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Phase transitions of aerosol particles in the sulfate-nitrate-ammonium-proton system.

机译：硫酸盐-硝酸盐-铵-质子系统中气溶胶颗粒的相变。

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摘要

Atmospheric particles are important in Earth's radiation budget because they can scatter light directly back to space and serve as nuclei for cloud formation. Aerosol particles also play a critical role in the chemistry of the atmosphere by providing surfaces for heterogenous reactions and serving as sinks and sources of atmospheric gases. Sulfate-nitrate-ammonium (SNA) particles are particularly important because, on a global basis, they make the largest anthropogenic contribution to the aerosol mass budget. The magnitude of the effect of SNA particles on radiative forcing and chemical reactions depends on their physical state. Aqueous particles scatter light more efficiently than do crystalline particles and chemical reaction rates are usually faster on aqueous particles than dry particles. Therefore, accurate prediction of the effect of SNA particles on radiative forcing and reaction rates requires knowledge of their physical state and how physical state changes with relative humidity. While deliquescence relative humidities can be accurately predicted using thermodynamic models, there is currently no theory that can accurately predict crystallization relative humidities.; In this thesis, the crystallization properties at 293 K of aerosol particles composed of SO42-, NO3-, NH4+, and H+ are studied using aerosol flow tube infrared spectroscopy. An innovative experimental protocol is employed to restore water content to the aerosol particles and thus remove the ambiguity of their physical state after exposure to low relative humidity. The six crystals formed include (NH4)2SO4, (NH4) 3H(SO4)2, NH4HSO4, NH 4NO3, 2NH4NO3·(NH4) 2SO4, and 3NH4NO3·(NH4 )2SO4.; The infrared aerosol spectra for the six solids formed are determined based upon a linear decomposition analysis of the recorded spectra. Small nonzero residuals occur in the analysis because aerosol spectra depend on particle morphology, which changes slightly across the range of compositions studied. Although particles of NH4NO3(aq) and NH 4HSO4(aq) do not crystallize even at 1% relative humidity, additions of 0.05 mole fraction SO42-(aq) or NO 3-(aq) ions promote crystallization, respectively. 2NH 4NO3·(NH4)2SO4(s) and (NH4)3H(SO4)2(s) appear to serve as good heterogeneous nuclei for NH4NO3(s) and NH4HSO4(s), respectively. 2NH4NO3·(NH 4)2SO4(s) crystallizes over a greater range of aqueous compositions than 3NH4NO3·(NH4) 2SO4(s).; The liquid water content of the particles after exposure to complex relative humidity histories is compared to the predictions of the Aerosol Inorganics Model. Depending on composition and relative humidity history, it is possible for a particle to follow one of several different crystallization pathways. This results in an external mixture of solid particles from an initially homogeneous population of aqueous particles. Increasing the number of cycles between high and low relative humidity allows particles to reconstruct and increases the percentage of particles following the most thermodynamically stable pathway.
机译：大气粒子在地球的辐射预算中非常重要，因为它们可以将光直接散射回太空并充当形成云的核。气溶胶颗粒在大气化学中也起着至关重要的作用，它为异质反应提供了表面，并充当了大气的汇和源。硫酸盐-硝酸盐-铵（SNA）颗粒特别重要，因为在全球范围内，它们对气溶胶质量预算的人为贡献最大。 SNA粒子对辐射强迫和化学反应的影响大小取决于其物理状态。水性颗粒比晶体颗粒更有效地散射光，并且水性颗粒上的化学反应速率通常比干燥颗粒快。因此，要准确预测SNA粒子对辐射强迫和反应速率的影响，需要了解其物理状态以及物理状态如何随相对湿度变化的知识。虽然可以使用热力学模型准确预测潮解相对湿度，但目前尚无理论可以准确预测结晶相对湿度。本文利用气溶胶流管红外光谱技术研究了由SO42-，NO3-，NH4 +和H +组成的气溶胶颗粒在293 K时的结晶特性。采用了创新的实验规程，以将水含量恢复到气溶胶颗粒中，从而消除了暴露于低相对湿度后其物理状态的歧义。形成的六个晶体包括（NH 4）2 SO 4，（NH 4）3 H（SO 4）2，NH 4 HSO 4，NH 4 NO 3，2NH 4 NO 3·（NH 4）2 SO 4和3NH 4 NO 3·（NH 4）2 SO 4。根据所记录光谱的线性分解分析确定所形成的六种固体的红外气溶胶光谱。由于气溶胶光谱取决于颗粒形态，因此在分析中会出现少量的非零残差，该颗粒形态在所研究的成分范围内略有变化。尽管即使在1％的相对湿度下NH4NO3（aq）和NH 4HSO4（aq）颗粒也不会结晶，但是加入0.05摩尔分数的SO42-（aq）或NO 3-（aq）离子会分别促进结晶。 2NH 4NO3·（NH4）2SO4（s）和（NH4）3H（SO4）2（s）似乎分别充当NH4NO3和NH4HSO4的良好异质核。 2NH 4 NO 3·（NH 4）2 SO 4在比3NH 4 NO 3·（NH 4）2 SO 4大的含水组合物中结晶。将暴露于复杂的相对湿度历史后的颗粒中的液态水含量与“气溶胶无机模型”的预测值进行比较。取决于组成和相对湿度历史，颗粒有可能遵循几种不同的结晶途径之一。这产生了最初均质的水性颗粒群的固体颗粒的外部混合物。增加在高和低相对湿度之间的循环次数可以使颗粒重建，并增加遵循热力学最稳定路径的颗粒百分比。

著录项

  • 作者

    Schlenker, Julie Christine.;

  • 作者单位

    Harvard University.;

  • 授予单位 Harvard University.;
  • 学科 Atmospheric Sciences.
  • 学位 Ph.D.
  • 年度 2006
  • 页码 105 p.
  • 总页数 105
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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