Abstract
Atmospheric Lifetime Experiment/Global Atmospheric Gases Experiment/Advanced Global Atmospheric Gases Experiment (ALE/GAGE/AGAGE) measurements of CCl4 at five remote surface locations from 1978 to 1996 are reported. The Scripps Institution of Oceanography (SIO) 1993 absolute calibration scale is used, reducing the concentrations by a factor of 0.77 compared to previous ALE/GAGE reports. Atmospheric concentrations of CCl4 reached a peak in 1989–1990 of 104.4±3.1 parts per trillion (ppt) and have since been decreasing 0.7±0.1 ppt yr−1. Assuming an atmospheric lifetime of 42±12 years, the emissions averaged 94−11+22 × 106 kg from 1979 to 1988 and 49−13+26 × 106 kg frorn 1991 to 1995. The reduction in the emissions in 1989–1990 coincided with a substantial decrease in the global production of the chlorofluorocarbons (CFCs). The total emission of CCl4 from countries that report annual production is estimated to have declined from 11% in 1972 to 4% in 1995 of the CCl4 needed to produce the CFC amounts reported. This implies that nonreporting countries released substantial amounts of CCl4 into the atmosphere in the 1980s and that their releases have exceeded those from the reporting countries since 1991.
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