a smaller interhemispheric gradient (Figure 4b, 

bottom plot) and because of a lower frequency of occurrence of 
12 

a. 11 • • 10 

c: ~ 9 .. • o en .. "' ., .. ~ E a > ~ 

~ 8. ·SMO 

"O~ - avg ~I/) .. • • .. • j' .., _ .. "O "' 6 c: ::> • "'"O .. :'\ u; '(ii .. • .. .. o~ 

' • • • • , CGO n.- q;O 4 • \ • - avg 

' • • • • 3 Samoa 

2 ~ Cape Grom 

1 l ~- 1 -L--1 ~....! .1 I.. .i__J 

~---·--"~-~-~~---~-

---·~-M--~-~---·~- Month 

Fig. 4a. (Top) APO monthly standard de' iations of the residuals of the 

flask data from the curve fits. Results arc shown for both Samoa and Cape 

Gnm. and the first 6 months arc repeated. The annual average residual at 

each station is indicated on the right. There is hulc to distinguish Samoa 

and Cape G1 im. am.I 1l11!1t: i~ only weak evidence of a seasonal trend in the 

residuals at both stations. (Bollom) The absolute magnuude of the northsouth interhemisphcric gradient, calculated each month, and using Cape 

Grim and Cape Kumukahi data as representative of the southern and 

northern hemisphere. respectively. 

~ 

> 

c:12 E 

Q_ 

10 ,--~

• ii' 

/ Somo• ~ 

~ ~ 08' • • SMO I/) ~ 

i I::~ · · . . . · · l/ ~ e t '°' . . • .. . . . ... .. . ON 0 0 2 - .-,. • : .. • ... I u oo l ~ -~C~•~pe~G~·~·m----~-~-~- --~~~. CGO 

Month 

Fig. 4b. Top and bollom plots as fo r Figure 4a. As for Figures 2 and 3, 

APO and COi changes are visually comparable between Figures 4a and 4b. 

In contrast 10 APO. C0 1 shows a clear seasonal pauem in variability at 

Samoa, indicated here with higher standard deviations. whereas Cape Grim 

does not appear to show any seasonality. The pattern at Samoa appears to 

correlate well with the north·south interhemispheric gradient. Contrasting 

the magnitude of APO variability with COi, it can be seen that the APO 

signal is much '"noisier" , re flecting the presence of larger sources and sinks 

for Oi in the southern hemisphere compared 10 C01• 

ANP air masses arriving at Samoa [Halter et al., 1988]. By 

contrast even when air masses are entirely of southern 

hemispheri c origin, APO vari ability is still high because regional 

sources and sinks prevent the air from becoming as well 

homogeni zed in APO. Figure 4a shows linle distinction in APO 

vari ability between Samoa and Cape Grim, further supporting 

this conclusion. In addition, the backward wind trajectory 

analyses of Harris and Ol1111a11s [ 1997] showed that air masses 

originating from the southern hemispheric AANz anticyclone 

arriving at Samoa were more variable in their originating altitude 

than air masses arri ving from ANr or Asp. Because the source 

and sink mechanisms fo r APO occur via air-sea gas exchange, 

this altitudinal variability in air mass origin will contri bute 

fu rther to the variability observed in the APO signal at Samoa. 

Furthermore, the frequency of occurrence of air arriving from the 

AA,~Z anticyclone was higher during austral winter and spring, 

coinciding with the lowest C02 vari ability. 

Thus APO variability is a function of the interhemispheric 

gradient, the frequency of occurrence of air masses origmating 

from ANP when this gradient is large, and the frequency of 

occurrence of air masses originating from AANZ· These th ree 

effects, with regional sources and sinks of comparable magnitude 

in both hemispheres, combine to result in higher variability in the 

APO signal than the C0 2 signal, and very linle if any seasonal 

pattern to this APO variability. 

SUMMARY 

A 7-yr record of atmospheric 0 2'N2 ratios and C02 

concentrations measured from flask samples collected at 

American Samoa have been presemed. These data show 0 2/N2 

ratios decreasing a nd C0 2 concentrations inc reasing because of 

the combustion of fossil fuels. 0 2'N2 ratios are decreasing at a 

faster rate than the observed C0 2 increase because of the uptake 

of some fossil fuel-emined C02 by the oceans. Uptake of C0 2 

by the land biosphere also influences both the 0 2/N2 and C0 2 

trends. When compared to other stations in the fl ask sampling 

network, data from Samoa are unusual. exhibiting higher shortterm variability and seasonal cycles not in phase with other 

stations. This has been noted before from measurements of C0 2, 

methyl chloroform, and ozone and has been anributed to the 

unique geographical position of Samoa in relation to the IPCZ 

and SPCZ, whose positions vary seasonally, resulting in different 

air masses arriving at Samoa at different times of the year. The 

Scri pps atmospheric 0 2 data, expressed as APO, exhibit 

characteristics different from other atmospheric gases. The main 

differences are greater magnitude in the short-term variability, 

but, in contrast, almost no seasonal panern to this vari ability. 

This is explained by significant regional sources and sinks 

existing for APO in both hemispheres, in contrast to C0 2, and 

related to this, a dependence on the altitudinal origins of air 

masses arriving at Samoa in addition to a dependence on the 

latitudinal origins. 

125 

REFERENCES 

Balkansk i, Y .. P. Monfray, M. Bau lc. and M. Heimann. Ocean primary 

production derived from satellite data: An evaluation with 

atmospheric oxygen measurements, Global B11111eoche111. Cycles, 13, 

257-27 1. 1999. 

Battle, M., M.L. Bender, P.P. Tans, J.W.C. White, J.T. Ell is, T. Conway, 

and R.J. Francey, Global carbon sinks and their variability infe rred 

from atmospheric Oi and o"C. Science, 287, 2467-2470, 2000. 
Bender, M., T. Ellis, P. Tans, R. Francey, and D. Lowe, Variability in the 

0 1/N1 ratio of southern hemisphere air. 199 1-1 994: Implications for 

the carbon cycle, G/obt1/ Bioge11che111 . Cyc:les. 10, 9-2 1, 1996. 

Bonniak, J.C., The wind climatology of American Samoa. NOAA Tech. 

Memo .. ERLARL-98, 67 pp., Boulder. CO, 198 1. 

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, 15,9 14- 15,9 18, 1988. 

Hams. J.M., and SJ. Oltmans, Variations in tropospheric ozone related to 

transpon at American Samoa. 1. Ge11phys. Res., 102. 8781-8791. 1997. 

Hanle), D.E .. and R.X. Black. Mechanistic anal) sis of intcrhemispheric 

transpon . Geophys. Res. Leu .. 22. 2945-2948. 1995. 

Keding. R.F.. Measuring correlations between atmospheric oxygen and 

carbon dioxide mole fractions: A preli minary rn1dy in urban air. 1. 

,\1mm_ Chem .. 7. 153-176, 1988 

Keeling, R.F.. and S.R Shcnz. Seasonal and intcrannual variations in 

atmospheric oxygen and 11nplications fo r the global carbon cycle. 

i\'a1t1re. 358. 723-727. 1992. 

Keeling. R.F.. R.P Na1jar. M.L. Bender. and P.P Tans. What 

atmospheric oxygen measurements can tell us about the global carbon 

cycle. Gl11bal Bwgeochem. Cydes, 7, 37-67, 1993. 

Keeling. R.F., S.C Pipe1, and M. Heimann. Global and hemispheric C0 1 

sinks deduced from changes in atmospheric 0 1 concentration, Nt1111re, 

381. 218-221. 1996 

Keeling, R.F .. B.B. Stephens. R G. Najiar. S.C. Doney. D. Archer. and 

~I Heimann. Seasonal 'ariations in the atmospheric 0 1/N1 ratio in 

relation to the kinetics of air-sea gas exchange. Globt1I 8 111geoche111. 

Cffle.1. 12. 141- 163. 1998a 

Keeli ng, R.F .. A.C. t> lanning, E.M. McEvoy. and S.R. Shertz. Methods 

fo r measuring changes in atmospheric 0 1 concentration and their 

applications in southern hemisphere air, 1. Geophys. Res .. 103, 

338 1-3397. I 998b. 

Machta, L .. and E. Hughes, Atmospheric oxygen in 1967 to 1970, 

Science. 168. 1582-1584, 1970. 

Manning, A.C., Temporal variability of atmospheric oxygen from both 

continuous measurements a nd a nask sampling network. Tools for 

studying the global carbon cycle. Ph.D. thesis. University of 

Califo rnia. San Diego. La Jolla, California. 2000. 

Pri nn, R , D. Cunnold. P. S11n111onds. F. Alyea, R. Boldi. A Cr•m ford. 

P. Fraser, D. Gutzler, D II an Icy. R. Rosen. and R Rasmussen, 

Global a,·cragc rnncentrat1on and trend for hydroxy I radicals 

deduced from ALE/GAGE tnchlorocthane (methy I chloroform) data 

for 1978- 1990. 1. Geo11hy.<. Re.1 , 97. 2445-2462. 1992 

Reinsch. C.M .. Smoothing b) spline functions .. \'11111 . . \1<11h. JO. 177-

183. 1967. 

Se,eringhaus, J.P .. Studies of the terresmal 0 1 and carbon cycles in 

sand dune gases and 1n Biosphere 2. Ph.D. th.:;,h. Columbia 

Univcrsit). Ne\\ York, 1995 

Stephens, B.B .. R.F. Keeling, i\1 11.:imann. K.D. Six, R l\lurnane. and 

K. Caldeira. Testing global ocean carbon cycle models using 

measuremen ts of atmospheric 01 and CO~ concen tration, Global 

Bwgeoche111. Cycles, 12. 213-230. 1998. 

Wataman. L.S, D.\V. Nelson WD Komhyr. T B. Ham>. K \V. 

126 

Thoning, and P.P. Tans. Atmo>phcric carbon dioxide mcas1ircmcnts at 

Cape t> latatula, American-Samoa. 1976-1987, 1. Geo11hn Rn, 9./, 

14.8 17-14,829. 1989. 
Artificial Windshielding of Precipitation Gauges in the Arctic 

RICHARD J. MCCLURE 

S11il C1111ser1>ati1111 Servic:e, A11 c:h11rage, Alaska 99508-./362 

INTRODUCTION 

Precipitation gauges can pro vide good measurements of 

the water equivalent of sno w precipitation , provided the 

gauge is protected or shielded from wind effects. 

Unfortunately, there are no standards for collecting snow 

precipitation. Gauges located in exposed and windy areas 

may be totally unshi elded, partiall y shielded by one or 

more buildings, or equipped with one of several types of 

artificial shields. The variou s shielding options in 

common use, therefore, produce a wide range of gauge 

catch efficiency. Also, the various studies of artificial 

shields in the United States and Canada have produced a 

wide range of results. This must be, in part, due to the 

wide range of weather conditions under whi ch the various 

studies have been conducted. A lin gering problem is 

appl ying the results to the local conditions of Alaska's 

tundra regions. 

METHODS 

A study of the windshield alternatives, under the unique 

conditions of Alaska 's arcti c coastal region , was set up at 

the CMDL Barrow facility during September 1989. 

Snowfall catches from four installed precipitation storage 

gauges were compared with tha1 from an existing storage 

gauge protected by a Wyoming shield [Hanson , 1988). 

Two of the fou r gauges were shielded, one wi th a Nipher 

shield [Goodison et al., 1983] and the other with an Alter 

shie ld [Alter, 1937), and two were unshielded. One of the 

unshielded gauges was serviced on an event basis, the 

same as the three shielded gauges. The other unshielded 

gauge was treated as if ii were a remote gauge, allowing 

rime to build up and dissipate naturally to see what effects 

rime had on the overall catch. The four gauges arc each 

20.3 cm in diameter x 100 cm tall, mounted with the 

orifice 2 m above the normal ground surface. The existing 

Wyoming-shielded gauge is 30.5 cm in diameter x 2 m tall 

and is equipped with a Leupold-Stevens water-level 

recorder. Because the anchors melted out in the 

permafrost, the 1993 wind storms blew over the Wyoming 

wind shield. This was an unusual wind event for that time 

of yea r. The gauge was not rebu ilt. 

RESULTS 

Six winter seasons of total precipitation are ava il able 

for comparison of the four gauges in Table I. 

The results continue to confirm the catch of the Alter 

shield is 37 to 58% of the Nipher shield with the 

unshielded gauges ranging from IO to 36% of the Nipher 

shielded precipitation gauge. 

