Aerosol particles have important effects on our world. In the context of the biosphere, aerosols contribute to air pollution and also influence human health. The ongoing COVID-19 pandemic has drawn attention to viral transmission routes, and in turn the dynamics of aerosol particles and the usefulness of filter materials for providing protection against the inhalation of aerosol particles. In order to provide information concerning the efficacy of various materials for the construction of masks for respiratory protection, our lab carried out a study on the penetration of aerosol particles through seventeen materials. The size-resolved percent penetration of various materials by non-biological surrogate particles with diameters ranging from 25 to 500 nm was measured at three face velocities (0.70 cm s-1, 4.30 cm s-1, 13.0 cm s-1). This study showed that some household or commercially-available materials (an allergen filter and an industrial composite filter) and combinations thereof are better choices than others for the preparation of homemade face masks. Additionally, it was found that thicker materials, and materials composted of fibers characterized by smaller diameters, provided better protection against particle inhalation. This study comprises the first part of my dissertation (Chapter II). Aerosols also influence weather via aerosol-cloud interactions, and climate via the direct and indirect aerosols effects. One process through which these particles affect weather and climate is through the nucleation process within clouds, which is required for cloud formation. Nucleation can proceed via droplets at warmer temperatures, or ice crystals at colder temperatures. The latter type of nucleation may proceed through several mechanisms which are not well understood and difficult to model. In order to bridge this gap, a series of ice nucleation workshops have taken place over the last few decades, with a reinvigoration in ice nucleation research during the last fifteen years. The most recent ice nucleation workshop, the third phase of the Fifth International Ice Nucleation Workshop (FIN-03), brought several groups of researchers together for three weeks at Storm Peak Laboratory in Steamboat Springs, Colorado in September 2015. The purpose of this workshop was to facilitate the intercomparison of ice nucleation instruments in a field campaign setting, including Frankfurt Ice nucleation Deposition Freezing Experiment (FRIDGE), the Colorado State University Ice Spectrometer (CSU-IS) and Continuous Flow Diffusion Chamber (CSU-CFDC), the North Carolina State University Cold Stage (NCSU-CS), and a Droplet Measurement Technologies Spectrometer for Ice Nuclei from the Massachusetts Institute of Technology (MIT-SPIN). The results of FIN-03 will comprise the second part of this dissertation (Chapter III). The effect of aerosol particles phase on ice nucleation is another facet of aerosol science which merits further work. Some studies have shown that glassy or viscous particles may effectively act as ice-nucleating particles, while others show that glassy particles may inhibit ice nucleation. We began a study on the effect of aerosol particle phase on ice nucleation efficiency, which is as yet incomplete. Particle phase was studied via measurements of viscosity and the temperature at which each sample transitioned from the liquid phase to a glassy phase. Ice nucleation measurements will be carried out in the future, after my departure from Texas A&M University. The currents results of this study make up the third part of this dissertation (Chapter IV).
