Assessment of ozone formation, precursor sensitivity, and pollution control under Heatwaves: Based on direct OPR observations.

Due to complex photochemical processes, controlling frequent ozone (O3) pollution in China presents a challenge, particularly during heatwaves. To accurately establish the relationship between O3 and its precursors-volatile organic compounds (VOCs) and nitrogen oxides (NOx)-continuous direct observations of the ozone production rate (OPR) were conducted for the first time in the Yangtze River Delta. The observation results indicate that the peak OPR fluctuates significantly between 6.12 and 27.29 ppbv/h, with high temperatures and elevated VOCs being direct drivers of O3 pollution. Further analysis reveals that OPR reaches its peak when the ratio of photochemically consumed VOCs to NOx concentration is 2.00 ppbv ppbv-1, a threshold that also effectively delineates O3 sensitivity regimes. Notably, precursor sensitivity tests based on OPR demonstrate that the contribution of some alkenes from anthropogenic sources to OPR is substantially underestimated due to their photochemical consumption. Heatwaves accelerate the increase in this ratio, leading to a rapid rise in the peak OPR while simultaneously expediting the transition of O3 toward the NOx-limited regime, complicating efforts to control O3 pollution under low NOx conditions. This study provides robust support for the early warning and dynamic control of O3 pollution.