Improving Solubility and Activity Estimates of Multifunctional Atmospheric Organics by Selecting Conformers in COSMOtherm

Abstract

We estimated aqueous solubilities and activity coefficients of atmospherically relevant highly oxidized multifunctional organic compounds in binary mixtures with water at temperatures between 278.15 and 338.15 K, using the COSMOtherm program. Physicochemical properties of organic aerosol constituents are needed in the modeling of atmospheric aerosol processes. As experimental data is often impossible to obtain, reliable estimates from theoretical approaches are a promising path to fill this gap. We investigated the effect of intramolecular hydrogen bonds on the estimation of these condensed phase properties, attempting to improve the agreement between experimental and estimated values. Citric, tartaric, malic and maleic acid, which are often used in atmospheric models as representatives of oxidized compounds, were selected to benchmark our calculations. In addition, we estimated aqueous solubilities and activity coefficients of α-pinene-derived organosulfates and highly oxidized isoprene-derived organic compounds, for which no experimental data is available. Our results indicate that the absolute aqueous solubility and activity coefficient estimates of citric, tartaric, malic and maleic acid, and likely other multifunctional organics, can be improved significantly by selecting conformers based on their intramolecular hydrogen bonding in COSMOtherm calculations.