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.

化学反应控制了排放到大气中的许多主要物种的去除速率，并控制了次要物种的产生。主要的大气氧化剂是OH根部。与OH的反应启动去除许多有机化合物，氮氧化物和其他物种，例如二氧化硫（SO2）。在SO2的情况下，OH的气相氧化会产生硫酸，从而增加气溶胶质量，并且也可以充当成核剂，在大气中形成新颗粒 - 通过直接散射太阳辐射来影响气候，并通过影响通过影响会导致液滴形成，从而可以液滴形成，从而做出实质性的冷却贡献。了解氧化速率对于准确预测这些因素对大气组成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：由烷烃的臭氧溶解形成的稳定的Criegee中间体（SCI）的反应。eozone.ozone可以用作直接氧化剂，与碱（物种与一个或多个双键）反应。这类化合物包括大多数生物反应性碳排放，这些碳排放占据了大气中释放的有机化合物。气相臭氧反应会产生反应性中间体SCI，其寿命为几秒钟（或更少 - 这是大气中的关键不确定性）。一段时间以来，SCI可以与其他物种反应，特别是包括SO2。然而，当前普遍接受的智慧是，与水蒸气或分解的反应主导了对流层中SCI的去除，因此它们不被认为是重要的氧化剂。最近的一系列证据正在改变这一图像 - 指向缺少SO2氧化机制的模型研究。田间和腔室研究表明，在烷烃水平升高和最近的实验室的存在下，SO2氧化增强。研究发现，至少一个SCI物种与SO2和NO2的反应非常快，并且H2O非常慢（至少在考虑的特定实验条件下）。如果该结论是普遍的，则简单的计算表明SCI反应与OH的SO2在边界层中的气相氧化相当。相关的硫酸盐气溶胶增加将暗示辐射强迫计算的重大变化。同样，NO2的氧化增强将导致硝酸盐产生增加。但是，至关重要的是，最近的结果与SCI反应系统的先前实验室研究不符，这可能是由于方法和条件差异（试剂丰度，压力，时标等）的差异，这与大气中的相关性很大。我们将使用Euphore（欧洲光电反应器）腔室，这将使我们能够复制环境条件（使用人造空气样本和真实空气样本），以与它们在大气中形成相同的方式产生SCI（即通过烯烃Ozonylosysysissy）并直接监控其对SO2和NO2的影响。这种方法将避免（大）外推的不确定性，这些推断会影响对先前研究的解释。我们的实验将通过复制真实气氛的实验来证实（或其他方式）SCI反应的重要性，并可以通过直接检查来分析；此外，我们将确定一系列SCI物种反应的动力学参数，该参数将用于修改大气化学模型中SCI形成的机制。然后，我们将应用于此类模型（MCM和GEOS-CHEM），以量化SCI反应对局部和全局尺度上大气氧化的贡献。