[Concentrations and Size Distributions of Water-soluble Inorganic Ions in Aerosol Particles in Taiyuan, Shanxi]

Size-resolved filter samples were collected in Taiyuan every other week from June 2012 to May 2014. The mass concentrations of water-soluble ions (Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺, F^-, Cl^-, NO₃^- and SO₄^2-) were measured by ion chromatography. The results showed that the total concentrations of measured water-soluble ions were (15.39±9.91), (21.10±15.49) and (36.34±18.51) μg·m^-3 in PM_1.1, PM_2.1 and PM₉, respectively. In PM_1.1 and PM_2.1, secondary water-soluble ions (SO₄^2-, NO₃^- and NH₄⁺) comprised 87.59% and 86.30% of all water-soluble ions, respectively, while in PM₉, SO₄^2- and Ca²⁺ comprised 32.78% and 28.54% of all water-soluble ions, respectively. SO₄^2- and NH₄⁺ had higher concentrations in winter and summer, and lower in spring and autumn. NO₃^-, K⁺and Cl^- presented similar seasonal variation with a descending order of winter >autumn >spring >summer, and Ca²⁺ and Mg²⁺ followed the sequence of spring >winter >autumn >summer. SO₄^2- and NH₄⁺ showed a unimodal size distribution and the peak in the fine mode shifted from 0.43-0.65 μm in spring and autumn to 0.65-1.1 μm in summer. NO₃^- showed a bimodal size distribution. NO₃^- and NH₄⁺ were dominated by the fine mode peaking at 0.43-2.1 μm in winter, and NO₃^- was dominated by the coarse mode peaking at 4.7-5.8 μm in summer. K⁺, Na⁺and Cl^- also showed a bimodal size distribution with the fine mode at 0.43-1.1 μm and the coarse mode at 4.7-5.8 μm. Ca²⁺, Mg²⁺ and F^- were unimodal with the peak in the coarse mode of 4.7-5.8 μm. On heavily polluted days, the mass concentrations of secondary water-soluble ions and Cl^- accumulated, and secondary water-soluble ions were unimodal with the peak in the fine mode of 1.1-2.1 μm. However, on clear days, secondary water-soluble ions showed a bimodal size distribution with the fine mode at 0.43-0.65 μm and the coarse mode at 4.7-5.8 μm. The peak of secondary water-soluble ions in the fine mode shifted. PCA analysis showed that the sources of water-soluble ions were dominated by the secondary formation, coal combustion, industrial emission, biomass burning, and soil particles or falling dust.