Evaluation Of Pm2.5 Fluxes In The "2+26" Cities: Transport Pathways And Intercity Contributions

To comprehensively evaluate the transport pathways and regional sources of PM2.5 in the "2 + 26" cities, air quality simulations using WRF-Chem were pursued over January, April, July, October 2015. The seasonal characteristics, vertical distributions of PM2.5 fluxes, and transport pathways were investigated. The model reasonably predicted the meteorological parameters (e.g., T2, Q2, WS10, and WD10) and air pollutants in both evaluated domains. The horizontal PM2.5 fluxes were strong in October (1221 kt, -1222 kt) and April (1119 kt, -1142 kt) and weak in January (933 kt, -997 kt) and July (589 kt, -809 kt). The directions of horizontal flux contributors relative to their target cities were entirely different in January and July. The same pattern can also be found at vertical layers. However, there was no uniform direction seen in April and October. A total of 14 pathways at the boundaries of the "2 + 26" cities were identified. The SW-NE pathways, which were dominant in Beijing and Tianjin with flux contributions of 65% and 75%, were found in all four months. The NW-SE pathways, which were the major pathways of Taiyuan (87%), and the W-E pathways, which were the major pathways of Zhengzhou (44%) and Jinan (43%), always showed different directions in January and July, following the directions of prevailing winter and summer monsoon winds. Moreover, Shijiazhuang (42%) and Handan (48%) were dominated by S-N pathways, which showed different patterns throughout the four months. The results could be helpful for implementing policies aimed at ecological compensation and joint air pollution control.