[Characteristics and Sources of PM_2.5 Pollution During Winter in Handan City from 2016 to 2020]

To explore the characteristics and sources of PM_2.5 pollution in winter of Handan City in the past five years, PM_2.5 samples were collected in winter of 2016 to 2020, and eight types of water-soluble inorganic ions were analyzed. The principal component analysis(PCA) model was used to analyze the types of pollution sources, and the backward trajectory and potential source contribution factor(PSCF) were used to simulate the transport trajectory and pollution sources. The results showed that the PM_2.5 concentration in winter of 2018 was the highest, increasing by 60.44%, 25.46%, 91.43%, and 21.53% compared with that in 2016, 2017, 2019, and 2020, respectively. In the winter of 2020, the concentration of water-soluble inorganic ions(WSIIs) decreased by 18.86% compared with that in 2016, and WSIIs/PM_2.5 decreased to 26.69%. The PM_2.5 concentration(110.20-209.65 μg·m^-3) at night was higher than that in the daytime(95.21-193.00 μg·m^-3). The concentration of NO₃^- and NH₄⁺ increased more at night. On the contrary, the concentration and proportion of Cl^-decreased annually. In the winter of 2020, the daytime concentrations of K⁺, Ca²⁺, Na⁺, and Mg²⁺ decreased by 69.72%, 97.10%, 90.91%, and 74.51% compared with that of 2018, and the night concentrations decreased by 66.67%, 95.38%, 91.67%, and 77.78%, respectively. In 2020, the concentrations of NO₃^-, SO₄^2-, and NH₄⁺ on polluted days were 4.90, 5.80, and 5.20 times those on non-polluted days, with the largest increase in five years. PCA results showed that the main sources of pollution were secondary sources, coal sources, biomass combustion sources, and road and building dust. The backward trajectory and PSCF analysis results showed that pollution transport continued to exist between south-central Mongolia and central Inner Mongolia in winter and was influenced by the transport between northern Henan and Handan and central Hebei and Handan in winter of 2016 and 2017, whereas the latter had a greater impact in winter of 2018-2020.