Disentangling the effects of meteorology and emissions from anthropogenic and biogenic sources on the increased surface ozone in Eastern China

Abstract

China's Clean Air Actions have substantially improved ambient PM_2.5 air quality since 2013. However, ozone (O₃) pollution in urban areas has worsened in recent years, particularly in the eastern region. The formation of O₃ in these high emission areas is highly complex and regulated by numerous factors. Utilizing the Weather Research and Forecasting model coupled with Chemistry (WRF-Chem), this study conducted a comprehensive analysis through nine sensitivity experiments for the years 2013 and 2017, aimed at disentangling the relative contributions of major factors (e.g., meteorological factors, anthropogenic emissions, biogenic emissions, and aerosol feedback mechanisms) to the observed O₃ concentration trends in Jiangsu, a developed region of China with increasing trend of O₃ level. Our findings indicate a pronounced increase in mean daily maximum 8-h average (MDA8) O₃ levels in the economically vibrant southern Jiangsu, contrasted with a decrease in the less developed northern regions. The study identifies anthropogenic emissions change as the primary driver of O₃ variations, with significant impacts also attributed to meteorological conditions and aerosol feedback effects, while biogenic emission shifts play a lesser role. In terms of meteorological factors, we discovered that the alteration in meteorological thermal factors (enhanced solar radiation and temperatures) in 2017, compared to 2013, exerted a more pronounced influence on the formation of O₃ than the change in thermally driven dynamic factors (boundary layer height and wind speed). Moreover, the study observes a shift in O₃ formation sensitivity from VOC-sensitive to transitional or NO_X-sensitive regimes, signifying a notable transformation in the regional atmospheric chemistry conducive to O₃ generation. Aerosol feedback effects, through complex pathways including photolysis rate alterations and modifications in the vertical O₃ distribution, further compound the challenge of mitigating O₃ levels. Our research underscores the necessity for adaptive, region-specific strategies to mitigate O₃ pollution, providing potential insights for policymakers to formulate effective control measures.