TABLE I. Comparison of Total Precipitation 

of the Four Remaining Gauges 

Unshielded Unshielded 

Nipher Aller Serviced Unserviced 

Oct. 5. 1993-

June I, 1994 76.2 111111 38. 1 mm no record 23.9 mm 

% ofNipher 50% 31% 

Oct. I, 1994-

June 17, 1995 104.6 mm 54.6 mm 36.3 mm 37.3 mm %ofNipher 52% 35% 36% 

Oct. 3, 1995-

June 3, 1996 84.1 mm 49.3mm 28.7 mm 23.9 mm % ofNipher 58% 34% 28% 

Oct. 3, 1996-

June 5, 1997 80.8 mm 30.0 mm 10.4 mm 7.9 mm % of Nipher 37% 13% 10% 

Oct. I, 1997-

June 2, 1998 89.4 mm 45.5 mm 18.3 mm 29.5 mm 

% ofNipher 51 % 20% 33% 

Oct. I, 1998-

June 2, 1999 11 3.8 111111 59.9 mm 36.6 mm 38.9 mm 

% of Nipher 53% 32% 34% 

Ack11owledg111e11/. Appreciation is expressed to D. Endres, 

Station Chief, Barrow, Alaska, who serviced the precipitation 

gauges and collected the snow samples. 

127 

REFERENCES 

Alter. S.C., Shield storage precipitation gauges, M1111 .. \Vewher 

Rei-.. 65, 262-265, 1937. 

Goodison, B.E .. W.R. Turner, and J.E. Metcalfe, A Nipher-type 

shield for recording prec1p11ation gauges, Prue:.. 51h 

Symp11si11111 1111 Mer e11r11/ogic:al Obsenaritms and l1u1r11 -

111 e111C1ti1111 , Toronto, Ontario, Canada, pp. 2- 126. Am. Meteorol. Soc., Boston. 1983. 

Hanson, C.L .. Precipitation measured by gauges protected by the 

Wyoming shi eld and the dual-gauge system, Prnc:.. 56rh 

\Vesrem S1111ll' C1111fere11ce. Kalispell . MT, pp. 174-177. 

Colorado State University, Fort Collins, 1988. 
Investigation of the Transfer Function between Atmosphere and Snow 

Concentrations of Hydrogen Peroxide at South Pole 

JosEPH R. McCONNELL 

Oil'isill11 <1' Hydmloi,:ic Scie11ces. Dese/'/ Research /11sti1111e, Re1111119512 

ROGER C. B ALES 

Depar1111e111 llf Hydmloi,:y a11d \Vmer Resources, U11i1·ersity of Arizo1111. T11cso11 115721 

/ / 

Oxidation by OH is the main atmospheric sink for many 

environmentally important gases including methane (C ~). 

carbon monoxide (CO), and halogenated hydrocarbons involved 

in stratospheric ozone depletion. With a very short lifetime, OH 

is not preserved in snow and ice. Hydrogen peroxide (H20 2) is a 

sink for OH, and, because H20 2 is preserved in polar snow, firn , 

and ice, an ice core record of H20 2 is potentially a proxy for 

changes in atmospheric OH through time. In addition, recent 

springtime depletion of stratospheric ozone has changed the level 

of solar radiation in the lower troposphere over Antarctica, 

thereby changing tropospheric photochemistry and also the 

chemistry of the surface and near-surface snow. However, 

deposicion of H20 2 from £he atmosphere to the near-surface snow 

and firn is reversible; some fraction of the originally deposited 

mass cycles between the atmosphere and the snow as the snow 

ages and is buried while environmental conditions change. The 

result is an atmosphere-to-snow transfer relationship that is 

highly nonlinear with £emperature, as well as accumulation rate 

and accumulation ti ming. Our re ~earch 1s aimed at better 

understanding this transfer relationship and developing 

physically based numerical models of the transfer processes. 

The eventual goal is to quantitatively invert the ice core record to 

an atmospheric record of H20 2 and provide constraints on past 

OH concelllration. 

Field and modeling studies are conducted at a number of 

remote locations in the arctic and antarctic. The objective is to 

develop information on H20 2 transfer and preservation in as 

many depositional environments as possible for use in model 

development and validation. Current antarctic study sites are 

shown in Figure I. South pole is the key site for detailed process 

level studies because of a Jong record of high quality 

atmospheric and meteorological measurements, year round 

occupation, low mean annual temperature, and relatively high 

accumulation rate. Through our cooperative agreement with 

CMDL, surface and near-surface snow samples have been 

col lected since November 1994. Replicate snow samples are 

collected by CMDL staff approximately once each week 

throughout the year and shipped back to our laboratories in 

Tucson and Reno for chemical determinations. The record of 

H20 2 concentration in surface snow at south pole (Figure 2) 

shows a highly repeatable annual cycle with a distinct peak in 

mid-November of each year, well before the summer solstice. 

Efforts to understand and model both surface and near-surface 

snow concentrations at south pole have been described 

previously [McC011nell, 1997; McCon11ell and Bales, 1998; 

McC01111ell el al., I 997, 1998, 1999; S1e1rar1 and McConnell, 

1999). 

Fig. I. Locations of study si1es used by current atmosphere-snow 

transfer modeling. Also shown are the mean annual snow accumula1ion 

ra1cs and air temperatures. 

Collaboration with CMDL staff at the south pole continues 

under NSF grants 9903744 and 9811875. Five shallow firn cores 

were collected in 1999 and 2000 within 15 km of the station. 

128 

~ 20 . 

:::t 

';i 

0 

c 

(/) 

Q) 

u 

<1! 

't: 

::> 

(/) 10 ' 

0 --- - 1995 1996 

.-

1997 1998 1999 

Year 

Fig 2. Hydrogen peroxide in surface snow at south pole. Error bars 

show one standard deviation in replicate measurements. 
Three of these cores were sectioned and analyzed for H20 2 and 

formaldehyde (HCHO) on site al the Atmospheric Research 

Observatory (ARO). Formaldehyde, a highly volatile, 

photochemically linked atmospheric chemical species, is also 

preserved in snow and ice. Preliminary field and modeling 

results of HCHO transfer and preservation were reported by 

H11uer/i er al. [ 1999). An atmospheric H20 2 detector was 

installed in ARO and maintained for much of the 1999/2000 

summer field season under the supervision of CMDL staff. 

REFERENCES 

Hutterli, M.A., J.R. McConnell, R.W. S1ewart. R. Rii1hlisbcrger, and 

R.C. Bales, l\lodeling reversible a1mosphere-10-snow transfer of 

HCHO in An1arc1ica, Eos Trans. AGU. R0(46). Fl 98, 1999. 

McConnell. J.R .. ln\'cs1iga1ion o f the a1mospherc-snow 1ransfcr process 

for h)drogen peroxide. Ph.D. dissertation, Dcpartmenl of Hydrology 

and Waler Resources, University of Arizona, 1997. 

McConnell, J.R., and R.C. Bales, lnves1iga1ion of !he transfer function 

between atmosphere and snow concentrations of hydrogen peroxide 

al south pole, in Climllle M11nirori11g and Diag1111sr1cs labormory 

No. U, S11111111ary Reporr 1996-1997, edi1ed by D.J. Hoffman, J.T. 

Peterson, and R.M. Rosson. NOAA Environ. Res. Labs .. Boulder. 

CO, 142-144. 1998. 

l\lcConnell, J.R .. J. R. Winterle. R.C Bales, A.M. Thompson. and 

R. W. Stewart. Physically based tn\'Crsion of surface snow 

concentrations of hydrogen peroxide lO aimospheric concen1ra1ions 

at sou1h pole. Geophys. Res. Leu., 24(./), 441-444 , 1997. 

McConnell. J.R., R.C. Bales. R.\V. Stewart, A.M. Thompson, M.R. 

Alben, and R. Ramos, Physically based modeling of atmosphere-10-

snow-10-fim lransfer of hydrogen peroxide al south pole, J. 

Geophys. Res., 103(09), 10,561-10.570, 1998. 

McConnell, J.R., R.\V. Stewart, M. Hutterli, and R.C. Bales, Modeling 

reversible atmosphere-to-snow transfer and preservation of 

hydrogen peroxide in Antarctica, Eos Tram. AGU. 80(46). Fl 92, 

1999. 

Stewart, R.W., and J.R. McConnell, Antarctic pho1ochem1S1ry: 

Uncertainty analysis. Eos Tran.,. AGU, lW(./6), F197-198. 1999. 

129 
Stratospheric Ozone Climatology from Lidar Measurements at Mauna Loa 

STUART M CD ERMID, T HIERRY LEBLANC, RICHARD CAGEAO, AND DANIEL W ALSH 

Table Mm111rm11 Facility. Jet Propulsion Laborawry, Califomia l11stit11re ofTeclmology. \Vrigl111rnod. Califomia 92397 

INTRODUCTION 

The Jet Propulsion Laboratory (JPL) lidar at Mauna Loa 

Observatory (MLO) continues to make regular measurements of 

ozone, temperature, and aerosol profiles for the Network for the 

Detection of Stratospheric Change (NDSC) program. This report 

describes the development of an ozone climatology from one 

aspect of the lidar results. 

The rou1ine measurement modes for 1hc lidar are based upon 1he 

NDSC requiremenl for a long-1erm ozone survey. The usual 

mcasurcmems comprise an approximately 1.5-hour long data 

acquisition at the beginning of the nigh1 several limes a week, 

weather and ins1rnmcnt permitting (the normal s1arting lime is the 

end of astronomit.:al twiligh1 that ensures there is no sunlight 

tailing on any part of the a1mospherc sensed by the lidar). 

Additional full-night measurements have been made in the past 4 

years at given periods of the year to study the tidal signature in the 

middle atmospheric temperature [Leblanc et al .. 1999]. However. 

to avoid any contamination by possible diurnal variations, onl y the 

profiles taken before 0930 UT were selected to build this 

climatology. 111e data set from the full-night campaigns will be 

used in the future for the study of the ozone diurnal variations. 

This temporal selection leaves more than 800 profiles between 

July I. 1993, and June 30, 1999. The JPL lidars have participated 

in nume1ous 111erco mp 1i ~u n am.I validatiun t:>.t:rcises wi1h nearly 

co-located and/or simultaneous measurements. The results of 

these campaigns have been extensively published and clearly 

md1cate the quality of the lidar results [e.g., McDermid et al., 

1995: Tsou et al., 1995: Plane/ et al., 1995; Baily el al., 1996: 

Brnhl cl al., 1996: FroidemrLr el al., 1996; Gmnl el al. , 1998; 

Mc Peters el al., I 999]. 

OZONE PROFILES 

In the present study the ozone concentration profiles were 

1Illcrpolated to a I -km vertical interval in order to homogenize 

the entire data set. This operation reduces the magnitude of 

smaller vertical scale fluctuat1ons, but these fluctuations are not 

needed for the cl imatological study presented. Figure I shows 

two typical profiles measured at MLO in late winter and 

midsummer. Unlike at more northern latitudes, such as the JPL 

Table Mountain Facility, there is no significant seasonal change 

111 the altitude of the ozone peak. Also unlike northern 

midlatitudes, the ozone concentration in the lower stratosphere is 

not significantly higher in winter than in summer (5 x I 012 cm·3 

111 summer and 4-4.2 x I 012 cm·3 in winter near 24-26 km). 

Instead. the whole wimer profile tends to have lower values than 

the summer profile. This is consistent with a more photochemically and/or radiatively driven tropical ozone abundance 

where the role of transport and mixing by the mid- and highlatitude planetary waves is much less significant. However, 

there remains a layer in the winter lower stratosphere where 

ozone is slightly more abundant than in summer. This feature. 

typical of the extra-tropical latitudes, is expected to disappear 

closer to the equator. 

50 

45 

40 

,..... 

g 35 e.> 

-0 

B 

·.: 30 

< 

2 1-Aug-1998 

25 

20 -

15 -

0 l 2 3 4 5 6 

Ozone number density (10" cm·1

) 

Fig. I. Typical\\ intertimc and summertime ozone profiles a l MLO. 

OZONE CLIMATOLOGY 

The overall mean ozone number density was calculated as a 

function of altitude. The mean profile obtained is representative 

of an annual mean since the data distribution for each month is 

similar. Then , the deviations (in percent) from the quasi-annual 

mean were calculated for each day of measurement. 

130 

The two-dimensional comours of these filtered ozone de\'iations 

are shown in Figure 2. The color scale extends from -24£J (violet) 

to +24% (red) with a 4'7c contour interval. The white solid line 

near 25 km represents the mean altitude of the ozone concentration 

peak. This altitude is nearly constant throughout the entire year. 

The seasonal variation of the ozone concentration at MLO is not 

as pronounced as for higher latitudes. Figure 2 nevertheless 

highlights a residual annual cycle at 30 km and above, si milar to 

that observed at midlatitudes and related to the seasonal variation 

of the radiative balance of the upper stratosphere (more sunlight 

in summer). Figure 2 also reveals a springtime maximum near 

19-20 km as the result of a residual contamination by the 

midlatitude planetary wave acti\'ity. No clear annual cycle 1s 

observed below 25 km. However, despite the strong variabili ty at 

the bottom of the profiles (near the tropopause) persistent high 

ozone concentrations are observed during the summer months and 

persistent low concentrations are observed in December and 

January, indicating the dominant role of the photochemical and 

radiative effects over the dynamics. The annual cycles observed 

arc in agreement within a few percent with pre1ious climatologies such as that obtained from SAGE II data [Shiou111i a11d 

Hasebe, 1994). 
r-r -

Feb Apr Jun Aug Oct Dec 

-24 -16 -8 0 8 16 24 

Ozone deviation from annual mean (%) 

Fig. 2. Ozone number density deviation from the annual mean 

(%) as a fu nction of altitude (km) and day-of-year at MLO. Contour 

interval is 4%. 

