Increased VOC reactivity forcing ozone pollution in the Yangtze River Delta region, China: Evidence from an eight-year observation at an urban site and implications for future control strategies

Ozone (O₃) is the most critical air pollutant in the Yangtze River Delta (YRD) region of China. This study performed long-term field observation of O₃ precursors and meteorological variables from 2015 to 2022 at an urban site in the YRD region, and we identified the driving forces and key sources of O₃ formation rate (OFR) and evaluated the future pathways for mitigating O₃ pollution, combining the positive matrix factorization and observation-based model (PMF-OBM). During 2015–2022, O₃ formation bypassed the NO_X titration trap and was in the volatile organic compound (VOC) and NO_X transitional regime, and the OFR increased. The changes of rapidly decreased NO_X mixing ratio and increased VOC reactivity were the main contributors to the increase in OFR with 69.2 %, while increased temperature, enhanced radiation and other factors contributed to the residual proportion. Our result indicates that simultaneous reductions in ambient VOCs and NO_X could significantly mitigate current O₃ pollution. The control measurements of O₃ pollution should be focused on VOC evaporative emissions (e.g., solvent usage and gasoline evaporation) and complemented by industrial emission and diesel engine exhaust. Furthermore, this study predicted the OFR could decrease around 2025 and that O₃ pollution would be under control, and the sustained reductions in pollutant emissions could enable substantial mitigation of O₃ pollution under the carbon peak and neutrality policies in China.