Climate-driven biogenic emissions alleviate the impact of man-made emission reduction on O₃ control in Pearl River Delta region, southern China

Abstract. O₃ concentrations in the Pearl River Delta (PRD) during summer are typically low and often overlooked. However, integrated observational data reveal a consistent increase in summer O₃ levels over recent decades (+0.96 ppb/year), contradicting China's efforts to reduce anthropogenic emissions. Our dynamically calculated natural emissions show that biogenic volatile organic compound (BVOC) emissions in the region significantly increased between 2001 and 2020, primarily due to climate change and alterations in vegetation cover, with climate-driven BVOC emissions accounting for approximately 80 % of the increase. Furthermore, parallel simulations using the WRF-CMAQ model indicate that climate-driven BVOC emissions, by enhancing atmospheric oxidative capacity and accelerating O₃ formation, have weakened or even offset the benefits of anthropogenic emission reductions, contributing 6.2 ppb to O₃ formation and leading to an unexpected rise in O₃ levels. This study enhances our understanding of the mechanisms behind natural emissions in urban O₃ formation under climate change and provides insights for future O₃ pollution control strategies.