GLOBAL TRENDS AND EMISSION ESTIMATES OF CCL4 FROM IN-SITU BACKGROUND OBSERVATIONS FROM JULY 1978 TO JUNE 1996

Atmospheric Lifetime Experiment/Global Atmospheric Gases Experiment/Ad vanced Global Atmospheric Gases Experiment (ALE/GAGE/AGAGE) measuremen ts of CCl4 at five remote surface locations from 1978 to 1996 are repo rted. The Scripps Institution of Oceanography (SIO) 1993 absolute cali bration 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 (+22)(-11) x 10(6) kg from 1979 to 1988 and 49(+26)(-13) x 10(6) kg fr om 1991 to 1995. The reduction in the emissions in 1989-1990 coincided with a substantial decrease in the global production of the chloroflu orocarbons (CFCs). The total emission of CCl4 from countries that repo rt 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. Th is implies that nonreporting countries released substantial amounts of CCl4 into the atmosphere in the 1980s and that their releases have ex ceeded those from the reporting countries since 1991.