[Characteristics of the Size Distribution of Water Soluble Inorganic Ions in Sanya, Hainan]

Size-resolved filter samples were collected in Sanya every other week from June 2012 to May 2014. The mass concentrations of water-soluble inorganic ions, including anions (Cl^-, NO₃^-, SO₄^2-) and cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, Ca²⁺) were measured by ion chromatography. The results showed that the total concentrations of measured water-soluble inorganic ions were (8.91±7.27) and (11.34±9.37) μg·m^-3 in PM_2.1 and PM_2.1-9, respectively. In PM_2.1, SO₄^2- and NH₄⁺ comprised 72.2% of all water-soluble inorganic ions, while in PM_2.1~9, Cl^-, Ca²⁺ and Na⁺ comprised 67.6% of all water-soluble inorganic ions. In PM_2.1, the total concentrations of water-soluble inorganic ions had highest concentrations in winter and lowest concentrations in summer. In PM_2.1~9, the total concentrations of water-soluble inorganic ions presented the highest concentrations in summer. SO₄^2- and NH₄⁺ showed bimodal size distributions and the peaks in the fine mode shifted from 0.43-0.65 μm in spring, summer and autumn to 0.65-1.1 μm in winter. NO₃^-, Na⁺, Cl^-, Ca²⁺ and Mg²⁺ were unimodal with the peaks in the coarse mode of 4.7-9.0 μm. K⁺ showed bimodal size distribution with the fine mode at 0.43-0.65 μm and the coarse mode at 4.7-5.8 μm. PCA analysis showed that water-soluble inorganic ions were mainly affected by the secondary formation, sea salt and soil particles or falling dust.