Variation characteristics of air combined pollution in Beijing City

With a decrease in fine particulate matter (PM2.5) due to the implementation of air pollution prevention-control measures, ozone (O3) has risen in China especially in urban areas recently. It becomes more and more important to control air combined pollution with high concentration of PM2.5 and O3. We analyzed the characteristics of air combined pollution in Beijing from 2014 to 2019 in this paper. Results indicated that the trough O3 showed an upward trend of 4.5 mu g m- 3 yr- 1, while the peak decreased by -1.1 mu g m- 3 yr- 1. There were three typical atmospheric chemical stages in the interaction between O3 and PM2.5 in summer through observations. The first was an intense photochemical stage with the synchronous and rapid growth of O3 and PM2.5. The O3 concentration varied from 68 mu g m- 3 to 206 mu g m- 3 when PM2.5 <= 35 mu g m- 3. While secondary inorganic ions (SNA) ranged from 2 to 21 mu g m- 3 especially SO42- (0.8-12 mu g m- 3). The second was an aerosol chemical generation stage with the rapid increase of PM2.5 and SNA under high O3 concentration. O3 was maintained at a high concentration between 198 mu g m- 3 and 241 mu g m- 3 when PM2.5 was within the range of 35-125 mu g m- 3. SNA increased from 12 mu g m- 3 to 96 mu g m- 3. The third was a high PM2.5 pollution stage suppressing the generation of O3 when PM2.5 >= 125 mu g m- 3. O3 began to decline with the growth of PM2.5 and decreased from 224 mu g m- 3 to 130 mu g m- 3. Ultraviolet radiation (UV) decreased from 13 MJ m- 3 in the first to 8 MJ m- 3 in this stage.