燃煤城市及其周边地区“双代”后大气环境颗粒物的化学特征

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

2020年10月,燃煤工业城市邯郸市完成“气代煤”、“电代煤”工程。为研究“双代”工程后细颗粒物(PM_(2.5))的化学特征,采集2018—2020年邯郸市冬季4次污染过程以及2020年其周边地区(魏县和鸡泽县)冬季1次大气污染过程PM_(2.5)样品,进行水溶性离子和碳质气溶胶分析。结果显示,相较于2015年“双代”工程实施初期,2020年邯郸市冬季PM_(2.5)质量浓度下降40.8%,表明“双代”工程的实施,使邯郸市空气质量得到有效的改善。4次污染过程中邯郸市PM_(2.5)呈碱性,平均质量浓度分别为(153.9±97.7),(164.5±78.7),(137.3±72.9)和(161.8±84.3)μg/m^(3),魏县和鸡泽县PM_(2.5)平均质量浓度为(123.5±47.3)和(124.5±53.4)μg/m^(3)。水溶性离子分析显示,SNA(NH4+,NO_(3)-和SO42-)质量浓度最高,占水溶性离子总质量浓度的85.3%~90.0%。相较于邯郸市2016年冬季,“双代”工程后作为燃煤示踪物的Cl-质量浓度下降48.0%,表明“双代”工程取得良好成效。NO_(3)-与SO42-质量浓度比显示,移动源(汽车尾气)的贡献高于固定源(燃煤)。碳质气溶胶分析显示,总碳(TC)在邯郸市PM_(2.5)中占比下降55.2%。邯郸市、魏县和鸡泽县有机碳(OC)与元素碳(EC)质量浓度比均大于2,表明存在二次有机碳(SOC)污染。相关性分析与主成分分析结果显示,“双代”工程实施过程中邯郸市碳质气溶胶主要来源由燃煤、汽车尾气逐渐转变为生物质燃烧。通过潜在源分析,邯郸市、魏县和鸡泽县主要潜在源区为山西中部、山东西北部以及河南北部。

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(PM_(2.5)) after the “coal substitution” policy, the PM_(2.5)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 PM_(2.5)concentration in the winter decreased by 40.8% in 2020,compared with the initial stage of the implementation of the “coal substitution” policy in 2015. It indicated that the implementation of the “coal substitution” policy effectively improved the air quality. During the four pollution periods, the PM_(2.5)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/m~3,respectively. The average mass concentration of PM_(2.5)in Wei and Jize were(123.5±47.3) and(124.5±53.4) μg/m~3,respectively. The analysis of water-soluble ions showed that the content of SNA(NH4+,NO_(3)-,and SO42-) was the highest, accounting for 85.3%-90.0% of the total concentration of water-soluble ions. Compared with that in 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)-to SO42-mass concentration showed that the contribution of mobile sources(vehicle exhaust) was higher than that of stationary sources(coal combustion). The carbon aerosol analysis showed that the proportion of total carbon(TC) in PM_(2.5)decreased by 55.2%. In all survey regions, the organic carbon(OC) to elemental carbon(EC) ratio was greater 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 gradually 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.