Characterizing the Effects of Aerosol Sulfate, Phase State and Aging on Atmospheric Secondary Organic Aerosol Formation from Isoprene Epoxydiols

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  • Chen, Yuzhi
    • Affiliation: Gillings School of Global Public Health, Department of Environmental Sciences and Engineering
Abstract
  • Atmospheric fine particulate matter (PM2.5, aerosols with aerodynamic diameters <= 2.5 μm) has a key role in Earth’s climate system as well as adversely affects air quality and human health. Organic matter is a substantial PM2.5 component and is mostly generated from atmospheric oxidations of volatile organic compounds (VOCs). Atmospheric oxidation of isoprene, the most abundant VOC emitted from trees, is currently estimated to contribute ~ 30% of the global organic mass fraction of PM2.5. Acid-driven multiphase chemistry of isoprene epoxydiols (IEPOX), key isoprene oxidation products under low-nitric oxide (NO) conditions, with acidic inorganic sulfate (Sulfinorg) aerosol yields substantial amounts of secondary organic aerosol (SOA) through rapid formation of polyols, low-volatility organosulfates (OSs) and oligomers. Over the last decade, IEPOX multiphase chemistry has been recognized as the main source of isoprene-derived SOA. However, unknowns/uncertainties in the formation/sink pathways, formation/sink rates, and resulting chemical composition of isoprene-derived SOA have led to underestimations of PM2.5 mass in isoprene-rich regions by current air quality and climate models.This dissertation research combines laboratory experiments, field measurements, and modeling to fundamentally improve our detailed chemical understanding of the effects of aerosol sulfate, phase state, and aging on the atmospheric transformation of IEPOX into PM2.5. Laboratory experiments revealed rapid conversion of acidic Sulfinorg aerosol into particulate OSs by IEPOX, resulting in measurable and predicted changes in aerosol physicochemical properties, which impeded additional IEPOX multiphase reactivity. These effects were tentatively investigated by a chamber box model, with the outcome anticipated to change the predicted IEPOX-derived SOA mass by large-scale chemical transport models. Heterogeneous hydroxyl radical (•OH) oxidation (or aging) of IEPOX-derived OSs was found to yield highly oxygenated multifunctional OSs, and these laboratory findings were further confirmed by the chemical characterization of ambient PM2.5 samples collected from field measurements. This dissertation provides new mechanistic insights into the formation/sink mechanisms, kinetics, chemical composition, and changes in aerosol physicochemical properties of IEPOX-derived SOA. As these aspects are highly interdependent, it is critical for existing air quality and climate models to consider these new findings to improve the prediction of IEPOX-derived SOA, and ultimately their public health and climatic impacts.
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  • In Copyright - Educational Use Permitted
Advisor
  • Surratt, Jason D.
Degree
  • Doctor of Philosophy
Degree granting institution
  • University of North Carolina at Chapel Hill Graduate School
Graduation year
  • 2021
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