SURFACE OZONE DEPLETION IN ARCTIC SPRING SUSTAINED BY BROMINE REACTIONS ON AEROSOLS

NEAR-TOTAL depletion of the ozone in surface air is often observed in the Arctic spring, coincident with high atmospheric concentrations of inorganic bromine1-5. Barrie et al.1 suggested that the ozone depletion was due to a catalytic cycle involving the radicals Br and BrO (ref. 6); however, these species are rapidly converted to the nonradical species HBr, HOBr and BrNO3, quenching ozone loss. McConnell et al.7 proposed that cycling of inorganic bromine between aerosols and the gas phase could maintain sufficiently high levels of Br and BrO to destroy ozone, but they did not specify a mechanism for aerosol-phase production of active bromine species. Here we propose such a mechanism, based on known aqueous-phase chemistry, which rapidly converts HBr, HOBr and BrNO3 back to Br and BrO radicals. This mechanism should be particularly efficient in the presence of the high concentrations of sulphuric acid aerosols observed during ozone depletion events3.