EARLY TRENDS IN THE GLOBAL TROPOSPHERIC ABUNDANCE OF HYDROCHLOROFLUOROCARBON-141B AND HYDROCHLOROFLUOROCARBON-142B

Hydrochlorofluorocarbons (HCFCs) are rapidly replacing chlorofluorocar bons (CFCs) as foam-blowing agents, solvents, and refrigerants. These substitutes, however, still contain chlorine and have the potential to deplete stratospheric ozone. Although the ozone destruction capacity of HCFCs is believed to be significantly less than that for CFCs, conc ern over unrestricted chlorine input to the atmosphere from HCFC use h as prompted proposals for future limits on production. Here we report the first global time-series for mixing ratios of HCFC-141b (1,1-dichl oro-1-fluoroethane) and HCFC-142b (1-chloro-1,1-difluoroethane) in air collected at seven remote sampling stations. Global mean mixing ratio s in mid-1993 were 0.7 parts per 10(12) (ppt) for HCFC-141b and 4.3 pp t for HCFC-142b. The global atmospheric abundance of HCFC-141b increas ed by 0.9 ppt, or a factor of approximately 3, in 1993. Global abundan ce of HCFC-142b increased by 1.1 ppt yr-1 during 1992-1993. The result s suggest that HCFCs are currently used extensively for replacing CFCs in selected applications. Furthermore, measured levels are significan tly higher than expected based on available emission estimates and con sumption predictions.