Measurements of atmospheric chlorodifluoro-methane (HCFC-22), based upon a new calibration scale developed in this laboratory, suggest a global tropospheric mean that is ∼28% lower than determined previously from surface-based measurements. A global mean of 101.8 (±1.2, 1 s.d.) ppt and interhemispheric difference of 13 (±1) ppt were determined for HCFC-22 in 1992 from air collected in flasks from seven remote sites located between 82° N and 90° S. These results are consistent with mixing ratios predicted from recent emission estimates and a lifetime for HCFC-22 of 13.6 (+1.9, −1.5) yr. Based upon the analysis of flasks and archived air samples from mid-1987 through 1992, a mean growth rate for HCFC-22 of 7.3 (±0.3)% yr−1 was estimated for this period.
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