Characteristics and source apportionment of water-soluble inorganic ions in atmospheric particles in Lvliang, China

Seasonal atmospheric particulate matter samples with different particle sizes (< 2.5 μm [PM2.5], 2.5–5 μm [PM2.5–5], 5–10 μm [PM5–10], and 10–100 μm [PM10–100]) were collected to analyze the mass concentration and distribution characteristics of nine water-soluble ions (WSIs; F−, Cl−, NO3−, SO42−, Na+, NH4+, K+, Mg2+, and Ca2+) in Lvliang in China. The results of chemical composition analysis indicated that the average concentration of total WSIs was 29.08 µg·m−3 and accounted for 40.45% of PM2.5, 80.99% of which was attributable to SO42−, NH4+, and NO3−; the concentration demonstrated obvious distribution characteristics. NO3− and NH4+ primarily exist as NH4NO3 and (NH4)2SO4, respectively, in fine particles but as NaNO3 and NH4Cl, respectively, in coarse particles. The PM2.5 was alkaline overall, and K+ and NH4+ caused the highest RC/A values in autumn. Stationary sources contribute more to WSIs in particulates than mobile sources. The secondary transformation degree of SO2 was higher than that of NOx, especially in fine particles. The positive matrix factorization (PMF) and potential source contribution function (PSCF) models were combined to determine the sources of WSIs in PM2.5. Through use of the PMF model, five source factors were categorized: secondary aerosols (43.0%), biomass combustion (21.7%), coal combustion (17.6%), dust (10.9%), and vehicular traffic (6.8%). The results of the PSCF model suggested that the transport of pollutants from Shanxi, northwestern Shaanxi, Gansu, Inner Mongolia and Henan, had the greatest effect on air quality in Lvliang.