DERIVED QUANTITIES 

For a convenient comparison with model results and other 

observations, the ozone number densities measured by the lidar 

were convcrtt:<l into ozone mixing ratios. The Mass 

Spectrometer Incoherent Scatter Extended-90 (MSISE) 

empirically modeled air densities and temperatures [Hedin, 

1991] were used to calculate the ozone-mixing ratio as a function 

of pressure. Figure 3 shows the seasonal variations of the 

derived ozone mixing ratios for the periods. Since the densities 

and temperatures (i.e., pressures) used do not come from actual 

simultaneous measurements, a slight vertical distortion of the 

contours is expected, especially during the winter months. This 

distortion can lead to some I 0-15% differences in the regions of 

sharp vertical gradient like in the late spring and summer lower 

stratosphere. 

DISCUSSION AND CONCLUSION 

A 6-year stratospheric ozone climatology obtained by the JPL 

DIAL instrument located at Mauna Loa Observatory (19.5°N) 

has been described. The lidar provided high-resolution vertical 

profiles of nighttime ozone number density between - 15-50 km 

several nights a week since 1993. The climatology presented is 

typical of early night ozone values and includes a negligible 

fraction of Pinatubo-influenced ozone values [Parrish er al., 

1998]. It includes ozone values typical of a time of low solar 

acti vity since the measurement period is approximately centered 

on the 1996 I I-year solar cycle minimum. 

At MLO the ozone concentration tends to be higher during the 

summer months and lower during the winter months throughout 

the entire ozone layer. Only a weak signature of the extratropical latitudes is observed near 19-20 km with a secondary 

ozone maximum in late March-early April. As emphasized pre1.0 

-

~ -

2.0 

-

G) 5.0 ] 

~ 10.0 

20.0 £ 

50.0 

100.0 

Feb Apr Jun Aug Oct Dec 

1 2 3 4 5 6 7 8 9 

Ozone Mixing ratio (ppmv) 

Fig. 3. Ozone mixing ratio (ppmv) at MLO, derived using the ozone 

results in Figure 2 and MSISE-90 density and temperature data, as a 

function of pressure altitude (hPa). 

viously, the 1993-1999 measurement period at MLO is nearly 

centered on the 1996 I I-year solar cycle minimum. Therefore, 

the upper stratospheric ozone values are expected to be slightly 

lower (-2-3%) than those obtained over a full solar cycle 

[Chandra and McPeters, 1994). 

The current climatology will be complemented by ongoing 

detailed investigations of the day-to-day variability of the 

tropopause height, diurnal variations, interannual variability 

(Quasi-Biennial Oscillation, El Nino and the Southern 

Oscillation, solar cycle, etc.) and the long-term trends of ozone. 

The results from these investigations, combined with the present 

climatology, will eventually provide a comprehensive overview 

of the stratospheric ozone vertical distribution at MLO. 

Acknowledgment. The work described in this report was carried out 

by the Jet Propulsion Laboratory, California Institute of Technology, 

under an agreement with the National Aeronautics and Space 

Administration. 

REFERENCES 

Baily, P.L., D.P. Edwards, J.C. Gille, L.V. Lyjak, S.T. Massie, A.E. 

Roche, J.B. Kumer, J.L. Mergenthaler, B.J. Connor, M.R. Gunson, J.J. 

Margitan, I.S. McDermid, and T.J. McGee, Comparison of cryogenic 

limb array etalon spectrometer (CLAES) ozone observations with 

correlative measurements, J. Geophys. Res .. IOI, 9737-9756, 1996. 

131 

Bruh!, C., S.R. Drayson, J.M. Russell, P.J. Crutzen, J.M. Mcinerney, P.N. 

Purcell, H. Claude, H. Gernandt, T.J. McGee, and l.S. McDermid, 

Halogen Occultation Experiment ozone channel validation, J. Geophys. 

Res., JOI, 10,217- 10,240, 1996. 

Chandra, S., and R.D. McPeters, The solar cycle variation of ozone in the 

stratosphere inferred from Nimbus 7 and NOAA 11 satellites, J. 

Geoplzys. Res., 99, 20,665-20,671 , 1994. 

Froidevaux. L., W.G. Read, T.A. Lungu, R.E. Cofield, E.F. Fishbein, D.A. 

Flower, R.F. Jarnot, B.P. Ridenoure, Z. Shippony, J.W. Waters, J.J. 

Margitan, I.S. McDennid, R.A. Stachnik, G.E. Peckham, 
G. Braathen, T. Deshler, J. Fishman, D.J. Hofmann, and S.J. Oltmans, 

Validation of UARS Microwave Limb Sounder ozone measurements, 

J. Geophys. Res .. 101, 10,017- 10,060, 1996. 

Grant, W.B., M.A. Fenn, E.V. Browell, T.J. McGee, U.N. Singh, M.R. 

Gross, LS. McDermid, L. Froidevaux, and P.-H. Wang, Correlative 

stratospheric ozone measurements with the airborne UV DIAL 

system during TOTE/VOTE, Geophys. Res. Lett., 25, 623-626, 

1998. 

Hedi n, A.E .. Extension of the MSlS thennosphere model into the middle 

and lower atmosphere, J. Geophys. Res., 96, 1159-1172, 1991. 

Leblanc, T., LS. McDermid, and D.A. Ortland, Lidar observations of the 

middle atmospheric thern1al tides and comparison with the High 

Resolution Doppler Imager and Global Scale Wave Model. I. 

Methodology and winter observations at Table Mountain (34.4°N), J. 

Geophys. Res., 104, I l,9 17- 11 ,929, i999. 

McDennid, l.S., S.M. Godin, T.D. Walsh, Results from the Jet 

Propulsion Laboratory stratospheric ozone lidar during STOIC 1989, J 

Geuphys. Res., JOO, 9263-9272, 1995. 

McDermid, I.S., T.J. McGee, and D.P.J. Swart. NDSC lidar 

intercomparisons and validation: OPAL and ML03 campaigns in 

1995. in Adva11ces i11 Armospheric Remote Se11si11g with Lidar, pp. 

525-528. Springer-Verlag, New York, 1996. 

McPeters, R.D. , D.J. Hofmann, M. Clark. L. Flynn, L. Froidevaux, M. 

Gross, B. Johnson, G. Koenig, X. Liu, l.S. McDermid, T. McGee, F. 

Murcray, S. Oltmans, A. Parrish, R. Schnell, U. Singh, J.J. Tsou., 

T.D. Walsh, and J.M. Zawodny, Results from the 1995 stratospheric 

ozone profile intercomparison at Mauna Loa (ML03), J. Geophys. 

Res., 104, 30,505-30,514, 1999. 

Parrish, A., B.J. Connor, J.J. Tsou, G. Beyerle, LS. McDermid. and 

S.M. Hollandsworth, Microwave ozone and lidar aerosol profile 

observations at Table Mountain, California, following the Pinatubo 

eruption, J. Geophys. Res .. 103, 22,201-22,208, 1998. 

Planet, W.G., A.J. Miller, J.J. DeLuisi, D.J. Hofmann, S.J. Oltmans, 

J.D. Wild, I.S. McDermid, R.D. McPeters, and B.J. Connor, 

Comparison of NOAA- I I SBUV/2 ozone vertical profiles with 

correlative measurements, Geophys. Res. Leu., 23, 293-296, 

1995. 

Shiotani, M., and F. Hasebe, Stratospheric ozone variations in the 

equatorial region as seen in stratospheric aerosol and gas 

experiment data, J. Geophys. Res .. 99, 14,564-14,584, 1994. 

Tsou, J.J., B.J. Connor, A. Parrish, l.S. McDermid, and W.P. Chu, 

Ground-based microwave monitoring of middle atmosphere ozonecomparison to lidar and stratospheric and gas experiment-II 

satellite-observations, J. Geophys. Res., JOO, 3005-3016, 1995. 

132 
Microwave Measurements of Middle Atmospheric Water Vapor 

From Mauna Loa, 1996-2000 

GERALD E. NEDOLUHA, RICHARD M . BEVILACQUA, R . MICHAEL GOMEZ, AND BRIAN C. HICKS 

Nal'a/ Research LL1boratory. Code 7227, \Vashi11gto11, D.C. 20375-5320 

INTRODUCTION 

Measurements have been taken of middle atmospheric water 

vapor at Mauna Loa, Hawaii (19.5°N, 204.4°E) since March 

1996. TI1ese measurements are taken at 22 GHz using the Naval 

Research Laboratory Water Vapor Millimeter-wave 

Spectrometer (WYMS). Because of 1he relatively small seasonal 

variations, combined wi1h the small 1ropospheric water vapor 

signal, Mauna Loa is an ideal site for the monitoring of long 

term changes in middle atmospheric water vapor. 

Measurements of water vapor provide important information 

on several processes in the middle atmosphere. Water vapor is 

an ideal transport tracer and has been used in numerous studies 

of atmospheric transport in the middle atmosphere [e.g., 

Bevilacqua et al., 1990; Nedoluha et al. , 1996; Summers et al., 

1997). Water vapor is also the reservoir of odd hydrogen in the 

middle atmosphere, and is, therefore, important to ozone 

chemistry. Variations in humidity in the middle atmosphere, 

therefore, have implications for variations in ozone [Siskind and 

Summers, 1998]. Changes in middle atmospheric water vapor 

may also impact stratospheric temperatures and thus indirectly 

affect ozone depletion [Kirk-Davidoff et al., 1999]. 

WVMS MEASUREMENTS 

The WYMS ins1rument deployed at Mauna Loa is the third 

such instrument to be deployed. It is essentially identical to the 

WYMS2 instrument that operated at 1he Network for 1he 

Detection of Stratospheric Change (NDSC) site at Table 

Mountain, California (34.4°N, 242.3°E) from August 1993 to 

November 1997. These instruments are both very similar to the 

WYMS I instrument 1hat is taking measurements at the NDSC 

site at Lauder, New Zealand (45.0°S, l 69.7°E). 

The retrieval of a vertical water vapor profile with groundbased microwave measurements relies upon the change in 

pressure as a function of altitude. The line width of the spectrum 

monotonically decreases with altitude because of the dependence 

on pressure broadening. Thus the resultant signal, which is the 

sum of the emission from all altitudes, can be deconvolved to 

retrieve a vertical profile. Details of the measurement technique 

and instrumentation are given by Nedoluha et al. ( 1995, 1996). 

Nedoluha et al. [ 1999] compared the WYMS3 instrument at 

Mauna Loa with Halogen Occultation Experiment (HALOE). 

Once differences in resolution are taken into account, the 

average difference is <10% at almost all altitudes between 40 

and 80 km. The only exception is a small range near 60 km 

where the average HALOE measurements show an unexpected 

local minimum in mixing ratio. The differences between the 

measurements taken at Mauna Loa and Table Mountain in 1996 

and 1997 were generally consistent with the latitudinal 

difference in water vapor measured by HALOE. In particular, 

the shape of the difference profile between the two WYMS sites 

was very similar to the shape of the difference profile for the 

HALOE measurements at these latitudes between 40 and 70 km. 

In Figure I the mixing ratios retrieved from 40 to 80 km using 

500 scan (- 1 week) integrations are shown. There is a summer 

peak in the upper mesospheric mixing ratio consistent with the 

upward motion of the atmosphere in the Mountain or Lauder [cf. 

Nedoluha et al., 1997). There is no sign of the positive trend in 

water vapor that was observed by the WYMS instruments and by 

HALOE in the early 1990s [Nedoluha et al., 1998). There is a 

suggestion of a very slight negative trend since 1996, a result 

that is qualitatively consistent with the global variation in 

stratospheric water vapor observed during this period by 

HALOE [Randel et al. , 1999]. 

Fig. I. Weekly integrated spectra of water vapor mixing ratios retrieved 

from WVMS3 measurements at Mauna Loa. The data are smoothed 

using a Gaussian filter with a (lie) width of 25 days. 

Ack11owledgme11ts. We wish to thank S. McDermid, Rich Cageao, 

and D. Walsh for their technical assistance with the Mauna Loa 

radiometer. This project is funded by NASA under the Upper 

Atmospheric Research Program. 

