Atmospheric carbon dioxide record from continuous in situ measurements at Point Barrow, Alaska

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

1973-1998

Methods

A UNOR-2 nondispersive infrared CO2 analyzer (NDIR) was used from the start of the measurements at Point Barrow until August 1978. A URAS-2T analyzer (Hartmann and Braun) was used from August 1978 until September 1991. An ULTRAMAT 5E analyzer (Siemens) has been used since then.

Recent modifications were made to the CO2 system to reduce the amount of reference gas usage. The glass H2O cryotrap was relocated between 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).

Data selection steps include 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. For data from 1983 to present, a third selection step based on residuals from a spline fit (Thoning 1989) is applied.

Point Barrow, Alaska
U.S.A. Coastal seashore
71°19' N, 156°36' W
11 m above MSL

Trends

Based on this continuous CO2 record, since 1974 the annual atmospheric CO2 concentration at Point Barrow has risen from 333.94 parts per million by volume (ppmv) to 367.41 ppmv in 1998. Atmospheric CO2 concentrations at Point Barrow show an annual seasonal cycle with yearly minimum values recorded in August and annual maximum values recorded in April or May. Peterson et al. (1982) reported that concentrations of CO2 at Point Barrow for 1973-1979 rose 4-5 ppmv and exhibited a seasonal cycle of 15.2 ppmv. Conway et al. (1988) reported a growth rate of 1.26 ppmv yr-1 for Point Barrow from 1981-1984 and a global growth rate of 1.43 ppmv yr-1 for 1981-92 (Conway et al. 1994) based on NOAA/CMDL flask data.

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.

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.

Peterson, J.T., W.D. Komhyr, T.B. Harris, and L.S. Waterman. 1982.
Atmospheric carbon dioxide measurements at Barrow, Alaska, 1973-79. Tellus 34:166-75.

Peterson, J.T., W.D. Komhyr, L.S. Waterman, R.H. Gammon, K.W. Thoning, and T.J. Conway. 1986.
Atmospheric CO2 variations at Barrow, Alaska, 1973-82. Journal of Atmospheric Chemistry 4:491-510.

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. Tans, T.J. Conway, and L.S. Waterman. 1987.
NOAA/GMCC calibrations of CO2-in-air reference gases: 1979-85. NOAA Technical Memorandum ERL ARL-150. Environmental Research Laboratory, Boulder, Colorado.

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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February 2000