[Seasonal Variation and Source Analysis of the Water-soluble Inorganic Ions in Fine Particulate Matter in Suzhou].

A total of 87 daily PM _2.5 samples were collected in the urban area of Suzhou city during 2015, representing spring, summer, autumn, winter, respectively. Mass concentration of PM _2.5 was analyzed gravimetrically. Water-soluble inorganic ions, including F ^- , Cl ^- , NO ₃ ^- , SO ₄ ^2- , Na ⁺ , NH ₄ ⁺ , K ⁺ , Mg ²⁺ and Ca ²⁺ , were determined by ion chromatography. The average mass concentration of PM _2.5 was (74.26±38.01) μg·m ^-3 . The seasonal variations of PM _2.5 concentrations decreased in the order of winter > spring > autumn > summer. The average total mass concentrations of 9 ions was (43.95±23.60) μg·m ^-3 , and the order of concentration of ions was NO ₃ ^- > SO ₄ ^2- > NH ₄ ⁺ > Na ⁺ > Cl ^- > K ⁺ > Ca ²⁺ > F ^- > Mg ²⁺ . Seasonal variation of ion concentrations was significant, with the highest concentration observed in winter and the lowest in summer. The secondary inorganic species, including SO ₄ ^2- , NO ₃ ^- and NH ₄ ⁺ (SNA) were the major components of the water-soluble ions in PM _2.5 . SNA's correlations with each other were significant. SO ₄ ^2- , NO ₃ ^- and NH ₄ ⁺ were probably in the form of NH ₄ NO ₃ and (NH ₄ ) ₂ SO ₄ . The [NO ₃ ^- ]/[SO ₄ ^2- ] ratio approaching to 1 implied that mobile sources were as important as stationary sources. Ion balance calculations indicated strong correlations between anion and cation equivalents. The PM _2.5 was acidic. Industrial emission, combustion process, secondary formation and fugitive dust were the major sources of the water-soluble ions in PM _2.5. .