High Temporal Resolution PM_2.5 Source Analysis Study In A Typical Coking City In Shanxi

In recent years,with the air pollution prevention and control campaign,Jiexiu City air pollution has made significant improvements,the concentration of various pollutants have dropped to varying degrees,but due to the economic structure of Jiexiu City’s reliance on the coking industry and is located in the basin terrain,making the concentration of pollutants in the counties of Shanxi is still at a high value,air quality in the national ranking of the bottom for a long time,especially fine particulate matter(PM_2.5)concentration is still is still at a high level.In response to the current pollution situation,this study conducted online observations of organic matter,water-soluble inorganic ions,metal elements and related gaseous pollutants in PM_2.5 in 2021,and explored the pollution characteristics of gaseous pollutants and PM_2.5 components in different seasons.After that,the sources of organic aerosols（OA）were first analyzed by multilinear engine model（ME-2）,and then the main sources of PM_2.5 in different seasons were analyzed by combining OA factors,inorganic ions and metal elements by positive matrix factorization model（PMF）,so as to provide important scientific and technological support for the fine control of atmospheric PM_2.5 in Jiexiu City.The main conclusions are as follows:（1）The annual average value of PM_2.5 is 50.4±44.6μg/m³ and its mass concentration is highest in winter（65.4±64.7μg/m³）and lowest in summer（37.6±64.7μg/m³）,44.2±36.3μg/m³ and 54.6±40.8μg/m³ in spring and autumn respectively.Non-refractory fine particulate matter(NR-PM_2.5)mass concentrations similarly show that winter（52.3±57.5μg/m³）>autumn（47.7±42.4μg/m³）>spring（32.7±23.2μg/m³）>summer（27.2±19.9μg/m³）;OA has the highest contribution to NR-PM_2.5 in the four seasons,with spring（39.1%）summer（39.7%）autumn（39.8%）and winter（39.5%）.NO₃^-is the secondary inorganic component with the highest contribution to NR-PM_2.5 in spring,summer and autumn（27.1%,24.6%and 24.4%）.SO₄^2-is the secondary inorganic component with the highest contribution to NR-PM_2.5 in winter（20.8%）;influenced by coal combustion,the contribution of Cl^-to NR-PM_2.5 is the winter was the largest（3.3%）.（2）The sum of the concentrations of the 10 metallic elements in the order of the size of each season is winter（4999.6±7723.3ng/m³）>spring（3592.7±3470.3ng/m³）>autumn（2731.3±1831ng/m³）>summer（1485.5±644.5ng/m³）,Ca,K,and Fe are the major contributors of metal elements in the four seasons.The concentrations of Pb,Ca,K,Fe,Mn,Ti and Ba are higher in winter than in the other three seasons,while the concentrations of Se,Zn and Cu were higher in autumn than in the other three seasons.The differences in mass concentrations of each metal between seasons are mainly due to the combined effects of changes in anthropogenic emission structures（e.g.,coal combustion）and meteorological conditions.（3）Four major types of organic aerosols are identified by ME-2 model in winter and autumn,namely:hydrocarbon-like OA（HOA）,cooking OA（COA）,coal combustion OA（CCOA）and oxygenated OA（OOA）.Three major types of organic aerosols are identified in spring and summer,namely HOA,COA and OOA.The highest contribution of OOA to OA is observed in the four seasons,with the magnitude being summer（82.9%）>spring（80.6%）>autumn（78.6%）>winter（53.2%）in that order,indicating that the oxidation of organic matter in the sampling area is obvious.Among the primary organic aerosols,the highest contribution of CCOA is found in winter（19.5%）,indicating the prevalence of coal combustion,while the highest contribution of HOA is found in spring and summer（11.2%,8.8%）,and the highest contribution of COA in autumn（9.3%）.（4）PMF source analysis in different seasons show the same sources of cooking,motor vehicles,road dust,machinery manufacturing industry and coking industry,with the difference that coal combustion and secondary aerosols are resolved in winter and autumn,while two secondary aerosols,namely oxidized organic aerosols and secondary nitrates,are resolved in spring and summer.The contribution of secondary aerosols among PM_2.5 sources in the four seasons is in descending order:summer（48%）>spring（46.9%）>autumn（46.4%）>winter（34.2%）.Among the primary emission sources,coal combustion is the main contributor to PM_2.5 in the sampling area in winter（18.4%）.The coking industry is the highest contributor to PM_2.5 in spring,summer and autumn with 23.5%,20.9%and 15.6%,respectively.The study indicates that the coking industry and coal combustion in the sampling area are the main primary sources of PM_2.5pollution,so it is critical to control the coking industry and coal combustion in the sampling area.