重庆市不同粒径颗粒物中水溶性离子污染特征

于2010年3月~2011年2月和2017年1~12月在重庆主城区连续采集PM_1.0、PM_1.0~2.5和PM_2.5~10样品，采用离子色谱测定了样品中9种水溶性无机离子（WSIIs）含量，研究了近年来不同粒径颗粒物中主要离子的污染特征.结果表明，2017年重庆市PM_1.0、PM_1.0~2.5和PM_2.5~10中WSIIs年均浓度和占比分别为24.10，32.89，39.11μg/m³和41.8%、40.3%、38.6%，较2010年均有所下降（39.85，47.84，57.12μg/m³和49.2%、46.6%、36.2%），但NO₃^-浓度和占比呈上升趋势（分别上升12.3%~27.8%和53.1%~78.2%），且成为2017年冬季首要离子.SO₄^2-、NO₃^-、NH₄⁺、Cl^-、K⁺和Na⁺主要分布在细粒子中，F^-、Mg²⁺和Ca²⁺主要分布在粗粒子中.重庆颗粒物呈弱碱性，其中粗粒子碱性强于细粒子，NH₄⁺主要以（NH₄）₂SO₄和NH₄NO₃的形式存在.与2010年不同，2017年细粒子中SO₄^2-和NO₃^-浓度均随相对湿度增大而快速上升，非均相反应已成为2017年SO₄^2-和NO₃^-形成的重要途径，且在PM_1.0中尤为突出.随污染加重，不同粒径下各类WSIIs演化特征各异，其中2017年细粒子中NO₃^-浓度及其对WSIIs贡献大幅升高，并成为重污染形成的主因，而SO₄^2-和扬尘源示踪物（Mg²⁺、Ca²⁺）贡献呈下降趋势.与2010年相比，2017年各粒径中NO₃^-/SO₄^2-比值随污染加重大幅升高，且重污染日比值均大于1.0.细粒子中WSIIs主要来源于二次转化，粗粒子主要来源于扬尘.2017年扬尘污染较2010年有所减缓，但二次源对WSIIs贡献上升明显，尤其是NO₃^-的二次生成，因此对NOx排放源的管控是WSIIs减排的重要途径.研究结果对了解近年来重庆市大气颗粒物污染来源及形成机制研究具有重要参考价值.

Characteristics ofwater-solubleionsinmulti-sizeparticlesin Chongqing

PM_1.0, PM_2.5 and PM₁₀ samples were collected from March 2010 to February 2011 and January 2017 to December 2017 in the urban area of Chongqing. The mass concentrations of nine water-soluble inorganic ions (WSIIs) were determined by anion chromatography, and characteristics of WSIIs inmulti-size particles during recent years were investigated. The results showed that the annualmean concentrationsof WSIIs in PM_1.0, PM_1.0~2.5 and PM_2.5~10 were 24.10, 32.89 and 39.11μg/m³ respectively, accounting for 41.8%, 40.3% and 38.6% of PM respectively in 2017. The annual mean concentrations of WSIIs in PM in 2010 (39.85, 47.84 and 57.12μg/m³ respectively) were higher than that in 2017, and so were thefractions (49.2%, 46.6% and 36.2% respectively). However, the concentrations and fractions of NO₃^- in PM increased by 12.3%~27.8% and 53.1%~8.2% respectively from 2010 to 2017, and NO₃^- was the primary ion in 2017 winter. SO₄^2-, NO₃^-, NH₄⁺, Cl^-, K⁺, and Na⁺ were mainly distributed in fine particles, while F^-, Mg²⁺ and Ca²⁺ were the major WSIIs components in coarse particles. The particles in Chongqing were slightly alkaline, especially coarse particles, and NH₄⁺ were existed in the form of (NH₄)₂SO₄ and NH₄NO₃. Compared with that in 2010, the concentrations of both SO₄^2- and NO₃^- increased with the increase of relative humidity in fine particles in 2017. RH-dependent heterogeneous reactions contributed greatly to the formation of sulfate and nitrate in 2017, especially in PM_1.0. With the aggravation of pollution, the evolution processes of different ions were differentinmulti-size particles. Among them, the concentrations and fractions of NO₃^- in WSIIs increased significantly and NO₃^- was the primarily driver of heavy pollution in fine particles in 2017, while the contributions of SO₄^2- and the ions from dust (Mg²⁺ and Ca²⁺) decreased. In addition, themass ratios of NO₃^-/SO₄^2- in different particle size increased with the aggravation of pollution and were higher than 1.0 during the heavy pollution days in 2017, but not in 2010. The main sources of WSIIs in fine particles were secondary formation, while dust was the major source of WSIIs incoarse particles. The pollution of dust in 2017 was lighter than that in 2010, but the contribution of secondary formation was increased significantly from 2010 to 2017, especially the formation of nitrate in Chongqing. The control of NO_x emission sourcesis critical to reduce WSIIs emission. Results provided important information for the study of the sources and formation mechanisms of the atmospheric particles in Chongqing.