REFERENCES 

Bevilacqua. R.M .. D.F. Strobel, M.E. Summers, J.J. Oli vero, and 

M. Allen, The seasonal variation of water vapor and ozone in the 

upper mesosphere: Implications for venical transport and ozone 

photochemistry. J. Geophys. Res .. 95. 883-893, 1990. 

133 
Kirk-Davidoff. D.B .. E.J. Hintsa. J.G. Anderson, and D.W. Ke ith, 

The effect of climate change o n ozone depleti on through changes 

in stratospheric water vapour, Na 111re. 402, 399-40 I, 1999. 

Nedoluha , G.E .. et a l., Ground-based measurements of water vapor 

in the middle atmosphere, J. Geophys. ~ .. JOO. 2927-2939, 

1995. 

Nedoluha, G.E .. ct al., Measurements of water vapor in the middle 

atmosphere and implications for mesospheric transport, J. 

Geophys. Res .. IOI. 2 1. 183-2 1, 193, 1996. 

Nedoluha. G.E., e t al.. A comparati ve study of mesosphe ric water 

vapor measuremen ts from the ground-based Water Vapor 

Millimeter-wave Spectrometer and space-based instruments, J. 

Geophys. Res .. I 02. 16,64 7- 16,66 1, 1997. 

Ncdoluha , G.E .. ct al., Increases in middle a tmos pheric water vapor 

as observed by the Halogen Occuhation Experiment and the groundbased Water Vapor Millimeter-wave Spectrometer from 1991 to 

1997, J. Geophys. Res., 103, 353 1-3543. 1998. 

Nedoluha, G.E .. et al., Measurements of middle atmospheric water vapor 

from low latitudes and midlatitudes in the Northern Hemisphere, 

1995- 1998, J. Geo11hys. Res., 106. 19,257- 19,266, 1999. 

Randel, W.J .. et al., Space-time pauem s of trends in stratospheric 

constituents derived from UARS measurements, J. Geop/Jys. Res .. 

104. :m 1-3121. 1999. 

Siskind, D.E., and M.E. Summers, Implications of enhanced mesospheric 

water vapor observed by HALOE, Geophys. Res. Lei., 25, 2133-2136, 

1998. 

Summers, M.E., D.E. Siskind, J.T. Bacmeister, R.R. Conway, S.E. 

134 

Zasadil, and D.F. Strobel, Seasonal variations of middle atmospheric 

CH4 a nd HiO with a new chemical-dynamical model, J. Geophys. 

e.~ .. 102, 3503-3526, 1997. 
Carbon Flux Using Eddy Covariance Methodology in Arctic 

Coastal Wet Sedge Tundra 

WALTER C. 0ECHEL, R OMMEL ZULUETA, AND H YOJUNG KWON 

Global Clu111Ke Research Gm11p. Sa11 DieKo Suue U11i1·ersi1y. Califomia 92182 

INTRODUCTION 

Tower-based eddy covari ance measurements provided a near 

continuous temporal record of mass and energy over hectare 

spa11al-scales. However, in a regional context, these 

measurements still represent a "point'" measurement [Baldocchi 

er al .. 1996; Vo11rliris a11d Oechel, 1997, 1999]. Aircraft-based 

measurements ~rov de a relatively detailed measure of the largescale (e.g., km ) spatial variance in mass and energy exchange, 

but because of safety reasons, are temporally restricted to 

daytime periods and favorable weather conditions [Cra11ford er 

al., 1996; Desjardins er al., 1997]. The information gained from 

each technique is complimentary and essential for understanding 

spatial and temporal patterns in nuxes [Desjardins er al., 1997]. 

Two of the primary objecti ves of the National Science 

Foundation Arctic Transitions in the Land-Atmosphere System 

(ATLAS) nux program are to quantify the plot (0.5 m2), 

landscape (0.5-4 ha). and regional (e.g .. 3 km2

) net ecosystem 

exchange (NEE) over several growing seasons and to develop 

methods for scaling point-measurements or mass and energy nux 

ove1 \·aryi ng spatial and temporal scales [\\'el/er er al .. 19951. 

As a preliminary exercise to fullill these objectives. it is 

important to quantify the interrelationships between the mass and 

energy !luxes measured from different sampling techniques. The 

data presented here provide a baseline for comparison with 

future aircraft nux measurements. 

METHODS 

Fluctuations in wind speed, temperature. C02, and 1120 vapor 

were measured at 2.5 m above ground le\ el. Vertical wind speed 

and temperature tluctuations were measured at 10 Hz using a 

three-dimensional sonic anemometer-thermometer (SWS2 I l/3K. Applied Technologies Inc., Boulder, Colorado) aligned 

into the mean wind. Carbon dioxide and H20 vapor nuctuations 

were measured at I 0 Hz with a fast response open-path infrared 

gas analyzer. The C02 and H20 vapor channels of both sensors 

were cali brated at a minimum of every other week with 300 and 

400 ppm standard gases and a portable dewpoint generator (Ll610. LI-COR Inc.. Lincoln, Nebraska), respectively. For 

detailed information on methodology sec \1011rlitis and Oechel 

[ 1997, 1999]. 

Barrow and Atqasuk are the northern and southern anchor 

points, respectively. for the aircraft transect. The Barrow site 

(7 1°19'N, 156°36'\V) is located in the Barrow Environmental 

Observatory (BEO) that covers several square kilometers 

dedicated to long-term arctic research and includes several 

different representative wet-moist coastal sedge tundra types. It 

is located 2 km south of the Arctic Ocean and comprised of lowand high-centered polygon ice wedges (polygon troughs) and 

drained lake tundra land forms [Brown er al., 1980]. The 

Atqasuk site [70°29'N, 157°25'W] is located 100 km south of 

Barrow, Alaska. Soils are developed on aeolian sands of 

Quaternary age [Evereu, 1980]. The site is comprised of a 

variety of moist-wet coastal sedge tundra and moist-tussock 

tundra surfaces in the more well-drained upland areas [Batzli, 

19801. Vegetation that dominate the area include the tussockforming sedge, Eriophorum vagi11at11111 , as well as other 

evergreen and deciduous forbs and shrubs [Ko111arko1•a and 

Webber, 1980; Walker et al., 1989]. This site is also an intensive 

site for year-round measurements of net C02 nux and energy 

balance. Atqasuk's more continental climate and sandy substrate 

make a useful contrast with conditions at Barrow. 

RESULTS 

Net sink activity increased up to 4.0 gC nf2 d1, thaw depth 

(active layer depth) was -32 cm, and soil moisture content was 

66% between mid-July and late July 1999 at the Barrow site 

(Figure I). As thaw depth increased and soil moisture content 

decreased (to 631ft in early August) s111k strength of C02 tlux 

decreased because of the soi l respiration caused by microbial 

activation in the soil. Arter a precipitation event in mid-August, 

soi l moisture content increased up to 71 '7c, and there was rapid 

135 

]'. 

-to 

..s -10 '""' ... 

~ 

~ · 30 

.. o 

-jO 

80 

~ -- SoUliol.1>lft ~ -J'.tf:(lplUl..WR\ 

l! H Jl 

B 

v 

j 10 

~ 6j ~ 

0 

"' 60 

"'1 """ Stp Oct 

Fig. l. Seasonal trend of daily integrated net C01 tlux with lhaw depth. 

soil moisture content. and precipitation nt Barrow in 1999. 
increase of sink acllvlly (to 6.2 gC m·

2 d.1

) even though thaw 

depth was -37 cm deep. It is assumed that soil moisture affected 

soil temperature, which in turn affected soil respiration, and there 

was a decrease of soil respiration resulting in a strong sink 

acti vity of net C0 2 fl ux. In late Aug ust net sink acti vity was 

small ; thaw depth increased up to -41 cm; and soil moisture was 

76%. 

Acknowledgment. The authors thank Dan Endres. S1ation Chief at the 

CMDL Barrow sta1ion, for providing facilities, help in maintaining the 

tower, and periodic assistance with instrumenlation and data acquisition 

computers. 

R EFERENCES 

Baldocchi. D.D., R. Valentini. S. Running. W. Oechel, and R. Dahlman, 

Strategies for measuring and modeling carbon dioxide and waler 

vapor nuxes over terrestrial ecosystems. Global Cl11111g e Biol .. 2, 159-

168, 1996. 

Batzli. G.O.. Patterns of vegetation and herbivory in arctic tundra: 

Results from the Research on Arctic Tundra Em ironment (RATE) 

program. Arel. Al11. Res .. 12. 40 1-578. 1980. 

Brown, J. PC. Miller, L.L. Tieszen, and F.L. Bunnell, A11 Arwc 

Ecosystem: The Coaswl T1111dra tll Barroll', Almk11, 571 pp .. Dowden. 

Hutchinson, and Ross. Stroudsburg. PA. 1980. 

Crawford, T.L., R.J. Dobosy. R.T. McMillen, C.A. Vogel, and B.B. 

Hicks. Air-surface exchange measurement in heterogeneous regions: 

Extending tower observations with spatial structure obserwd from 

small aircraft. Global Clu111ge Biol.. 2, 275-285. 1996. 

Desjardins, R.L .. J.I. MacPherson, L. Mahrt, P. Schuepp, E. Pancy. H. 

Neumann, D. Baldocchi. S. Wofsy, D. Fitzjarrald, H. Mccaughey, and D. 

W. Joiner, Scaling up nux measurements for the boreal forest using 

aircraft-tower combinations, J. Geophys. Res., 102. 29, 125-29,133, 1997. 

Everett, K.R .. Distribution and variability of soils near Alkasook, Alaska, 

Arc. Alp. Res .. 12. 433-446, 1980. 

Komarkova. V., and P.J. Webber, Two low arc1ic vegetation maps near 

Atkasook, Alaska, Arc. Alp. Res., 12, 447-472, 1980. 

Vourlitis. G.L .. and W.C. Oechel, Landscape-scale C02, water vapor, and 

energy nux of moist-wet coastal tundra ecosystems over two growing 

seasons, J. Ecol .. 85, 575-590, 1997. 

Vourlitis G.L., and W.C. Oechel, Eddy covariance measurements of net 

C01 nux and energy balance of an Alaskan moist-tussock 1undra 

ecosystem, J. Ecol., 80, 686-701, 1999. 

Walker, D. A .. E. Binnian. B.M. Evans. N.D. Lederer. E_ Nordstrand, and 

P.J. Webber, Terrain, vegetation, and landscape evolution of 1he R4D 

resear'h site. Brooks Range Foothills. Alaska. Ho/11rc1. Ecol .. 12. 238-

261, 1989. 

Weller, G .. F.S. Chapin 111, K.R. E\eren. J.E. Hobbie, D. Kane. W.C. 

136 

Oechel. C.L. Ping, W.S. Reeburgh. D. Walker. and J. Walsh. The arcuc 

nux study: A regional view of trace gas release. J. Biogeogr .. 22, 365-

374, 1995. 
Preliminary Intercomparison Results from the NDSC Microwave Ozone 

Profiling Instrument at Manna Loa Observatory 

ALAN PARRISH 

Uni1•ersi1y of Ma.m1ch11se11s, Amhersl, Ma.uach11se11s 01003 

I. S. B OYD AND B. 1. CONNOR 

Nmional lns1i1111e for \Valer and A1111ospheric Research, Lauder, New Zealand 

I. S. MCDERMID 

l ei Propulsion Labom1ory. Table Mmu1win Facili1y. \Vrighnrnod, Califomia 92397 

S. O LTMANS 

NOAA Cli111a1e M1111i1orini11111tl Dia11nos1ics u1bora1ory. Boulder, Colorado 80303 

J. J. Tsou Science Applirn1i1111s ln1en1111i111111l Corporarion, Ha111p1<111, Virginia 23666 

J. M. ZAWODNY 

Na1ion11l Aermuw1ics and Space Ad111inis1ra1irm, umgley Research Cenler, Hamprnn. Virginia 23681 

Since July 1995, the University of Massachusetts has operated 

a microwave ins1rument that measures vertical profiles of 

stratospheric ozone at the Climate Monitoring and Diagnostics 

Labora1ory (CMDL) Mauna Loa Observatory (MLO). Results of 

intercomparisons with four other ozone profiling experiments 

using data recorded during 1995- 1998 are reported here. 

The microwave instrument measures a spectral line produced 

by a ro1ational transi1ion of ozone at 110.836 GHz. Profiles 

covering an altitude range of 56-0.1 hPa (about 20-66 km) are 

retri eved from the details of the pressure-broadened line shape. 

The 'erucal resolution of the measurements is 8- 10 km from 

abou1 20 to 40 km. At higher altitudes it smoothly degrades to a 

maximum of 17 km at about 60 km. Details regard111g the 

111strumcnt arc given in Parrish et al. [ 1992), Co1111or et al. 

[ 1995) and Tsou et al. [ 1995). 

The microwave instrument participated in the Network for 

Detection of Stratospheric Change (NDSC) sponsored ML03 

in1ercomparison campaign [McPeters et al., 1999) in July 1995. 

