| Author: | Xiong, Enyu |
| Title: | Budgets of atmospheric oxygenated volatile organic compounds and their impacts on surface ozone pollution in China |
| Advisors: | Guo, Hai (CEE) |
| Degree: | Ph.D. |
| Year: | 2026 |
| Department: | Department of Civil and Environmental Engineering |
| Pages: | 232 pages : color illustrations |
| Language: | English |
| Abstract: | Oxygenated volatile organic compounds (OVOCs) significantly influence atmospheric radical cycling and ozone (O₃) formation, yet their roles remain inadequately quantified. This study integrates field observations, box modeling, and regional modeling to analyze the multi-scale impacts of OVOCs on atmospheric photochemistry, with a focus on their contribution to surface O₃ pollution in China. The first part of this thesis combined a comprehensive set of field measurements and observational-based box model simulations to investigate the roles of OVOCs in radical photochemistry at the Hok Tsui (HT) background site in the Pearl River Delta (PRD) during fall 2020. Using box model simulations constrained by 23 measured OVOCs, I demonstrated that OVOC photolysis dominated local ROₓ production and regulated OH levels. Using 23 measured OVOCs as constraints accounted for 50% to 90% of missing OH sinks across different photochemical scenarios. Such discrepancies were mainly caused by the model’s misrepresentation of key isoprene oxidation products (methyl vinyl ketone, methacrolein, methylglyoxal) and secondary biacetyl. Nevertheless, without observational constraints of these key OVOC species, the model would simulate large biases in ROₓ (-14% to + 10%) and net O₃ production (-11% to +7.9%). These findings highlighted the necessity of observational constraints on reactive OVOCs, particularly dicarbonyls, for accurate radical and ozone modeling. For the second part of this study, I compared the simulated budgets and abundances of OVOCs in China from the GEOS-Chem model against field measurements, with the goal of evaluating our current understanding of OVOCs in China. I simulated seasonal surface concentrations of ten primary VOC species and eight key OVOC species and compared the simulated results to regional observations, which were mostly sampled in summer. Daytime isoprene was underestimated by 12–99% nationally, leading to generally low OVOC predictions. In the Beijing-Tianjin-Heibei (BTH) area, the simulated concentrations of the eight key OVOCs were on average 23% lower than the observations due to underestimated daytime precursor concentrations. Furthermore, the model mis-represented the diurnal patterns of OVOC concentrations in summer, with the simulated OVOC concentrations peaking at night, while the observed OVOC concentrations peaked during the day. In the Yangtze River Delta (YRD), the simulated OVOCs were higher than the observations by 2 to 6 folds due to overestimated aromatics concentrations and potential uncertainties associated with oceanic emissions. In the Sichuan Basin (SCB), the model generally reproduced the observed concentrations of major VOC precursors, yet the model still overestimated the average OVOC concentrations by 63%. In the Pearl River Delta (PRD), the model underpredicted aromatics and isoprene concentrations and slightly underestimated OVOC abundances. I further evaluated the individual budgets of major OVOCs across four Chinese regions using the GEOS-Chem model. The budget analyses indicated that 61% to 99% of the eight key OVOCs in China were photochemically produced, with strong seasonal variation. VOC oxidation accounted for over 80% of OVOC production in winter, especially in northern and eastern regions. In summer, isoprene, methyl vinyl ketone, and methacrolein contributed 56% to 72% of methylglyoxal production. Combined with the analyses in Part 2, I hypothesized that the model may be yielding too little methylglyoxal from the oxidation of aromatics, alkanes, and isoprene warrant further analysis and investigation. In summary, this thesis elucidated the knowledge gaps of our current understanding of atmospheric OVOC photochemistry, quantified OVOCs' cascading impacts on radical budgets and ozone pollution, and provided actionable recommendations for addressing those knowledge gaps. |
| Rights: | All rights reserved |
| Access: | open access |
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