UC San Diego

Atmospheric aerosols can impact Earth’s climate and the chemistry of the atmosphere through a variety of processes and pathways. For example, atmospheric aerosols affect Earth’s climate directly by scattering or absorbing solar radiation or indirectly by interacting with clouds and impacting their physiochemical properties. Aerosols are unique microenvironments, distinct from the bulk, and therefore their physiochemical properties result in differences between bulk and aerosol phase processes, such as reactivity and kinetics, acidity and interaction with light. Despite the fact that the effects of aerosols on atmospheric chemistry have been studied in previous work, there remains considerable uncertainties associated with aerosol chemistry resulting in gaps between atmospheric chemistry models and field observations. By better understanding chemical processes occurring within aerosols, as well as cloud or fog droplets, and the factors that influence them, we can help reduce some of the uncertainties in atmospheric models. This dissertation investigates sulfur oxidation chemistry in the atmosphere to better understand factors influencing the rate of oxidation and the extent of formation of inorganic sulfate. In particular, we investigated the influence of various atmospherically relevant conditions (presence of organic compounds, ionic strength, etc.) in the oxidation of inorganic S(IV), sulfite/bisulfite, to inorganic S(VI), sulfate/bisulfate, compounds in the presence and absence of transition metals. Most importantly, a new role of transition metal catalyzed formation of organosulfur compounds has been found. Furthermore, in this dissertation, the further development of the Aerosol Optical Tweezer system to study the chemistry within individual aerosols is discussed. Utilizing the Aerosol Optical Tweezer coupled with cavity enhanced Raman spectroscopy it is shown that this method can be used to investigate changes within a droplet, such as: (i) pH changes induced by coalescence with acidic aerosol; (ii) reactions within the droplet, like monitoring oxidation of S(IV) and; (iii) reaction of glyoxal with sulfite to yield organosulfur compounds. The findings presented in this dissertation can improve our understanding of the factors influencing sulfur oxidation chemistry and help to further develop a method to study the chemistry occurring within single aerosols to reduce some of the uncertainty associated with aerosol chemistry to improve atmospheric chemistry models.