During that campaign the microwave instrument, two lidars, and 

Stratospheric Aerosol and Gas Experiment-II (SAGE-II) agreed 

within 5% from 22-43 km. Agreement at that level between 

microwave, SAGE-II, and one set of lidar measurements 

conti nued up to abouI 50 km. A further assessment, including a 

relative trend analysis, can now be made from intercomparisons 

using data obtained since the end of the ML03 campaign 

1hrough 1998. 

Microwave data were recorded from July-September 1995, 

November 1995-March 1996, and from July 1996 on. Calibrated 

profiles were retrieved from these data through December 1998 

and are considered preliminary because we arc aware of two 

small. correctable defects in the data. First, the 1997 data were 

processed on a different implementation of the cali bration and 

re1rieval software. There is a slight difference between profiles 

produced by this algorithm and its predecessor in 1he 20-25 km 

region. Second. a small amount of 1995 and 1996 data may be 

affected by an occasional intermillent electronic fault that 

became apparent in 1997. Affected 1997 data were deleted from 

this dataset. While the microwave group intends to reprocess the 

data to eliminate the known defects, it is believed that the errors 

produced by these faults are small enough to make it worthwhile 

to proceed with the comparison described in the following text. 

The previously described microwave data were compared with 

those produced by lidar, ozonesonde, SAGE-II [ C1m11old et al., 

1989). and Halogen Osci llation Experiment (HALOE) [Brnhl et 

al., 1996) instruments. The lidar was provided and operated by 

the Jct Propulsion Laboratory (JPL), California Institute of 

Technology [McDermid et al., 1990), and sondes were launched 

nearby at Hilo by CMDL personnel [Olt111w1s et al., 1998, and 

references therein]. Profiles 111 number density versus altitude 

format were converted to mixing ratio versus pressure assuming 

hydrostatic equilibrium with the NOAA National Center for 

Environment Prediction (NCEP) temperature profiles in the 

calculation. There are two points to note regarding Ihe 

comparison datasets: The Kl solution concc111ra1ion in the 

sondes was increased from I% to 2% in April 1998 for reasons 

discussed in Oltmm1s et al. [ 1998). Data from earlier fli ghts 

were adjusted to be consistent with those using the new solution. 

Problems with the lidar data that affect the profiles below 25 km 

have been found, and a revised dataset is being prepared. 

Therefore, the mi crowave-lidar comparison was cut off at 24 hPa 

(about 25 km.). 

137 

The average difference between the microwave profiles and 

those from the other instruments is mostl y less than 5% (Figure 

I). The spread of differences in the several comparisons is 

largest in the lower stratosphere (-40 hPa), from -8 to +12%. 

The difference would be slightly positive when averaged over 

the SAGE, HALOE, and ozonesonde comparisons, suggesting 

that 1he microwave measurements may be biased slightly high. 

However, the large spread makes this result inconclusive. In the 

middle stratosphere (-10 hPa), the microwave values are 

generall y a few percent smaller than the others. For both the 

SAGE-I! and HALOE comparisons, the a\'eragc differences stay 

below 5-6% up to 0.6 hPa, and the variability in individual 

difference profiles remains small. Although microwave-lidar 

differences grow rapidly abo\'e a few hPa, similar increases are 

seen between sets of measurements made with two lidar 

instruments during intercomparison campaigns (e.g., McPeters et 

al. [ 1999]). The vari ability in the microwave-lidar difference 
(a) (c) 

'° Cl. '° Cl. 

E. :S Q) ~ :; 10 :J 10 

"' "' "' Q) "' 

~ 

ct Cl. 

'I 

'1 

'I 

I 

100 100 Sunn .. Mun 11. pair• 

Sunut ..-un 12l>•lrt 

- - All Pll" Mun 3M palrt -- All Palu Mean 27 palrt 

......... St1nd1rd OtYlatlon ······ Sl1nd11d Ot vlal10n 

·20 ·10 10 20 JO 40 ·20 ·10 10 20 30 •O 

Percent Difference Percent Difference 

. ' ~. (b) (d) . 

,'1 

' ,, 

I ~ •. 

I• 

'° '° ,. I ' 

Cl. a.. , 1 •• I 

E. E. ' ' I 

~ Q) ' ' I 

:; 10 ' ' I :J 10 ·'.1 "' "' I . 

"' "' ' Q) Q) ~- ' 1. 

a: 0:: I I I 

100 SunrlH MHn 1 S ptln 

100 Sunni Mun 12 pain 

-- All Pain Mun 1'0 p1ln -- All Pain Mean 21 pair• 

.... St1nd1rd Oovlotll>n · St.nd1td Otvl1llbn 

·20 ·10 10 20 JO 40 ·20 ·10 10 20 30 40 

Percent Difference Percent Difference 

Fig. I. Sohd lines: Difkrences between ozone profil es recorded with the microwave instrument at Mauna Loa and those recorded with the co-located 

(a) JPL lidar. (b) NOAA ozonesondes, and during overpasses of the (c) HALOE (version 19) and (d) SAGE-II (version 5.96) instruments averaged from 

August 1995 1hrough December 1998. Dolled lines: The root-mean-square of individual difference profiles. The percent difference is calculated by 

subtracting the specified instnunent ozone amount from the microwave ozone amount, dividing by the sum of the ozone amount from the two 

ins1rumcnts, and multiplying by 100. 

profiles also increases rapidly above 4-5 hPa. These facts suggest 

that the increasing average difference between these lidar and 

mi crowave measurements with altitude above a rew hPa is due to 

the decreasing intensities of the signals returned to the lidar. We 

have not extended comparisons to higher altitudes because of the 

difficulty in accounting for the effect of diurnal, photolysisinduced changes in ozone levels along the line of sight of the 

satellite-borne occultation type instruments. 

Regression analyses were performed to calculate relative trends 

between our measurements and the others used in the preceding 

difference profile discussion; results are shown as functions of 

altitude (Figure 2). There are 110 sonde-mi crowave coincidences, 

386 lidar-microwave coincidences, 29 HALOE coincidences, and 

27 SAGE coincidences. There are statistically significant altitudedependent relative trends or 1-2% per year between the mi crowave 

and lidar measurements around 5 hPa. The relative trends in the 

other comparisons are more uncertain. Because they generally 

138 

have the same sign and similar magnitude in this region, there may 

have been some form of systematic change in the microwave 

measurements during the 1995-1998 period. Because the present 

microwave dataset is known lo have small defects that occur 

irregularly, it seems more likely that any systematic effect in the 

microwave data is quasi-random in nature than a steady drift. If 

so, the magnitude of the relative trends would decrease with 

increasing record length, even in the absence of an upgraded 

microwave data set. 

A preliminary set of microwave ozone profiles (covering 

about 20-66 km) measured at MLO during 1995 through 1998 

was compared with ozonesonde, lidar, SAGE-II, and HALOE 

profiles measured nearby. The average differences depend most 

strongly on the instrument being compared in the lower 

stratosphere. Above 30 hPa (about 24 km). the differences are 

generally less than 5% at altitudes where the comparison 

instruments are expected to work well. Relative trends of 1-2% 
-RENO: h'tCRCWAVE - SONOE 

,:o'~ --------~ ·c ~-~-----~ 

- ·c - 5 0 IC - IC -:'; a ' 0 

TRE"O: MiCRCl'1AVE - HALOE -RE1" 0: v .CRO\'IAVE - SAGE-II 

"' :>: 

§ < CD 

" " ~ 1ol 

_J ;r 

:::> 

'[ :;., "' t'.! 

3:: a: 

a. 

t 

I 

·co: ____ J 100 -

- ·o -5 0 IC -IC - 5 0 10 

P£=<C=::'~· p[:o vt;.tc ;c::~cE~ ... PER "~.:. ::) 

Ftg. 2 Rclati'e trends \ersus pressure calculated by linear regression 

from m11:rowave profile> at Mauna Loa. thos<: recorded b) co-located 

JPL lidar. and NOAA sondcs, and during o\'erpasscs of the SAGE-II and 

HALOE instruments. Error bars correspond to 1hc 95c:t confidence 

tnterv:1l Trends are calculated from August 1995 through Dcccmber 

1998 

per year were found between time series of lidar and 111i1:1uwa\t: 

measurements. The other three trend comparisons are less 

certain, but suggest that the lidar-microwave trends may be 

caused by flaws in the present microwave data. These trends arc 

expected to integrate down as the record length increases. The 

rel ative trend also may be reduced when the microwave data are 

reviewed and uniforml y reprocessed. 

Ack11owledgme11ts. The microwa\'e. hdar. SAGE-II. and HALOE 

experiments are supported by NASA. and the ozonesondes are 

supported by NOAA. 

REFERENCES 

Bruh!. C.. S.R. Drayson. J.M. Russell. P J Crutzen. J.1'1 1'1clnerne). 

P.N. Purcell. H. Claude. H. Gernandt. T.J. 1'1cGee. and I S. 

1'1cDermid, HALOE Ozone Channd Validati on, J. Geophys. Res .. 

IOI. 10,2 17-10.240. 1996. 

Connor, B.J., A. Parrish. J.J. Tsou. and M.P. McCormick. Error 

analysis for the ground-based microwave ozone measurements 

during STOIC, J Geophys. Res .. JOO, 9283-9291. 1995. 

Cunnold. D.M .. W.P. Chu. R.A. Barnes. 1\1.P l\lcCorn11ck, and R.E. 

Veiga, Validation of SAGE-II ozone measurements. J Geophys. 

Res .. 9./, 8447-8.t60. 1989. 

McDermid. l.S., S.M Godin, and L.O. Lindquist, Ground-based 

laser DIAL system for long-term measurements of stratospheric 

ozone. App. Opt .. 29. 3603-3612. 1990. 

t\kPctcrs. R D .. D.J Hofmann. 1\1 Clark. L. Fro1devaux. ~I Gross. 

B. Johnson. G. Koenig. l.S. McDerimd. F. l\turcray. S Oltmans. 

A. Parrish. U. Singh. J.J Tsou. and J Zawodny, Results from the 

1995 stratospheric ownc profile 1111erco111panson al t\tauna Loa. J. 

Geopliys. Res .. JO./, 30.505-30.5 1-1 . 1999. 

Olt111ans. S .. M. Clari... R. E,·ans. E Hackathorn. J Harm. B. 

Johnson. G. Koenig. 1\1 O'Neill. D Quincy. and H Vomel. 0£0nc 

and Water Vapor tn Climate ,\1111111",-,"K 1111d Dwg1w.wn 

L11b11ra1"ry Summary Rep"rt "'"- 2./ D.J Hofmann et al (Eds ). 

NOAA En,iron. Res Labs .. Boulder, CO. pp. 76-90. 1998. 

Parmh. A .. B.J Connor. J.J. Tsou. l.S t\ lcDer111id. and \VP Chu. 

Ground-based microwa\'c monitoring of stratospheric otone. J. 

Geophn. Res .. 97. ~5-11-25-16. 1992 

Tsou. J.J .. B.J. Connor A Parri'h I S l\lcDermid. and \\' P. Chu. 

139 

Ground based 1111cro"a'c 11101111onng of rmddle atmo,phere 

ozone: Comparison 10 lidar and Stratospheric Aerosol and Gas 

Experiment II sat..:lhtc obserrnt ion ~. J Geophys. Res .. JOO. 3005-

3016. 1995. 
Advanced Global Atmospheric Gases Experiment (AGAGE) 

R.G. PRINN 

Mass£1ch11se11s /m1i1111e ojTed11111logy, Cambridge, MllSS£1ch11se11s 02139 

R.F. WEISS 

Scripps /11sti1111im1 of Ocewwgraphy. U1111•er.1ity of Ct1lifomiu, St111 Dief(o. La J11/lt1. California 92093 

D.M. CUNNOLD 

Georgit1 /11 sti1111e ofTec/111ology. Atlcmw. Georgia 30332 

P.J . FRASER 

CS/RO. Di1'i.ri1111 of A111w.fpheric Research. V1c111ria. Australia 3195 

P.G. SIMMONDS 

U11i1•er.1i1y of Bris111I. Sdwol ofChemistry, Bristol. U11ited Kingdom BS8 ITS 

INTRODUCTION 

In this global network program continuous high-frequency gas 

chromatographic measurements of biogenic and anthropogenic 

gases are carried out at globall y distributed sites in order to 

quantitatively determine the source and sink strengths and 

circulation of a large number of chemically and radiatively 

important long-lived gases. The program that started in 1978 1s 

conveniently di vided into three parts associated with three 

changes in instrumentation: the Atmospheric Lifetime 

Experiment (ALE), the Global Atmospheric Gases Experiment 

(GAGE) and the Ad\ anccd Global Atmospheric Gases 

Experiment (AGAGE). 

AGAGE began during the 1993- 1996 umc period. AGAGE, 

which continues to the present, has two instrumental 

components. First, a highl y improved gas chromatographic 

system measures fi ve biogenic/anthropogcnic gases (CH4, N20. 

