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·(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.