TRENDS: ATMOSPHERIC CARBON DIOXIDE

Atmospheric carbon dioxide record from continuous in situ measurements at the South Pole

Graphics

Digital Data

K.W. Thoning and P.P. Tans

National Oceanic and Atmospheric Administration, Climate Monitoring and Diagnostics Laboratory, Boulder, Colorado 80303, U.S.A

Period of Record

1975-1998

Methods

A URAS-2T nondispersive infrared CO₂ analyzer (NDIR) manufactured by Hartmann and Braun was used at the Amundsen Scott station on the South Pole from the start of measurements until December 1990. Since then, a Siemens ULTRAMAT 5E CO₂ analyzer. The CO₂ NDIR at the South Pole experienced intermittent noise and stability problems during 1996 and 1997. A replacement analyzer is planned for installation, possibly during the austral summer of 1998.

Modifications were made to the CO₂ system to reduce the amount of reference gas usage. The glass H₂O cryotrap was relocated between the the inlet air pumps and the gas manifold and NDIR analyzer. With this setup the first cryotrap dries only the ambient air samples, and the second cryotrap dries the references gases and the dried ambient air. The volume of gas that the reference gases need to flush away after each gas change was greatly reduced making lower flow rates possible. The flow rate was reduced to ~ 150 cc min^-1 from 300 cc min^-1. This change increased the life expectancy of the working reference gas tanks to about six months.

Details on the sampling methods, NDIR apparatus, and calibration standards are provided in Komhyr et al. (1983), Thoning et al. (1987, 1995), and Zhang et al. (1997).

Additional data selection steps for the data through 1982 include an iterative selection based on deviations from a 5-day mean. For data after 1982, an hour-to-hour difference criterion that rejects data that change by more than 0.25 parts per million by volume (ppmv) from one hour to the next and selection based on residuals from a spline fit (Thoning 1989) have been applied instead.

South Pole, Antarctica
Ice and snow-covered plateau
89°59' S, 24°48'W
2810 m above MSL

Trends

Since 1975, annual atmospheric CO₂ mixing ratios at the South Pole Observatory (SPO) have risen from 329.33 parts per million by volume (ppmv) to 363.61 ppmv in 1998.

Gillette et al. (1987) reported that, except for 1976, the continuous data from SPO for 1975-1982 showed good agreement with the SIO and CMDL flask data collected at the South Pole and with the results of the Australian Commonwealth Scientific and Industrial Research Organisation aircraft monitoring program.

Gillette et al. (1987) found the average growth rate of CO₂ at the South Pole for 1975-1982 was 1.32 ± 0.66 ppm yr^-1 and the amplitude of the seasonal cycle ranged from 1.59 ± 0.36 before 1979 to 1.02 ± 0.18 ppm after 1979. For comparison, Conway et al. (1988) reported a growth rate of 1.22 ppm yr^-1 for the CMDL flask sampling data from the South Pole for 1981-1984.

References

Conway, T.J., P. Tans, L.S. Waterman, K.W. Thoning, K.A. Masarie, and R.H. Gammon. 1988.

Atmospheric carbon dioxide measurements in the remote global troposphere, 1981-84. Tellus 40(B):81-115.

Conway, T.J., P.P. Tans, L.S. Waterman, K.W. Thoning, D.R. Kitzis, K.A. Masarie, and N. Zhang. 1994.

Evidence for interannual variability of the carbon cycle from the National Oceanic and Atmospheric Administration/Climate Monitoring and Diagnostics Laboratory Global Air Sampling Network. Journal of Geophysical Research 99(D11):22831-55.

Gillette, D.A., W.D. Komhyr, L.S. Waterman, L.P. Steele, and R.H. Gammon. 1987.

The NOAA/GMCC continuous CO₂ record at the South Pole, 1975-1982. Journal of Geophysical Research 92:4231-40.

Komhyr, W.D., L.S. Waterman, and W.R. Taylor. 1983.

Semiautomatic nondispersive infrared analyzer apparatus for CO₂ air sample analyses. Journal of Geophysical Research 88:1315-22.

Thoning, K.W. 1989.

Selection of NOAA/GMCC CO₂ data from Mauna Loa Observatory. In W.P. Elliot (ed.), The Statistical Treatment of CO₂ Data Records. NOAA Technical Memorandum ERL ARL-173. Air Resources Laboratory, Silver Spring, Maryland.

Thoning, K.W., P.P. Tans, and W.D. Komhyr. 1989.

Atmospheric carbon dioxide at Mauna Loa Observatory 2. Analysis of the NOAA GMCC data, 1974-85. Journal of Geophysical Research 94(D6):8549-65.

Thoning, K.W., T.J. Conway, N. Zhang, and D. Kitzis. 1995.

Analysis system for measurement of CO₂ mixing ratios in flask air samples. Journal of Atmospheric and Oceanic Technology 12(6):1349-56.

Zhang, N., P.P. Tans, and K.W. Thoning. 1997.

A high precision manometric system for absolute calibrations of CO₂ in dry air. Journal of Geophysical Research 102(D5):5885-94.

CITE AS: Thoning, K.W. and P.P. Tans. 2000. Atmospheric CO₂ records from sites in the NOAA/CMDL continuous monitoring network. In Trends: A Compendium of Data on Global Change. Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn., U.S.A.

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