Variation characteristics of water-soluble ions in PM2.5 in Xi'an during 2020-2021
Five water-soluble ions,including NO3-,SO4-2,NH4+,Cl-and F-,were detected and ana-lyzed in 181 PM2.5 effective samples by ion chromatography.The results showed that the annual aver-age concentration of PM2.5 in Xi'an was(71.04±51.80)mg·m-3,and the seasonal variation char-acteristics were:winter>spring>autumn>summer.The annual average concentration of five water-soluble ions was(28.24±31.79)mg·m-3,and the seasonal variation characteristics were:winter>spring>autumn>summer.Concentrations of ions were ranked as:NO-3>SO2-4>NH+4>Cl->F-.NO-3 accounted for the highest proportion in winter,spring,and autumn,while SO2-4 accounted for the highest proportion in summer.The annual average values of SOR and NOR were 0.34 and 0.17,respectively,indicated a higher degree of conversion of SO2 and NO2 into secondary ions SO2-4 and NO-3.With the aggravation of pollution,the proportion of water-soluble ions in PM2.5 increased sig-nificantly,the concentration and proportion of NO-3 continued to increase,while the proportion of SO42-decreased.The annual average value of NO-3/SO2-4 was 2.13.Fixed sources contributed significantly to atmospheric pollution in summer,while mobile sources dominated in winter,spring,and autumn.
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