Evaluation and Development of Algorithms to Describe Organic Aerosol Formation Public Deposited

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  • March 22, 2019
Creator
  • Parikh, Harshal M.
    • Affiliation: Gillings School of Global Public Health, Department of Environmental Sciences and Engineering
Abstract
  • SOA modeling frameworks in regional and global-scale air quality models have utilized parameterized approaches (2-product or VBS) to predict SOA from primary VOC species. SOA formation routinely employs NOx-dependent SOA yields for various primary VOC species, that act as precursors of SOA. The result is formation of empirical semi-volatile products. Recent studies have also included OA formation due to aging of semi-volatile and intermediate volatility VBS products from emissions of primary organic gases, formed due to evaporation of semi-volatile POA in the atmosphere. The semi-volatile products are partitioned into the particle liquid-phase frequently using the absorption theory of Pankow that assumes instantaneous thermodynamic equilibrium for gas-particle partitioning. Further, in the last few years, the role and complexity of uptake of polar species on aqueous-phase under high relative-humidity conditions has been recognized, and new detailed mechanisms and overall uptake coefficients have been proposed. The goal of this dissertation is to propose new SOA algorithms and to evaluate existing and the newly proposed SOA algorithms, by numerically simulating outdoor smog chamber experiments performed at UNC. The experiments include a variety of aromatic precursors (toluene and xylenes), under varying conditions of seed type, initial seed concentration, and relative humidity. In addition, the initial gas-phase conditions for experiments include different conditions of a non-SOA-forming hydrocarbon (HCmix) mixture (comprising of short-chain alkanes/alkenes), diesel exhaust and/or meat cooking emissions. The first and second part of this dissertation highlights the problems associated with the applicability of the thermodynamic equilibrium assumption for current empirical parameterizations under certain environmental conditions (low initial particle concentration, presence of HCmix and low RH). SOA is severely over-predicted under these conditions. A pseudo mass-transfer limiting dynamic gas-particle partioning approach is proposed. This approach substantially improves model performance under the mentioned conditions. For high RH conditions, the incorporation of particle aqueous-phase chemistry highlights the importance of aqueous-phase SOA. In the third part of the dissertation, we propose an alternative hybrid SOA framework that successfully uses a condensed kinetic modeling approaches to predict SOA from aromatic oxidation and a parameterized VBS approach to predict SOA from complex diesel exhaust and meat cooking emissions.
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  • In Copyright
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  • ... in partial fulfillment of the requirements for the degree of Doctor of Philosophy in the Department of Environmental Sciences and Engineering (School of Public Health).
Advisor
  • Vizuete, William
Degree granting institution
  • University of North Carolina at Chapel Hill
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