Composition Characteristics And Source Analysis Of Water-soluble Ions In PM_2.5 In Jiaozuo City

Since the beginning of the new century,with the rapid development of China’s economy and society and the continuous improvement of urbanization rate,a large range of air pollution continues to appear in some cities,which has attracted extensive attention from the society and researchers.In order to explore the composition characteristics and sources of water-soluble ions in atmospheric PM_2.5in Jiaozuo city,samples of PM_2.5in Jiaozuo city were collected from September 2017 to August 2018,and nine main water-soluble inorganic ions(NH₄⁺、Mg²⁺、Ca²⁺、K⁺、Na⁺、NO₃^-、SO₄^2-、Cl^-、F^-)were determined,and their mass concentration and composition characteristics were analyzed.The source of water-soluble ions was qualitatively analyzed by combining correlation analysis,principal component analysis and PMF model,and the backward track of air mass in Jiaozuo city was discussed by using HYSPLIT model during the study.This study can help to master the characteristics of atmospheric particulate pollution in Jiaozuo city,and provides scientific basis for the prevention and control of air pollution.The main conclusions show that:（1）The annual average concentration of PM_2.5in Jiaozuo is 72.03μg·m^-3.Seasonal change is characterized by winter>spring>autumn>summer,and the average mass concentrations were 99.75μg·m^-3、69.02μg·m^-3、68.21μg·m^-3and 43.51μg·m^-3.The number of days exceeding the standard accounted for 35.14%,52.22%,28.39 and 4.34%respectively in the current quarter.（2）The annual average concentration of total water-soluble ions in PM_2.5in Jiaozuo was50.64±34.72μg·m^-3,each the size of the water soluble ionic order to NO₃^->SO₄^2->NH₄⁺>Ca²⁺>Cl^->K⁺>Na⁺>F^->Mg²⁺.The average mass concentrations of secondary inorganic ions NO₃^-,SO₄^2-and NH₄⁺（SNA）were 42.74±34.40μg·m^-3,accounting for about84.40%of the total water-soluble inorganic ions,and the most important component of inorganic ions in Jiaozuo city.The total ion concentration and SNA concentration in the pollution period were higher than that in the cleaning period.（3）Ion equilibrium analysis showed that the average value of CE/AE was 1.31,and the water-soluble inorganic ions were generally weakly alkaline.The mean values of SOR and NOR were both greater than 0.1,indicating that there was a strong secondary photochemical oxidation reaction during the study period.The annual mean of SOR（0.49）was greater than NOR（0.28）,indicating that the sulfur oxidation reaction was stronger than the nitrogen oxidation reaction.The ratio of NO₃^-/SO₄^2-mass concentration was 1.25,indicating that the source of water-soluble ions in Jiaozuo city was mainly affected by the moving source.（4）Correlation analysis results show that SNA in PM_2.5of Jiaozuo has a good correlation throughout the year.However,the correlation between NO₃^-and SO₄^2-was poor in autumn and summer.The correlation between Ca²⁺and K⁺,Na⁺and Mg²⁺in spring and summer is good,indicating that construction dust and soil dust are the main sources in spring and summer.In and winter,Mg²⁺and K⁺,and there may be coal combustion or biomass combustion sources.（5）The results of positive determination matrix factorization analysis of PMF showed that secondary ions contributed the most to PM_2.5in jiaozuo city during the sampling period,mainly including secondary nitrate（36.91%）and secondary sulfate（30.86%）,followed by soil dust source（14.01%）and combustion source（11.38%）,while industrial sources and biomass combustion sources contributed less（6.83%）.（6）The results of backward trajectory clustering analysis show that the local source air mass is the main source of air mass in all seasons in Jiaozuo city（30%～50%）,and there are also long-distance air masses from northwest and north China in autumn and winter,which are greatly affected by soil dust pollutants,and there are air masses from east and south China in spring and summer.