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Surfactant behavior in atmospheric aerosols.

机译：大气气溶胶中的表面活性剂行为。

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摘要

Atmospheric aerosols are very important in the Earth climate system due to their role in cloud formation and the global radiation budget. However, there are still many unanswered questions about how the composition of the aerosol varies and how this composition affects the climate system. While aerosols contain a mix of organic and inorganic material, a sub-fraction of the organic material in atmospheric aerosols is surface active, arranging itself into organic films at the gas-aerosol interface. These films can inhibit trace gas uptake, affecting atmospheric chemistry and composition, and they can also impact water uptake, influencing cloud formation properties. Additionally, these films can depress surface tension of atmospheric aerosols, leading to enhanced cloud nuclei. Organic film behavior strongly depends on aerosol pH as well as ionic content, and given the complexity of atmospheric chemistry, hundreds of possible surfactants could exist at a given time in atmospheric aerosols. Therefore, it is imperative to study and understand the formation of organic films and their behavior at atmospherically relevant conditions.;In this work, we focus on three main questions about surfactant systems: 1. Do organic films form at all atmospherically relevant conditions? 2. How can complex reactive systems be modeled in terms of surface tension and light absorbing reaction products? and 3. What are the different effects that oxidation of organic films can have on cloud condensation nuclei activity? We studied systems of long chain fatty acids and alpha-dicarbonyls in aqueous aerosol mimics by using pendant drop tensiometry to measure surface tension, UV-VIS to measure the formation of light-absorbing products, Aerosol chemical ionization mass spectrometry (Aerosol-CIMS) to characterize the reaction products, and a continuous flow streamwise thermal gradient cloud condensation nuclei counter (CFSTGC) to measure the CCN activity.;We found that organic films of oleic acid and stearic acid formed at all atmospherically relevant conditions (high ionic content and pH 0-8), though the efficacy of the surface film at depressing surface tension changed as the ionization state of the organic changed. Reactive systems of methylglyoxal and glyoxal showed the formation of some cross-reaction products that added to the total product mass formed; however, most of the products formed were from self-reaction. The formation of light absorbing products as well as the surface tension could be described solely by the effects of the isolated organics combined in parallel, rather than including any terms about cross-reaction species. The oxidation of mixed inorganic-organic aerosols with a sodium oleate film showed little change in CCN activity as compared to pure inorganic aerosols, but the same oxidation with an oleic acid film showed depressed CCN activity. This led to the idea that oxidative aging in the atmosphere might not always increase the hygroscopicity of aerosols. Overall, the results of this thesis demonstrate how variable aerosol properties are due to the organics present within complex aerosol compositions. This work will help direct future laboratory studies on atmospherically relevant systems in order to help elucidate an understanding of surfactant behavior in atmospheric aerosols.
机译：由于大气气溶胶在云形成和全球辐射预算中的作用，因此在地球气候系统中非常重要。但是，关于气溶胶的成分如何变化以及这种成分如何影响气候系统，仍然存在许多悬而未决的问题。气雾剂包含有机和无机材料的混合物，而大气气雾剂中有机材料的一部分却具有表面活性，在气体-气雾剂界面处将其自身排列成有机膜。这些薄膜可以抑制痕量气体的吸收，影响大气的化学和组成，还可以影响水的吸收，影响云的形成。另外，这些薄膜可以降低大气气溶胶的表面张力，从而导致云核增强。有机膜的行为在很大程度上取决于气溶胶的pH值和离子含量，并且鉴于大气化学的复杂性，大气中的气溶胶在给定的时间可能存在数百种可能的表面活性剂。因此，必须研究和了解有机薄膜的形成及其在大气相关条件下的行为。；在这项工作中，我们关注关于表面活性剂系统的三个主要问题：1.有机膜是否在所有与大气相关的条件下形成？ 2.如何根据表面张力和光吸收反应产物来模拟复杂的反应体系？ 3.有机膜的氧化对云凝结核活性有什么不同的影响？我们通过使用悬滴法测量表面张力，UV-VIS来测量光吸收产物的形成，气溶胶化学电离质谱（Aerosol-CIMS）来研究水性气溶胶模拟物中的长链脂肪酸和α-二羰基化合物的体系。表征反应产物，并使用连续流动的流式热梯度云凝结核计数器（CFSTGC）来测量CCN活性。;我们发现在所有与大气有关的条件下（高离子含量和pH 0的条件下）都形成了油酸和硬脂酸的有机膜。 -8），尽管表面膜降低表面张力的功效随着有机物的电离状态的改变而改变。甲基乙二醛和乙二醛的反应体系表明形成了一些交叉反应产物，这些产物增加了所形成的总产物质量。但是，形成的大多数产品都是自反应的。光吸收产物的形成以及表面张力可以仅通过平行组合的分离的有机物的作用来描述，而不是包括关于交叉反应物质的任何术语。与纯无机气雾剂相比，用油酸钠膜氧化混合的无机-有机气溶胶的CCN活性几乎没有变化，但是用油酸膜进行的相同氧化反应却显示出CCN活性降低。这导致了这样的想法，即大气中的氧化老化可能并不总是会增加气溶胶的吸湿性。总体而言，本论文的结果证明了复杂的气溶胶组合物中存在的有机物是如何导致气溶胶性能变化的。这项工作将有助于指导未来对大气相关系统的实验室研究，以帮助阐明对大气气溶胶中表面活性剂行为的理解。

著录项

  • 作者

    Schwier, Allison N.;

  • 作者单位

    Columbia University.;

  • 授予单位 Columbia University.;
  • 学科 Atmospheric chemistry.
  • 学位 Ph.D.
  • 年度 2012
  • 页码 138 p.
  • 总页数 138
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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