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Reactions of Stabilised Criegee Intermediates in the Atmosphere: Implications for Tropospheric Composition & Climate

大气中稳定的 Criegee 中间体的反应：对对流层组成的影响

基本信息

批准号：
NE/K005448/1
负责人：
William Bloss
金额：
$ 35.82万
依托单位：
University of Birmingham
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%2FK005448%2F1
关键词：
Reactions Stabilised Criegee Intermediates Atmosphere

项目摘要

Chemical reactions govern the rate of removal of many primary species emitted into the atmosphere, and control the production of secondary species. The dominant atmospheric oxidant is the OH radical; reaction with OH initiates the removal of many organic compounds, nitrogen oxides and other species such as sulphur dioxide (SO2). In the case of SO2, gas-phase oxidation by OH produces sulphuric acid, which increases aerosol mass, and may also act as a nucleating agent, forming new particles in the atmosphere - affecting climate by directly scattering solar radiation, and indirectly by affecting could droplet formation, making very substantial cooling contributions. Understanding oxidation rates is critical to accurate prediction of the impacts of these factors upon atmospheric composition and climate. This project will determine the importance of an additional potential atmospheric oxidant: reactions with stabilised criegee intermediates (SCIs), formed from the ozonolysis of alkenes.Ozone can act as a direct oxidising agent, reacting with alkenes (species with one or more double bonds). This class of compounds includes most biogenic reactive carbon emissions, which dominate the organic compounds released to the atmosphere. Gas-phase ozone-alkene reactions produce reactive intermediates, SCIs, which have lifetimes of a few seconds (or less - this is a critical uncertainty) in the atmosphere. It has been known for some time that SCIs can react with other species, notably including SO2; however the current generally accepted wisdom is that reaction with water vapour, or decomposition, dominates the removal of SCIs in the troposphere, and so they are not considered to be important oxidants.A number of recent pieces of evidence are changing this picture - model studies pointing to missing SO2 oxidation mechanisms; field and chamber studies pointing to enhanced SO2 oxidation in the presence of elevated levels of alkenes, and recent lab. studies which found that reactions of at least one SCI species with SO2 and NO2 are very fast, and with H2O very slow (at least under the specific experimental conditions considered). If this conclusion is generalised, simple calculations indicate that SCI reactions would be comparable to those of OH for the gas-phase oxidation of SO2 in the boundary layer. The associated sulphate aerosol increase would imply a significant change to radiative forcing calculations. Similarly, enhanced oxidation of NO2 would lead to increased nitrate production. Critically however, the recent results are not consistent with previous laboratory studies of the SCI reaction system, potentially as a consequence of differences in approach and conditions (reagent abundance, pressure, timescales etc.) which diverge substantially from those of relevance to the atmosphere.In this project, we will apply a new approach to this critical and timely issue: application of an atmospheric simulation chamber to directly assess the importance of SCIs as oxidants. We will use the EUPHORE (European Photoreactor) chamber, which will allow us to replicate ambient conditions (using both artificial and real air samples), produce SCIs in a manner identical to their formation in the atmosphere (i.e. through alkene ozonolysis) and directly monitor their impacts upon SO2 and NO2. This approach will avoid the uncertainties of (large) extrapolation which affect interpretation of previous studies. Our experiments will confirm (or otherwise) the importance of SCI reactions through experiments which replicate the real atmosphere and may be analysed by direct inspection; in addition we will determine kinetic parameters for the reactions of a range of SCI species, which will be used to revise the mechanism for SCI formation in atmospheric chemical models. We will then apply to such models (the MCM and GEOS-Chem) to quantify the contribution of SCI reactions to atmospheric oxidation on both local and global scales.

化学反应控制着排放到大气中的许多初级物种的去除速度，并控制着次级物种的产生。主要的大气氧化剂是OH自由基；与OH的反应启动了许多有机化合物、氮氧化物和其他物种的去除，如二氧化硫(SO2)。在二氧化硫的情况下，氢氧化氢的气相氧化产生硫酸，从而增加气溶胶质量，也可以作为成核剂，通过直接散射太阳辐射在大气中形成新的颗粒-影响气候，并通过间接影响大气中的氢氧化物和二氧化硫，从而形成液滴，从而对冷却做出非常重大的贡献。了解氧化速率对于准确预测这些因素对大气成分和气候的影响至关重要。这个项目将确定另外一种潜在的大气氧化剂的重要性：与稳定的克里吉中间体(SCI)的反应，这种反应是由烯烃的臭氧分解形成的。臭氧可以作为直接氧化剂，与烯烃(具有一个或多个双键的物种)反应。这类化合物包括大多数生物源活性碳排放，这些碳排放到大气中的有机化合物占主导地位。气相臭氧-烯烃反应产生活性中间体SCI，它们在大气中的寿命为几秒(或更短--这是一个关键的不确定性)。SCI可以与其他物种反应已经有一段时间了，特别是包括SO2；然而，目前普遍接受的看法是，与水蒸气的反应或分解，主导了对流层中SCI的去除，因此它们不被认为是重要的氧化剂。最近的一些证据正在改变这一图景--模型研究指出了SO2氧化机制的缺失；现场和室内研究指出，在烯烃水平升高的情况下，SO2的氧化作用增强，最近的实验室研究也是如此。研究发现，至少有一种SCI物种与SO2和NO2的反应非常快，与H2O的反应非常慢(至少在所考虑的特定实验条件下)。如果这一结论被推广，简单的计算表明，对于边界层中SO2的气相氧化，SCI反应将与OH的反应相当。相关的硫酸盐气溶胶增加将意味着辐射强迫计算的重大变化。同样，加强NO2的氧化将导致硝酸盐产量的增加。然而，最关键的是，最近的结果与以前对SCI反应系统的实验室研究不一致，可能是由于方法和条件(试剂丰度、压力、时间尺度等)的不同造成的。在这个项目中，我们将应用一种新的方法来解决这个关键和及时的问题：应用大气模拟室来直接评估SCI作为氧化剂的重要性。我们将使用EUPHORE(欧洲光反应堆)小室，这将使我们能够复制环境条件(使用人工和真实空气样本)，以与它们在大气中形成相同的方式产生SCI(即通过烯烃臭氧分解)，并直接监测它们对SO2和NO2的影响。这种方法将避免影响先前研究解释的(大)外推的不确定性。我们的实验将通过复制真实大气的实验来确认(或以其他方式)SCI反应的重要性，并可通过直接检验进行分析；此外，我们还将确定一系列SCI物种反应的动力学参数，这些参数将用于修正大气化学模型中SCI形成的机制。然后，我们将应用于这样的模式(MCM和GEOS-Chem)，以量化SCI反应在局部和全球尺度上对大气氧化的贡献。