Integrating Observations and Model Simulations to Uncover Chemical and Physical Drivers of Organic Aerosol Composition in Urban Taiwan

This study investigates the composition, sources, and transformation processes of organic aerosols (OA) in Xitun, a near-industrial urban area in Taichung City, Taiwan, during a field measurement campaign in November 2023. Using a real-time Aerosol Mass Spectrometer (AMS) combined with Positive Matrix Factorization analysis, five organic aerosol components are identified: hydrocarbon-like OA (HOA), aged hydrocarbon-like OA (aged-HOA), semi-volatile oxygenated OA (SV-OOA), low-volatility oxygenated OA (LV-OOA), and background species. Oxygenated OA (OOA), primarily comprising secondary organic aerosol (SOA) formed through the oxidation of gas-phase precursors, accounted for 43–60% of the total OA mass, while HOA and aged-HOA, mainly derived from primary organic aerosol (POA) emitted by traffic and industrial sources, contributed approximately 30% of the total OA mass. To simulate OA evolution, a two-box model is developed, incorporating physical processes, including advection and entrainment, which are characterized using CO concentration simulations. The results align closely with those from the Community Multiscale Air Quality (CMAQ) model. With the physical processes well-constrained, the chemical processes are added to the model to quantify the chemical production and loss of selected volatile organic compounds (VOCs) and the formation of semi-volatile organic compounds (SVOCs) species, distinguishing between anthropogenic and biogenic VOC sources contributing to SOA formation. The oxidation rates of OA will be further determined through model simulations constrained by AMS observations. This study offers valuable insights into the sources, oxidation processes, and evolution of organic aerosols, providing a basis for comprehensive modeling approaches and enhancing our understanding of their impacts on air quality and human health.