Reactive uptake of ozone on solid potassium iodide

Abstract

Heterogeneous processes impact the rate of both trace gas uptake and chemical conversion within the atmosphere. Sea-salt particles are among the most abundant aerosols globally and provide reactive surface sites for heterogeneous reactions. Ozone, a powerful trace gas oxidant found in both the troposphere and stratosphere, is believed to oxidize alkali halides in the form of sea-salt aerosols. This chemistry is considered to be a significant candidate for the formation of reactive gas-phase molecular halogens. Recent studies suggest that although iodide is a minor component of sea-salt spray its concentration at the interface of aqueous solutions and at the interface of dried solid crystalline sea-salt particles is greatly enhanced relative to the bulk concentration. X-ray photoelectron spectroscopy studies described here show, under conditions in which a low defect density KI surface is completely devoid of adsorbed water molecules, that surface oxidation by ozone results in a thin layer of KIO3 that is self-passivating. An average reactive sticking probability is determined to be gamma(avg) = 1.4 (+/- 0.7) x 10(-4). Results of the low defect density system are compared with the results of a defect-rich polycrystalline KI surface which does not form a passivating film under the conditions of our experiments. In the presence of water, under atmospheric conditions, the surface oxidation of KI to KIO3 is likely to have important consequences on the release of gas-phase molecular iodine into the atmosphere via the Dushman reaction.