黄石市大气PM_2.5中水溶性离子浓度特征及来源分析

To investigate the composition, chemical characteristics and sources of water-soluble inorganic ions, PM_2.5 samples were collected with a MiniVol portable air sampler from March 2012 to February 2013 in Huangshi City, Hubei Province. Nine water-soluble inorganic ions (NH₄ ⁺, Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^-, NO₃ ^-, SO₄ ^2- and F^-) were analyzed by ion chromatography (IC), and the possible sources of these species were determined with the positive matrix factorization (PMF) method. The average mass concentrations of total water-soluble ions were (61.5±26.8)μg/m³, accounting for 63.9% of the PM_2.5 mass. The concentrations of these species were in the order of ρ(SO₄ ^2-)>ρ(NO₃ ^-)>ρ(NH₄ ⁺)>ρ(Na⁺)>ρ(Cl^-)>ρ(Ca²⁺)>ρ(K⁺)>ρ(F^-)>ρ(Mg²⁺). The water-soluble ions were mainly composed of secondary ions (NH₄ ⁺, NO₃ ^- and SO₄ ^2-), accounting for 74.4% of total water-soluble ions. The ratio of ρ(NO₃ ^-) to ρ(SO₄ ^2-) was in the range of 0.12-1.29, with a mean value of 0.53±0.30, indicating that anthropogenic stationary sources had more contributions to the atmospheric pollution in Huangshi City. The sulfur oxidation rate (SOR) and nitrogen oxidation rate (NOR) were greater than 0.10 in the four seasons, suggesting that sulfate and nitrate in PM_2.5 were formed mainly through secondary transformation. The overall correlation between cations and anions in spring, summer, autumn and winter were strong (R²=0.98), and the annual PM_2.5 components were partial acidic. PMF analysis indicated that the major sources of PM_2.5 were combustion, secondary transformation and soil/mineral dust. In conclusion, results showed that SNA were the main water-soluble ions in PM_2.5 in Huangshi City, and combustion, secondary transformation and soil/mineral dust were the main sources.