[Spatio-temporal Characteristics and Influencing Factors of Ozone Suppression Events Under High Temperature in China].

Temperature is a key meteorological factor affecting ozone formation. In general, a positive correlation is observed between ozone and temperature, that is, ozone concentration increases with the increase in temperature. However, this relationship may change at extremely high temperatures. When the temperature exceeds a threshold value, the ozone concentration tends to decrease, which is referred to as an ozone suppression event. Ozone suppression events lead to greater uncertainties in the prediction of future air quality under climate change. Based on the national air quality monitoring data, reanalysis data, and meteorological observation data, this study used the Z test to systematically analyze the spatio-temporal characteristics of the critical temperature( T _x ) and frequency of ozone suppression events in China during the warm season(April to September) from 2013 to 2020 and further analyzed the possible influencing factors for the occurrence of ozone suppression events. The results showed that approximately 18% of the sites in China experienced ozone suppression events in the warm season from 2013 to 2020. The sites with a high frequency of ozone suppression events were mainly distributed in the central and western regions of China, such as Sichuan, Xinjiang, and Shaanxi, with an average frequency of ten times per year. The critical temperature( T _x ) ranged from 19.2 to 39.3℃, and the T _x of most sites showed an increasing trend from 2013 to 2020. The high values of T _x were mainly distributed in the central and western regions such as Sichuan, Chongqing, Hunan, and Hubei, whereas the low values of T _x were concentrated in the Qinghai-Tibet Plateau. Contrary to the interannual trend of T _x , the frequency of ozone suppression events decreased significantly in the Beijing-Tianjin-Hebei Region and exhibited a characteristic of "increase-decrease-increase" in the Fenwei Plain, the Yangtze River Delta, and the Chengdu-Chongqing regions. The most significant effect of extreme high temperature on ozone suppresion was found in the Pearl River Delta Region. In addition, ozone precursors(e.g., NO ₂ ) and meteorological conditions(wind speed and direction) were possible factors affecting the occurrence of ozone suppression events.