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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/K003941/1
负责人：
Andrew Rickard
金额：
$ 5.08万
依托单位：
University of York
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%2FK003941%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率，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反应引发许多有机化合物、氮氧化物和其他物质如二氧化硫（SO2）的去除。在二氧化硫的情况下，气相氧化OH产生硫酸，这增加了气溶胶质量，也可能作为成核剂，在大气中形成新的颗粒-通过直接散射太阳辐射影响气候，并间接影响水滴的形成，做出非常大的冷却贡献。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。该项目将确定额外的潜在大气氧化剂的重要性：与稳定的criegee中间体（SCIs）的反应，该中间体由烯烃的臭氧分解形成。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质）反应。这类化合物包括大多数生物源活性碳排放，它们在释放到大气中的有机化合物中占主导地位。气相臭氧-烯烃反应产生活性中间体SCIs，其在大气中的寿命为几秒（或更短-这是一个关键的不确定性）。一段时间以来，人们已经知道SCIs可以与其他物种反应，特别是包括SO2;然而，目前普遍接受的观点是，与水蒸气的反应或分解，主导了对流层中SCIs的去除，因此它们不被认为是重要的氧化剂。现场和室内研究表明，在烯烃水平升高的情况下，SO2氧化作用增强，最近的实验室。研究发现，至少一种SCI物质与SO2和NO2的反应非常快，与H2O的反应非常慢（至少在考虑的特定实验条件下）。如果这一结论是普遍的，简单的计算表明，SCI反应将是可比的OH的气相氧化的SO2在边界层。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。类似地，NO2的氧化增强将导致硝酸盐产量增加。然而，最重要的是，最近的结果与SCI反应系统的先前实验室研究不一致，可能是方法和条件（试剂丰度，压力，时间尺度等）差异的结果。在这个项目中，我们将采用一种新的方法来解决这个关键而及时的问题：应用大气模拟室来直接评估SCIs作为氧化剂的重要性。我们将使用EUPHORE（欧洲光反应器）室，这将使我们能够复制环境条件（使用人工和真实的空气样品），以与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。我们的实验将确认（或以其他方式）SCI反应的重要性，通过实验复制的真实的大气，并可能通过直接检查进行分析，此外，我们将确定动力学参数的范围SCI物种的反应，这将被用来修改SCI形成的机制，在大气化学模型。然后，我们将适用于这些模型（MCM和GEOS-Chem），以量化SCI反应对局部和全球尺度大气氧化的贡献。