Heterogeneous reaction of gaseous ozone with aqueous iodide in the presence of aqueous organic species

The fast reaction of gaseous ozone, O₃(g), with aqueous iodide, I^-(aq), was found to be affected by environmentally relevant cosolutes in experiments using cavity ring-down spectroscopy (CRDS) and electrospray ionization mass spectrometry (ESIMS) for the detection of gaseous and interfacial products, respectively. Iodine, I₂(g), and iodine monoxide radical, IO(g), product yields were suppressed in the presence of a few millimolar phenol (pK_a = 10.0), p-methoxyphenol (10.2), or p-cresol (10.3) at pH 3 but unaffected by salicylic acid (pKa₂ = 13.6), tert-butanol, n-butanol, or malonic acid. We infer that reactive anionic phenolates inhibit I₂(g) and IO(g) emissions by competing with I ^-(aq) for O₃(g) at the air/water interface. ESIMS product analysis supports this mechanism. Atmospheric implications are discussed.