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Atmospheric Carbon Dioxide Record from Alert, NWT, Canada

graphics Graphics   data Data


L.P. Steele, P.B. Krummel and R.L. Langenfelds
Commonwealth Scientific and Industrial Research Organization (CSIRO),
Atmospheric Research,
Aspendale, Victoria, Australia, 3195

Period of Record

July 1991 - December 2006


Individual measurements have been obtained from flask air samples returned to the CSIRO GASLAB. Typical sample storage times range from days to weeks for some sites (e.g. Cape Grim, Aircraft over Tasmania and Bass Strait) to as much as one year for Macquarie Island and the Antarctic sites. Experiments carried out to test for changes in sample CO2 mixing ratio during storage have shown significant drifts in some flask types over test periods of several months to years (Cooper et al., 1999). Corrections derived from the test results are applied to network data according to flask type.

Samples were analysed by gas chromatography with flame ionization detection after methanization of CO2 to CH4. One Carle gas chromatograph, labeled "Carle-3" (C3) was used over the length of the record. Further details of CSIRO's global sampling network, sampling procedure, and analytical techniques are provided elsewhere (e.g., Francey et al., 1996); measurement uncertainty is discussed by Francey et al. (2003).

Data are reported in the WMO CO2 Mole Fraction Scale. The link to this scale was established with nine 'primary' high-pressure cylinder standards of synthetic mixtures of CO2 and CO in "zero air" (hydrocarbon-free air) calibrated by NOAA/CMDL in 1992, with a subset recalibrated in 1994. The relative stability of the primary suite is monitored using frequent comparisons with about 15 long-lived secondary standards. The link to the international scale is monitored by a variety of on-going comparisons involving high-pressure cylinder standards (e.g., WMO Round Robins, IAEA CLASSIC, cylinder exchanges with NOAA, etc.), as well as 6-per-month flask-air-sharing comparisons of samples collected at Cape Grim, Australia. More detailed calibration information is given by Francey et al. (2003).

These data represent monthly means, calculated as the mean of daily values from a smooth curve fit to the data using the curve-fitting routines described by Thoning et al. (1989).

Map showing the location of Alert, NWT, Canada

Alert, NWT, Canada
82°27' N, 62°31' W, 6 m above MSL


These measurements indicate a rise in annual average atmospheric CO2 concentration from 357.72 parts per million by volume (ppmv) in 1992 to 383.05 ppmv in 2006, or an increase in annual average of about 1.81 ppmv/year. These flask data may be compared with other flask measurements from the Scripps Institution of Oceanography, available through 2004 in TRENDS; both indicate an annual average increase of 1.72 ppmv/year throuth 2004. Differences may be attributed to different sampling times or days, different numbers of samples, and different curve-fitting techniques used to obtain monthly and annual average numbers from flask data. Measurement error in flask data is believed to be small (Masarie et al., 2001).


  • Cooper, L.N., L.P. Steele, R.L. Langenfelds, D.A. Spencer, and M.P. Lucarelli. 1999. Atmospheric methane, carbon dioxide, hydrogen, carbon monoxide, and nitrous oxide from Cape Grim flask air samples analysed by gas chromatography. Baseline Atmospheric Program (Australia) 1996, edited by J.L. Gras, N. Derek, N.W. Tindale, and A.L. Dick, pp. 98-102, Bureau of Meteorology and CSIRO Atmospheric Research, Melbourne, Australia.
  • Francey, R.J., L.P. Steele, R.L. Langenfelds, M.P. Lucarelli, C.E. Allison, D.J. Beardsmore, S.A. Coram, N. Derek, F.R. de Silva, D.M. Etheridge, P.J. Fraser, R.J. Henry, B. Turner, E.D. Welch, D.A. Spencer, and L.N. Cooper. 1996. Global Atmospheric Sampling Laboratory (GASLAB): supporting and extending the Cape Grim trace gas programs. Baseline Atmospheric Program (Australia) 1993, edited by R.J. Francey, A.L. Dick, and N. Derek, pp. 8-29, Bureau of Meteorology and CSIRO Division of Atmospheric Research, Melbourne, Australia.
  • Francey, R.J., L.P. Steele, D.A. Spencer, R.L. Langenfelds, R.M. Law, P.B. Krummel, P.J. Fraser, D.M. Etheridge, N. Derek, S.A. Coram, L.N. Cooper, C.E. Allison, L. Porter and S. Baly. 2003. The CSIRO (Australia) measurement of greenhouse gases in the global atmosphere, report of the 11th WMO/IAEA Meeting of Experts on Carbon Dioxide Concentration and Related Tracer Measurement Techniques, Tokyo, Japan, September 2001. S. Toru and S. Kazuto (editors), World Meteorological Organization Global Atmosphere Watch, 97-111.
  • Langenfelds, R.L., L.P. Steele, C.E. Allison, and R.J. Francey. 2001. GASLAB Calibration Information, Internal Report, CSIRO Atmospheric Research, Aspendale, Australia.
  • Masarie, K.A., R.L. Langenfelds, C.E. Allison, T.J. Conway, E.J. Dlugokencky, R.J. Francey, P.C. Novelli, L.P. Steele, P.P. Tans, B. Vaughn, and J.W.C. White. 2001. NOAA/CSIRO Flask Air Intercomparison Experiment: A strategy for directly assessing consistency among atmospheric measurements made by independent laboratories, J. Geophys. Res., 106, 20445-20464.
  • 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 - 1985, J. Geophys. Res., 94, 8549-8565.

CITE AS: Steele, L. P., P. B. Krummel and R. L. Langenfelds. 2007. Atmospheric CO2 concentrations from sites in the CSIRO Atmospheric Research GASLAB air sampling network (August 2007 version). 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, TN, U.S.A.

December 2007