Tropospheric ozone depletion events

During springtime in the polar regions, unique photochemistry convertsinert halide salt ions (e.g. Br^-) into reactive halogenspecies (e.g. Br atoms and BrO) that deplete ozone in the boundary layerto near zero levels. Since their discovery in the late 1980s, researchon these ozone depletion events (ODEs) has shown the central role ofbromine photochemistry. Due to the autocatalytic nature of the reactionmechanism, it has been called bromine explosion. It is still not fullyunderstood how salts are transported from the ocean and oxidized tobecome reactive halogen species in the air. Other halogens (chlorine andiodine) are also activated through mechanisms coupled to brominechemistry. The main consequence of halogen activation is chemicaldestruction of ozone, which removes the primary precursor of atmosphericoxidation, and generation of reactive halogen atoms/oxides that becomethe primary oxidizing species. The different reactivity of halogens ascompared to OH and ozone has broad impacts on atmospheric chemistry,including near complete removal and deposition of mercury, alteration ofoxidation fates for organic gases, and export of bromine into the freetroposphere. Recent changes in the climate of the Arctic and state ofthe Arctic sea ice cover are likely to have strong effects on halogenactivation and ODEs.

External links

* [http://www.atmos-chem-phys.net/7/4375/ Halogens and their role in polar boundary-layer ozone depletion]