Distributions of brominated organic compounds in the troposphere and lowerstratosphere

A comprehensive suite of brominated organic compounds was measured from who le air samples collected during the 1996 NASA Stratospheric Tracers of Atmo spheric Transport aircraft campaign and the 1996 NASA Global Tropospheric E xperiment Pacific Exploratory Mission-Tropics aircraft campaign. Measuremen ts of individual species and total organic bromine were utilized to describ e latitudinal and vertical distributions in the troposphere and lower strat osphere, fractional contributions to total organic bromine by individual sp ecies, fractional dissociation of the long-lived species relative to CFC-11 , and the Ozone Depletion Potential of the halons and CH3Br. Spatial differ ences in the various organic brominated compounds were related to their res pective sources and chemical lifetimes. The difference between tropospheric mixing ratios in the Northern and Southern Hemispheres for halons was appr oximately equivalent to their annual tropospheric growth rates, while the i nterhemispheric ratio of CH3Br was 1.18. The shorter-lived brominated organ ic species showed larger tropospheric mixing ratios in the tropics relative to midlatitudes, which may reflect marine biogenic sources. Significant ve rtical gradients in the troposphere were observed for the short-lived speci es with upper troposphere values 40-70% of the lower troposphere values. Mu ch smaller vertical gradients (3-14%) were observed for CH3Br, and no signi ficant vertical gradients were observed for the halons. Above the tropopaus e, the decrease in organic bromine compounds was found to have some seasona l and latitudinal differences. The combined losses of the individual compou nds resulted in a loss of total organic bromine between the tropopause and 20 km of 38-40% in the tropics and 75-85% in midlatitudes. The fractional d issociation of the halons and CH3Br relative to CFC-11 showed latitudinal d ifferences, with larger values in the tropics.