Spatial and temporal distribution, chemical characteristics, and sources of ambient particulate matter in the Beijing-Tianjin-Hebei region.

Particulate matter (PM) pollution is severe in the Beijing-Tianjin-Hebei (BTH) region. Although the air quality has improved, the average PM2.5 and PM10 concentrations in 2016 were still higher than the National Ambient Air Quality Standard by 2.0 and 1.7 times, respectively. Using the empirical orthogonal function (EOF) method to analyze the spatial characteristics of its 13 cities, it was found that the BTH region could be categorized into four districts. The first district included Xingtai, Shijiazhuang, and Baoding; the second district included Handan, Hengshui, and Langfang; the third district included Beijing, Tangshan, Cangzhou, and Tianjin; and the fourth district included Qinhuangdao, Chengde, and Zhangjiakou. PM2.5 samples were collected synchronously in five typical cities, and it was shown that the major chemical constituents of PM included organic carbon (OC), nitrate (NO3-), sulfate (SO42-), ammonium (NH4+), elemental carbon (EC), Si, Cl-, Fe, Al, and Mg. The species with the highest contents were OC in the winter, SO42- and NH4+ in the summer, and NO3- in the spring. The highest concentrations of OC, NO3-, EC, Si, Cl-, Al, and Mg were found in Baoding, and the highest concentrations of SO42-, NH4+, and Fe were found in Shijiazhuang. The sources of PM2.5 were analyzed using the positive matrix factorization model. The major sources of PM2.5 in the BTH region included coal combustion (10.9%-18.6%), secondary inorganic aerosols (35.4%-42.4%), vehicle emissions (10.6%-18.6%), soil/road dust (10.6%-23.6%), and industrial emissions (8.6%-18.2%).