Analysis And Forecasting On PM_2.5 Episodes Over Beijing-Tianjin-Hebei Region By Using WRF-Chem Model

The Weather Research and Forecasting model coupled to Chemistry(WRF-Chem model) was modified with an online primary PM2.5 source apportionment method to simulate a severe aerosol pollution episode that occurred over the Beijing-Tianjin-Hebei (BTH) region of China from October 29 to November 8, 2015. The temporal and spatial distributions and transport characteristics of this episode were examined, and the quantified primary PM2.5 contributions by various geographical source regions to the BTH region were also analyzed in this study. The results showed that pollution in this region was mainly due to the combined effects of the synoptic conditions, terrain, and boundary layer characteristics. Before the heavy pollution event, the most parts of the BTH region were controlled by northwest wind, and the local primary PM2.5 contribution to the BTH region accounted for 90.7%. During the heavy pollution period, the BTH region was under isobaric synoptic conditions with light horizontal winds and a stable temperature stratification structure and a lower PBLH, allowing pollutants to accumulate easily in the region. Large quantities of pollutants were transported to the BTH region from Shandong, Jiangsu, Anhui, and Henan provinces via the southerly wind, accounting for 11.6%, 9.2%, 6.7% and 11.8%, respectively. Therefore,regional contributions increased, and other polluted areas, especially the long-distance transport from a source in the Yangtze River Delta city group region,contributed about 15.9%.In addition, the paper also forecasted a pollution case and captured a trend in a haze pollution event using the numerical forecast in the BTH region from March 8 to 21,2016. We studied the pollution processes and the formation mechanism. We have a preliminary analysis of the weather situation, the boundary layer characteristics and the PM2.5 processes of formation, development, maturity and dissipation in this case study, the source contribution of primary PM2.5 in BTH region was analyzed,too. The primary pollutant source apportionment has an effect on prevention strategy,which has a certain effect on reducing regional pollution.