祁连山老虎沟地区夏季大气颗粒物中水溶性离子的变化特征

为了研究青藏高原东北缘老虎沟地区大气颗粒物中水溶性无机离子组分的变化特征，于2016年7月16日至8月11日共采集13个PM_2.5样品和4套粒径分级样品。研究结果显示：非沙尘期间，水溶性离子总质量浓度为2.35 μg·m^-3，主要离子SO₄^2-、Ca²⁺、NH₄⁺和NO₃^-的浓度分别为1.28、0.33、0.32和0.28 μg·m^-3，约占水溶性离子浓度总和的94%；沙尘期间，水溶性无机离子总质量浓度为12.63 μg·m^-3，是非沙尘期间浓度的5倍，主要离子SO₄^2-、Ca²⁺、Cl^-、Na⁺和NO₃^-的浓度依次为5.36、4.77、0.80、0.62和0.61 μg·m^-3，约占水溶性离子浓度总和的96%。分级样品分析结果表明，NO₃^-主要分布在粗颗粒模态，可能是前体物在粉尘表面发生非均相反应产生。在沙尘时期，SO₄^2-主要为粉尘贡献，集中分布在粗颗粒模态。在非沙尘时期，SO₄^2-在粗颗粒模态和积聚模态都有较多的分布。积聚模态的SO₄^2-主要是通过前体物与NH₃发生均相反应产生。据估算，非沙尘时期的二次反应对PM_2.5中SO₄^2-的贡献约为80%。

The changing characteristics of soluble ions in PM2.5 in summer over Laohugou region in the Qilian Mountains

In order to investigate the characteristics of water-soluble ions in atmospheric particles in northeast margin of the Tibetan Plateau,a field study was carried out at the Qilian Shan Station of Glaciology of Ecologic Environment from 16 July to 11 August,2016.A total of 13 PM2.5 filter samples and 4 sets of size-segregated aerosol samples had been taken.Results indicated that sum of total water-soluble ions concentrations was 2.35 μg · m-3 in non-dust period,which was slightly higher than the results observed in 2012,with the concentrations of SO42-,Ca2+,NH4+,NO3-being 1.28,0.33,0.32,and 0.28 μg · m-3,accounting for 94％ of the total water-soluble ions.The sum of total water-soluble ions concentrations was 12.63 μg · m-3 in dust period,which was five times of that in non-dust period,with the concentrations of SO42-,Ca2+,C1-,Na +,NO3-in this period being 5.36,4.77,0.80,0.62,0.61 μg · m-3,accounting for 96％ of the total water-soluble ions.From the analysis of size-segregated samples,one can see that NO3-was mainly distributed in the coarse mode,probably formed by the heterogeneous reaction of precursors on surface of atmospheric particles.In all periods,SO24-shows an obvious peak in the coarse mode at size bin of 1.8 ～ 3.2 μm,mainly from mineral dust and in nondust period,SO42-also shows a significant peak in the accumulation mode at the size bins of 0.18 ～0.32 μm or 0.32 ～ 0.56 μm,formed from secondary chemical reactions.The estimated contribution of the secondary chemical reactions to SO]-is 80％.