Periodic Pollution Characteristics of PM2.5 in Typical Industrial Cities along Taihang Mountains in Autumn and Winter of 2021

Based on the use of multiple linear regression models, the air quality of Jiyuan City, a typical industrial city, was analyzed at different stages from October 2021 to March 2022. The impact characteristics of the change of meteorological factors on PM2.5, PM2.5 pollution level, and the difference in the growth rate of pollutant concentration before and after the start of winter heating (15 Nov 2021) were studied to explore the characteristics of PM2.5 pollution in cities along Taihang Mountain in autumn and winter. Results reveal that in the first stage (1 Oct–14 Nov 2021), 26.1% of PM2.5 hourly concentration change was determined using meteorological factors, and the correlation between any single factor and PM2.5 was ＜36%. In the second stage (15 Nov–31 Dec 2021), 72.4% of the hourly concentration change of PM2.5 was determined using meteorological factors. Wind direction, relative humidity, and visibility had considerable influences on PM2.5, and the correlation between PM2.5 and relative humidity and visibility was the highest (61.5% correlation with relative humidity and 73.1% correlation with visibility). In the third stage (1–31 Jan 2022), 53.2% of hourly concentration change of PM2.5 was determined using meteorological factors, and the relative humidity and wind speed had no considerable effect on the hourly change of PM2.5, which is associated with the considerable effect of long-range migration and detention of pollution clusters in this stage. In the fourth stage (1 Feb–31 Mar 2022), 32.2% of PM2.5 hourly concentration change was determined using meteorological factors. Wind speed had no considerable effect on PM2.5 hourly change because it was affected by sand and dust. During the pollution period in autumn and winter in Jiyuan City, the main components of particulate matter were NO₃⁻, NH₄⁺, OC, and SO₄²⁻, with the proportion of secondary inorganic ions (SO₄²⁻, NO₃⁻, and NH₄⁺) being＞65.7%, and the secondary pollution was severe. Thus, the growth rates of particle component concentrations show that, with the increase in pollution, the growth rates of NO₃⁻, S, EC, and Cl⁻ decrease while those of SO₄²⁻, OC, K⁺, and NH₄⁺ exhibit a “slow–fast” trend.