[Seasonal Characteristics and Source Analysis of Water-soluble Inorganic Ions in PM_2.5 in Suqian City]

To study the seasonal pollution characteristics and sources of water-soluble inorganic ions in atmospheric PM_2.5 in Suqian City, 171 samples were collected at three monitoring points, which were in the water vapor channel, from May 2017 to January 2018. The mass concentrations of PM_2.5 and nine water-soluble inorganic ions were analyzed. The results showed that the annual average concentration of water-soluble inorganic ions in PM_2.5 in Suqian City was (44.08±34.61) μg ·m^-3, accounting for 41.8% of PM_2.5. The concentrations of these species were in the order of ρ(NO₃^-) > ρ(SO₄^2-) > ρ(NH₄⁺) > ρ(ρl^-) > ρ(Na⁺) > ρ(Ca²⁺) > ρ(K⁺) > ρ(F^-) > ρ(Mg²⁺); NO₃^-, SO₄^2-, and NH₄⁺ accounted for 75.6% of the total water-soluble ions. The annual average ratio of ρ(NO₃^-) to ρ(SO₄^2-) was 1.53±0.88, indicating that mobile sources contributed more to PM_2.5 pollution. Based on the correlation analysis of NH₄⁺ and SO₄^2-, NO₃^- may exist in the form of (NH₄)₂ SO₄, NH₄HSO₄, or NH₄NO₃. According to the principal component analysis, secondary transformation, industrial pollution, biomass burning, and dust were the major sources of water-soluble inorganic ions. PM_2.5concentrations were positively related to relative humidity in winter. Water vapor transmission is more likely to promote PM_2.5 accumulation in winter.