The characterization of water-soluble inorganic ions in PM2.5 during a winter period in Xi'an, China.

The characteristics of water-soluble inorganic ions (WSIIs) during a winter period in a suburb of Xi'an, China, were investigated. Our results show that the total mass concentration of the dominant WSIIs (8) was 91.27 µg m-3, accounting for 50.1% of the total mass concentration of PM2.5 (particulates with a size of 2.5 µm or less). Secondary inorganic aerosols (SO42−, NO3− and NH4+) were the most abundant ions, accounting for up to 95.12% of the total ions. By using the anion and cation equivalence ratio method, PM2.5 was shown to have weak alkalinity, and the chemical forms of WSIIs were mainly (NH4)2SO4 and NH4NO3. The sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) suggested that larger proportions of SO42− and NO3− were formed by gas-phase SO2 and NO2 in the sampling site. Ratio analysis also indicated that anthropogenic sources significantly contributed to WSII pollution. Among the anthropogenic sources, fixed pollution sources were found to be dominant over mobile sources. [ABSTRACT FROM AUTHOR]