[Characteristics and Control Strategies on Summertime Peak Ozone Concentration in Shanghai]

With the continuous development of air pollution control measures, the concentration of PM_2.5 in Shanghai has shown a conspicuous downward trend in recent years. However, frequent O₃ pollution events have highlighted the urgent need to explore the occurrence patterns of O₃ pollution and develop scientific strategies for reducing O₃ peaks. This study examines data from July 2017, when the cumulative number of O₃ pollution days in 17 cities in the Yangtze River Delta was 165 days, of which Shanghai was the most serious, with an exceedance rate of 64.5%. During this period, the average concentration of NO₂ in Shanghai was 27.1 μg·m^-3 and volatile organic copunds (VOCs) mixing ratio was 22.5×10^-9. By analyzing ozone precursor concentrations and meteorological factors, we determined that these events mainly resulted from a combination of unfavorable meteorological conditions such as high temperature, low humidity, low wind speed, and high precursor emissions. WRF-CMAQ scenario simulations showed that a reduction in precursor emissions in Shanghai alone would have a limited controlling effect on regional O₃ pollution. Thus, regional joint control is recommended when widespread pollution events occur. Our analysis shows that if VOCs in Shanghai and nine neighboring cities can be reduced by 30%, the maximum 8-h O₃ concentration in Shanghai could be reduced by 7.2%. If the reduction number of these cities rises to 17, the maximum 8-h O₃ concentration reduction rate in Shanghai will increase to 7.8%. It is also recommended that the VOCs:NO reduction ratio should be strictly controlled at more than 3:1, or else the O₃ concentration in some areas will increase.