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 . 6H(2)O, 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 salt with NO2 in air, which appears at least in part to be due to liberation of bound water of hydration in the crystalline hydrates. The reaction order with respect to NO2 is (1.8 +/- 0.2) (2 sigma) when the reaction of the synthetic sea salt is carried out in He but only (1.2 +/- 0.2) (2 sigma) when air is used as the carrier gas. For comparison, the reaction order for the NO2-NaCl reaction was reexamined and found to be (1.8 +/- 0.3) (2 sigma) in He and (1.6 +/- 0.3) (2 sigma) in air, in agreement with previous work(19) using this technique. It is assumed for slopes greater than or equal to 1.6 that N2O4 is the reacting species for the purpose of expressing the kinetics in the usual form of reaction probabilities. For the N2O4-NaCl reactions in He and air, and for the N2O4-synthetic sea salt reaction in He, the reaction probabilities are similar (similar to 10(-4)). The reaction of synthetic sea salt with NO2 in the presence of air is treated in terms of a first-order reaction with NO2 being the reactive species, which gives a reaction probability for the NO2-synthetic sea salt reaction of similar to 10(-8). The atmospheric implications are discussed.