DIBROMOMETHANE (CH2BR2) MEASUREMENTS AT THE UPPER TROPOSPHERE AND LOWER STRATOSPHERE

Stable brominated hydrocarbons, beside their role in the geochemical c ycling of bromine, mall enter the stratosphere, sphere, where they can efficiently catalyze ozone destruction through the release of inorgan ic bromine (Br-y). Three vertical profiles of dibromomethane (CH2Br2) are reported here, derived ecl from the analyses of air samples collec ted by the MPAE balloon-borne cryogenic sampler at 17 degrees N in 199 0 and at 68 degrees N in 1992 and 1995. Upper tropospheric volume frac tions of this compound from below detection limit to 1.7 pptv were mea sured. Although CH2Br2 was already below the detection limit at the tr opopause during one of those flights, it was present in the first 2-4 km of the stratosphere in measurable quantities during the other two f lights. Concurrent CH3Br and Halons 1211 (CBrClF2) and 1301 (CBrF3) me asurements suggest that CH2Br2 could contribute up to 20% of Br-y rele ased in this altitude region while it could deliver around 10% of the total bromine entering the stratosphere.