| In this paper, the WRF-Chem model was used to analyze the temporal and spatial variations of the near-surface concentrations of ozone (O3), nitrogen dioxide (NO2), and fine particulate matter (PM2.5) over Beijing-Tianjin-Hebei region in August2007. The simulation results were evaluated with surface observations. Model comparisons indicated that the model can reproduce the temporal and spatial variations of O3and PM2.5reasonably well, successfully capturing several polluteon events in August2007. However, the model performance was not as good for NO2. The correlation coefficients between the model simulations and the observations were0.69-0.86for O3,0.44-0.49for PM2.5, and0.27-0.43for NO2. In August, the monthly mean concentrations of O3in Beijing and Tianjin were about30ppb, lower than the other areas in this region, whereas relativeely high03concentrations (about60ppb) were predicted in the west of the Beijing-Tianjin-Hebei region and over the Bohai bay. The PM2.5showed higher concentration levels in the south than in the north within the Beijing-Tianjin-Hebei region with the monthly mean concentrations ranging from120to240μg/m3. The monthly mean O3concentration at14:00in August was about60ppb in Beijing and Tianjin, lower than those in the surrounding areas. The mean PM2.5concentrations at14:00in August showed higher levels (100-120μg/m3) in the south parts of the study domain and the Bohai bay areas. An O3pollution episode occurred in August17, when air temperature in Beijing reached33℃at14:00, resulting in high concentrations of O3(80-110ppb). Meanwhile, the concentrations of PM2.5were high over the west and the north of the Bohai bay with a maximum above120μg/m3. Among the PM2.5concentrations, the secondary aerosols formed through chemical reactions, the primary aerosols released directly and sea salt aerosols account for about50-110ug/m3,10-20μg/m3and1-7μg/m3, respectivey, indicating the secondary aerosols were the main contributor to PM2.5in this episode. |
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