The Effect Of Trace Gases On The Composition Of Fine Particle In Atmosphere In Nanchang City

In this study,the samplings of PM_2.5 and NH₃ were carried out from January to December 2020 in East China University of Technology of Nanchang City.Eight major water-soluble inorganic ions(including SO₄^2-,NO₃^-,NH₄⁺,Ca²⁺,K⁺,Cl^-,Mg²⁺and F^-)of PM_2.5 were measured.Combined with the air quality（NO₂ and SO₂）data and meteorological data from nearby environmental monitoring station,the seasonal variation of PM_2.5 and NH₃ pollution levels in Nanchang City was discussed.The effect of gas-particle transformation of trace gases on PM_2.5components was studied.The PMF model was used to analyze the contribution of various sources to PM_2.5 ions in different seasons,and the backward trajectory was used to further analyze air mass trajectory.The main conclusions were as follows:During the sampling period,95%of NH₃ were in the range of 0～12μg·m^-3,and the daily average concentrations of NH₃ and SO₂ and NO₂ were 5.83μg·m^-3,8.88μg·m^-3,28.81μg·m^-3,respectively.The NH₃ concentration was the highest in summer(7.85μg·m^-3),followed by spring(3.10μg·m^-3),and the average concentration in autumn(4.96μg·m^-3),and the lowest in winter(4.08μg·m^-3).The order of the seasonal average concentrations of SO₂ and NO₂were spring>summer>autumn>winter,and spring>winter>autumn>summer,respectively.The NH₃ was positively correlated with SO₂,but negatively correlated with NO₂,and SO₂ was positively correlated with NO₂.The average daily concentration of PM_2.5 in Nanchang City was 32.71μg·m^-3,and the order of its seasonal changes was winter>spring>autumn>summer.According to air quality standards,the number of clean days accounted for about 95.2%of the total sampling days.The ratio of PM_2.5/PM₁₀ in Nanchang City generally ranged from 50%to60%in spring,summer and autumn,while increased significantly between 65%and 80%in winter,indicating relatively low air quality in winter.The average concentration of the eight water-soluble ions accounted for 61.8%of PM_2.5,and the secondary ion（SNA）accounted for 85.7%and 53.1%of the total water-soluble ions and PM_2.5,respectively.The dominant existence forms of,secondary inorganic ions SO₄^2-,NO₃^-and NH₄⁺were mainly exist in the form of combination of NH₄NO₃and（NH₄）₂SO₄.The average values of SOR,NOR and NHR were generally greater than 0.10,indicating that the secondary reaction in atmospheric particulates in Nanchang City were active;NHR was positively correlated with PM_2.5and SNA,which indicated that the aerosol transformation of NH₃-NH₄⁺plays a important role on the formation of secondary aerosols.Based on the PMF model,the sources of PM_2.5 in Nanchang City are mainly come from secondary sources,biomass burning,industrial and dust sources.PM_2.5 was mainly from secondary source（50.4%）in winter,from biomass burning（accounted for 60.37%and 54.35%,respectively）in spring and autumn,and from industry（55.79%）in summer.The atmospheric pollutants in Nanchang mainly came from local sources（over 50%）in spring and summer based on the backward trajectory of the air mass.In autumn and winter,the local sources accounted for only 20%-35%,and the regional air mass circulation from the surrounding cities accounted for nearly 65-80%,and thus regional pollutant transmission has become an important cause of air pollution in these seasons.