Source Analysis And Sulfur Isotopic Composition Of PM_2.5 In Taiyuan And Its Surrounding

PM_2.5 is one of the main pollutants in ambient air.The composition,source and formation mechanism of PM_2.5 are complex,so people have paid much attention to it.Yuci college town is close to Taiyuan,and its ambient air is affected with the moving of colleges and universities of Taiyuan.The study on the spatial and temporal distribution characteristics,sources and mutual relations of water-soluble ions and carbonaceous components in PM_2.5 in these two regions is of great significance for the local government to prevent and control major pollution and improve the environmental air quality.In this study,PM_2.5 samples in the heating season and the non-heating season in Taiyuan and Yuci college town were collected by a medium flow sampler（2050,Laoying）.And the water-solubie ions,carbonaceous components and sulfur isotopic composition(δ³⁴S)were measured by ion chromatograph（Dionex Aquion RFIC,Thermo Scientific）,Sunset Model 5L OCEC instrument and EA-Delta V Advantage Isotope Ratio MS,respectively.The spatial and temporal distribution characteristics of water-soluble ions and carbonaceous components were studied.The source of PM_2.5 was analyzed by using Hybrid Single Particle Lagrangian Integrated Trajectory and PMF model,and the sulfur isotope technology was used to prelimatively discuss the source of sulfate in PM_2.5 in Yuci college town in the non-heating season.The main conclusions were as follows:The average annual concentrations of total water-soluble ions in PM_2.5in Taiyuan and Yuci college town in 2017-2018 were 27.56μg/m³ and 28.33μg/m³,respectively.There was a strong correlation between Taiyuan and Yuci college town.The average annual concentration of water-soluble ions in PM_2.5 in Yuci college town was 28.02μg/m³ in 2020,which was basically the same as the average annual concentration in 2017-2018.SO₄^2-,NO₃^-and NH₄⁺were the most water-soluble ions,and their mass concentrations accounted for 68.75%,73.87%and 81.15%of the total water-soluble ions in PM_2.5 of Taiyuan,Yuci college town in2017-2018 and Yuci college town and in 2020 respectively.The seasonal variation characteristics of water-soluble ions in PM_2.5 in Taiyuan and Yuci college town were consistent.The concentrations of water-soluble ions in the heating season were greater than those in the non-heating season.The variations of SOR Taiyuan and Yuci college town in 2017-2018 were consistent,that is,SOR in the non-heating season was larger than that in the heating season,while NOR was low throughout the year.This indicated that SO₄^2-and NO₃^-in PM_2.5 of Yuci college town in 2020 are mainly derived from the secondary transformation of SO₂ and NO₂.The ion balance showed that PM_2.5 in Taiyuan and Yuci college town were alkaline during the study seasons.There are good correlations between SO₄^2-,NO₃^-and NH₄⁺,and their chemical forms are all of（NH₄）₂SO₄ and NH₄NO₃.NH₄⁺also exists in the form of NH₄Cl,besides（NH₄）₂SO₄and NH₄NO₃ in the non-heating season.The average annual concentrations of organic carbon（OC）and elemental carbon（EC）in PM_2.5 in Taiyuan were 12.61μg/m³ and 6.76μg/m³,respectively.The average annual concentrations of OC and EC in PM_2.5 in Yuci college town were 11.73μg/m³ and6.91μg/m³.The seasonal variation of OC and EC was the same,and the concentrations of OC and EC in the heating season were larger than those in the non-heating season.In the heating season,central heating will discharge a large number of pollutants.And low temperature and low atmospheric boundary layer lead to atmospheric stability,which is not conducive to the diffusion of atmospheric pollutants,leading to high concentrations of OC and EC in the heating season.The correlations between OC1,OC3,OC4 and volatile organic compounds（VOCs）were good in the non-heating season.And the correlations between OC1,OC2,OC3,OC4 and VOCs were all bad.The correlations between EC and OC1,OC2,OC3,OC4 in the heating season were all good,indicating that the source of carbonaceous components in the heating season is relatively simple.The HYSPIT model shows that PM_2.5 in Taiyuan and Yuci college town in the heating season in 2017-2018 were affected by the long-distance transportation of air mass from the northwest direction and the local pollutants.PM_2.5 was mainly affected by the long-distance transportation of air mass from the north to west direction in the non-heating season.PMF model was used to analyze the sources of PM_2.5 in Taiyuan and Yuci college town in2017-2018.Five pollution sources were determined,which were coal burning,dust,vehicle exhaust,biomass combustion and secondary pollution sources.The contribution of coal burning and vehicle exhaust was the highest in Taiyuan,which was 40.09%and 18.22%,respectively.The contribution of vehicle exhaust and biomass combustion was the highest in Yuci college town,which was 31.62%and 25.16%,respectively.Theδ³⁴S values of particulate matter emitted from industrial coal burning,vehicle exhaust and biomass combustion are 5.90‰,2.46-10.88‰and 12.39-15.09‰,respectively.The averageδ³⁴S values of sulfate in PM_2.5 of Yuci college town in non-heating season are5.07‰.Using sulfur isotope technology,it is found that industrial coal burning and vehicle exhaust are the main sources of SO₄^2-in PM_2.5 of Yuci college town in the non-heating season.