CHCl3• CO, and H2) and fi ve anthropogenic gases (CCl3F, 

CCl 2F2• CH3CCl3, CCl 2FCCIF2, and CCl4) [Prum el al .. 1995; 

Fraser et al.. 1996; Cwmold el al., 1997: Simmonds el al., 

I 998a]. Each species 1s measured 36 t11nes per day using an 

electron capture detector (ECO), !lame io111Lation detector (FID), 

or mercuric oxide reduction detector (MRD); the latter detector 

is for CO and H2 and is currently present at only two of the 

stations, Mace Head, Ireland, and Cape Grim, Tasmania. 

Second, a new gas chromatographic-mass spectrometric 

system (GC-MS) began measuring a \\ ide range of 

hydrochlorotluorocarbons and hydrotluorocarbons (CH2FCF3 

(HFC-I 34a), CH3CCl 2F (HCFC-14 I b), CH.,CCIF2 (HCFCl 42b), etc.) [Simmonds el al., 1998b] that arc now servi ng as 

interim or permanent alternatives to the chlorolluorocarbons and 

other long-lived halocarbons regulated by the Montreal Protocol 

[ UNEP, 1996]. Also measured by the GC-MS system arc the 

methyl halides (CH3CI, CH,Br, CH31) and the halons (CBrF.i. 

CBrCIF2). AGAGE also included development and use of new, 

much more accurate absolute calibrations for most of the 

measured gases. 

The ALE, GAGE, and AGAGE stations have been located in 

five globally distributed localities: (a) Ireland: first at Adrigole, 

52°N. 10°\V (1978- 1983), then at Mace Head, 53°N, 10°W 

( 1987-present): (b) USA West Coast: first at Cape Meares, 

Oregon. 45°N. I 24°W ( 1979-1989). then at Trinidad Head, 

California, 41 °:--1, 124 °\V ( 1995-present ): (c) Ragged Point , 

Barbados, J 3°N. 59°\V ( 1978-present); (d) Cape Matatul a. 

American Samoa, 14°S, 171°\V (1978-prcscnt): (e) Cape Gnm, 

Tasmania, 41 °S, I 45°E ( 1978-present). 

The AGAGE operation at Samoa has significant added value 

because it enables a direct intercomparison with the similar realtime measurements (and also with the tlask measurements) by 

CMDL. This intercomparison has already aided us in determining the net effect of calibration and instrumental differences 

on the measurements by each group, so that the data from both 

the AGAGE and CMDL networks can be utiliLed in combination 

by theoreticians to investigate chemical and meteorological 

phenomena. 

RECENT PROGRESS 

Accomplishments over the entire period from 1978 through 

the present have recently been published [Pri1111 el al. , 2000). In 

the publication, the instrumentation and calibrations used rn the 

ALE, GAGE and AGAGE experiments and a history of the 

majority of the anthropogenic ozone-deplet111g and climateforcing gases in air, based on these experiments, 1s described in 

detail. Beginning in 1978 these three successive automated high 

frequency in situ experiments have documented the long-term 

behavior of the measured concentrations of these gases O\'er the 

past 20 years and show both the evolution of latitudinal gradients 

and the high frequency variability from sources and circulation. 

These experiments enable estimation of the long-term trends 111 

total chlorine contained 1n long-lived halocarbons involved 111 

ozone depiction, and these measurements are summarized using 

inverse methods to determine trace gas lifetimes and emissions. 

Finally, a combined observational and modeled reconstruction of 

the evolution of chlorocarbons by latitude in the atmosphere over 

the past 60 years is provided that can be used as boundary 

conditions for interpreting trapped air in glaciers and oceanic 

measurements of chlorocarbon tracers of the deep ocea111c 

circulation. 

140 

The ALE/GAGE/AGAGE data arc available through the U.S. 

Department of Energy (DOE) CDIAC World Data Center (email to: cpd@oml.gov, Dataset No. DB-I 00 I). Some specific 

conclusions from the data arc [Pri1111 el al .. 20001: 

(I) For ozone-depicting gases, ALE/GAGE/ AGAGE and 

other measurements show: (a) Major changes in the rates of 

accumulation of many ozone-depleting gases occurred in the 
1990s. Mole fractions of C H3CC13, CC14, and CC13F have been 

decreasing for several years; mole fractions of CC12FCCIF2 

reached approximately constant levels and are now beginning to 

decrease very slowly; the rate of accumulation of CCl2F2 has 

slowed significantly. However, mole fractions of N20 continue 

to steadily increase. The latitudinal gradients of CC13F, CC12F2, 

CC12FCCIF2 , C H3CC13 and to a lesser extent, CC14 , are 

essentiall y zero, o r are rap idly approaching zero, consistent with 

rapid decreases in their largely northern hemisphe ri c emissions 

[see also Fraser et al., 1996; Simmonds el al., l 998a; Prinn et 

al., 1995]. (b) International compliance with the Montreal 

Protocol is so far resulti ng in c hlorofluorocarbon and 

c hlorocarbon mole fractions equ al to or lower than target levels. 

(c) Levels of total chlorine contai ned in 10 dominant halocarbons 

in the global lower troposphere have apparently reached 

maximum values of about 3.6 ppb and are beginning to decrease 

slowly (to about 3.5 ppb in 1997). This decrease is driven 

largely by declines in C H_iCCl3 and to a lesser extent, CCl4 [see 

also Cunnold et al., 1997; Prinn et al., 1999; K111)'lo et al., 

1999). 

(2) Optimal esti mations u sing global ALE/GAGE/AGAGE 

measurements and atmospheric chemical models show: (a) The 

chlorofluorocarbons have atmosphe ric lifetimes consistent with 

destruction in the stratosphere being their principal removal 

,mechanism. (b) Estimation of the lifetime of CH3CCl3 continues 

to provide an accu rate determination of the weighted-average 

global O H concentration , but the rapidly decreasing mole 

fractions o f CH1CC13 will ultimately limit its usefulness for this 

purpose. (c) Multi-annual vari ations in chlorofluorocarbon and 

chlorocarbon emissions are consistent approximately with 

variations estimated independently from industrial production 

and sales data where available (CCl2FCCIF2 and CCl2F2 arc 

exceptions). 

(3) The mole fractions of the major hydrochlorofluorocarbons 

and hydrofluorocarbons that are replacing the regulated 

halocarbons are rising rapid ly in the atmosphere (specifically in 

the 1994 to 1998 time period at rates of about 44% per year for 

CH2FCF.i. 13% per year for C H3CCIF2, and 28% per year for 

CH3CC12F at Mace Head, Ireland). With the exception of 

C HCIF2, which was in u se well before the latter three species, 

they are not yet at levels to significantly contribute to 

atmospheric chlorine loading [see also Miller et al., 1998; 

Simmonds et al., I 998b]. In the future, these replacement 

species could provide independent estimates of the globalweighted average O H concentration provided their industrial 

emissions are mo re accurately documented . 

(4) The curre nt rapidly changing magnitudes and geographical 

locations of emissions of chlorocarbons and chlorofluorocarbons 

may mandate a more dense measurement network than provided 

presently by AG ACE alone in order to obtain accurate solutions to 

inverse problems involving regional emissions and lifetime 

estimation; at a mi nimum, the d ata from all existing networks 

(ALE/GAGE/AGAGE, CMDL, etc.) should be carefully 

intercalibrated, so they can be utilized to better compute global and 

regional average concentrations. 

(5) In the future, analysis of pollution events measured using 

high freq uency in situ measurements of chlorofluorocarbons and 

the ir replacements may enable emission estimates at the regional 

level that are suffic ientl y accurate to be used for identi fying 

regional noncompliance with the Montreal Protocol [see also 

De1went et al., I 998a, b]. 

Acknowledgments. In its initial years the global network (ALE) was 

supported by grants from the Chemical Manufacturers Association and 

later also by the Upper Atmospheric Research Program of the National 

Aeronautics and Space Administration (NASA). GAGE was 

subsequently supported by multiple grants from NASA. In its latest 

phase (AGAGE), support came (and comes) primarily from NASA 

(grants NAGW-732, NAGl-1805, NAG5-3974 to MIT; grants NAGW2034, NAG5-4023 to SIO), with important contribu tions also from the 

United Kingdom Department of Environment (now Department of 

Environment, Transport and the Regions) (contracts PECO 7110/154 and 

EPG 1/1/37 and 1/1/82 to lnscon), Commonwealth Scientific and 

Industrial Research Organization (Australia), Bureau of Meteorology 

(Australia), and the Alternative Fluorocarbons Environmental 

Acceptability Study (AFEAS). Support for the Barbados Station during 

GAGE/AGAGE has been shared approximately equally between NASA 

and the National Oceanic and Atmospheric Administration (NOAA). 

We also thank NOAA for their infrastructure support at the Samoa 

Station by Cooperative Agreement. The suite of six CH.i-in-air standards 

used for AGAGE was purchased by CSIRO Atmospheric Research from 

Nippon Sanso with funds secured from the Multi Function Polis 

(Australia) Agency. 

141 

REFERENCES 

Cunnold, D.M., R.F. Weiss, R.G. Prinn, D.E. Hartley, P.G. Simmonds, 

P.J. Fraser, B.R. Miller, F.N. Alyea, and L. Porter, GAGE/AGAGE 

measurements indicating reductions in global emissions of CCl3F and 

CCiiF1 in 1992-1994, J. Geoplrys. Res., 102, 1259-1269, 1997. 

Derwent. R.G., P.G. Simmonds, S. Seuring. and C. Dimmer, Observation 

and interpretation of the seasonal cycles in the surface concentrations 

of ozone and carbon monoxide at Mace Head, Ireland from 1990 to 

1994. At11111.t. Em·imn .. 32(2), 145- 157, I 998a. 

Derwent. R.G., P.G. Simmonds. S. O'Doherty, and D.B. Ryall, The 

impact of the Montreal Protocol on halocarbon concentrations in 

northern hemisphere baseline and European air masses at Mace Head, 

Ireland, from 1987-1996, Atmos. E111·iro11, 32(21),3689-3702, 1998b. 

Fraser, P.J., D.M. Cunnold, F.N. Alyea, R.F. Weiss, R.G. Prinn, 

P.G. Simmonds, B.R. Miller, and R.L. Langenfelds, Lifetime and 

emission estimates of I, 1,2-trichlorotrifiuoroethane (CFC-113) from 

daily global background observations, June 1982 to June 1994, 1. 

Geophys. Re.t., IOI , 12,585-12,599, 1996. 

Kurylo, M.J., et al., Short-Lived Ozone-Related Compounds, Chapter 2, in 

Sciemijic A.ue.u111e11t of Ow11e Depletio11: 1998, World Meteorological 

Organization (WMO) Global Ozone Research and Monitoring Project, 

Geneva, Report 44, pp. 2.1-2.56, 1999. 

Miller, B.R., J. Huang, R.F. Weiss, R.G. Prinn, and P.J. Fraser, 

Atmospheric trend and lifetime of chlorodifiuoromethane (HCFC-22) 

and the global tropospheric OH concentration, J. Geophys. Res., 103, 

13,237- 13,248, 1998. 

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 CH,CCh and global OH concentrations, 

Scie11 ce. 269, 187- 192, 1995. 

Prinn, R.G., et al., Long-Lived Ozone-Related Compounds, Chapter I, in 

Scie11tijic A.uess111e111 of Oyme Depletion: 1998, World Meteorological 

Organization Global Ozone Research and Monitoring Project, Geneva, 

Report 44, WMO, pp. 1. 1-1.54, 1999. 

Prinn, R.G., R.F. Weiss, P.J. Fraser, P.G. Simmonds, D.M. Cunnold, 

F.N. Alyea, S. O'Doherty, P. Salameh, B.R. Miller, J. Huang, R.H.J. 

Wang, D.E. Hartley, C. Harth, LP. Steele, G. Sturrock, P.M. Midgley, 

and A. McCulloch, A history of chemically and radiatively important 

gases in air deduced from ALE/GAGE/AGAGE, J. Geophys. Res., 

105(Dl 4), 17,75 1-1 7,792, 2000. 

Simmonds, P.G., D.M. Cunnold, R.F. Weiss, R.G. Prinn, P.J. Fraser, 

A. McCulloch, F.N. Alyea, and S. O'Doherty, Global trends and 

emission estimates of CC ~ from in situ background observations 

from July 1978 to June 1996. J. Geoplrys. Re.t., 103, 16.0 17- 16.027, 

1998a. 
Simmonds, P.G .. S. ODoheny, J. Huang, R.G. Prinn. R.G. Derwent, 

D. Ryall. G. Nickless. and D.M. Cunnold, Calculated trends and the 

atmospheric abundance of 1. 1, I ,2-tetrafluoroethane. 1.1 -dichloro- lfluoroethane, and l-chloro-1 , l-difluoroethanc using automated in-situ 

gas chromatography-mass spectrometry measurements re~orded at 

Mace Head, Ireland from October 199-t to March 1997, 1. Geilphys. 

