Gas phase studies of the kinetics of Criegee Intermediates

Criegee 中间体动力学的气相研究

基本信息

批准号：
NE/K005316/1
负责人：
Carl Percival
金额：
$ 11.92万
依托单位：
University of Manchester
依托单位国家：
英国
项目类别：
Research Grant
财政年份：
2013
资助国家：
英国
起止时间：
2013 至无数据
项目状态：
已结题

来源：
https://gtr.ukri.org/projects?ref=NE%2FK005316%2F1
关键词：
Gas phase studies kinetics Criegee

项目摘要

The Earth's atmosphere is a complex mixture of gases, liquids and even solids. This mainly gaseous envelope around us performs many vital functions e.g. it protects us from harmful ultraviolet light (high energy light) from the Sun through the stratospheric ozone layer. Through the water cycle, clouds are formed in the atmosphere that redistributes water in the Earth systems. These clouds also cool the planet by acting like mirrors, reflecting some of the energy from the Sun back to outer space. This cooling mechanism is essential to the Earth system to permit an equitable surface temperature to exist that allows all the diverse life forms on it to exist. As well as this natural cooling mechanism, so called greenhouse gases in the atmosphere (e.g. carbon dioxide, CO2 and methane CH4) absorb infrared energy released by the Earth and trap some of it, very similar to the analogy of putting on a blanket and warm the Earth's surface up. Both these natural cooling and warming mechanisms are essential to a habitable surface and as long as they stay in balance, the surface temperature will remain reasonably constant. However, over the last 200 years humans have been increasing the level of greenhouse gases in the atmosphere by burning fossil fuels and evidence shows that this is leading to an overall warming of the surface of the Earth. The consequences of even a modest increase in average global surface temperature are significant for human, animal and plant life.It is known that chemicals released naturally by plants (unsaturated organic molecules such as alkenes) can react with oxidants in the atmosphere to produce extremely fast reacting intermediates, so called Criegee intermediates (CI). However, recent studies by us have shown that these Criegee intermediates react rapidly with a number of species present in the atmosphere such as sulphur dioxide (SO2). Ultimately, these reactions lead to the formation of sulphuric acid, which is very good at promoting aerosol formation (cloud precursors). Under polluted environments, aerosol formation may have detrimental effects on health but in the background atmosphere, promotion of cloud formation leads to a cooling of the Earth's surface. We have assessed the possible impact of these natural emissions of chemicals using computer models of the atmosphere and it appears that this process may be very important in producing cloud precursors and therefore be having an important impact on the Earth's climate (cooling it). However, we have only been able to investigate the reactions of two possible Criegee intermediates and there are potentially thousands of different ones. Whilst it would be impossible to study them all and indeed not a sensible endeavour, it is important to study different types of Criegee intermediates. If they all have a similar reactivity then the impact on the atmosphere is likely to be true and would then be important to include in climate models. In order to investigate how quickly these Criegee intermediates react with species such as SO2 we have devised an experiment in the laboratory that takes advantage of recent developments in optics. Using laser light to generate these Criegee intermediates we will be able to detect them using a highly sensitive technique called cavity ringdown spectroscopy (CRDS). In the experiment the Criegee intermediate is generated in a closed system where light is trapped between two highly reflective mirrors. As the light bounces backwards and forwards between the mirrors it may be absorbed by the Criegee intermediate and so less light is left. The greater the level of Criegee intermediate made the less light is reflected back and forth and so we have a way to measure this species. In this way we will be able to investigate how fast these Criegee intermediates react with a number of important gases in the Earth's atmosphere.

地球的大气层是气体、液体甚至固体的复杂混合物。我们周围的主要气体包层执行许多重要功能，例如它可以保护我们免受来自太阳穿过平流层臭氧层的有害紫外线（高能光）的影响。通过水循环，大气中形成云，重新分配地球系统中的水。这些云还像镜子一样，将太阳的部分能量反射回外太空，从而冷却地球。这种冷却机制对于地球系统至关重要，它允许存在公平的表面温度，从而允许其上所有不同的生命形式存在。除了这种自然冷却机制之外，大气中所谓的温室气体（例如二氧化碳、CO2 和甲烷 CH4）也会吸收地球释放的红外能量并捕获其中的一部分，这与盖上毯子取暖的类比非常相似地球表面向上。这些自然冷却和变暖机制对于宜居表面至关重要，只要它们保持平衡，表面温度就会保持相当恒定。然而，在过去的 200 年里，人类通过燃烧化石燃料不断增加大气中的温室气体水平，有证据表明，这正在导致地球表面整体变暖。全球平均表面温度即使是小幅上升，也会对人类、动物和植物生命产生重大影响。众所周知，植物自然释放的化学物质（不饱和有机分子，如烯烃）可以与大气中的氧化剂发生反应，极快地产生化学物质。反应中间体，所谓 Criegee 中间体 (CI)。然而，我们最近的研究表明，这些 Criegee 中间体会与大气中存在的许多物质（例如二氧化硫 (SO2)）快速反应。最终，这些反应导致硫酸的形成，硫酸非常有助于促进气溶胶（云前体）的形成。在污染环境下，气溶胶的形成可能对健康产生不利影响，但在背景大气中，促进云的形成会导致地球表面变冷。我们使用大气的计算机模型评估了这些化学物质自然排放的可能影响，看来这一过程对于产生云前体可能非常重要，因此对地球气候产生重要影响（使其冷却）。然而，我们只能研究两种可能的 Criegee 中间体的反应，并且可能有数千种不同的中间体。虽然研究所有这些是不可能的，而且实际上也不是明智的努力，但研究不同类型的 Criegee 中间体很重要。如果它们都具有相似的反应性，那么对大气的影响可能是真实的，并且将很重要纳入气候模型中。为了研究这些 Criegee 中间体与 SO2 等物质反应的速度有多快，我们在实验室中设计了一项利用光学最新发展的实验。使用激光生成这些 Criegee 中间体，我们将能够使用称为腔衰荡光谱 (CRDS) 的高灵敏度技术来检测它们。在实验中，Criegee 中间体是在一个封闭系统中生成的，其中光被捕获在两个高反射镜之间。当光线在镜子之间来回反射时，它可能会被 Criegee 中间体吸收，因此留下的光线较少。 Criegee 中间体的水平越高，来回反射的光就越少，因此我们有一种方法来测量这个物种。通过这种方式，我们将能够研究这些 Criegee 中间体与地球大气中许多重要气体反应的速度有多快。