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

At least seven organic bromine compounds have been positively identified in the atmosphere1,2 (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and others have been observed in coastal seawater samples (C2H5Br, C3H7Br and CHBr2Cl) (S. A. P. and R. A. Rasmussen, unpublished data).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 ozone3,4. 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.