Search

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 PM 2.5 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 ANO 3 is significant, reaching 1075%. However, there is almost no impact on AEC, or ASO 4 from the chemical mechanisms. The impact of chemical mechanisms on NO and O 3 concentration is between the aforementioned two, with a relatively small degree of impact. The influence of chemical mechanisms on PM 2.5 concentration is 35%, while the meteorological factors are 65% under the experiments. 3) For the photochemical species, the peak frequencies of NO 2 concentration in the two experiments are 27.1 ppbV and 5.9 ppbV, respectively, and the peak frequency of NO 2 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 NO 2 generation. The numerical model is a good tool to quantify the effect of chemical mechanisms and meteorological factors. In addition, the concentration of NO 2 in Beijing is decreasing from urban to exurb areas in terms of spatial distribution, and the spatial variation of PM 2.5 is also the same. • The influence of chemical mechanisms on PM 2.5 concentration is 35%, while the influence of meteorological factors is 65%. • The chemical mechanisms have varying impact on the PM components, a significant on ANO 3 , while a little impact on ASO 4. • The difference in the peak frequency of the normal distribution on NO 2 between the two experiments reached 8 ppbV. [ABSTRACT FROM AUTHOR]

The accuracy of determining atmospheric chemical mechanisms is a key factor in air pollution prediction, pollution-cause analysis and the development of control schemes based on air quality model simulations. However, the reaction of NH 3 and OH to generate NH 2 and its subsequent reactions are often ignored in the MOZART-4 chemical mechanism. To solve this problem, the gas-phase chemical mechanism of NH 3 was updated in this study. Response surface methodology (RSM), integrated gas-phase reaction rate (IRR) diagnosis and process analysis (PA) were used to quantify the influence of the updated NH 3 chemical mechanism on the O 3 simulated concentration, the nonlinear response relationship of O 3 and its precursors, the chemical reaction rate of O 3 generation and the meteorological transport process. The results show that the updated NH 3 chemical mechanism can reduce the error between the simulated and observed O 3 concentrations and better simulate the O 3 concentration. Compared with the Base scenario (original chemical mechanism simulated), the first-order term of NH 3 in the Updated scenario (updated NH 3 chemical mechanism simulated) in RSM passed the significance test (p < 0.05), indicating that NH 3 emissions have an influence on the O 3 simulation, and the effects of the updated NH 3 chemical mechanism on NOx-VOC-O 3 in different cities are different. In addition, the analysis of chemical reaction rate changes showed that NH 3 can affect the generation of O 3 by affecting the NOx concentration and NOx circulation with radicals of OH and HO 2 in the Updated scenario, and the change of pollutant concentration in the atmosphere leads to the change of meteorological transmission, eventually leading to the reduction of O 3 concentration in Beijing. In conclusion, this study highlights the importance of atmospheric chemistry for air quality models to model atmospheric pollutants and should attract more research focus. [Display omitted] • The chemical reaction of NH 3 in the chemical mechanism of MOZART-4 was updated. • Impact of updated NH 3 chemical mechanism on O 3 formation further investigated. • Improved O 3 simulation by updating NH 3 chemical mechanism. • Updated NH 3 chemical reaction affects NOx-VOC-O 3 differently in different cities. • Updated scenario lowers Beijing's O 3 concentrations via chemistry and meteorology. [ABSTRACT FROM AUTHOR]