Diffuse Reflectance Infrared Studies of the Reaction of Synthetic Sea Salt Mixtures with NO2: A Key Role for Hydrates in the Kinetics and Mechanism

Abstract

The heterogeneous reactions of oxides of nitrogen with NaCl as a model for sea salt particles have been the focus of many studies, due to their potential to act as precursors to atomic halogens in the troposphere. While a great deal has been learned about the kinetics and mechanisms of NaCl reactions, it is not clear how well this extrapolates to the complex mixture of inorganics found in sea salt. We report here diffuse reflectance infrared Fourier transform spectrometry (DRIFTS) studies in which nitrate formation on the salt surface is followed with time during the reaction of gaseous NO2 with synthetic sea salt at 298 K in the presence of either He or air as the carrier gas. The infrared bands due to surface nitrate formed during the reaction of NO2 are shown to be similar to those from the reaction of MgCl2·6H2O, a major hydrate in the mixture which was used as a surrogate for all of the crystalline hydrates. Significant amounts of surface-adsorbed water are generated in the reaction of synthetic sea ...