[Pollution Characteristics of Inorganic Water-soluble Ions in Atmospheric Particulate Matter in Chengdu Plain]

To study the pollution characteristics of water-soluble ions in atmospheric particulate matter in Chengdu Plain, and identify the composition, distribution, time and spatial variation, achieve targeted control of heavy pollution and haze days, 1476 samples were collected at five monitoring sites during August 2013-July 2014, in which eight kinds of inorganic water-soluble ions (SO₄^2-, NO₃^-, NH₄⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺, Cl^-) were determined by ion chromatography. The results showed that the total mass concentrations of 8 ions in PM_2.5-10 and PM_2.5 were 11.35 and 36.93μg·m^-3, accounting for 37.8% and 46.6% respectively, and SNA (SO₄^2-, NO₃^- and NH₄⁺) in PM_2.5-10 and PM_2.5 contributed 81.1% and 89.9% to the total ions, respectively. The concentration of water-soluble ions was highest in winter and lowest in summer. ρ(SO₄^2-)/ρ(PM_2.5) was highest in summer and autumn, while ρ(NO₃^-)/ρ(PM_2.5) was highest in winter and lowest in summer. SNA, Cl^-, K⁺mostly distributed in PM_2.5, Ca²⁺ and Mg²⁺ in PM_2.5-10. PM_2.5 was generally neutral, the water-soluble ions in which existed as (NH₄)₂SO₄, NH₄NO₃, KNO₃, NaCl, KCl and so on. ρ(NO₃^-)/ρ(SO₄^2-) revealed that the main source of PM_2.5 was given priority to fixed sources. Sulfur oxidation ratio (SOR) and nitrogen oxidation ratio (NOR) were 0.31 and 0.13, respectively, which had opposite changing trend with a highest SOR in summer and NOR in winter. PM_2.5 had the characteristics of regional pollution complex, and SNA was the dominant factor causing the increase of ρ(PM_2.5).