Source Apportionment Of PM_2.5 Over The Beijing-Tianjin-Hebei And Surrounding Areas Based On The WRF-CMAQ/ISAM Model

Since the implementation of the Reform and Opening-up Policy,China has made remarkable achievements in economic construction,while serious air pollution arose at the same time.In recent years,the problem of fine particulate matter(PM_2.5)pollution in Beijing,Tianjin,Hebei（BTH）and surrounding areas during autumn and winter has attracted.particular attention.In this study,a two-level nested WRF-CMAQ system is applied to simulate the air pollution issues in the BTH and surrounding areas from October 2016 to March 2017.A source apportionment（SA）tool,i.e.ISAM,is implemented simultaneously within the framework of CMAQ to investigate the sources of fine particulate matter for 28 cities across the BTH and surrounding areas.Generally,the performance of WRF-CMAQ is reasonably good in reproducing the major meteorological parameters and pollutant concentrations,and the output of ISAM agrees well with the original results of CMAQ.According to the sectoral SA results,residential sector is estimated to be the predominant source of PM_2.5 during this period,especially in those months with the highest PM_2.5 concentrations.Besides,the contributions of industry and transportation sectors are important during the non-heating period.The regional SA results show that the local emissions are predicted to be the largest contributors of PM_2.5 for most cities,while the surrounding cities also make considerable contributions.In terms of the pollutant transport paths,southwest path and southeast path have the highest contributions to Beijing and Tianjin,respectively.When the air quality is getting worse in the two cities,the contributions of the other 27 cities are getting much higher,meaning that the other cities have noteworthy negative influence on the air quality in Beijing and Tianjin under this circumstance.Based on the combinational results of sector-region contributions,the local residential emissions are the most important sources of PM_2.5 in Beijing and Tianjin during this period,while the local transportation and industry sectors and the residential sectors of surrounding cities are also important.The analysis of a representative short-term heavily polluted event in Beijing shows that the concentrations of PM_2.5 can reach a very high peak within a short time,and the sectoral and regional sources of PM_2.5 are quite different for different phases of this event.In this study,we obtain the results of SA of PM_2.5 in the BTH and surrounding areas for different source regions,sectors and time periods.According to these results,localized pollution prevention strategies can be formulated for every city in this area.Furthermore,this study can provide helpful information to the continuous improvement of long-term regional air quality and the setting up of emergency response system to cope with the short-term heavily polluted events.