Molecular dynamics simulations of periodic and specific ion effects of environmentally relevant heterogeneous systems

Sodium chloride solutions have been used extensively to model seawater in both theoretical and experimental studies of the surface composition and chemistry of atmospheric aerosols. The prediction of the presence of chloride at the liquid-vapor interface has been particularly important for heterogeneous reactions involving the formation of halogen gases from sea salt aerosol. However, sodium is not the only cation present in atmospheric aerosols. Inland aerosols originating from wind-blown dust and cloud water droplets both contain mineral salts. In this dissertation we use classical molecular dynamics simulations to explore the effect of alkali and alkaline earth metal cations on chloride partitioning at the liquid/vapor interface. A correlation is observed between average induced dipole of a halide anion and its surface propensity. Additionally, we explore the effect of co-dissolved halide ions on the interfacial partitioning of nitrate. In sodium nitrate solution at finite concentrations, molecular dynamics simulations suggest that nitrate is depleted from the liquid/vapor interface. Previous studies by Wingen et al. have shown that sodium chloride can affect the partitioning of nitrate at the liquid/vapor interface. Chloride is present at the liquid/vapor interface. Sodium is attracted to the chloride, and nitrate is attracted to the sodium. In this way the addition of chloride is predicted to result in increased interfacial concentrations of nitrate relative to neat solution. In collaboration with X-ray photoelectron spectroscopy experiments and nitrate photolysis experiments we confirm that addition of bromide and iodide has a similar effect.