Anthropogenic Influences on Coastal and Tropical Biogenic Aerosols: Advancing Data-Science-Driven Chemical Analysis for Climate and Public Health

Human activity significantly impacts the quantities, properties, and formationmechanisms of aerosols derived from biogenically produced organic chemicals. In this work, new methods are developed to expand speciated analysis of complex mixtures, and these methods are applied to two classes of human-impacted ambient aerosols: coastal marine aerosol, and tropical organic aerosol. The organic composition of both marine and tropical organic aerosol are largely uncharacterized, with over 85% of individual species separated and catalogued in each data set not present in current mass spectral libraries. Previously utilized methods for quantifying and characterizing novel atmospheric organics rely on manual judgements by individual researchers and are therefore highly inefficient and subject to errors that are difficult to quantify but assumed to be significant. To address this challenge, in Chapter 2 this work presents Ch3MS-RF, a machine learning-based model for predicting the chemical characteristics and instrument response factors of novel atmospheric organics based on their mass spectral fragmentation pattern and chromatographic retention. Chemical properties successfully modeled by Ch3MS-RF include carbon number, oxygen/carbon ratio, average carbon oxidation state, and volatility. This model achieves significant improvements in quantification accuracy over previous methods and enables novel atmospheric organics to be visualized in important chemical properties spaces for atmospheric chemistry, including the volatility basis set and Kroll diagram. Chapter 3 investigates the composition of the organic fraction of sea spray aerosol over a mesocosm phytoplankton bloom experiment conducted using coastal sea water. Results indicate that anthropogenic pollutants, including personal care products, oils, and urban compounds, significantly contribute to the organic fraction of sea spray aerosol, and that biological activity can transform this carbon pool by producing new biogenic species and transforming anthropogenic compounds. Chapter 4 focuses on a single class of anthropogenic coastal pollutants from the same experiment, the benzothiazoles. Benzothiazole is found to be emitted from ocean water in both gas and aerosol phases, and gas phase benzothiazole has the capacity to contribute to secondary aerosol formation when oxidized in the atmosphere. In the primary sea spray aerosol, a diverse suite of benzothiazole-containing species are observed, in concentrations and speciations that are not reflective of those observed in the dissolved organic phase in seawater. Chapter 5 applies similar methods to aerosol samples collected at a semiremote field site in the central Amazon which is impacted by both fires and urban emissions. A high degree of interseasonal uniqueness was observed in secondary products formed in the atmosphere, indicating significant seasonal dependencies of secondary aerosol formation processes. Unique products observed under pristine conditions in the Amazonian wet season and fire impacted conditions in the dry season are not currently included in mass spectral libraries and are not replicated using common laboratory oxidation techniques, highlighting the importance of expanding chamber oxidation studies to simulate a wider range of ambient conditions to elucidate important ambient reaction mechanisms. A chemically speciated view of how human activity alters the properties of terrestrial tropical and marine aerosols will improve our mechanistic understanding of anthropogenic effects on aerosol properties, thereby improving our ability to predict selected aspects of aerosol-climate feedbacks to changing human behavior.

Advisor: Goldstein, Allen H