Mass spectrometry of interfacial layers during fast aqueous aerosol/ozone gas reactions of atmospheric interest

The oxidations of sulfite and iodide in the interfacial layers of aqueous microdroplets exposed to O3(g) for 1 ms are investigated by online mass spectrometry of the electrostatically ejected anions. S(IV) oxidation losses in Na2SO3 microdroplets are proportional to [S(IV)] [O3(g)] up to ∼90% conversion. I− is more abundant than HSO 3 - in the interfacial layers of equimolar (Na2SO3 + NaI) microdroplets and ∼3 times more reactive than HSO 3 - toward O3(aq) in bulk solution, but it is converted with minimal loss to I 3 - and IO 3 - plus a persistent ISO 3 - intermediate. These observations reveal unanticipated interfacial gradients, reactivity patterns and transport phenomena that had not been taken into account in previous treatments of fast gas–liquid reactions.