Pollution Characteristics Of Water-soluble Ion In PM_2.5 In Main Urban Area Of Hengyang City

In order to further understand the physical and chemical characteristics of fine particles in Hengyang city,this study discussed the pollution characteristics of PM_2.5 from the perspective of water-soluble ions.In this study,50 PM_2.5 samples were collected in main urban area of Hengyang city in January,April,July and September of 2019,and the mass concentrations of PM_2.5 and nine water-soluble ions were determined by gravimetric method and ion chromatography.The following conclusions were drawned by the characteristics of its concentration,the pH of PM_2.5,the secondary transformation of gaseous precursors,combination of Ammonium salt,Ionic correlation and source of pollutants.?1?The daily average mass concentration of PM_2.5 in the main urban area of Hengyang was 15.98¹66.81?g/m³,with an average value of55.90?g/m³,and the seasonal variation was winter?94.25?g/m³?>spring?64.76?g/m³?>autumn?38.30?g/m³?>summer?26.30?g/m³?.The daily average mass concentration of total water-soluble ions ranged from5.23 to 92.89?g/m³,with an average value of 30.89?g/m³,accounts for48.32%of the mass concentration of PM_2.5.The average annual mass concentration of each ion was in order:NO₃^->SO₄^2->NH₄⁺>Cl^->K⁺>Ca²⁺>Na⁺>F^->Mg²⁺,SNA is the three main ions,accounts for 93%of total water-soluble ions.?2?During the sampling period,atmospheric aerosols were acidic in autumn and winter,alkaline in spring and summer.With the increase of PM_2.5 mass concentration,particulate matter gradually changed from alkaline to acidic.?3?The seasonal order of SOR and NOR was:winter>spring>autumn>summer.Obvious secondary transformation of SO₂ occurred in all four seasons,NO₂ transformed in winter,spring and autumn.Compared with the clean days,both SOR and NOR increased significantly in polluted days and the trend was consistent with the mass concentrations of PM_2.5,SO₄^2-and NO₃^-.Secondary transformation of gaseous precursors leaded to contamination.?4?In winter,ammonium salt mainly existed in three forms:NH₄HSO₄,NH₄NO₃ and?NH₄?₂SO₄.In spring and summer,ammonium salt mainly existed in forms of?NH₄?₂SO₄ and NH₄NO₃.In autumn,ammonium salt mainly existed in forms of?NH₄?₂SO₄ and NH₄NO₃,and there was also a small amount of NH₄HSO₄.?5?Through a brief analysis of the correlation of nine water-soluble ions in PM_2.5 and sources of pollutants,this article initially judged that air pollutants in the main urban area of Hengyang mainly came from industrial emissions,garbage incineration,coal and motor vehicle emissions,mineral dust.The rapid accumulation and secondary transformation of NO_X emitted by mobile sources in a short time was the most important reason for the rapid rise of haze and particulate concentration.