Reactive Bromine Compounds

Abstract

Bromine, a minor constituent in the Earth’s atmosphere - with its 50-fold higher efficiency of ozone destruction compared to chlorine - contributes significantly to the ozone hole formation and wintertime stratospheric ozone depletion over northern mid and high latitudes. In addition ozone episodes observed in the Arctic during polar sunrise are solely due to atmospheric bromine. CH₃Br, CH₂Br₂ and CHBr₃ are the major brominated gases in the atmosphere, of which CH₃Br being most abundant, contributes about 50% and CH₂Br₂ around 7 to 10% of the total organic stratospheric bromine. Bromocarbons with shorter lifetimes like CHBr₃, CH₂BrCl, CHBr₂Cl, CHBrCl₂ and CH₂Brl decompose before reaching the stratosphere, and are responsible for the ozone episodes. But for CH₃Br, which has also significant anthropogenic sources, all the aforementioned bromocarbons are mostly of marine origin. Halons (H-1211, H-1301, H-2402, H-1202) are solely anthropogenic and are far more stable. They decompose only after reaching the stratosphere. It is estimated that 39% of the stratospheric organic bromine (≈ 7 pptv) loading is due to these halons. Increases are being still registered in the atmospheric abundance of halons in spite of production restrictions. Though extensively investigated, the existing knowledge with regard to the production and degradation of atmospheric bromine gases, is not commensurate with its importance.