GLOBAL TROPOSPHERIC DISTRIBUTION AND CALIBRATION SCALE OF HCFC-22

Measurements of atmospheric chlorodifluoro-methane (HCFC-22), based up on a new calibration scale developed in this laboratory, suggest a glo bal tropospheric mean that is approximately 28% lower than determined previously from surface-based measurements. A global mean of 10 1.8 (/- 1.2, 1 sd.) ppt and interhemispheric difference of 13 (+/- 1) ppt w ere determined for HCFC-22 in 1992 from air collected in flasks from s even remote sites located between 82-degrees-N and 90-degrees-S. These results are consistent with mixing ratios predicted from recent emiss ion 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-I 987 t hrough 1992, a mean growth rate for HCFC-22 of 7.3 (+/- 0.3)% yr-1 was estimated for this period.