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首页> 外文学位 >Constraining Sources and Sinks of Atmospheric Trace Gases: Spectroscopy and Kinetics of C1-C3 Criegee Intermediates and the Isotopic Composition of Lightning-Produced N2O
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Constraining Sources and Sinks of Atmospheric Trace Gases: Spectroscopy and Kinetics of C1-C3 Criegee Intermediates and the Isotopic Composition of Lightning-Produced N2O

机译：大气痕量气体的约束源和汇：C1-C3受激分子中间体的光谱学和动力学以及闪电产生的N2O的同位素组成

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摘要

This dissertation presents a series of research projects designed and carried out to elucidate the physical chemistry and assess the atmospheric relevance of (1) carbonyl oxide radicals (i.e., Criegee intermediates) produced in alkene ozonolysis and (2) nitrous oxide (N2O) produced in lightning-induced corona discharges. The results provide UV absorption spectra and reaction rate coefficients for Criegee intermediates that will help constrain the formation and loss pathways of aerosol nucleation precursors such as H2SO4 and oxidized volatile organic compounds, and the isotopic signature of N2O formed in lightning that can help distinguish various N2O sources in atmospheric measurements.;Criegee intermediates are byproducts of the reaction of alkenes with ozone. Bimolecular reactions of Criegee intermediates can lead to the production of low-volatility organic compounds and acids in the atmosphere, which in turn play a role in determining the concentration, size, and optical properties of aerosols. Recently, a novel method for producing measurable quantities of stabilized Criegee intermediates in the laboratory paved the way for the development of new experimental techniques to study their chemical properties and predict their importance in the atmosphere. For this dissertation, a unique apparatus combining time-resolved UV absorption in a flow cell with laser depletion in a molecular beam was adapted to obtain the absolute absorption spectrum of CH3CHOO with high resolution and accuracy relative to previous spectral measurements by other groups. The resulting absorption cross sections imply a photolysis lifetime of about seven seconds in the atmosphere, long enough for CH3CHOO to participate in unimolecular and bimolecular reactions. The broad absorption band with weak structure in the long-wavelength region of the spectrum represents a "spectral fingerprint" for identifying CH3CHOO in future studies, and the cross sections provide valuable benchmarks for theory to characterize electronically excited states of CH 3CHOO.;The fast reaction of CH2OO with water dimer is thought to dominate CH2OO removal in the atmosphere. However, reaction rates can vary considerably under different conditions of temperature, humidity, and pressure. A temperature-controlled flow cell was designed to measure the transient absorption of CH2OO and obtain rate coefficients for its reaction with water dimer from 283 to 324 K. The rate of the reaction of CH2OO with water dimer was found to exhibit a strong negative temperature dependence, pointing to the participation of a hydrogen-bonded pre-reactive complex between CH2OO and two water molecules. Due to the strong temperature dependence, and shifting competition between water dimer and water monomer, the effective loss rate of CH2OO by reaction with water vapor is highly sensitive to atmospheric conditions. The role played by the stable pre-reactive complex suggests that similar