Pollution Characteristics And Source Apportionment Of PM_2.5 In Atmospheric Particulate Matter In Taiyuan City

Taiyuan City is a national energy and industeial base with complex topography,where atmospheric pollutants are difficult to diffuse.In this study,9 species of main water-soluble inorganic ions and 6 species of low-molecular-weight organic acids in PM_2.5 were determined from September 2017 to April 2018.The source of water-soluble inorganic ions was qualitatively analyzed by PMF model and correlation analysis.The potential source contributions of the pollutants were analyzed by HYSPLIT model and PSCF model.It provides a scientific basis for the treatment of PM_2.5 pollution in Taiyuan City.The results showed that:?1?The average concentration of PM_2.5 was higher in winter than that in autumn,then than that in spring.Three species secondary inorganic ions were the most important components,accounting for 75.41%.The secondary ions were mainly composed of?NH₄?₂SO₄ and NH₄NO₃.NO₃^-/SO₄^2-indicated that the fixed source was the main source of secondary salts.SOR increased significantly with increasing humidity,and which was more obvious when the relative humidity was greater than 40%.The SOR value was higher in spring than that in autumn.NOR also like SOR.?2?The average concentrations of organic acids in autumn and winter were in order oxalic acid>acetic acid>formic acid>succinic acid>methanesulfonic acid>glutaric acid;Oxalic acid and glutaric acid,succinic acid and methanesulfonic acid were mainly derived from secondary reactions of industrial and automobile.As the temperature decreases in winter,secondary reaction weakened,and the concentrations of glutaric acid,succinic acid,and methanesulfonic acid decreased.The sources of low-molecular-weight organic acids in the atmosphere were mainly primary sources such as biomass combustion,and the secondary sources such as photochemical reactions were emitted by some industrial and automobile.?3?Under heavy pollution days in different four months.The pollution source during this period may come from coal burning in December and January.The process of pollution in February may come from the firecrackers during the Spring Festival.The pollution processes in March were mainly based on mobile sources.The combustion of biomass fossil fuel was an important source of PM_2.5.SOR and NOR results showed that the occurrence of secondary reactions of SO₂ and NO₂ were promoted in the polluted weather.?4?Based on the PMF model,the four major sources of PM2.5 in Taiyuan City were sedcondary particales accounting for 48.32%,industrial sources for 22.39%and combustion sources for 17.01%,soil dust for 12.29%,respectively.F^-and Cl^-were mainly contributed by coal combustion and partly by industrial production.Ca²⁺and Mg²⁺were mainly contributed by soil-related sources.Na⁺and K⁺were mainly derived from biomass burning,further from the soil.Secondary ions were mainly caused by human activities.?5?Analysis of potential source contribution showed that the secondary ions were mainly from the secondary reactions of SO₂ and NO₂ emitted from coal-fired sources in Shanxi,Shaanxi,Henan and southwestern of Hebei;agricultural activities and biomass burning in southern Hebei were important factors affecting the concentration of K⁺and NH₄⁺in Taiyuan City;Na⁺and Mg²⁺were more affected from Gansu and western Inner of Mongolia.?6?The backward air mass trajectory cluster analysis indicated that the four groups of air masses in Taiyuan City were from the northwest and local sources,respectively.The pollutions from the local and western Inner Mongolia were the most serious,which were the most important part of the total air mass.The air mass from Mongolia was clean.SO₄^2-,NO₃^-and NH₄⁺were still the most important components of all air masses;and the clean air masses from the north were still dominated by secondary sources;The impact of soil dust source in the north was more pronounced than that in Taiyuan.