Effects of chemical mechanism and meteorological factors on the concentration of atmospheric pollutants in the megacity Beijing, China

To distinguish the effects of chemical mechanisms and meteorological factors on air pollution in the megacity of Beijing, the sensitive numerical experiments with the third-generation air quality modeling system (WRF-SMOKE-CMAQ) are designed for a one-year simulation in 2018. The results indicate that: 1) the modeling system plays well in performance in the megacity of Beijing in 2018. The correlation coefficient of the simulated PM2.5 concentration and the observation value reaches 0.74, while the normal mean bias is −14%–32% in the National Standard Air Quality observation stations in Beijing. 2) The impact of chemical mechanisms on pollutants such as ANO3 is significant, reaching 1075%. However, there is almost no impact on AEC, or ASO4 from the chemical mechanisms. The impact of chemical mechanisms on NO and O3 concentration is between the aforementioned two, with a relatively small degree of impact. The influence of chemical mechanisms on PM2.5 concentration is 35%, while the meteorological factors are 65% under the experiments. 3) For the photochemical species, the peak frequencies of NO2 concentration in the two experiments are 27.1 ppbV and 5.9 ppbV, respectively, and the peak frequency of NO2 observed concentration is 19.1 ppbV, near to the simulation in the baseline group, which illustrates that the chemical mechanism includes a large amount of NO2 generation. The numerical model is a good tool to quantify the effect of chemical mechanisms and meteorological factors. In addition, the concentration of NO2 in Beijing is decreasing from urban to exurb areas in terms of spatial distribution, and the spatial variation of PM2.5 is also the same.