The Effect of Inorganic-Organic Physicochemical Properties on CCN Activity of Complex Mixtures

Abstract

Aerosol effects on Earth’s climate are a major source of uncertainty in predictions of radiative forcing. The physical and chemical composition of aerosols modify cloud reflectivity and lifetime, which exert a strong, but uncertain, cooling effect on the climate; this indirect effect is attributed to aerosols’ ability to form cloud condensation nuclei (CCN). Aerosol particles are often mixtures of inorganic and organic components, and their composition impacts their water-uptake, hygroscopicity and droplet formation. Atmospheric organic aerosol have a wide range of thermodynamic physicochemical properties, therefore introducing complexity in hygroscopicity and droplet formation predictions. To shed light on complex aerosols, this thesis uses laboratory based measurements and characterization techniques to elucidate organic physicochemical property effects on aerosol water uptake. Results of this work will better inform current hygroscopicity models. One such property is an organic compound’s ability to partition to the surface (hence, surface-activity). Organic partitioning can be enhanced during organic-inorganic interactions, known as salting out effects. The effects of salting-out and surface-active organic partitioning on water uptake of mixed organic-inorganic aerosols are investigated. Furthermore, we introduce new computationally efficient parameterizations for subsaturated and supersaturated droplet growth and CCN predictions. Results also show that both organic functional group and aerosol viscosity can also influence salting out and salting-in effects. Specifically, these properties can be predicted and influence the presence of liquid-liquid phase separation (LLPS) and subsequent aerosol water uptake processes. This work finds that organic functional groups, especially for nitrogen containing species, drive interactions with inorganic components; these interactions result in experimental water uptake that deviates from traditionally used hygroscopicity models. Therefore, organic functional groups and internal aerosol phase morphology are critical to improving our scientific understanding of aerosol-climate effects.