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Atmospheric Carbon Monoxide 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

February 1992 - December 2001


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) to as much as 1 year for Macquarie Island and the Antarctic sites. Experiments carried out to test for changes in sample CO 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. (Data from the "S160" flasks have been rejected due to large and variable drift.)

Samples were analyzed by gas chromatography with a mercuric oxide reduction gas detector. CO reduces HgO to Hg vapour which is detected by UV absorption. One Trace Analytical gas chromatograph, labeled "RGA3-1" (R1) was used over the length of the record. Further details of CSIRO's global sampling network, sampling procedure, and analytical techniques are provided elsewhere (Francey et al., 1996); measurement uncertainty is discussed by Langenfelds et al. (2001).

Data are linked to the gravimetrically-derived scale of NOAA/CMDL (Novelli et al., 1991) using a single high-pressure cylinder standard with a CO-in-dry-air mole fraction of 196 ppb. This standard is one of five synthetic mixtures of CO2, CH4 and CO in zero air, in the range 30-196 ppb, that were calibrated at NOAA/CMDL between 1992 and 1994. Stability of the CSIRO scale and variations in instrument response are monitored with ~20 high-pressure cylinder standards, with lifetimes of 4-10+ years, spanning a CO mole fraction range of 20-400 ppb. More detailed calibration information is given by Langenfelds et al. (2001).

A number of observed systematic influences complicate the inter-comparability of atmospheric CO measurements made by different laboratories. Comparison of CSIRO and NOAA flask measurements indicates a mean difference of 5.9 ± 1.7 ppb; that is, the differences frequently exceed 10% of the measured CO concentrations at high latitudes in the Southern Hemisphere (where the lowest CO concentrations are typically found). More details and possible reasons for the differences are discussed in detail by Masarie et al. (2001).

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).

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


An annual cycle of CO is evident, largely due to an increase in its destruction by the OH radical during the summer months. Additional influences include spatial and seasonal differences in source strength associated with varying trajectories of arriving air at different times of the year. Annual average CO mixing ratios at Alert in 2001 had decreased by about 13 percent of their 1993 value. A string of abnormally high monthly mixing ratios during the winter of 1998-1999, coupled with higher than normal mixing ratios during the previous summer, led to an anomalously high annual average for 1998. Elevated CO mixing ratios were observed on a global scale during 1998 (see Langenfelds et al., 2002).


  • 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.
  • Langenfelds, R.L., L.P. Steele, C.E. Allison and R.J. Francey. 2001. GASLAB Calibration Information, 2001. Internal Report, CSIRO Atmospheric Research, Aspendale, Australia.
  • Langenfelds, R.L., R.J. Francey, B.C. Pak, L.P. Steele, J. Lloyd, C.M. Trudinger, and C.E. Allison. 2002. Interannual growth rate variations of atmospheric CO2 and its delta 13C, H2, CH4, and CO between 1992 and 1999 linked to biomass burning, Global Biogeochem. Cycles 16(3), pages 21-1 to 21-22.
  • 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.
  • Novelli, P.C., J.W. Elkins, and L.P. Steele. 1991. The development and evaluation of a gravimetric reference scale for measurements of atmospheric carbon monoxide, J. Geophys. Res. 96, 13,109-13,121.
  • 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. 2003. Atmospheric CO concentrations from sites in the CSIRO Atmospheric Research GASLAB air sampling network (October 2002 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.

February 2003.