07 How will stratospheric chlorine change in the future?
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This article is from the Ozone Depletion: Stratospheric Chlorine and Bromine FAQ, by Robert Parson rparson@spot.colorado.edu with numerous contributions by others.
07 How will stratospheric chlorine change in the future?
Since the 1987 Montreal Protocol (see Part I) production of
CFC's and related compounds has been decreasing rapidly, and
in consequence their rate of growth in the atmosphere has
fallen dramatically [Elkins et al. 1993] [Prinn et al. 1995]
[Montzka et al. 1996] The data below show that CFC-12 concentrations
have nearly stabilized while CFC-11 has actually begun to decrease.
Growth Rate, pptv/yr
Year CFC-12 CFC-11
1977-84 17 9 [Elkins et al. 1993]
1985-88 19.5 11 "
1993 10.5 2.7 "
1995 5.9 -0.6 [Montzka et al. 1996]
Methyl chloroform and carbon tetrachloride are also decreasing, while
CFC-113 has stabilized. Overall, tropospheric chlorine from halocarbons
peaked in 1995 and has begun to decline. The time scale for mixing
tropospheric and lower stratospheric air is about 3-5 years, so
_stratospheric_ chlorine is expected to peak in about 1998 and
then to decline slowly, on a time scale of about 50 years.
[WMO 1994] [Montzka et al. 1996]
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