ATMOSPHERIC ORGANIC AEROSOLS: THE EFFECT OF PHYSIOCHEMICAL PROPERTIES ON HYGROSCOPICITY

Abstract

Aerosols, tiny solid or liquid particles, are ubiquitous in the atmosphere yet their impact on climate remains poorly understood. One prominent way aerosols are able to impact the climate is through their ability to uptake water and form clouds. The chemical diversity and aerosol interactions in the atmosphere can greatly complicate the investigation of aerosol-cloud interactions. This complexity is expressed with a large uncertainty associated with aerosols’ role on climate change. This dissertation investigates the aerosol-cloud interaction by measuring the water uptake of atmospherically relevant aerosols. Our results highlight the importance of accounting for various physiochemical properties when exploring the water uptake of atmospheric aerosols. One such property is liquid-liquid phase separation (LLPS) in ternary mixtures. Our work offers new evidence, insight, and a paradigm shift to the contribution of LLPS to supersaturated droplet activation. We complemented this finding with a theoretical model, that incorporates solubility, O:C ratio, and LLPS, for predicting κ-hygroscopicity of ternary mixtures. Another physiochemical property that was shown to play a key role in droplet activation of polymeric aerosols is chemical structure. Our study shows that polycatechol is more hygroscopic than polyguaiacol and the difference in hygroscopicity is attributed to the density of hydroxyl groups in both structures. Polycatechol has a higher density of hydroxyl groups than polyguaiacol, resulting in polycatechol having stronger water uptake affinity than polyguaiacol. When maintaining the same structural makeup by investigating the water uptake of two isomeric compounds, we discovered that solubility was the driving force in water uptake. The more soluble isomer o-aminophenol was more hygroscopic than p-aminophenol. Hence, a small change in the position of functional groups can impact solubility which in turn influence hygroscopicity. Lastly, we explored the presence of gas-phase organics on the water uptake of isomers with a wide range of solubilities. Our work highlights that gas-phase organics, specifically ethanol, can influence the water uptake of aerosols. Ethanol was shown to increase water uptake efficiencies based on solubility, with the least soluble compound showing stronger affinity to water uptake. Overall, this thesis advances our knowledge and understanding of aerosol-cloud interactions and its implications on climate change.