Chemical characteristics of particulate matter in the atmospheric environment after “coal substitution” policy in coal combustion cities and their surrounding areas

In October 2020，the policy of “coal⁃to⁃gas” and “coal⁃to⁃electricity” was completed in Handan，a coal⁃ burning industrial city. In order to investigate the chemical characteristics of fine particulate matter (PM2.5) after the “coal substitution” policy，the PM2.5 samples were collected in the winter of Handan during four pollution periods from 2018 to 2020 and one pollution period in the counties of Wei and Jize in 2020 to analyze the water⁃soluble ions and carbonaceous aerosols. In Handan，the PM2.5 concentration in the winter decreased by 40.8% in 2020，comparedwith the initial stage of the implementation of the “coal substitution” policy in 2015. It indicated that the implementa⁃ tion of the “coal substitution” policy effectively improved the air quality. During the four pollution periods，the PM2.5 was alkaline with the average mass concentrations were (153.9±97.7)，(164.5±78.7)，(137.3±72.9) and (161.8± 84.3) μg / m3 ，respectively. The average mass concentration of PM2.5 in Wei and Jize were (123.5±47.3) and (124.5± 53.4) μg/m3，respectively. The analysis of water⁃soluble ions showed that the content of SNA (NH+，NO-，and SO2-)434 was the highest，accounting for 85.3%-90.0% of the total concentration of water⁃soluble ions. Compared with thatin the winter of 2016 in Handan，the concentration of Cl- ，as a tracer of coal combustion，decreased by 48.0% after the“coal substitution” policy， explaining the good results of the “ coal substitution” policy. The ratio of NO-3 totionary sources (coal combustion). The carbon aerosol analysis showed that the proportion of total carbon (TC) in PM2.5 decreased by 55.2%. In all survey regions，the organic carbon (OC) to elemental carbon (EC) ratio was grea⁃ ter than 2，demonstrating the existence of secondary organic carbon (SOC) pollution. The results of correlation analysis and principal component analysis showed that the main sources of carbon aerosols in Handan gradual⁃ ly changed from coal combustion and vehicle exhaust to biomass combustion during the implementation of the “coal substitution” policy. According to the potential source analysis，the main potential source areas of Handan，Wei，and Jize were central Shanxi，northwest Shandong，and north Henan.