Estimating the contribution of regional transport to PM_2.5 air pollution in a rural area on the North China Plain

PM_2.5 air pollution in metropolises as well as some medium-sized cities in the North China Plain have aroused many researchers' interest, but less attention has been paid to the rural areas of this region. In this study, four months of daily PM_2.5 samples were collected from a rural site in Lingcheng (a district of Dezhou City in Shandong Province) during different seasons in 2013 and 2014. Analysis of the samples indicates that the PM_2.5 air pollution was severe over this area with the four-month average concentration of 105.9 μg/m³, three times higher than China's guideline for this pollutant (35 μg/m³). In winter, the monthly average concentration was as high as 151.2 μg/m³. In order to identify the potential source regions, the Integrated Source Apportionment Method within Community Multiscale Air Quality model (CMAQ-ISAM) was applied during the wintertime. The regional source apportionment results show that local emissions in Lingcheng only contributed 15.4% to PM_2.5 concentrations, with 12.6% and 28.1% from its circumjacent areas in Dezhou City and the six surrounding cities, respectively. Regional transport from areas farther away and the boundaries account for 31.6% and 11.1%, respectively. This indicates that the ambient PM_2.5 at Lingcheng is not affected only by emissions from local and circumjacent areas; regional and long-range transport should also be considered. Further analysis indicated that with increasing degrees of pollution, the contributions from local and circumjacent regions showed a clear downward trend, while the contributions from northern and southwestern areas, which most of the trajectories passed through during periods of heavy haze, showed an obvious upward trend.