The tropospheric photochemistry of formaldehyde

甲醛的对流层光化学

基本信息

  • 批准号:
    NE/D001498/1
  • 负责人:
  • 金额:
    $ 13.95万
  • 依托单位:
  • 依托单位国家:
    英国
  • 项目类别:
    Research Grant
  • 财政年份:
    2006
  • 资助国家:
    英国
  • 起止时间:
    2006 至 无数据
  • 项目状态:
    已结题

项目摘要

The atmosphere of Earth is mostly composed of nitrogen (N2) and oxygen (O2) gases, but there are many more complicated and reactive chemical compounds present at very low concentrations that have a considerable impact on the properties of the atmosphere. It is well known, for example, that carbon dioxide and methane are important greenhouse gases. The hydroxyl radical (OH) is present at tiny concentrations (typically 1 OH radical for every 25,000,000,000,000 other molecules of air) but is the main chemical species in the atmosphere that oxidises organic compounds such as methane and other hydrocarbons to form CO2 and water. This oxidation is similar to the chemistry that goes on when a flame burns natural gas, but occurs at much lower temperatures in the atmosphere (down to as low as -50oC at altitudes of about 10 km). Atmospheric chemists thus need to be confident that they have identified all possible sources of the OH radical in order to understand the chemistry of the atmosphere, and how pollutants such as organic compounds are oxidised and removed from air. Formaldehyde molecules, with the chemical formula HCHO, are formed from the complicated processes that follow from reaction of methane and other organic molecules with OH, and can absorb ultraviolet (UV) radiation from the sun. With the energy it gains from this UV light, formaldehyde can split of a hydrogen atom (to form H + HCO) or can break up into a molecule of hydrogen (H2) and one of carbon monoxide (CO). The second process has very little effect on the chemistry of the atmosphere, but both H atoms and HCO radicals react quickly with oxygen in air to make OH (and another related reactive species denoted as HO2). This so-called 'photochemistry' of formaldehyde, meaning chemistry caused by absorption of light, is thus very important for influencing the concentration of OH in the atmosphere, but is poorly understood because of the complicated way in which formaldehyde absorbs UV light and dissociates into atomic or molecular fragments. This project will explore this photochemistry using one UV laser as a source of well-characterised UV light of precisely known energy and wavelength (for visible light, different wavelengths correspond to different colours), and a second laser to measure how much HCO is formed. In addition, we will measure how strongly the formaldehyde molecules absorb (i.e., remove) different wavelengths of UV light; this information is important if we want to find out how much formaldehyde is actually in any particular region of the atmosphere, whether using a satellite or a ground-based apparatus to observe the atmosphere and thus to make the measurement. The measurements of formation of HCO and absorption of UV by HCHO will be made in our lab more precisely and directly than any previous studies of formaldehyde photochemistry, and over a range of temperatures and pressures of N2 and O2 to simulate the conditions in the atmosphere from the Earth's surface up to an altitude of 10 km (the start of the stratosphere). We will make the measurements across the ultraviolet up to the region of the UV bordering on the violet and blue end of the visible spectrum. These wavelengths will cover the range of UV from the sun that reaches the Earth's surface and which is absorbed by formaldehyde molecules. The results of the measurements will be fed into computer programs designed to simulate the chemistry taking place in the Earth's atmosphere, and we will thus learn about what differences formaldehyde photochemistry makes to formation of OH radicals, and to removal of low-level pollutants such as hydrocarbons and other organic molecules.
地球的大气主要由氮气(N2)和氧气(O2)组成,但也有许多更复杂和活性的化合物以非常低的浓度存在,对大气的性质有相当大的影响。例如,众所周知,二氧化碳和甲烷是重要的温室气体。羟基自由基(OH)以微小的浓度存在(通常每25,000,000,000,000个其他空气分子有1个OH自由基),但它是大气中的主要化学物质,可以氧化有机化合物,如甲烷和其他碳氢化合物,形成CO2和水。这种氧化类似于火焰燃烧天然气时发生的化学反应,但发生在大气中的温度要低得多(在约10公里的高度低至-50 ° C)。因此,大气化学家需要确信他们已经确定了OH自由基的所有可能来源,以了解大气的化学性质,以及有机化合物等污染物如何被氧化并从空气中去除。甲醛分子的化学式为HCHO,由甲烷和其他有机分子与OH反应后的复杂过程形成,可以吸收太阳的紫外线(UV)辐射。利用从紫外线中获得的能量,甲醛可以分裂氢原子(形成H + HCO),或者可以分解成氢分子(H2)和一氧化碳分子(CO)。第二个过程对大气的化学性质几乎没有影响,但H原子和HCO自由基都能与空气中的氧气迅速反应,生成OH(以及另一种相关的活性物质,表示为HO 2)。这种所谓的甲醛的“光化学”,意味着由光吸收引起的化学,因此对于影响大气中OH的浓度非常重要,但由于甲醛吸收紫外线并解离成原子或分子碎片的复杂方式而知之甚少。该项目将探索这种光化学,使用一个紫外激光器作为具有精确已知能量和波长(对于可见光,不同的波长对应于不同的颜色)的良好表征的紫外光的来源,以及第二个激光器来测量形成了多少HCO。此外,我们将测量甲醛分子吸收的强度(即,甲醛的含量取决于不同波长的紫外线;如果我们想知道大气中任何特定区域实际上有多少甲醛,无论是使用卫星还是地面设备来观察大气,从而进行测量,这些信息都很重要。HCO的形成和HCHO对紫外线的吸收的测量将在我们的实验室中进行,比以前任何甲醛光化学的研究都更精确和直接,并且在N2和O2的温度和压力范围内模拟大气中的条件从地球表面到海拔10公里(平流层的开始)。我们将在整个紫外线范围内进行测量,直到可见光谱的紫色和蓝色端的紫外线区域。这些波长将覆盖从太阳到达地球表面并被甲醛分子吸收的紫外线的范围。测量结果将被输入计算机程序,以模拟地球大气中发生的化学反应,从而了解甲醛光化学对OH自由基形成的影响,以及对碳氢化合物和其他有机分子等低水平污染物的去除。

