An interhemispheric comparison of the concentrations of bromine compounds in the atmosphere

Abstract

At least seven organic bromine compounds have been positively identified in the atmosphere^1,2 (CH₃Br, CH₂Br₂, CHBr₃, CH₂BrCl, CF₃Br, CF₂BrCl and C₂H₄Br₂) and others have been observed in coastal seawater samples (C₂H₅Br, C₃H₇Br and CHBr₂Cl) (S. A. P. and R. A. Rasmussen, unpublished data). The atmospheric chemistry of bromine compounds has considerable consequence in the stratosphere, where bromine acts as a more efficient catalyst than chlorine in removing ozone^3,4. Several bromine compounds also fulfil an important role in the geochemical cycling of the element through the troposphere⁵. Here we present measurements of four bromine compounds (CF₃Br, CH₃Br, CH₂Br₂ and CHBr₃) over a large latitudinal range (40° N to 75° S). These data suggest that the major source of bromine in the atmosphere could be bromoform (CHBr₃), probably emitted from the ocean and with a short lifetime due to photolysis. Our data also suggest that the major emission of methyl bromide (CH₃Br), and hence most bromine entering the stratosphere, will be anthropogenic.