Weak Acids Enhance Halogen Activation on Atmospheric Water's Surfaces

We report that rates of I-2(g) emissions, measured via cavity ring-down spectroscopy, during the heterogeneous ozonation of interfacial iodide: I-(surface, s) + O-3(g) + H+(s) ->-> I-2(g), are enhanced several-fold, whereas those of IO center dot(g) are unaffected, by the presence of undissociated alkanoic acids on water. The amphiphilic weak carboxylic acids appear to promote I-2(g) emissions by supplying the requisite interfacial protons H+(s) more efficiently than water itself, at pH values representative of submicrometer marine aerosol particles. We infer that the organic acids coating aerosol particles ejected from ocean's topmost films should enhance I-2(g) production in marine boundary layers.