Exploring Atmospheric Autoxidation of Organic Emission from Volatile Chemical Products

Author: Yu, Hongmin

Year: 2026

Degree: Dissertation (Ph.D.)

Advisor: Wennberg, Paul O.

Committee Members: Flagan, Richard C.; Wennberg, Paul O.; Okumura, Mitchio; Kroll, Jesse H.

Option: Environmental Science and Engineering

DOI: 10.7907/gpy6-5p94

Abstract

The atmospheric chemistry of organic peroxy radicals (RO₂), which are formed by the gas-phase oxidation of volatile organic compounds (VOCs), governs the chemical fate of VOCs in Earth’s atmosphere. Upon formation, RO₂ react through bimolecular or unimolecular pathways to produce functionalized closed-shell products with lower volatility, which can partition into condensed phase and contribute to formation of secondary organic aerosol (SOA). While the major RO₂ bimolecular reactions (e.g. RO₂ + NO, RO₂ + HO₂) are well-known, the importance of RO₂ unimolecular chemistry, such as gas-phase autoxidation, is recognized more recently. Gas-phase autoxidation chemistry, which is initiated by a RO₂ intramolecular H-shift reaction, transforms VOCs into highly oxygenated organic molecules (HOMs) that are important SOA precursors. In this thesis, I investigate the atmospheric autoxidation chemistry of several classes of VOCs used as solvents or effective ingredients in consumer and industrial products - also known as volatile chemical products (VCPs) - which represents an emerging source of urban anthropogenic VOCs. Four simple molecules were selected as proxies from various VCP classes to probe the autoxidation chemistry of these compound classes (diethyl ether from simple ethers, 2-ethoxyethanol from glycol ethers, 1,2-diethoxyethane from diethers, and ethyl propionate from esters). Gas-phase oxidation experiments, together with computational analyses, were conducted to examine the H-shift reactions of RO₂ derived from those systems and evaluate how specific functional groups influence RO₂ H-shift rate coefficients. While H-shift processes in ether, glycol ether, and diether-derived RO₂ are accelerated and can compete with their bimolecular reactions with NOx species under modern urban atmospheric conditions, ester functionalities are found to suppress autoxidation chemistry and formation of HOMs. Overall, this work provides mechanistic insights into the ways in which functional groups modulate RO₂ autoxidation pathways and production of HOMs, thereby improving understanding of how VCP emissions may contribute to urban SOA formation.

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