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

Tropospheric ozone (O-3) 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 O-3 concentration, while there is still a dearth of investigations of nocturnal O-3. Here, by analyzing the data of 1,313 sites from the China National Environmental Monitoring Center, we show a remarkable increase in the nocturnal O-3 concentration during summertime of 2015-2019 in most regions of China, revealing an aggravation of nocturnal O-3 pollution. Combining with a GeoDetector model and statistical analysis, we clarify that the aggravation of nocturnal O-3 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 O-3 may have enhanced the nocturnal particulate nitrate (NO3-) formation through N2O5 heterogeneous hydrolysis, and thereby driving the variation and long-term trend of nocturnal NO3-

Automated summary

The concentration of nighttime ozone (O-3) has been increasing in China in recent years, which has become a growing environmental concern. By analyzing data from 1,313 sites in China, it was found that there was a significant increase in nocturnal O-3 concentration during the summer of 2015-2019, indicating an aggravation of nocturnal O-3 pollution. The aggravation of nocturnal O-3 pollution is mainly caused by a decrease in ambient nitrogen dioxide (NO2) concentration and wet scavenging.