重庆市北碚城区气溶胶中水溶性无机离子的质量浓度及其粒径分布

Mass Concentrations and Size Distributions of Water-soluble Inorganic Ions in Atmospheric Aerosols in Beibei District,Chongqing

为了研究重庆市北碚区城区气溶胶中水溶性无机离子的浓度和分布特征,于2014年3月~2015年2月利用安德森采样器连续采集大气气溶胶分级样品,并用离子色谱法分析了不同粒径(9.00、5.80、4.70、3.30、2.10、1.10、0.65和0.43μm)中Na^+、NH~_4^+、K^+、Mg^(2+)、Ca^(2+)、F-、Cl-、NO_3^-、SO_4^(2-)这9种水溶性无机离子.结果表明,SO_4^(2-)、NH~_4^+、NO_3^-、Cl-、Na^+、K^+主要分布在细粒子中,Mg^(2+)、Ca^(2+)、F-主要分布在粗粒子中.SNA(SO_4^(2-)、NH~_4^+和NO_3^-三者的简称)呈明显单峰型分布,其峰值均出现在0.65~1.10μm的液滴模态,且在细粒子中主要以(NH4)2SO4和NH4NO3形式存在.SO_4^(2-)的形成主要来自云内过程,部分来自SO_2的氧化.Na^+、Cl-、Mg^(2+)在粗、细粒子中呈双峰型分布;K^+在0.43~1.10μm呈单峰型分布;F-、Ca^(2+)在粗粒子中出现峰值.观测期间,PM2.1和PM9.0中总水溶性离子的年均质量浓度分别为(32.68±15.28)μg·m^(-3)和(48.01±19.66)μg·m^(-3),且浓度具有相似季节变化特征,均表现为冬季>春季>夏季>秋季.大部分离子(Na^+、NH~_4^+、K^+、Cl-、NO_3^-、SO_4^(2-))浓度表现为冬春季偏高,夏秋季偏低;而少数离子(F-、Mg^(2+)、Ca^(2+))浓度在秋季最低,其他季节浓度变化稍有不同.SNA是PM2.1中最主要的水溶性离子;而PM9.0中水溶性离子的主要成分除了SNA外,还包括Ca^(2+).PM2.1和PM9.0中阳离子总浓度明显高于阴离子,且不同离子间均具有一定的相关性.主成分分析结果表明,该地区水溶性离子的主要来源包括机动车尾气的排放源、燃烧源、土壤源和建筑道路扬尘.分析气象因素的影响,发现气温对二次离子的生成有明显关系(P<0.05),而相对湿度、风速的影响则不显著(P>0.05).

In order to study the concentration and distribution characteristics of water-soluble inorganic ions in aerosol particles of the Beibei district of Chongqing,aerosol samples were collected with an Andersen cascade impactor between March 2014 and February2015. Water-soluble inorganic ions,including Na^＋,NH4^＋,K＋,Mg^2＋,Ca^2＋,F^-,Cl^-,NO3^-,and SO4^2- were determined for different particle sizes（9. 00,5. 80,4. 70,3. 30,2. 10,1. 10,0. 65,and 0. 43 μm） using the ion chromatography method. Results showed that SO4^2-,NH4^＋,NO3^-,Cl^-,Na＋,and K＋were mainly distributed in fine particles,while Mg^2＋,Ca^2＋,and F^-were mainly present in coarse particles. SNA（SO4^2-,NH4^＋,and NO3^-） exhibited clear unimodal distribution,with peaks in the droplet mode of 0. 65-1. 10 μm,mainly present in the form of（NH4）2 SO4 and NH4 NO3 in fine particles. The formation of SO4^2- is mainly attributed to in-cloud processes and partly to oxidation of SO2. Na＋,Cl^-,and Mg^2＋exhibited bimodal distribution in coarse and fine particles; K＋was a single peak distribution in the range of 0. 43-1. 10 μm,while peaks of F^-and Ca^2＋concentrations were in coarse particles. Average annual concentrations of total water-soluble ions in PM2. 1 and PM9. 0 were（32. 68 ± 15. 28） μg·m^-3 and（48. 01 ±19. 66） μg·m^-3 over the observation period. Seasonal variations of PM2. 1 and PM9. 0 concentrations decreased in the order of winter spring summer autumn. This was the same for most ions,but a small number of ions（F^-,Mg^2＋and Ca^2＋） had a different patternin the spring,summer,and winter. The SNA were the major components of water-soluble ions in PM2. 1,and Ca^2＋was the major component of water-soluble ions in PM9. 0 besides SNA. The concentration of cations was significantly higher than that of anions＇ in PM2. 1 and PM9. 0,with a certain correlation between different ions. Emissions from motor vehicle exhaust,combustion processes,soil sources,and fugitive dust were the major sources of water-soluble ions in this area. The effect of air temperature on secondary ions is significant（P〈0. 05）,but relative humidity and wind speed have no significant effect（P〈0. 05）.