Res., 103, 16,029- 16,038, 1998b. 

United Nations Environmental Programme (UNEP), Handbook fo r the 

/11tematii111t1/ Treaties filr the Protectii111 ii/ the ~o11e Layer. 4th ed. , 

Nairobi. Kenya. 1996. 

142 
Winter Sampling of Shallow Firn Air at the South Pole to Understand Processes 

Affecting Firn Atmospheric Histories and Ice 

Core Gas Records 

JEFFREY P. SEVERINGHAUS 

Sc:ripp.t /11 sti1111i1111 o/Oce111111J:raphy. U11i1-ersity 11/C11/if11mi11 . 51111 Diego, Lti }111/11, CA 92093-02·/.I 

In January and July 1998 a cooperative project was carried out 

at the South Pole CMDL Clean Air Laboratory to sample air 

from the top 15 m of the snow (firn). The goal was to better 

understand gas fractionation processes that may affect the 

atmospheric gas histories obtained from the air in the deep lirn 

column. Previous studies in summer have shown a marked 

1socopic anomaly in the top 10 m of the firn, driven by thermal 

fractionation in response lo the strong temperature gradient in the 

top few meters. No samples had been taken in winter, however, 

so Scripps Institution of Oceanography (S IO) was curious to 

know (I) if the opposite sign of the temperature gradient 

produced an opposite isotope anomaly, as expected, (2) if the air 

111 the firn convects spontaneously during winter in response to 

colder air overlying warmer air, which could bias the ice core 

record of gas isotopes. and (3) if adsorption and desorption on 

sno\1 grains could explain anomalies in some halogenated 

species. For comparison a summer sampling was done first. 

Both data sets show the expected isotope fractionation because of 

temperature gradients. The winter data reveal a robust isotope 

anomaly of opposite sign, as expected, that exceeds a diffusiononly model prediction driven by Automatic Weather Station 

surface temperature data. No evidence for vigorous gas mixing 

because of convection was found, although the mistit of the data 

to the model may suggest slow downward motion or a sampling 

arufact. It appears unlikely that rectification of seasonality 

biases the deep firn or ice core record at this site, although this 

study is just a "snapshot" and may have missed episodic events. 

No evidence for adsorption or desorption was found. 

I NTRODUCTION 

The porous and permeable layer or snow on top of polar ice 

sheets is typically 50-100 m thick and is known as the firn layer. 

At the base of this layer the firn is continuously transformed into 

11npermeable ice. The air in firn mixes slowly with the 

atmosphere, primarily by molecular diffusion [Schwander et al., 

1988]. Consequently, the mean age of the air (defined as the 

time elapsed since the air crossed the surface) increases 

downward in the firn and reaches several decades at sites with 

thick firn [Schll'ander et al., 1993). 

A number of recent studies have exploited this fact to 

reconstruct atmospheric concentration histories of various gases, 

such as halocarbons [Bwler el al., 1999], 0/N, ratios and N,O 

[Ba11le et al., 1996), and 13C of CO, [Frc;11 c~y et al., 1999]. 

Other recent studies have taken advantage of the fact that 

temperature gradients in the firn arising from rapid climate 

variation leave an isotope record of abrupt climate change in 

trapped air in ice cores [Se1·eri11gha11s el al., 1998; Le11e11berger 

el al., 1999; Severi11gha11s and Brook. 1999; L<mg e1 al. , 1999). 

At many polar sites, surface temperature varies by >30°C 

seasonally. This creates strong temperature gradients in the top 

few meters of the firn due to the fact that the firn at - I 0 m depth 

closely maintains the mean annual temperature at all times 

[Parerso11, 1969]. Theory predicts that these gradients will lead 

to a characteristic pattern or thermally fractionated gases in the 

upper - 15 m of the tirn column. A model of heat and gas 

diffusion in the firn enables a precise numerical prediction of the 

magnitude and shape or this pattern, when forced with the known 

surface temperature history. The model has no adjustable 

parameters and thus serves as a stringent test of our 

understanding of the physical processes governing gas-isotope 

ratios in shallow firn: 

Gravitational thermal 

settling diffusion 

I I 

ac =~(oc:.T>[ac _ 1::.1118 +ndT]) a, a: a: RT tt: 

where 

C isotope delta value (e.g .. 8''N) 

time 

: depth 

D effective molecular diffusl\ uy or gas 1n porous snow 

T temperature, K 

l!i.!11 mass difference between isotopes 

g gravitational acceleration 

R gas constant 

n thermal diffusion sensitivity, 'kc K I 

( I ) 

A separate model of heat delivers temperatures to the gas 

model [Alley and Koci, 1990]. Comparison of the modeled 

temperature proliles with several measurements (taken from 

thermisters buried in the borehole) shows good agreement 

(Figure I a). 

143 

SAMPLING AND ANALYSIS 

Because of the diffi culty of handling samples outdoors in 

wi nter, gas sampling was arranged to be done from indoors. 

Using a hand coring tool, on January 18, 1998, a 15-m deep 

borehole located 42 m due grid E of the NE corner of the Clean 

Air Building was drilled. Tubes with stainless steel intake 

screens on the ends were placed in the hole at desired depths, and 
a. 

o Feb. 8, 1998 

--model 

o July 28, 1998 

········-model 

ol"l"'t'l"'"',,..,,.,.,...,..,,..,.,.,.,,.'TT"l',.,...:"TTTT",.,.. 

2 

4 

6 

E 

_c 8 ~ 

Q. 

Cl) 

"O 10 

12 

14 

-60.00 -50.00 -40.00 

temperatur e, oc 

2 

4 

6 

8 

10 

12 

14 

0 

2 

4 

6 

8 

10 

12 

14 

b. Winter 28 J uly 1998 

" x 

• o 

" 0 

... 0 .. 

-0.08 -0.04 0.00 

• &'fN 

--model 

x 60/N/3 

0 6"'0/2 

• o' Ar 4 

- ''1JOel 

o 6~Ar/2 

Y o·'Kr/48 

--rnodel 

• 613: Xe/96 

--model 

deviation from atmosphere, per mil 

c. Summer Feb. 8, 1998 

• 

• 

... • 

. .. OP 

0 0.05 0. 1 0.15 02 0.25 0.3 

per mil deviation from atmosphere 

Fig. I Depth profiles of measured temperature (a) and gas composition in the shallo\1 fim at the south pole. Wmter samplmg Cb) re\·cals a large 

negat1w isotope excursion due to thermal isotope fractionation caused by the cold temperatures at the surface rdal11..: to the temperature at IO m 

depth Summer sampling (c) reveals the opposite pattern. as expected Model calculations (sho1rn as Imes) are base<l on the measured surface 

temperature l11sto1') for this Site and the kno11 n <l1ffus111lles of these gases. Gra11tat1onal settling causes a st.:ad) hn.:ar downward mcreas..: that 1s 

independent of season and that is additive to the thermal fracllonallon signal The strong 11 inter anomal). e1en stronger than predicted from 1he 

model. argues against an) ngorous convecti1·e mixing that would hal'e erased the signal by homogemzing 11 11 ith the atmo>phac. 

the tubes were extended into the building for samples lo be taken 

indoors. The hole was backfilled with snow and layers of slush 

to impede downward movement of surface air. After backfilling, 

the tubes were pumped on to remo\'e as much contamination as 

possible. Sampling by pumping on the tubes was done on 

February 8 and again on July 28. This technique is similar lo that 

144 

used to sample air in sand dunes [Se1·eri11gha11s l't al., 1997]. 

Samples were pumped at ~ L min for 16 minutes to nush the 

lines and the sample nasks. The air 11 as dried by passing it 

through a column packed with granular phosphorous pen1oxide. 

The air was stored in 2-L !low-through glass flasks as described 

by 8011/e e1 al. [ 1996]. ask~ were analyzed mass 
spectrometricall y at the University of Rhode Island and SIO for 

"N/"N and "'Ar/"Ar ratios and other gas ratios including 

"'Ar/"Ar, 110/160 of 0 2

, O/Nl' "Kr/"' Ar, and '"Xe/'"Ar. Results 

of two aliquots, measured for 8'5N, 8"0, and 80/N2 from 3 m 

depth at south pole February 8, were rejected on the basis of high 

CO, concentrations (22 and 31 % above normal) that suggested 

gross contamination with laboratory air. 

R ESULTS 

Gravitational settling enriches the heavier molecules at the 

bottom of a stagnant air column in proportion to the mass 

difference fu11, so gravity should affect 8"'° Ar four times as much 

as 8"N [Li11de111a1111 a11d Aston, 1919; Craig et al., 1988; Sowers 

et al. , 1989; Sclrll'a11der, 1989]. In other words, if gravity were 

the only process acting on a gas mixture, 8''N would be equal to 

8"'° Ar/4. To facilitate comparison all results arc presented here 

with the 8 value divided by fu11. 

SIO wanted to know what the shallow firn gas profile did in 

winter when the temperature gradient was reversed from the 

more commonly studied summer profile. In winter cold dense air 

overlies warmer air in the firn and might become unstable and 

undergo Bernard convection [Po11·ers et al., 1985]. If the 

wintertime thermal diffusion anomaly were not expressed 

because of convection, the mean annual thermal fractionation 

signal would be nonzero even when annual mean temperature 

change was zero. In other words, there would be a rectifier of 

seasonal temperature change, and this signal would be 

transmitted to the deep firn and create a bias in the bubble airbased thermal diffusion paleoindicator. 

The tendency to undergo Bernard convection in a porous 

media can be estimated from the dimensionless Rayleigh number 

[Powers et al.. 1985]. Taking the coefficient of thermal 

expansion of air as O.OO-i5 K ', the depth of the layer with strong 

temperature gradient as 5 m, the temperature difference across 

this layer as I 0 K, the permeability of the firn as 4 x IQ ., m', the 

dynamic viscosity of air as 1.4 x 10' kg m' s·', and the thermal 

diffusivity as 0.22 m' s ', a Rayleigh number of 4 is obtained. 

This 1s sufficiently close to the critical value for the onset of 

convection ( I 0-30) that natural convection in snow cannot be 

ruled out by this calculation. Further. this assumes a onedimensional firn without irregularities (snow dunes or sastrugi) 

that might get convection started much more easily. If vigorous 

convective stirring during winter were important, one would 

expect to see a greatly attenuated thermal fractionation signal. In 

fact a fully developed negative isotope anomaly, \\ ith an 

amplitude slightly larger than that predicted by a pure diffusion 

model driven by observed surface air temperature (Figure I b) 

was observed. The summer data are shown for comparison 

(Figure I c). 

The marked deviation of the winter data from the deeper part 

of the model is not understood. It seems possible that gradual 

downward flow is advecting the values obtained at shallower 

depths to deeper levels, as hypothesized at Siple Dome (J. 

Severinghaus, Thermal fractionation of air in polar firn by 

seasonal temperature gradients, in preparation, 2000). 

Alternatively, intermittent turbulent convective mixing may be 

weak enough that it does not homogeni ze and erase the isotope 

fractionation, yet strong enough that it acts to transport the 

isotope signal downward into the firn faster than would 

molecular diffusion alone. In other words, mixing by eddy 

diffusion would double or triple the effective diffusivity over the 

molecular diffusivity. Adding an arbitrary intermittent eddy 

diffusion term to our model produces this effect, demonstrating 

plausibility but not proof. 

CONCLUSIONS 

Seasonal effects penetrate no deeper than 40 m in the firn at 

current measurement precision. Therefore, the firn-ice transition 

at 114 m is effectively isolated from seasonality and records a 

time-averaged value of the fluctuations in the shallow firn. 

Trapped air in ice is, therefore, susceptible to rectification in 

principle. The gas isotope profile observed in the shallow firn 

during winter is nearly symmetrical to that observed during 

summer, suggesting that they should cancel in the annual mean. 

However, this conclusion assumes that the sampling dates were 

representative of average conditions and did not miss strong 

episodes of convection by chance. Deep firn isotopes do tit a 

pure gravitational model well, though, indicating that seasonal 

anomalies probably do cancel [Ba11le et al., 1996]. No sign of 

thermally driven adsorption or desorption was seen. These 

conclusions should be regarded as valid for one site at one time, 

and generalized to other sites with caution. 

Ack11owledg111e111s I 1hank R~lph Keeling. Mark Batlle, and 1-hchael 

Bender for discussions; James Butler fo r mviting me to do a w1ntert1mc 

sampling at the sou1h pole using CMDL rc.:sources: LL Na1han Hill of 

CMDL for taking 1he samples; Julie Palais of NSF-OPP for making 1hc 

soulh pole !ravel possible; l\lichael Bender for hos11ng J.P.S. in his 

laboratory at the Universi1y of Rhode Island; Alexi Grachcv for making 

thermal diffusion sensitivity measurements; and Charles R. Stearns at 

the University of Wisconsin-1\ladison for surface temperature data from 

the Automa1ic Weather Station Project funded by the National Science 

Foundation (NSF). Support came from NSF grant OPP 9725305. 

