Complete Bromide Surface Segregation in Mixed NaCl/NaBr Aerosols Grown from Droplets

Abstract

Sea-salt aerosols are a source of atmospheric bromine responsible for ozone depletion. The availability of bromine from sea-salt aerosols to heterogeneous phase chemical reactions is determined by its local concentration at the aerosol surface. We report here complete surface segregation of bromine in mixed NaCl/NaBr aerosols grown by drying droplets, thus mimicking the atmospheric process by which solid sea-salt aerosols are generated. For d=70 nm solid aerosols, complete surface segregation is observed for solution Br/Cl ratios below 2%. These findings set a size-dependent upper limit on the bromine surface enrichment that can be reached in solid salt aerosols grown from sea-water droplets in the atmosphere.