Halogens and their role in polar boundary-layer ozone depletion

[摘要] During springtime in the polar regions, unique photochemistryconverts inert halide salt ions (e.g. Br⁻) into reactive halogenspecies (e.g. Br atoms and BrO) that deplete ozone in the boundarylayer to near zero levels.Since their discovery in the late 1980s,research on ozone depletion events (ODEs) has made great advances;however many key processes remain poorly understood. In this articlewe review the history, chemistry, dependence on environmentalconditions, and impacts of ODEs.This research has shown thecentral role of bromine photochemistry, but how salts aretransported from the ocean and are oxidized to become reactivehalogen species in the air is still not fully understood. Halogensother than bromine (chlorine and iodine) are also activated throughincompletely understood mechanisms that are probably coupled tobromine chemistry. The main consequence of halogen activation ischemical destruction of ozone, which removes the primary precursorof atmospheric oxidation, and generation of reactive halogenatoms/oxides that become the primary oxidizing species. Thedifferent reactivity of halogens as compared to OH and ozone hasbroad impacts on atmospheric chemistry, including near completeremoval and deposition of mercury, alteration of oxidation fates fororganic gases, and export of bromine into the free troposphere.Recent changes in the climate of the Arctic and state of the Arcticsea ice cover are likely to have strong effects on halogenactivation and ODEs; however, more research is needed to makemeaningful predictions of these changes.

[学科分类] 大气科学