VERTICAL-DISTRIBUTION OF METHYL-BROMIDE IN THE STRATOSPHERE

Seven vertical profiles of methyl bromide measured between 1987 and 19 95 in the tropical, mid-latitude and Arctic stratosphere are reported. Three of these profiles are previously unpublished, and four are prev iously published and are here reevaluated and brought on to the same c alibration scale as the other ones. The profiles were derived by the a nalysis of air samples collected hi: the MPAE balloon-home cryogenic s ampler at various latitudes and at heights from around 6 km to around 30 km. Methyl bromide was not detected above the first 7 hn of the tro pical stratosphere, while at higher latitudes it sometimes persisted t o altitudes greater than 13 km above the tropopause. Concurrent measur ements of the man-made Halons 1211 (CBrClF2) and 1301 (CBrF3) and the natural compound CH2Br2 indicate that methyl bromide accounts for 55-7 0% of the bromine transported into the stratosphere from these four sp ecies.