Modeling wintertime air pollution and understanding trans-boundary transportation of air pollutants over the "2+26" cities in northern China

Severe air pollution has been one of the most urgent environmental problems to be resolved in China and has attracted widespread concern in society and academia in recent years. The Beijing-Tianjin-Hebei area (BTH), the Yangtze River Delta (YRD), the Pearl River Delta (PRD), and the Sichuan Basin are the most polluted regions in China. After the release of the National Action Plan of Air Pollution Prevention and Control in 2013, air quality over BTH area were significantly improved in the past five years. However, severe and frequent haze still occurs over BTH and surrounding regions, especially in wintertime. In 2017, the Ministry of Environmental Protection (MEP) in China began to set up the comprehensive air pollution control strategies for "2+26" cities in northern China ("2" represents Beijing and Tianjin, "26" represents 26 major cities in Hebei, Henan, Shanxi, and Shandong). In this study, the Weather Research and Forecasting Model with Chemistry (WRF/Chem) is applied to understand the comprehensive air pollution over BTH and surrounding area and quantify the trans-boundary transportation of air pollutants over the "2+26" cities. Simulations over two domains, East Asia and northern China, using one way nesting were performed at 36- and 12-km horizontal grid resolution, respectively, for the period of January 2015. 37 simulation scenarios are simulated to understand the transportation of air pollutants between provinces, city clusters, and inter-cities. Our results indicate that in general, the WRF/Chem model can reproduce the air pollution over northern China and overall overestimates the PM_2.5 concentrations. The trans-boundary transport of PM_2.5 and its precursors are important in some cities. The improvements of aerosol chemistry and spatial accuracy of emission inventory are needed in future researches.