Weak acids enhance halogen activation on atmospheric waters surfaces

We report that rates of I₂(g) emissions, measured via cavity ring-down spectroscopy, during the heterogeneous ozonation of interfacial iodide: I^-(surface, s) + O₃(g) + H⁺(s) →→ I₂(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 I₂(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 oceans topmost films should enhance I₂(g) production in marine boundary layers.