天津冬季一次重污染过程颗粒物中水溶性离子粒径分布特征

Characteristics of the Size Distribution of Water-soluble Ions During a Heavy Pollution Episode in the Winter in Tianjin

为研究天津冬季重污染天气过程中颗粒物水溶性离子的粒径谱分布及二次离子生成机制,于2014年1月利用Anderson撞击式分级采样器在中国气象局天津大气边界层观测站内采集颗粒物样品,并使用离子色谱仪分析Na^+、NH_4^+、K^+、Mg^(2+)、Ca^(2+)、Cl^-、NO_3^-、SO_4^(2-)等8种水溶性无机离子(TWSII).结果表明,采样期间PM_(2.5)和PM_(10)质量浓度均值分别为(138±100)μg·m^(-3)和(227±142)μg·m^(-3),粗、细粒子中TWSII的平均浓度分别为(34.07±6.16)μg·m^(-3)和(104.16±51.76)μg·m^(-3).细粒子中SO_4^(2-)、NO_3^-和NH_4^+这3种离子的浓度远高于其他离子,且相关性较好,粗粒子中NO_3^-、SO_4^(2-)、Cl^-浓度较高.随着污染程度加剧,细粒子中TWSII浓度增加明显,粗粒子中则变化不大.水溶性离子的粒径谱分布显示,SO_4^(2-)以单模态分布,优良天峰值出现在0.43~0.65μm,NO_3^-在优良日呈现三模态分布,峰值分别出现在0.43~0.65、2.1~3.3和5.8~9.0μm,NH_4^+呈双模态分布,优良日峰值出现在0.43~0.65μm和4.7~5.8μm,污染日3种二次离子峰值均以0.65~1.1μm的单模态分布为主,与三者之间的热动力平衡过程有关.细粒子中NH_4^+除与SO_4^(2-)和NO_3^-结合外,还与部分Cl^-结合,粗粒子中NH_4^+全部与NO_3^-和SO_4^(2-)结合后,剩余的NO_3^-和SO_4^(2-)与其他阳离子结合.

To characterize the size distribution of water-soluble inorganic ions （ WSⅡ） during a heavy pollution episode, particle samples were collected by an Andersen cascade sampler in Tianjin in January 2014, and the concentrations of eight WSⅡ （Na ＋ , NH ＋4 , K ＋ , Mg2 ＋ , Ca2 ＋ , Cl - , NO -3 , and SO2 -4 ） during a typical haze episode were analyzed by ion chromatography. The sources and formation mechanisms of WS Ⅱ were analyzed based on their size distributions. The results showed that the daily average concentrations of PM2. 5 and PM10 were （138 ± 100） μg·m - 3 and （227 ± 142） μg·m - 3 , respectively, and the average concentration of total WSⅡ concentrations （TWSⅡ） in the coarse and fine particles were （34. 07 ＋ 6. 16） μg·m - 3 and （104. 16 ＋ 51. 76） μg·m - 3 , respectively. The concentrations of SO2 -4 , NO -3 , and NH ＋4 in the fine particles were much higher than concentrations of the other ions, and there were strong correlations between these three ions. The TWSⅡ on clear days, light pollution days, and heavy pollution days were （41. 55 ± 12. 41） μg·m - 3 , （94. 46 ± 31. 19） μg·m - 3 , and （147. 55 ± 27. 76） μg·m - 3 , respectively. On clear days, SO2 -4 showed a unimodal distribution, peaking at 0. 43-0. 65 μm; and NO -3 showed a trimodal distribution, peaking at 0. 43-0. 65 μm, 2. 1-3. 3 μm, and 5. 8-9. 0 μm. NH ＋4 had a bimodal distribution, peaking at 0. 43-0. 65 μm and 4. 7-5. 8 μm. On heavy pollution days, however, the size distributions of these three secondary inorganic ions switched to a unimodal size distribution, peaking at 0. 65-1. 1μm. Unimodal NH ＋4 mainly coexisted with SO2 -4 and NO -3 , and the excess NH ＋4 was found to be combined with Cl - in the fine particles. In the coarse particles, NH ＋4 completely coexisted with SO2 -4 and NO -3 .