Ozone Formation in a Representative Urban Environment: Model Discrepancies and Critical Roles of Oxygenated Volatile Organic Compounds

Abstract

Ozone (O₃) significantly impacts air quality. Despite reductions in PM_2.5 since the 2013 Clean Air Act, the level of the O₃ concentration has continued to rise in China, underscoring the need for targeted pollution control measures. This study examined the seasonal and spatial variations of pollutants and meteorological variables in a major industrial city in Eastern China. Three widely used approaches, including the ozone formation potential (OFP) calculation, an observation-based model (OBM), and a random forest algorithm, were employed to investigate O₃ formation in urban environments. Results show that oxygenated volatile organic compounds were the most significant contributors to summer urban O₃, whereas their impact was significantly reduced during the winter. Each O₃ formation evaluation model provided unique insights, with OFP offering rapid estimates, the OBM revealing detailed chemistry, and random forest capturing nonlinear interactions. However, the study also identified limitations in these models. OFP failed to account for seasonal variations in the level of O₃ formation, and the random forest model struggled to distinguish causal relationships from correlations. These findings highlight the need for caution when relying on a single model and underscore the importance of integrating multiple methods to gain an accurate understanding of urban O₃ formation dynamics, which is crucial to developing effective control strategies.