太原市大气颗粒物粒径和水溶性离子分布特征

Distribution Characteristics of Water-soluble Ions in Size-segregated Particulate Matters in Taiyuan

在太原市于2014年7月至2015年4月利用TE-235分级采样器采集PM_(10)分级颗粒物样品,通过离子色谱分析其中9种无机水溶性离子,报道了大气颗粒物(PM_(10))及其水溶性无机离子水平,探讨了其粒径分布、季节变化特征和来源.结果表明,采样期间太原市PM_(10)日平均浓度水平为173.7μg·m^(-3),超过了国家环境空气二级日标准限值(150μg·m^(-3),GB3095-2012);冬季PM_(10)浓度(199.1μg·m^(-3))和春季(194.2μg·m^(-3))较接近,远高于夏季水平(127.7μg·m^(-3)).PM_(10)在<0.95μm和3.0~7.2μm粒径段处呈双峰分布.PM_(10)中总离子浓度季节变化为冬季>夏季>春季,其中SO^(2-)_4、NO^-_3和NH^+_4是主要离子,占总离子的质量分数为66%~80%.分级离子中,SO^(2-)_4、K^+、NH^+_4、Cl^-以及冬、春季的NO^-_3在<0.95μm段呈单峰分布;Ca^(2+)、Mg^(2+)和夏季NO^-_3均在<0.95μm和3.0~7.2μm段呈双峰分布.相关性分析显示,风速增大对冬夏季的颗粒物及其水溶性离子有稀释作用,但春季沙尘天气则会导致其升高.通过NO^-_3/SO^(2-)_4和Mg^(2+)/Ca^(2+)比值发现,太原市颗粒物中NO^-_3和SO^(2-)_4主要来自于燃煤排放,Mg^(2+)和Ca^(2+)来源为扬尘和煤燃烧排放.

The distributions of size-segregated particles （PM10 ） and water-soluble ions （WSIs） in Taiyuan were studied from July 2014 to April 2015 by TE-235 aerosol sampling and ion chromatography analyzing. As the results shown, the daily PM10 level was 173. 7μg-m - 3 , which exceeded the Grade Ⅱ limitation value in the Ambient Air Quality Standard （150 μg-m - 3 , GB 3095-2012）. PM10 levels varied seasonally, and its were 199. 1 and 194. 2 μg-m - 3 in winter and spring, respectively, which were much higher than those in summer. The PM10 size-segregated was bimodal distribution for the range of 0-0. 95 and 3. 0-7. 2 μm. The concentration of WSIs was the highest in winter, followed by summer and spring. SO2 -4 , NO -3 and NH ＋4 were the main water soluble ions and accounted for 66%to 80 % of the total WSIs. SO2 -4 , K ＋ , NH ＋4 and Cl - showed a unimodal distribution at 〈 0. 95 μm in all samples, while Ca2 ＋ and Mg2 ＋ showed a bimodal distribution at 〈 0. 95 μm and 3. 0-7. 2 μm. NO -3 showed a unimodal size distribution at 〈 0. 95 μm in winter and spring, compared with a bimodal distribution at 〈 0. 95 μm and 3. 0-7. 2 μm in summer. By the correlation analysis, PM10 and WSIs decreased with the increase of wind speed in summer and winter other than in spring for the road-dust re-suspension by strong wind. Based on the ratio analysis of NO -3 / SO2 -4 and Mg2 ＋ / Ca2 ＋ , coal combustion was the main source of NO -3 and SO2 -4 , while Mg2 ＋and Ca2 ＋ were mainly from the dust and coal combustion.