145 

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Barrow Magnetic Observatory 

JACK TOWNSHEND 

Collexe ln1enu11io11al Geophysirnl Obsen•a/ol)'. Fairbanks, Alaska 99775-6920 

The Barrow Magnetic Observatory (BMO) is the 

northernmost of the U.S. Geological Survey (USGS) 14 

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13 USGS observatories are sent to the NOAA World Data 

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The primary instrumentation operated are: triaxial lluxgate 

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In August 1993, the USGS and NOAA negotiated a 

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observations, and provide some logistic support. The weekly 

absolute measurements and equipment service made by NOAA 

personnel are essential for maintaining high standards for the 

observatory operation and data quality. At the time of writing 

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the MOA. 

The Barrow Magnetic Observatory receives its authorization 

to operate from the USGS Central Region Geologic Hazards 

Team. 

Principal in vesti gators for the Barrow Observatory are 

located al the USGS College Observatory at the UAF in 

Fairbanks, Alaska, and the USGS Central Region Geologic 

Hazards Team, Geomagnetism Group. 

147 
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15 1 

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ACATS 

ACCENT 

ACE 

AERO NET 

AES 

AIRKIT 

ALT 

ANSTO 

AO 

APO 

ARM 

ARO 

ASA 

ATLAS 

ATMOS 

BACPAC 

BAO 

BBC 

BC 

BIF 

BND 

BRW 

BSI 

BSRN 

CAF 

CAMS 

CART 

CATS 

CCGG 

CCN 

CEPEX 

CERES 

CFC 

CGO 

ChEAS 

CIRES 

CMDL 

CN 

CNC 

COBRA 

CSIRO 

DEW 

DIAL 

DOC 

DOE 

DSRC 

DU 

ECI 

ECC 

ECO 

ECMWF 

EEC! 

ENEA 

EOS 

EPA 

ETL 

FID 

FSU 

FTIR 

FWHM 

FWNIP 

FWS 

GAS EX 

GAW 

GC 

GC-ECD 

8. Specialized Abbreviations and Acronyms 

Airborne Chromatograph for Atmospheric Trace Species 

Atmospheric Chemistry and Combustion Effects Near the Tropopause 

Aerosol Characterization Experiment 

Aerosol Robotics Network (NASA) 

Atmospheric Environment Service (Canada) 

Air Kitzis sampler 

Alen, Canada 

Australian Nuclear Science and Technology Organization 

Arctic Oscillation 

Atmospheric Potential Oxygen 

Atmospheric Radiation Measurement (DOE) 

Atmospheric Research Observatory (South Pole, Antarctica) 

Antarctic Suppon Associates 

Arctic Transmissions in the Land-Atmosphere System 

Atmospheric Trace Molecule Spectroscopy 

Bromine Air-sea Cruise Pacific 

Boulder Atmospheric Observatory 

British Broadcasting Company 

black carbon 

Balloon Innation Facility 

Bondville, Illinois 

Barrow Observatory, Barrow. Alaska (CMDL) 

Biospherical Instruments Inc., San Diego, California 

Baseline Surface Radiation Network 

Clean Air Facility (South Pole, Antarctica) 

Control and Monitoring System 

Cloud and Radiation Testbed 

Chromatograph for Atmospheric Trace Species 

Carbon Cycle Greenhouse Gases Group (CMDL) 

cloud condensation nuclei 

Central Equatorial Pacific Experiment 

Clouds and Eanh's Radiant Energy System 

chloronuorocarbon 

Cape Grim Observatory. Tasmania, Australia 

Chequamegon Ecosystem/ Atmosphere Study 

Cooperative Institute for Research in Environmental Sciences (University of Colorado) 

Climate Monitoring and Diagnostics Laboratory (NOAA) 

condensation nuclei 

condensation nuclei counter 

C01 Budget and Rectification Airborne 

The Commonwealth Scientific and Industrial Research Organization (Australia) 

distant early warning 

differential absorption lidar 

U.S. Depanment of Commerce 

U.S. Depanment of Energy 

David Skaggs Research Center (Boulder, Colorado) 

Dobson unit 

equivalent chlorine 

electrochemical cell 

electron capture detector 

European Center for Medium-Range Weather Forecasts 

effective equi valent chlorine 

Enre per le Nuove Tecnologie. !'Energia e l'Ambiente (Italy) 

Eanh Observing System 

Environmental Protection Agency 

Environmental Technology Laboratory (NOAA) 

name ionization detector 

Former Soviet Union 

Fourier transform infrared (spectrometer) 

ful l width at half maximum 

filter wheel nonnal incidence pyrheliometer 

U.S. Fish and Wildlife Service 

Gas Exchange Experiment 

Global Atmospheric Watch 

gas chromatograph 

gas chromatograph with electron capture detection 

152 
GCM 

GC-l\IS 

GEOSECS 

GFDL 

GMCC 

GPS 

HA LOE 

HATS 

HCFC 

HFC 

HMF 

HNI-I 

HOA 

HP 

IAC 

ICP 

IN DO EX 

INSTAAR 

IPASRC-1 

IPC 

IR 

ITCZ 

ITN 

JGOFS 

JPL 

KUl\I 

LACE 

LEAPS 

LEF 

l\IAKS 

MBL 

MFRSR 

MHS 

MLO 

MODTRAN 

MO PITT 

MRI 

1-.ISC 

lo.ISO 

1-.ISISE 

NARL 

NASA 

NCAR 

NCDC 

NCEP 

NDIR 

NDSC 

Nd:YAG 

NEE 

NILU 

NIP 

NIST 

NIWA 

NOAA 

NOAH 

NPC 

NREL 

NRL 

NSA 

NSF 

NWR 

NWS 

OAR 

OD 

ODR 

OMS 

OTTO 

PAN 

PANTHER 

PAR 

general circulacion model 

gas chromatograph \\ ich mass seleccive dececcion 

Geochemical Ocean Seccions 

Geophysical Fluid Dynamics Laboratory (NOAA) 

Geophysical Monicoring for Climatic Change (now CMDL) (NOAA) 

Global Positioning Syscem 

HALogen Occuhmion Experimenc 

Halocarbons and ocher Acmospheric Trace Species Group (CMDL) 

hydrochloronuorocarbon 

hydronuorocarbon 

Harvard Forest, Massachusens 

high northern hemisphere 

Heahh of the Acmosphere Air Quality Research Program (NOAA) 

Hewlcn Packard 

lnscituce of Atmospheric Chemistry (China) 

lncerComParison 

Indian Ocean Experiment 

lnsticuce for Arccic and Alpi ne Research (Uni versity of Colorado) 

Internacional Pyrgeometer and All-sky Scanning Radiometer Comparison 

International Pyrheliomccer Comparison 

infrared 

lncertropical Convergence Zone 

Grifton, North Carolina 

Joint Global Ocean Flux Study 

Jec Propulsion Laboratory 

Cape Kumukahi. Hawaii 

Lightweight Airborne Chromatograph Experiment 

Low Electron Auachment Potential Spcci.:s 

Park Falls. Wisconsin 

Martin and Ki tzis Sampler 

marine boundary layer 

muhifiher rotating shadowband radiomec.:r 

Mace Head, Ireland 

Mauna Loa Observatory. Hawaii (CMDL) 

Moderate Resolution Transminance Model 

Measun:ment Of Pollution ln The Troposphere 

Meteorology Research. Inc. 

1-.lcceorological Service of Canada 

mass seleccive dececcor 

mass speccromecer incoherent scancr - .:xtcnded (extended be)O\\ mesopause from original chermosphenc MSIS-86) 

Naval Arctic Research Lab racor~ 

National Aeronautics and Spac.: Adrniniscracion 

National Center for Acrnosphenc Research 

National Clirnacic Daca Center 

National Centers for Environmental Prediction (NOAA) 

non-dispersive infrared analyzer 

Network for che Detection of Scracospheric Change 

neodymium doped ynrium aluminum garnec (type of laser) 

nec ecosyscem exchange 

Norwegian Institute for Air Research 

normal incidence pyrheliornccer 

National lnscicuce of Standards and Technology (U.S. Depl. of Commerce) 

National Institute for Wacer and Atmospheric Research (New Zealand) 

National Oceanic and Atmospheric Administration (U.S. Depl. of Commerce) 

Nitrous Oxide and Halocompounds (CMDL) 

NREL Pyrheliometer Comparison 

National Renewable Energy Laboratory 

Naval Research Laboratory 

North Slope. Alaska 

National Science Foundation 

Niwoc Ridge. Colorado 

National Weather Service (NOAA) 

Oceanic and Acmospheric Research (NOAA) 

outside diameter 

orthogonal distance regression 

Observacions of the Middle Scracosphere 

automated flask GC-ECD instrument 

peroxyacetyl nitrate 

PAN and Trace Hydrohalocarbon ExpeRiment 

photosynthetically active radiation 

153 
PBL 

PCB 

PEI\! Tropics 

PFR 

PMOD 

POLARIS 

PPLN 

PSA 

PSAP 

QBO 

RAF 

RCF 

RF 

RITS 

SA 

SAFARI 

SAGE 

SC 

S.D. 

SEAR EX 

SEASPAN 

SGP 

SHA DOZ 

SHEBA 

SIO 

Sl\10 

SOLVE 

sos 

SOWER 

SPCZ 

SPO 

SRF 

SRI\! 

STAR 

STRAT 

SUNY 

SZA 

TDL 

TEI 

TIES 

Tl\IF 

TOMS 

TSI 

UCI 

UIC 

UNEP 

UPS 

URAS 

USDA 

USGS 

UTC 

UV 

UVB 

VIS 

WCRP 

WEPC 

WMO 

\VOCE 

WODC 

WOUDC 

WRC 

WRR 

WSA 

WYMS 

plane1ary boundary layer 

polychlorinaled biphe nyl 

Pacific Exploraiory Mission in 1he Tropics (a global 1roposphere experimenl) 

Precision filter radio111e1er 

Physikalisch-Me1eorologisches Observalorium Davos (World Radialion Cen1er) 

Pho1ochemis1ry of Ozone Loss in 1he Arc1ic Region in Summer 

periodically poled li1hiu111 nioba1e 

Palmer S1a1ion, An1arc1ica 

panicle sool absorp1ion pho1ome1er 

quasi-biennial oscillation 

Radialive amplification facior 

Radio111e1er Calibration Facilily 

radio frequency 

Radialivcly lmponanl Trace Species 

sa1ura1ion anomaly 

Southern African Fire-Almosphere Research Ini1ia1ive 

S1ra1osphcric Aerosol and Gas Experiment 

sky cover 

slandard dcvialion 

Sea-Air Exchange Experiment 

SEAREX South Pacific Aerosol Ne1work 

Southern Great Plains (Lamoni, Oklahoma) 

Sou1hern Hemisphere Addilional Ozone Soundings 

S1udy of !he Heat Budge! in the Arclic 

Scripps Institution of Oceanography (University of California. San Diego) 

Samoa Observatory. American Samoa (CMDL) 

SAGE-III Ozone Loss and Validation Experimelll 

Southern Oxidant Study 

Spec ial Observalions of OLOne and Waler in the Equa1orial Region 

Sou1h Pacific Convergence Zone 

South Pole Observatory. An1arc1ica (CMDL) 

solar radiation faci lily 

Standard Research 11.l alerial 

Solar and Thermal Almospheric Radiation Group {CMDL) 

Straiosphenc Tracers of A1111ospheric Transpon 

Slate Universily of New York 

solar zenilh angle 

!unable diode laser 

the rmal electron ins1rumcn1 

Tracer In1erco111parison Experiment for SOLVE 

Table Mou n1ain Facili1y 

To1al OLOne II.lapping Spectro111e1er 

Thermo Sys1e111s Incorporated 

Universil) of California. In me 

Ukpeag\ ik Inupiat Corporation (Alaska) 

United Na1ions Environmental Programme 

uninlerrupliblc power supply 

(a commercial C01 analyzer) 

Uniled Stales Depanrnenl of Agricuhure 

United Stales Geological Stir\C) 

Universal Time Coordinated 

uhraviolcl 

ultraviolet B band 

visible 

World Climate Research Program 

water equivalent precipitalion 

World Meteorological Organi1 ..ation. Geneva. Sw111.erland 

World Ocean Circulation Experimenl 

World Ozone Data Centre 

World Oz.one and Ullraviolet Data Cenlre (Canada) 

World Radiation Cen1er 

World Radialion Reference 

Sable Island, Canada 

Waier Vapor Millimeter-wa'e Spec1rometer 

154