Chemical Thermodynamics of Water Soluble Organic Compounds Found in Aqueous Atmospheric Aerosols: Modeling and Microfluidic Measurements

Abstract

Atmospheric aerosols, suspensions of tiny particulates in atmosphere, are known to have a major impact on Earth’s climate. Due to the highly chemically and physically complex nature of aerosol particles, large uncertainty in climate modeling arises when attempting to predict the aerosol effect. This dissertation comprises of (1) development of thermodynamic statistical mechanics models to predict solute and water content in aqueous aerosols, and (2) development of an experimental microfluidics approach to measure water loss and study liquid-liquid phase separation. The research effort will significantly advance understanding of aerosol particle thermodynamics by assessing the water content of multiphase particles containing soluble organic compounds, and reduce uncertainty in climate modeling associated with aerosol properties and dynamics. The specific objectives attained in this dissertation research are as follows. I. Aqueous Solution Thermodynamic Model Development: Thermodynamic analytic predictive models using statistical mechanics were developed for multicomponent systems across the entire range of equilibrium relative humidity (RH - 0 to 100%). The models predicted solute activity for a wide range of compounds consisting of partially dissociating organic and inorganic acids, fully dissociating symmetric and asymmetric electrolytes, and neutral organic compounds to capture their chemical behavior. II. Model Applications: (1) pH of aerosols was evaluated in a collaborative work, which is of significant interest due to its effect on the environment. (2) Hygroscopicity was estimated in a collaborative work, which has effects on the optical properties of aerosol particles. III. Experimental Microfluidics: The thermodynamic model was parameterized and validated with measurements of water uptake of multicomponent aerosol particles. The influence of relative humidity on phase behavior to assess the effects on water loss properties was studied for improved understanding of liquid-liquid morphologies. Hydrodynamic trapping of atmospheric aerosol chemical mimics in microfluidic channels was used to perform the experiments, that also represented supersaturated solutions. The efforts in this dissertation together will enhance understanding of atmospheric aerosol phase, solid/liquid/gas partitioning, and liquid-liquid morphologies found in the troposphere. Additionally, the measurements and modeling performed here are useful to any application that requires thermodynamic predictions of water content in complex fluids, like emulsions.