Date of Award

2019

Document Type

Open Access Dissertation

Degree Name

Doctor of Philosophy in Chemistry (PhD)

Administrative Home Department

Department of Chemistry

Advisor 1

Lynn R. Mazzoleni

Committee Member 1

Will H. Cantrell

Committee Member 2

Sarah A. Green

Committee Member 3

Marina Tanasova

Abstract

Ambient atmospheric aerosol is ubiquitous in the atmosphere, originating from a variety of natural and man-made sources. These microscopic particles have profound impacts on the global climate system as well as human health. The organic fraction of atmospheric aerosol is an extremely complex mixture which is not yet fully characterized. These unknown organic aerosol species contribute to the uncertainty in the effect of aerosol on climate and uncertainty in overall ambient aerosol toxicity. Light absorbing organic aerosol can interact with incoming solar radiation and contribute to atmospheric heating; however, the source apportionment and overall fate of these absorbing organic aerosol species are not fully understood. The burning of woody and vegetative materials (biomass) is expected to be one source, while secondary chemical reactions in aqueous phase aerosol and liquid water droplets are another. In this work, we have analyzed ambient samples from the Po Valley (Italy) and Pacific Northwest (USA) influenced by biomass burning. Using ultrahigh resolution mass spectrometry and subsequent molecular formula assignment, we observe an extreme level of molecular complexity in atmospheric aerosol. We make several key observations regarding both biomass burning organic aerosol and aqueous phase processing based on the molecular details and the observed elemental trends in the assigned formulas. We estimate oxidation levels, heteroatom functionalization, aromatic character, volatility and glass transition temperature based on reliable molecular formula assignments. Overall, this work describes a level of complexity in organic aerosol much greater than previously indicated. We suspect that any one analytical technique is likely to miss certain aspects of this mixture, and that a variety of analytical methods must be employed to fully characterize and resolve the complex mixture in atmospheric organic aerosol.

Available for download on Thursday, December 31, 2020

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