Characteristics And Source Analysis Of PM_2.5 Pollution In The Heating Season Of Typical Cities In Taiyuan Basin

In recent years,with the battle to protect the blue sky in China,the control of fine particulate matter(PM_2.5)has made positive progress,but the PM_2.5concentration in winter is still high,exceeding the standard phenomenon is still common,especially in the Taiyuan Basin,where the coking industry is concentrated.This study selected taiyuan basin（jiexiu）is a typical city in 2020were six standard heating seasons pollutant on-line monitoring,and for real-time monitoring of PM_2.5 components（including water-soluble ions,organic carbon and elemental carbon and metal element）,reported the general situation of heating season in jiexiu city pollution,and analyzes the characteristics of PM_2.5chemical composition,The causes of the typical heavy pollution process were discussed,and the source analysis was carried out.The main research results are as follows:（1）The average concentrations of PM_2.5,PM₁₀,SO₂ and NO₂ in heating season in Jiexiu City were 64.9,132.7,71.4 and 48.3 g/m³,respectively.PM_2.5and PM₁₀ accounted for 39.5%and 41.2%of the total monitoring days respectively.Through the diurnal variation,it is found that the air pollution is more serious at noon and evening.（2）The PM_2.5 components in Jiexiu City are mainly NH₄⁺,NO₃^-and SO₄^2-three water-soluble ions.The average NO₃^-/SO₄^2-ratio in atmospheric particulate matter is 1.09,indicating that both fixed sources and mobile sources contribute greatly in this area,and with the increase of pollution,the ratio of NO₃^-/SO₄^2-gradually decreases.It indicates that the emissions of fixed sources increase,leading to the occurrence of heavy pollution weather.From the wind speed and direction contribution figures of NO₃^-and SO₄²-,it can be seen that SO₄^2-mainly comes from local transformation,while NO₃^-mainly comes from regional transmission in the northeast direction.The ratio of sulfur conversion rate（SOR）is higher in moderate pollution and above,indicating that primary emission is the main contribution with the aggravation of pollution.NOR is higher in severe pollution.When RH is less than 40%,the homogeneous reaction is dominant.When RH is 40-60%,both homogeneous and heterogeneous reactions exist.When RH is more than 60%,the heterogeneous reaction is dominant.（3）According to the changes of OC and EC hourly concentration,there are two peaks in one day,namely,at noon and at night,indicating that the emission of bulk coal is larger in these two periods.The correlation between OC and EC is good,indicating that the sources of OC and EC in Jiexiu PM_2.5 are relatively consistent.The mean value of OC/EC in PM_2.5 in Jiexiu city was 3.04,indicating that secondary organic carbon was generated to different degrees in Jiexiu city.（4）PMF source analysis results show that the main sources of PM_2.5 in Jiexiu are secondary sources,coal burning sources,motor vehicle sources,industrial sources and dust sources,and their contribution ratios are 40.18%,23.30%,18.15%,12.69%and 5.69%,respectively.（5）According to the pollution level of air quality,the characteristic radar chart was used to judge the pollution sources.It was found that when the air quality was good,the pollution sources were mainly standard type,and all pollutants did not exceed the upper limit of the standard.When the air quality is slightly polluted,SO₂,CO,PM_2.5 and other pollutants are close to the upper limit of the standard,and the pollution type is coal burning.With the aggravation of pollution,PM_2.5 exceeds the standard upper limit.This type is a secondary type,indicating that the occurrence of heavy pollution is usually dominated by secondary transformation.