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Phase transitions of pure and mixed organic and inorganic particles Parsons, Matthew Timothy

Abstract

Aerosol particles in the Earth’s atmosphere play a significant role in such aspects as health effects, visibility effects, and climate effects. In order to quantify the effects of aerosol particles, it is important to have a thorough understanding of the fundamental behavior of the particles. To address this issue, this thesis investigates the phase transitions of atmospherically relevant particles consisting of organic materials, mixed inorganic-organic materials, and inorganic materials with solid inclusions with a combination of techniques. Techniques used were optical microscopy of particles in a flow cell and optical microscopy of particles in an electrodynamic balance. Phase transitions studied were deliquescence and homogeneous and heterogeneous crystallization as functions of temperature, chemical composition, or particle size. The deliquescence relative humidity (RH) and crystallization RH results were interpreted at a fundamental level in terms of the underlying thermodynamic and kinetic factors that influence phase transitions of small particles. It was found that the deliquescence RH for the organic and mixed inorganic-organic particles could be predicted with reasonable accuracy with solution thermodynamics over the range of conditions studied. Homogeneous and heterogeneous nucleation rates were determined from crystallization RH results and parametrized [i.e. parameterized] in terms of classical nucleation theory. The atmospheric implications of the deliquescence RH and crystallization RH results are discussed, with attention to the extrapolation of deliquescence RH and crystallization RH values obtained in laboratory measurements to the expected deliquescence RH and crystallization RH of corresponding particles in atmospheric scenarios. For remote and urban regions of the atmosphere, the results suggest that the deliquescence RH of mixed inorganic-organic particles may be slightly decreased from the deliquescence RH of the pure inorganic material for the compositions studied. In contrast, crystallization RH results suggest that mixed inorganic-organic particles may crystallize at significantly lower RH than the crystallization RH of the pure inorganic materials for remote and urban regions. The heterogeneous crystallization results suggest that solid inclusions used in this study can influence the crystallization RH of inorganic particles in the atmosphere. This work provides extensive characterization of the phase transitions of atmospherically relevant particles, which can be used to improve the general understanding of the effects of aerosol particles in the Earth’s atmosphere.

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