MEASUREMENTS OF HALOGENATED ORGANIC-COMPOUNDS NEAR THE TROPICAL TROPOPAUSE

The amount of organic chlorine and bromine entering the stratosphere h ave a direct influence on the magnitude of chlorine and bromine cataly zed ozone losses. Twelve organic chlorine species and five organic bro mine species were measured from 12 samples collected near the tropopau se between 23.8-degrees-N and 25.3-degrees-N during AASE II. The avera ge mixing ratios of total organic chlorine and total organic bromine w ere 3.50 +/- 0.06 ppbv and 21.1 +/- 0.8 pptv, respectively. CH3Cl repr esented 15.1% of the total organic chlorine, with CFC 11 (CCl3F) and C FC 12 (CCl2F2) accounting for 22.6% and 28.2%, respectively, with the remaining 34. 1 % primarily from CCl4, CH3CCl3, and CFC 113 (CCl2FCClF 2). CH3Br represented 54% of the total organic bromine. The 95% confid ence intervals of the mixing ratios of all but four of the individual compounds were within the range observed in low and mid-latitude mid-t roposphere samples. The four compounds with significantly lower mixing ratios at the tropopause were CHCl3, CH2Cl2, CH2Br2, and CH3CC13. The lower mixing ratios may be due to entrainment of southern hemisphere air during vertical transport in the tropical region and/or to exchang e of air across the tropopause between the lower stratosphere and uppe r troposphere.