UC San Diego

Plastics have become ubiquitous in the world’s oceans, and recent work indicates that they can transfer from the ocean to the atmosphere in sea spray aerosol (SSA). SSA is the largest contributor to annual aerosol mass load and is a significant source of plastic to the atmosphere. Plastic additives, including bisphenol-A (BPA), represent a sizable fraction of consumer plastics and have been measured consistently in air over both terrestrial and marine environments. However, the chemical lifetimes of BPA and mechanisms by which it degrades with respect to photochemical and heterogeneous oxidation processes in aerosols are unknown. The work in this dissertation utilized an extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) to monitor changes in aerosol composition with high time resolution. In Chapter 3, the photosensitized and OH- initiated heterogeneous oxidation kinetics of BPA in the aerosol phase consisting of pure-component BPA and internal mixtures of BPA, NaCl, and dissolved photosensitizing organic matter are presented. OH-initiated degradation is enhanced in the presence of chloride, likely due to the enhanced mobility of BPA in the more liquid-like particle due to the hygroscopicity of NaCl increasing the liquid water content within the aerosol. In contrast, photosensitized reactions were limited in the presence of chloride, which was attributed to quenching of triplet state formation by dissolved Cl− in the less viscous aqueous aerosol mixtures. In Chapter 4, the composition changes in SSA during a phytoplankton bloom are determined, including the temporal variability and trends dependent on specific biological processes occurring in seawater. Through this study, it was also established that EESI-TOF sensitivity is critically dependent on the sample's relative humidity after adjusting for pressure variations at the inlet and normalization to the reagent ion. In Chapter 5, the photosensitized degradation of BPA at high and low pH is investigated. At pH 3 and pH 11, the photosensitized degradation of BPA is inhibited, and the potential causes are discussed. This dissertation highlights important heterogeneous and photosensitized reactions which BPA undergoes, as well as the role of particle viscosity. Ultimately, this work contributes to our understanding of the lifetimes of hazardous plastic pollutants in SSA with implications for pollutant transport and exposure risks in coastal marine environments.