MEASUREMENTS OF HCFC-142B AND HCFC-141B IN THE CAPE-GRIM AIR ARCHIVE - 1978-1993

Stored air samples collected at Cape Grim, Tasmania since 1978, have b een analyzed by GC-MS to investigate the change in the tropospheric co ncentration of HCFC-142b and HCFC-141b over the past 15 years. Between April 1978 and September 1993 the concentration of HCFC-142b rose fro m 0.20 +/- 0.02 pptv to 3.0 +/- 0.3 pptv, with the majority of this in crease occurring from 1989 onwards. By mid-1993 the rate of increase h ad reached 0.9 +/- 0.1 pptv/yr. From 1982 to 1991 the average concentr ation of HCFC-141b was 0.08 +/- 0.01 pptv. A very sharp increase in co ncentration began in 1992. however, such that it reached 0.46 +/- 0.05 pptv by September 1993. Using a 2-D model of atmospheric chemistry, c onstrained by these observations, global emissions of these two compou nds have been calculated and found to differ from other estimates, Thi s is partly due to the background concentration levels which existed p rior to the start of the other estimated emissions.