[Air Pollution Characteristics and Quantitative Evaluation of Multi-scale Transport in the Beijing-Tianjin-Hebei Region in January, 2016].

Based on atmospheric monitoring data and the WRF-CAMx model, this study analyzed the characteristics of air pollution and performed a quantitative assessment of PM cross-border transport in the Beijing-Tianjin-Hebei (BTH) region in January 2016. The results showed that the average concentrations of PM, PM, SO, NO, and CO were 89.5 μg·m, 135.61μg·m, 57.55μg·m, 60.79μg·m, and 2.12 mg·m, respectively, indicating severe PM pollution. During the study period, surface-level PM in each city of BTH region was dominated by local emissions, which accounted for 45.4% to 69.9%. The regional transport contribution was supplemented by transport from within and outside of the BTH region, accounting for 4.8% to 49.7% and 4.9% to 29.6%, respectively. In addition, high wind speeds promoted the diffusion of local PM pollution and cities with high upwind pollution enhance regional-scale transport to downwind cities. The total inflow, outflow, and net flux of PM in Beijing (Shijiazhuang) in January 2016 were 1582.96 t·d (2036.89 t·d), -1171.09 t·d (-1879.12 t·d), and 411.87 t·d (157.77 t·d), respectively, indicating that PM inputs from surrounding cities per unit time were higher than external inputs to the surrounding cities. Furthermore, net PM flux showed notable vertical evolution; the total net flux of PM in Beijing and Shijiazhuang below 1782 m ranged from 17.86 to 64.18 t·d and -2.95 to 134.81 t·d, respectively, and both peaked 817 m above the ground at 64.18 and 134.81 t·d. Moreover, a significant increase the net PM inflow flux in Zhangjiakou and Shanxi explained the observed net flux peaks in these two cities.