Modeling Cl2 formation from aqueous NaCl particles: Evidence for interfacial reactions and importance of Cl2 decomposition in alkaline solution

Abstract

A series of experiments have demonstrated that a significant yield of chlorine gas is produced when mixtures of ozone and sodium chloride particles above their deliquescence point are irradiated at 254 nm. In order to obtain expressions for future modeling studies, a comprehensive model is used to analyze the system and to determine its sensitivity. This work reexamines and expands previous studies [Knipping et al., 2000]. The enhanced model, described in detail herein, reaffirms that current known physical and chemical processes fail to reproduce the observed Cl2 formation in the experiments. A methodological analysis, proposed as a framework for similar studies, of the physicochemical system supports the accountability of an overall mechanism initiated by the formation of a relatively stable complex of the hydroxyl radical and chloride ions at the gas-liquid interface for the observed chlorine generation. Different potential fates of the OH•••Cl surface•- intermediate are discussed. A rate expression and kinetic parameters are presented for the overall reaction of the interfacial mechanism. In addition, sensitivity studies underscore the importance of accurately modeling chlorine decomposition processes in alkaline solution - in particular, the reactions of chlorine with hydroxide, carbonate, and basic hydrogen peroxide. Recommended aqueous-phase rate constants for these reactions are drawn from a literature evaluation illustrating the limited availability and lack of agreement of related kinetic data. Copyright 2002 by the American Geophysical Union.