华南地区大气气溶胶中EC和水溶性离子粒径分布特征

Size-resolved mass concentrations of elemental carbon and inorganic water-soluble ions in South China

利用1988~2010年在华南地区广州、深圳、海口等多地采得的126组样品,初步分析了华南地区不同时段不同地区和水溶性离子成分的浓度变化及其粒径分布特征.结果表明：各站的AEC（等效元素碳）浓度和水溶性无机离子浓度差异较大,Na＋和Cl-基本表现为海岛站点〉海岸站点〉乡村站点〉城市站点,其余主要离子成分和AEC则表现为城市站点〉乡村站点〉海岸站点〉海岛.城市站点、乡村站点、海岸站点和海岛站点AEC质量浓度在不同年段随粒径分布的变化趋势比较一致的,基本呈双峰结构,主峰主要位于0.43~0.65μm,次峰主要位于4.7~5.8μm.根据各离子的粒径分布的相似性可以将各种离子的垂直分布形态分为3类：二次离子（SO4^2-、NO3^-和NH4^＋）呈现明显的三峰分布形态;F-、Ca^2＋、Mg^2＋、Na^＋和Cl^-呈双峰分布形态;K＋和AEC呈单峰分布形态,主峰位于细粒子模态.各成分浓度随高度的变化则呈现不同的变化规律.降水对气溶胶粒子的清除作用是显著的,尤其是粒径大于1μm的颗粒,而1.1~2.1μm的粒子段是降水清除的关键区.局地污染中,AEC质量浓度随粒径的分布呈现出了很明显的＂单峰＂结构,且主要集中在次微米段粒径范围内.

126 groups of size-segregated aerosol samples collected from Guangzhou, Shenzhen, Haikou and some other regions in South China during 1998-2010 were utilized to characterize the temporal-spatial variations of size-resolved mass concentrations of AEC and inorganic water-soluble ions. Notable regional differences were displayed, the mass concentrations of Na＋ and C1- at different sites presented the characteristics of island 〉 coastal 〉 rural 〉 urban. To the contrary, mass concentrations of other major ions and AEC were in the order of urban 〉 rural 〉 coastal 〉 island sites. During different observation periods, size-resolved mass concentrations of AEC showed a similar bimodal pattern for all sites, with the prominent peak located in the range of 0.43-0.65μm and the smaller peak distributed in a larger size range （4.7-5.81μm）. The vertical distributions of AEC and inorganic water-soluble ions can be categorized into three types according to the corresponding size-resolved mass concentrations. Specifically, the secondary ions （SO4^2-, NO3^- and NH4^＋） showed a distinct three-peak pattern, double-peak structures were found in the results of F, Ca^2＋, Mg^2＋, Na^＋ and Cl^-, both K＋ and AEC displayed a significant single peak in the fine-particle mode. The mass concentrations of AEC and inorganic water-soluble ions varied with the variation of height. Precipitations played a crucial role in the removal of aerosol particles larger than 1μm, especially on the size bins of 1.1-2.1μm. In local aerosol pollution episodes, the size-resolved mass concentration of AEC had a pronounced unimodal pattern within the submicron size ranges.