Application of data assimilation technology in source apportionment of PM2.5 during winter haze episodes in the Beijing-Tianjin-Hebei region in China

Abstract

Atmospheric fine particles (PM2.5) in the Beijing-Tianjin-Hebei region have a considerable impact on air quality. Quantitative analysis of PM2.5 transport within the boundary layer is still lacking. In this study, vertical observations from the lidar network were assimilated into the Community Multiscale Air Quality model. The integrated source apportionment method was used to investigate the contributions of PM2.5 in Beijing from January 10 to 18, 2018. After assimilation, the correlation coefficient values of the average diurnal vertical variation between the simulations and observations improved by 20.61%. The investigation of the regional transport at the different vertical layers indicated that: During the two pollution episodes, Beijing's local contribution was significant from the surface to 0.1 km, the maximum hourly mean contributions were 31.15 μg/m3 and 27.56 μg/m3, respectively. From 0.1 to 0.8 km, the local contribution was decreased to below 10 μg/m3, the contributions from the top 10 surrounding areas ranged from 9.51 μg/m3 (49.9%) to 20.42 μg/m3 (80.8%), which were 1.0–9.3 times greater than the local contribution. From 0.8 to 2.0 km, the local contribution decreased gradually, and the regional transport was mainly from Shanxi under prevailing wind fields. Based on lidar vertical observation data, our study revealed that the local contribution of Beijing played an important role in controlling the PM2.5 concentrations from the surface to 0.1 km, while the regional transport was considerable from 0.1 to 2.0 km, particularly from the severely polluted upwind region. It is critical to enhance regional joint emission control, especially during pollution episodes.