Elucidating ozone formation mechanisms in the central Yangtze River Delta region, China: Urban and rural differences.

Surface ozone (O) pollution has become a pressing air quality issue in eastern China in recent years. However, studies comparing O formation in urban and rural areas remain limited. This study presents a field campaign focusing on volatile organic compounds (VOCs) conducted at two sites in the central Yangtze River Delta (YRD) region during the warm season (June to August) of 2023. VOC pollution sources identified through positive matrix factorization (PMF) were integrated into a machine learning framework, along with nitrogen dioxide (NO) and meteorological factors, to quantify their impacts on O formation. The results show that urban areas have higher VOC concentrations, primarily driven by elevated levels of aromatics and oxygenated volatile organic compounds (OVOCs), compared to rural areas. PMF analysis identified six major VOC sources: industrial emissions, paint and solvent usage, biogenic emissions, combustion-related emissions, mobile sources, and liquefied petroleum gas usage. Mobile sources and industrial emissions are more significant in urban areas, while combustion-related emissions are more significant in rural areas. The machine learning model effectively captured the relationships between meteorological parameters, precursors, and O levels. Analysis revealed that meteorological factors are the primary drivers of O formation in rural areas, whereas both meteorological factors and precursors contribute equally in urban areas. Relative humidity and combustion source emerged as the most influential factors at both sites, though the significance of other factors varied due to environmental differences. These findings enhance our understanding of O pollution differences between urban and rural regions. The combined effects of meteorological factors, NO, and VOCs should be taken into account when formulating O pollution control policies.