Br2 production from the heterogeneous reaction of gas-phase OH with aqueous salt solutions:: Impacts of acidity, halide concentration, and organic surfactants

This study reports the first laboratory measurement of gas-phase Br(2) production from the reaction between gas-phase hydroxyl radicals and aqueous salt solutions. Experiments were conducted at 269 K in a rotating wetted-wall flow tube coupled to a chemical-ionization mass spectrometer for analysis of gas-phase components. From both pure NaBr solutions and mixed NaCl/NaBr solutions, the amount of Br(2) released was found to increase with increasing acidity, whereas it was found to vary little with increasing concentration of bromide ions in the sample. For mixed NaCl/NaBr solutions, Br(2) was formed preferentially over Cl(2) unless the Br(-) levels in the solution were significantly depleted by OH oxidation, at which point Cl(2) formation was observed. Presence of a surfactant in solution, sodium dodecyl sulfate, significantly suppressed the formation of Br(2); this is the first indication that an organic surfactant can affect the rate of interfacial mass transfer of OH to an aqueous surface. The OH-mediated oxidation of bromide may serve as a source of active bromine in the troposphere and contribute to the subsequent destruction of ozone that proceeds in marine-influenced regions of the troposphere.