Inter-city air pollutant transport in The Beijing-Tianjin-Hebei urban agglomeration: Comparison between the winters of 2012 and 2016

In recent years, with the continual urbanization of China, regional atmospheric environmental problems have become increasingly prominent. Although local emissions are an important cause of local pollution, the cross-boundary transmission of pollutants between cities also has an inevitable impact on regional pollution. In this study, the Weather Research and Forecasting (WRF) model coupled with the California Puff (CALPUFF) air quality model was used to study the transmission characteristics of four major air pollutants (SO2, NOx, PM2.5 and PM10) in the Beijing-Tianjin-Hebei urban agglomeration in China in winter, which is the season characterized by the highest levels of pollution. This urban agglomeration is the most polluted area in China. We compared the emission and transmission of pollutants at the city level based on data for January 2012 and 2016. We found that the emissions of most cities had declined since the implementation, in 2013, of the Action Plan for the Prevention and Control of Air Pollution. However, the emissions of three cities, Zhangjiakou, Chengde and Baoding, had significantly increased. Furthermore, the receptor cities and source cities also showed some changes. For example, in 2016, Chengde and Zhangjiakou changed from receptor to source cities, while Tangshan and Tianjin showed the opposite change in status. The likely reason for these changes was that some industries in heavily polluted cities had moved due to stringent atmospheric pollution policies. Moreover, the transmission range of source cities (e.g., Shijiazhuang) in 2016 was significantly smaller than that in 2012, and the transmission intensity also decreased. This case study aids our understanding of how inter-city air pollution transmission has been affected by environmental policy.