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 ((Figure presented.)) formation through N₂O₅ heterogeneous hydrolysis, and thereby driving the variation and long-term trend of nocturnal (Figure presented.).