Publication Type:Journal Article
Source:Journal of Geophysical Research: Atmospheres, Volume 99, Issue D1, p.1107 - 1126 (1994)
Keywords:Middle atmosphere: composition and chemistry, Troposphere: composition and chemistry
Thirteen years of Atmospheric Lifetime Experiment/Global Atmospheric Gases Experiment CCl3F and CCl2F2 measurements at five remote, surface, globally distributed sites are analyzed. Comparisons are made against shipboard measurements by the Scripps Institution of Oceanography group and archived air samples collected at Cape Grim, Tasmania, since 1978. CCl3F in the lower troposphere was increasing at an average rate of 9.2 ppt/yr over the period July 1978 to June 1988. CCl2F2 was increasing at an average 17.3 ppt/yr in the lower troposphere over the same period. However, between July 1988 and June 1991 the increases of CCl3F and CCl2F2 in this region have averaged just 7.0 ppt/yr and 15.7 ppt/yr, respectively. The rate of increase has been decreasing 2.4 ppt/yr2 and 2.9 ppt/yr2 over this 3-year period. Based on a recent scenario of the global releases of these compounds and using the new calibration scale SIO 1993, the equilibrium lifetimes are estimated to be and years for CCl3F and CCl2F2, respectively. Using these lifetime estimates and a two-dimensional model, it is estimated that global releases of these two chlorofluorocarbons in 1990 were 249±28×106 kg for CCl3F and 366±30×106 kg for CCl2F2. It is also estimated that combined releases of these chlorofluorocarbons in 1990 were 21±5% less than those in 1986.