A Modeling Study on Characteristics of a PM2.5 Pollution Process in Shandong Province

In this study, the Weather Research and Forecasting/Chemistry (WRF/Chem) model is applied to simulate a PM2.5 pollution process occurred in Shandong Province during 21-26 February 2014. With a focus on analysis and evaluation of simulation results and temporal and spatial variations of PM2.5 concentration, the authors explore the characteristics of PM2.5 in Shandong Province. The relationship between the pollution process and meteorological conditions is also investigated. The results indicate that weak southerly winds were prevailing during the period of PM2.5 accumulation, while the northwesterly winds were dominant during the process of PM2.5 dissipation. In addition, when severe pollution occurred over the Beijing-Tianjin-Hebei region, the northwesterly transported pollutants to Shandong, leading to a second high peak of PM2.5 concentration over some areas in Shandong before the PM2.5 dissipation. During the 6-day period of pollution, the average value of simulated PM2.5 concentration is 125 μg m^-3, the mean surface wind speed is 3.0 m/s, the boundary layer height is 370 m and the mean relative humidity is 70%, respectively. The results also indicate that the simulated PM2.5 concentration is strongly dependent on the boundary layer height. The regionally averaged PM2.5 concentration in Shandong Province is overestimated by about 10% in the model simulation, whereas the high values of observed PM2.5 (e.g. greater than 300 μg m^-3) at several stations are obviously underestimated in the model result. The model performs best in southern Shandong, followed the Shandong Peninsula. The model performance is less satisfactory in the middle and southwestern regions of Shandong.