Chemical Characterization of Secondary Organic Aerosol and Critical Intermediates from Isoprene Photooxidation Public Deposited

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Last Modified
  • March 22, 2019
Creator
  • Lin, Ying-Hsuan
    • Affiliation: Gillings School of Global Public Health, Department of Environmental Sciences and Engineering
Abstract
  • Isoprene is a substantial contributor to the global secondary organic aerosol (SOA) burden, with implications for public health and the climate system. The mechanism by which isoprene-derived SOA is formed and the influences of environmental conditions on isoprene SOA formation, however, remain unclear. As a result, systematic laboratory experiments and field studies are required to fully understand these atmospheric processes for the construction of accurate chemical mechanisms implemented in air quality models. Laboratory smog chamber studies investigate isoprene SOA formation by isolating interactions between SOA precursors and key environmental factors, such as levels of nitrogen oxides (NOx= NO + NO2), aerosol acidity, and relative humidity in a controlled atmosphere. Recently, NOx-dependent chemical pathways for isoprene SOA formation have been proposed based on mass spectrometric evidence. However, confirmation of proposed mechanisms and quantification of SOA constituents remain difficult owing to the lack of authentic standards. This dissertation systematically investigates the proposed heterogeneous reactions that lead to isoprene SOA formation in the troposphere by conducting a series of controlled chamber experiments coupled with organic synthesis and detailed SOA compositional analysis at the molecular level. First, by conducting smog chamber experiments with authentic standards of isoprene epoxydiols (IEPOX) and methacrylic acid epoxide (MAE), this dissertation identifies the formation of atmospheric epoxides derived from isoprene as key precursors to SOA formation under low-NOx and high-NOx conditions, respectively. Subsequently, the atmospheric relevance of chamber findings was confirmed by field measurements, and further supported by computational chemistry and atmospheric modeling. Finally, ambient aerosol samples collected using conditional approaches were analyzed to investigate the effects of aerosol acidity on heterogeneous isoprene SOA formation in the rural atmosphere influenced by anthropogenic sulfur dioxide (SO2) and ammonia (NH3) emissions. Chemical characterization of both laboratory-generated and ambient aerosol samples contributes to the scientific understanding of SOA formation processes that are critical for air quality model simulations and environmental management. Detailed compositional information of isoprene SOA will be helpful for hazard identification of these environmental stressors for evaluating public health risks from exposure to ambient fine particles in regions where isoprene emissions interact with anthropogenic pollutants.
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  • In Copyright
Advisor
  • Surratt, Jason
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill
Graduation year
  • 2013
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