Emissions of volatile organic compounds (VOCs) and their photooxidation with nitrogen oxides (NOx) play a significant role in atmospheric chemistry and have substantial effects on air quality. Understanding these processes in the ambient environments is a challenge, in part, due to uncertainties in emission sources and the complex chemical evolution of emissions. This dissertationleverages a comprehensive suite of ground-based and airborne observations to investigate the impacts of VOCs-NOxphotochemistry on atmospheric trace gas compositions, both in heavily polluted and pristine environments. In particular, this work focuses on observations of peroxyacyl nitrates (PANs) to provide a detailed diagnosis of photochemistry in the regions discussed throughout the dissertation.

East Asian countries such as South Korea and China have experienced severe air pollution problems. In this work, extensive observations of primary and secondary pollutants were conducted in two locations: a remote ground site in the Yellow River Delta, China, during the Ozone Photochemistry and Export from China Experiment (OPECE) in 2018, and a petrochemical producing region in South Korea during the Korea-United States Air quality (KORUS-AQ) campaign in 2016. Our findings during the field observations indicated that both regions are characterized by heterogeneous VOC composition with substantial emissions of alkenes and aromatics. Photooxidation of these VOCs led to efficient ozone production in a radical-limited environment. In addition, elevated levels of peroxyacetic nitric anhydride (PAN), as well as rarely measured homologs such as peroxybenzoic nitric anhydride (PBzN) and peroxyacrylic nitric anhydride (APAN), illustrated the unique atmospheric chemistry in East Asian environments.