Since collection of flasks began in May 1991, the monthly average mixing ratio of CFC-11 at Cape Grim, Tasmania, Australia, has increased slightly [after an anomalously high initial value of 269.8 parts per trillion by mole (ppt) in June 1991] to a value of 268.4 ppt in December 1992. Over nearly the same period, the monthly average mixing ratio of CFC-12 increased from 474.6 to 498.8 ppt. In 1992, the mean growth rate of CFC-12 was 17.6 ppt/year, whereas no statistically significant (at the P = .05 level) trend was found for CFC-11. This absence of growth in the CFC-11 mixing ratio reflects the recent worldwide declines in the production and emission of CFCs and is consistent with findings at other sites in the NOAA/CMDL network (Elkins et al. 1993).
From November 1991 to December 1992, the mixing ratio of HCFC-22 at Cape Grim increased from 93.0 to 98.6 ppt, averaging 6.0 ppt/year. This trend is highly significant (P = .0001).
The collective results presented here for HCFC-22 from the seven monitoring sites show a mean global mixing ratio of 100 ppt for March 1992, with a mean interhemispheric ratio (Northern hemispheric mixing ratio : Southern hemispheric mixing ratio) of 1.14. The mean global growth rate of HCFC-22 over the period of record was 7% per year (Montzka et al. 1993).
From May 1991 to February 1992, the mixing ratio of H-1211 at Cape Grim averaged 2.08 ppt, while that of H-1301 averaged 1.62 ppt. Neither H-1211 nor H-1301 showed any significant (at the P = .05 level) trend over this period. Comparing their data with published results from other investigators (covering the period 1978-92), Butler et al. (1992) concluded that significant declines have occurred in the growth rates of the atmospheric mixing ratios of both halons. These recent drops in growth are supported in general by industry production figures, emission estimates, and current appraisals of atmospheric lifetimes.
CITE AS: Elkins, J.W., T.M. Thompson, J.H. Butler, S.A. Montzka, R.C. Myers,
A.D. Clarke, T.H. Swanson, D.J. Endres, A.M. Yoshinaga, R.C. Schnell, M. Winey, B.G.
Mendonca, M.V. Losleben, N.B.A. Trivett, D.E.J. Worthy, V. Hudec, V. Chorney, P.J. Fraser,
and L.W. Porter. 1994. Atmospheric halocarbon records from the NOAA/CMDL flask sampling
program. In Trends: A Compendium of Data on Global Change. ORNL/CDIAC-65.
Carbon Dioxide Information Analysis Center, Oak Ridge National Laboratory, U.S. Department of Energy, Oak Ridge, Tenn.,
U.S.A.
Date created 12/06/96 (jaw)
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