Estimating aqueous solubility and hygroscopicity of amino acid particles with COSMOtherm

Abstract

Amino acids are the primary form of nitrogen in atmospheric aerosol particles. Understanding their aqueous solubility and hygroscopicity is essential for examining their interaction with water vapor and their role in regulating the atmosphere-biosphere nutrient cycle. We use the conductor-like screening model for real solvents (COSMO-RS) to investigate a group of amino acids and their mixtures with inorganic salts. Unlike other thermodynamic models, COSMO-RS allows for property calculations of amino acid groups and of zwitterionic forms. Salting-out effects are observed for most of the amino acids. There is good agreement between the model-derived water activity and measurement values from the literature, highlighting the importance of including zwitterions in the model. Using the model-derived water activity and Köhler theory, we compute the cloud droplet activation curves and find that the amino acids, with 1:1 mass ratio, increase the critical supersaturation of ammonium sulfate or sodium chloride particles by less than 0.15%-points.