The Aggravation of Summertime Nocturnal Ozone Pollution in China and Its Potential Impact on the Trend of Nitrate Aerosols

Tropospheric ozone (O3) concentration continued to increase over past years, thereby becoming a growing environmental concern in China. Most studies have focused on the analysis of daily maximum 8‐hr O3 concentration, while there is still a dearth of investigations of nocturnal O3. Here, by analyzing the data of 1,313 sites from the China National Environmental Monitoring Center, we show a remarkable increase in the nocturnal O3 concentration during summertime of 2015–2019 in most regions of China, revealing an aggravation of nocturnal O3 pollution. Combining with a GeoDetector model and statistical analysis, we clarify that the aggravation of nocturnal O3 pollution is mainly caused by reduction in both ambient nitrogen dioxide (NO2) concentration and wet scavenging in recent years. We further reveal that the increasing O3 may have enhanced the nocturnal particulate nitrate (NO3− ${{\mathrm{N}\mathrm{O}}_{3}}^{-}$) formation through N2O5 heterogeneous hydrolysis, and thereby driving the variation and long‐term trend of nocturnal NO3− ${{\mathrm{N}\mathrm{O}}_{3}}^{-}$. Plain Language Summary The high concentrations of nocturnal ozone exposure pose potential threats to the physiological characteristics of vegetation and crops. Here, we reveal the aggravation of nocturnal O3 pollution during summertime of 2015–2019 in most regions of China. The ambient NO2 reduction and weakened wet scavenging effect in recent years is further clarified as the dominant factor to cause the intensified nocturnal O3 pollution. We also show that the nocturnal O3 plays an important role in the nocturnal NO3− ${{\mathrm{N}\mathrm{O}}_{3}}^{-}$ formation through N2O5 heterogeneous hydrolysis, revealing that the interannual changes in nocturnal O3 likely has driven the variation and long‐term trend of nocturnal NO3− ${{\mathrm{N}\mathrm{O}}_{3}}^{-}$. Key Points Nocturnal O3 pollution was intensified in summer of 2015–2019 in China Reduction in both NO2 and wet scavenging leads to the worsening of nocturnal O3 pollution The aggravated nocturnal O3 pollution drives the nighttime NO3− ${{\mathrm{N}\mathrm{O}}_{3}}^{-}$ interannual variations