项目成果

期刊论文数量(5)
专著数量(0)
科研奖励数量(0)
会议论文数量(0)
专利数量(0)
Quantum yields for photochemical production of NO2 from organic nitrates at tropospherically relevant wavelengths.
在对流层相关波长下从有机硝酸盐光化学生产 NO2 的量子产率。
Cavity ring-down spectroscopy : techniques and applications
  • DOI:
  • 发表时间:
    2009
  • 期刊:
  • 影响因子:
    0
  • 作者:
    G. Berden;R. Engeln
  • 通讯作者:
    G. Berden;R. Engeln
Impacts of formaldehyde photolysis rates on tropospheric chemistry
  • DOI:
    10.1002/asl.251
  • 发表时间:
    2010-01-01
  • 期刊:
  • 影响因子:
    3
  • 作者:
    Cooke, M. C.;Utembe, S. R.;Shallcross, D. E.
  • 通讯作者:
    Shallcross, D. E.
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Andrew Orr-Ewing其他文献

Andrew Orr-Ewing的其他文献

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{{ truncateString('Andrew Orr-Ewing', 18)}}的其他基金

Ultrafast Photochemical Dynamics in Complex Environments
复杂环境中的超快光化学动力学
  • 批准号:
    EP/V026690/1
  • 财政年份:
    2021
  • 资助金额:
    $ 13.95万
  • 项目类别:
    Research Grant
Mapping Pathways in Photo-Catalytic Cycles using Ultrafast Spectroscopy
使用超快光谱绘制光催化循环中的路径
  • 批准号:
    EP/R012695/1
  • 财政年份:
    2018
  • 资助金额:
    $ 13.95万
  • 项目类别:
    Research Grant
Kinetic Studies of Reactive Intermediates from the Oxidation of Atmospheric Alkenes
大气烯烃氧化反应中间体的动力学研究
  • 批准号:
    NE/P013104/1
  • 财政年份:
    2017
  • 资助金额:
    $ 13.95万
  • 项目类别:
    Research Grant
Environmental applications of cavity enhanced spectroscopy in the mid infra-red region
腔增强光谱在中红外区的环境应用
  • 批准号:
    NE/H019758/1
  • 财政年份:
    2010
  • 资助金额:
    $ 13.95万
  • 项目类别:
    Training Grant
New Horizons in Chemical and Photochemical Dynamics
化学和光化学动力学的新视野
  • 批准号:
    EP/G00224X/1
  • 财政年份:
    2008
  • 资助金额:
    $ 13.95万
  • 项目类别:
    Research Grant
New frontiers in quantitative infra-red to ultraviolet spectroscopy using diode and quantum-cascade lasers
使用二极管和量子级联激光器定量红外到紫外光谱的新前沿
  • 批准号:
    EP/E018297/1
  • 财政年份:
    2007
  • 资助金额:
    $ 13.95万
  • 项目类别:
    Research Grant
Adventurous Research in Chemistry at the University of Bristol 2005
2005 年布里斯托大学化学冒险研究
  • 批准号:
    EP/D051231/1
  • 财政年份:
    2006
  • 资助金额:
    $ 13.95万
  • 项目类别:
    Research Grant

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