complexes could form between water dimer and other larger Criegee intermediates, and that the stability and relative energy of these complexes control the reaction rate with water and its temperature dependence.;N2O is the third most important greenhouse gas after CO 2 and methane, and is mainly emitted to the atmosphere as a byproduct of microbial activity in soils. The expanding use of nitrogen-containing fertilizers in agriculture has led to an increase in N2O atmospheric concentrations since preindustrial times. Isotopic measurements are a valuable tool to distinguish the influence of different sources of N2O, but the isotopic composition of N2O formed from corona discharge in lightning has not previously been measured. Here, a corona discharge cell apparatus was used to generate a corona discharge in flowing or static zero air, and the N2O formed at discharge cell pressures from ~0.1 to 10 Torr and discharge voltages from 0.25 to 5 kV was collected and measured with isotope ratio mass spectrometry to determine its isotopic composition. The results show enrichments in 15N of N2O up to 32‰ relative to the reactant N 2, and even larger enrichments in 15N of up to 77‰ at the central nitrogen atom. Large depletions in 18O as large as -71‰ relative to reactant O2 were also measured. The isotopic composition measured here may help to elucidate the chemical mechanisms leading to N2O formation and destruction in a corona discharge. Furthermore, the isotope-isotope relationships of the N2O produced in the corona discharge experiments are distinct from those of N2O from other sources, implying that isotopic measurements can be used to determine whether local variations in the atmospheric concentration of N2O are due to lightning activity, soil emissions, or biomass burning. (Abstract shortened by ProQuest.).
机译：本文提出了一系列研究项目，旨在阐明物理化学并评估（1）烯烃氧化分解中产生的碳氧自由基（即Criegee中间体）和（2）氧化氮中产生的一氧化二氮（N2O）与大气的相关性。雷电感应的电晕放电。结果提供了Criegee中间体的UV吸收光谱和反应速率系数，这将有助于限制气溶胶成核前体（如H2SO4和氧化的挥发性有机化合物）的形成和损失途径，以及闪电中形成的N2O同位素特征，可以帮助区分各种N2O沸石中间体是烯烃与臭氧反应的副产物。 Criegee中间体的双分子反应可导致大气中低挥发性有机化合物和酸的产生，进而在确定气溶胶的浓度，大小和光学特性方面发挥作用。最近，在实验室中生产可测量数量的稳定的Criegee中间体的新方法为开发新的实验技术铺平了道路，以研究其化学性质并预测其在大气中的重要性。对于本论文，将流动池中时间分辨的紫外线吸收与分子束中的激光消耗相结合的独特装置适用于获得CH3CHOO的绝对吸收光谱，其相对于其他小组先前的光谱测量具有高分辨率和准确性。所产生的吸收截面意味着在大气中的光解寿命约为7秒，足够长的CH3CHOO参与单分子和双分子反应。光谱的长波长区域中弱结构的宽吸收带代表了将来研究中识别CH3CHOO的“光谱指纹”，其横截面为表征CH 3CHOO的电子激发态提供了宝贵的理论依据。 CH 2 OO与水二聚体的反应被认为是大气中CH 2 OO去除的主导。但是，在不同的温度，湿度和压力条件下，反应速率会发生很大变化。设计了一个温度控制的流通池，以测量CH2OO的瞬态吸收并获得其与水二聚体反应的速率系数（从283至324 K）。发现CH2OO与水二聚体的反应速率表现出强烈的负温度依赖性指出CH2OO和两个水分子之间存在氢键结合的预反应复合物。由于强烈的温度依赖性以及水二聚体和水单体之间的竞争竞争，通过与水蒸气反应，CH2OO的有效损失率对大气条件高度敏感。稳定的预反应配合物发挥的作用表明，在水二聚体和其他更大的Criegee中间体之间可能形成类似的配合物，这些配合物的稳定性和相对能量控制着与水的反应速率及其温度依赖性。第三大温室气体，仅次于CO 2和甲烷，主要作为土壤微生物活动的副产品排放到大气中。自工业化时代以来，农业中含氮肥料的广泛使用导致N2O大气浓度增加。同位素测量是区分N2O不同来源影响的有价值的工具，但是以前从未测量过闪电中电晕放电形成的N2O同位素组成。在这里，使用电晕放电室设备在流动或静态零空气中产生电晕放电，并收集在放电室压力为〜0.1至10 Torr和放电电压为0.25至5 kV时形成的N2O，并用同位素比测量质谱法测定其同位素组成。结果表明，相对于反应物N 2而言，N2O在15N中的富集度最高为32‰，而在中心氮原子处，N2O在15N中的富集度最高为77‰。还测量了相对于反应物O2的18O中的大消耗量，最大消耗量为-71‰。此处测量的同位素组成可能有助于阐明导致电晕放电中N2O形成和破坏的化学机理。此外，电晕放电实验中产生的N2O的同位素-同位素关系不同于其他来源的N2O，这意味着同位素测量可用于确定N2O大气浓度的局部变化是否是由于雷电活动引起的，土壤排放或生物质燃烧。 （摘要由ProQuest缩短。）。

著录项

  • 作者

    Smith, Mica Caitlin.;

  • 作者单位

    University of California, Berkeley.;

  • 授予单位 University of California, Berkeley.;
  • 学科 Chemistry.;Atmospheric chemistry.;Physical chemistry.
  • 学位 Ph.D.
  • 年度 2016
  • 页码 137 p.
  • 总页数 137
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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