Response of ozone to meteorology and atmospheric oxidation capacity in the Yangtze river Delta from 2017 to 2020

China implemented a stringent clean air initiative to improve air quality in 2013. By 2017, fine particulate matter (PM2.5) levels in the Yangtze River Delta (YRD) region dropped significantly, but ozone (O3) pollution surged, which aroused concerns about its adverse impact on crops, climate and human health. Due to the complex influences of atmospheric processes, the variation of O3 is highly nonlinear, making the control of O3 pollution highly challenging. It is urgent to deepen the understanding of the role of meteorological factors and atmospheric oxidation capacity (AOC) during O3 episodes. To provide references for O3 pollution control, the study used the Weather Research and Forecasting model (WRF) and the Community Multi-scale Air Quality model (CMAQ) simulations in the YRD from 2017 to 2020 to analyze the causes of severe O3 pollution. Observations revealed a slight decline in heavily O3 polluted days in the YRD region and the simulation results showed that O3 pollution was more prevalent at temperatures above 25 degrees C and relative humidity below 80%. The increase in volatile organic compounds (VOCs), hydroxyl radical (OH) and nitrate radical (NO3) was also more conducive to the formation of O3 pollution. For areas that are primarily VOC-limited areas, such as Shanghai, a stricter policy on VOC control is needed to reduce O3 pollution more effectively.