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The Beijing–Tianjin–Hebei (BTH) region is a metropolitan area with the most severe fine particle (PM 2.5) pollution in China. An accurate emission inventory plays an important role in air pollution control policy making. In this study, we develop a unit-based emission inventory for industrial sectors in the BTH region, including power plants, industrial boilers, steel, non-ferrous metal smelting, coking plants, cement, glass, brick, lime, ceramics, refineries, and chemical industries, based on detailed information for each enterprise, such as location, annual production, production technology/processes, and air pollution control facilities. In the BTH region, the emissions of sulfur dioxide (SO2), nitrogen oxide (NOx), particulate matter with diameter less than 10 µ m (PM 10), PM 2.5 , black carbon (BC), organic carbon (OC), and non-methane volatile organic compounds (NMVOCs) from industrial sectors were 869, 1164, 910, 622, 71, 63, and 1390 kt in 2014, respectively, accounting for a respective 61 %, 55 %, 62 %, 56 %, 58 %, 22 %, and 36 % of the total emissions. Compared with the traditional proxy-based emission inventory, much less emissions in the high-resolution unit-based inventory are allocated to the urban centers due to the accurate positioning of industrial enterprises. We apply the Community Multi-scale Air Quality (CMAQ; version 5.0.2) model simulation to evaluate the unit-based inventory. The simulation results show that the unit-based emission inventory shows better performance with respect to both PM 2.5 and gaseous pollutants than the proxy-based emission inventory. The normalized mean biases (NMBs) are 81 %, 21 %, 1 %, and -7 % for the concentrations of SO2 , NO2 , ozone (O3), and PM 2.5 , respectively, with the unit-based inventory, in contrast to 124 %, 39 %, -8 %, and 9 % with the proxy-based inventory; furthermore, the concentration gradients of PM 2.5 , which are defined as the ratio of the urban concentration to the suburban concentration, are 1.6, 2.1, and 1.5 in January and 1.3, 1.5, and 1.3 in July, for simulations with the unit-based inventory, simulations with the proxy-based inventory, and observations, respectively, in Beijing. For O3 , the corresponding gradients are 0.7, 0.5, and 0.9 in January and 0.9, 0.8, and 1.1 in July, implying that the unit-based emission inventory better reproduces the distributions of pollutant emissions between the urban and suburban areas. [ABSTRACT FROM AUTHOR]

The regional transport of particulate matter with diameter less than 2.5 μm (PM2:5) plays an important role in the air pollution of the Beijing-Tianjin-Hebei (BTH) region in China. However, previous studies on regional transport of PM2:5 mainly aim at province level, which is insufficient for the development of an optimal joint PM2:5 control strategy. In this study, we calculate PM2:5 inflows and outflows through the administrative boundaries of three major cities in the BTH region, i.e., Beijing, Tianjin and Shijiazhuang, using the WRF (Weather Research and Forecasting model)-CMAQ (Community Multiscale Air Quality) modeling system. The monthly average inflow fluxes indicate the major directions of PM2:5 transport. For Beijing, the PM2:5 inflow fluxes from Zhangjiakou (in the northwest) and Baoding (in the southwest) constitute 57% of the total in winter and Langfang (in the southeast) and Baoding constitute 73% in summer. Based on the net PM2:5 fluxes and their vertical distributions, we find there are three major transport pathways in the BTH region: the northwest-southeast pathway in winter (at all levels below 1000 m), the northwest- southeast pathway in summer (at all levels below 1000 m) and the southwest-northeast pathway in both winter and in summer (mainly at 300-1000 m). In winter, even if surface wind speeds are low, the transport at above 300m can still be strong. Among the three pathways, the southwest-northeast happens along with PM2:5 concentrations 30 and 55%higher than the monthly average in winter and summer, respectively. Analysis of two heavy pollution episodes in January and July in Beijing show a much (8-16 times) stronger transport than the monthly average, emphasizing the joint air pollution control of the cities located on the transport pathways, especially during heavy pollution episodes. [ABSTRACT FROM AUTHOR]