沈阳大气气溶胶中水溶性无机离子的观测研究

Characteristics of Water-soluble Inorganic Ions in Atmospheric Aerosols in Shenyang

为了解沈阳大气气溶胶中水溶性无机离子浓度水平和季节变化,探究污染期与清洁期气溶胶特性的差异,本研究采集了2012年6月至2013年5月沈阳大气气溶胶分级样品,测定了其中水溶性无机离子浓度.结果表明,沈阳细粒子和粗粒子中水溶性无机离子的浓度总和分别为22.30μg·m^(-3)和14.29μg·m^(-3),其中含量最高的离子分别是SO^(2-)_4和Ca^(2+).细粒子中NH^+_4主要以(NH_4)_2SO_4和NH_4NO_3的形式存在,SO^(2-)_4/NO^-_3质量比为2.28.细粒子中水溶性无机离子的浓度总和(total water soluble inorganic ions,TWSI)季节变化明显,冬春季浓度高,夏秋季浓度低,化石燃料燃烧是细粒子中二次离子冬季出现高值的主要原因;粗粒子中TWSI季节变化不明显,秋季略高,冬季略低,风沙扬尘使秋季粗粒子中的Ca^(2+)出现了显著高值.SO^(2-)_4、NO^-_3、NH^+_4这3种离子浓度总和在冬季清洁期细粒子中比例为80%,污染期则上升为94%;清洁期的离子在细粒径段的峰值主要出现在0.43~0.65μm粒径处,而污染期的离子在细粒径段的峰值主要出现在0.43~2.1μm处,污染期SO^(2-)_4、NO^-_3、NH^+_4这3种离子在细粒径段的峰值由0.43~0.65μm处转移至1.1~2.1μm处,出现了由凝结模态向液滴模态转移的现象;清洁期气团主要生成在贝加尔湖附近,经高空远距离传输至采样点;而污染期气团主要生成并经过我国东北工业区,经低空短距离输送至采样点.

To investigate the levels and seasonal variation of water soluble inorganic components in ambient aerosol in Shenyang, 25 samples were collected with Andersen cascade sampler from Jun. 2012 to May. 2013 and nine water-soluble ions in samples were analyzed by IC. The different characteristics of aerosols between clean and pollution days in winter were discussed based on these samples. The results showed that the annual concentrations of total water soluble inorganic ions were 22. 30 μg-m - 3 and 14. 29μg-m - 3 in fine and coarse particles, and SO2 -4 and Ca2 ＋ were the most abundant ions, respectively. The ratio of mass concentration between SO2 -4 and NO -3 was 2. 28 and the NH ＋4 existed in the form of （NH4 ） 2 SO4 and NH4 NO3 in fine particles. The concentrations of total water soluble ions in fine particles were higher in winter and spring compared with those in summer and autumn, and they varied significantly between different seasons. The fossil fuel consumption led to the maximum values of secondary inorganic ions in fine particles during winter. The concentrations of total water soluble ions in coarse particles varied slightly though they were higher in autumn and lower in winter, and the wind-drifting sand was responsible for the higher concentration of Ca2 ＋ in autumn in coarse particles. The concentration of SO2 -4 , NO -3 , NH ＋4 accounted for 80% of total water soluble inorganic ions during clean days and rose to 94% during pollution days. The ions were mostly concentrated in the size ranges of 0. 43-0. 65 μm and 0. 43-2. 1 μm respectively during clean and pollution days in fine mode. The peaks of SO2 -4 , NO -3 , NH ＋4 in fine mode shifted from 0. 43-0. 65 μm to 1. 1-2. 1μm, which meant these ions were transformed from condensing mode to droplets mode during pollution days. The air mass produced at Lake Baikal and transported through high altitude to the sampling point caused clean days, however the air mass transported through industrial areas might bring pollutions to the sampling point then caused pollution days.