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

Abstract

Based on atmospheric monitoring data and the WRF-CAMx model, this study analyzed the characteristics of air pollution and performed a quantitative assessment of PM2.5 cross-border transport in the Beijing-Tianjin-Hebei (BTH) region in January 2016. The results showed that the average concentrations of PM2.5, PM10, SO2, NO2, and CO were 89.5 μg·m-3, 135.61μg·m-3, 57.55μg·m-3, 60.79μg·m-3, and 2.12 mg·m-3, respectively, indicating severe PM2.5 pollution. During the study period, surface-level PM2.5 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 PM2.5 pollution and cities with high upwind pollution enhance regional-scale transport to downwind cities. The total inflow, outflow, and net flux of PM2.5 in Beijing (Shijiazhuang) in January 2016 were 1582.96 t·d-1 (2036.89 t·d-1), -1171.09 t·d-1 (-1879.12 t·d-1), and 411.87 t·d-1 (157.77 t·d-1), respectively, indicating that PM2.5 inputs from surrounding cities per unit time were higher than external inputs to the surrounding cities. Furthermore, net PM2.5 flux showed notable vertical evolution; the total net flux of PM2.5 in Beijing and Shijiazhuang below 1782 m ranged from 17.86 to 64.18 t·d-1 and -2.95 to 134.81 t·d-1, respectively, and both peaked 817 m above the ground at 64.18 and 134.81 t·d-1. Moreover, a significant increase the net PM2.5 inflow flux in Zhangjiakou and Shanxi explained the observed net flux peaks in these two cities.