[Seasonal Variation of Water-soluble Ions in PM in Xi'an].

To explore the seasonal variations and sources of water-soluble ions, PM samples were collected from 2017 to 2018. Water-soluble ions including SO, NO, Cl, F, Na, Mg, NH, K, and Ca were determined via ion chromatography. Furthermore, the existing form of NH, nitrogen oxidation rate (NOR), sulfur oxidation rate (SOR), and [NO]/[SO] ratio were explored. The results showed that dust, coal combustion, biomass burning, and secondary aerosols were the dominant contributors to water-soluble ions. Ca, SO, NH, and NO were the main water-soluble ions in PM in Xi'an. Correlation analysis results showed that NH could not completely neutralize SO in spring; unneutralized SO could be mainly combined with K and Ca. NH mainly existed in the form of ① NHHSO and (NH)SO in summer; ② NHHSO and NHNO in autumn; and ③ (NH)SO and NHNO in winter. The yearly mean values of SOR and NOR were 0.35 and 0.16, respectively, indicating a high secondary aerosol transformation rate during the study period. The [NO]/[SO] ratio showed Xi'an was mainly affected by stationary sources in spring and summer, while the contribution of mobile sources in autumn and winter was greater than stationary sources.