| Description |
Atmospheric aerosols have a great impact on global climate. They can act as the location of chemical reactions, cloud condensation, and ice nuclei. Their morphology determines the interfaces that are exposed to atmospheric volatile compounds and would influence the type and the rate of the chemical reactions as well as the ice nucleating ability of aerosols. Global precipitation is predominantly facilitated by clouds containing ice. Therefore, understanding the morphology and the mechanism of ice nucleation in aerosols is important for climate science. In this dissertation, we develop coarse grain models, perform molecular dynamic simulations, and propose thermodynamic models to illustrate the fundamental physical properties that control the morphology, surface properties, and ice nucleating ability of atmospheric aerosols. We investigate the morphology of liquid−liquid phase separated atmospheric aerosol particles, and we demonstrate that the morphology of micron-sized two-phase particles can be determined from the surface tensions of their interfaces. We study the nucleation of ice in the presence of soft organic and graphitic surfaces, and the nucleation of alkanes in the presence of water and vapor surfaces. Through these studies we unravel the characteristics of surfaces that promote the heterogeneous nucleation of ice and alkanes. We build a theoretical framework based on Classical Nucleation Theory to predict the ice nucleation temperature for any arbitrary surface from its binding free energy to ice. This framework allows us to predict the ice nucleation temperature from equilibrium iv properties of the ice-binding surface and water, instead of performing costly nonequilibrium simulations or experiments. As the binding free energy of a surface to ice becomes stronger, we predict that water reaches a prefreezing region, which has never being discussed in literature before. We design surfaces that prefreeze ice in the region of stability of the liquid and demonstrate that they seed ice nucleation without supercooling. This dissertation provides insight into the morphology and nucleation mechanisms of aerosols, which are of fundamental importance for climate modeling. |
