Dibromomethane (CH sub(2)Br sub(2)) measurements at the upper troposphere and lower stratosphere

Stable brominated hydrocarbons, beside their role in the geochemical cycling of bromine, may enter the stratosphere, where they can efficiently catalyze ozone destruction through the release of inorganic bromine (Br sub(y)). Three vertical profiles of dibromomethane (CH sub(2)Br sub(2)) are reported here, derived from the analyses of air samples collected by the MPAE balloon-borne cryogenic sampler at 17 degree N in 1990 and at 68 degree N in 1992 and 1995. Upper tropospheric volume tractions of this compound from below detection limit to 1.7 pptv were measured. Although CH sub(2)Br sub(2) was already below the detection limit at the tropopause during one of those flights, it was present in the first 2-4 km of the stratosphere in measurable quantities during the other two flights. Concurrent CH sub(3)Br and Halons 1211 (CBrClF sub(2)) and 1301 (CBrF sub(3)) measurements suggest that CH sub(2)Br sub(2) could contribute up to 20% of Br sub(y) released in this altitude region while it could deliver around 10% of the total bromine entering the stratosphere.