Analysis of PM_2.5 pollution characteristics of a winter heavy pollution process in Xingtai City

In order to understand the pollution characteristics of heavy pollution process in Xingtai City in autumn and winter, PM_2.5 samples were collected at three points in the city, including No.1 Middle School, Neiqiu and Shahe, during the pollution process on November 10-16, 2018, to analyze the changes of PM_2.5 concentration and chemical composition. The results showed that during the heavy pollution process, the average PM_2.5 concentration of Xingtai City was 176.2 μg/m³, which exceeded the secondary standard limit of Ambient Air Quality Standards (GB 3095-2012) by 1.4 times. The water-soluble ions were mainly NO₃ ⁻, SO₄ ²⁻and NH₄ ⁺, with the average concentrations of （32.3±13.4）, （16.4±9.0） and （15.0±6.8）μg/m³, which accounted for 18.3%, 9.3% and 8.5% of PM_2.5, respectively. The concentration of the three ions increased by 0.8, 2.3 and 1.2 times when the pollution was aggravated compared with the initial stage of the pollution. The average concentration of OC was (12.9±5.8) μg/m³, accounting for 7.4% of PM_2.5, and the average concentration of EC was (4.6±1.4) μg/m³, accounting for 2.7% of PM_2.5. This pollution process in Xingtai City was dominated by secondary pollution, which was mainly affected by coal combustion and motor vehicle emissions.