Reducing uncertainties in Ozone formation via Chamber Studies of VOC Oxidation

钱伯斯是了解我们大气化学的重要工具。它们是在简化、可控但现实的条件下测试拟议机制的理想工具。HIRAC（Highly Instrumented Reactor for Atmospheric Chemistry）室是在NE/C513493/1项目期间建造的，具有以下几个显著特点：1）独特的是，对于室内室，我们可以直接使用FAGE技术监测OH和HO 2自由基。2)由于腔室是不锈钢结构，因此可以在对流层相关条件下改变压力。3)许多重要的物种可以通过各种技术进行测量。这使我们能够研究系统测量误差的可能性。预计对流层臭氧浓度将上升，对气候变化和空气质量产生影响。目前的提案旨在研究一些对确定臭氧水平很重要的反应。其机制很复杂，只能通过实验测量来解开。HIRAC具有一系列互补检测系统，是解决这些系统的理想工具。要研究的反应是：1）臭氧/烯烃反应已被证明是OH自由基的一个重要来源，特别是在夜间。我们建议测量OH和副产物产率作为烯烃结构的函数，以构建温度和压力依赖的结构活性关系。2)OH +芳香族化合物-由OH攻击芳香环和O2加成形成的过氧自由基可以通过两个通道反应，要么生成苯酚+HO 2（自由基再生），要么开环生成二羰基物质，这是重要的自由基和气溶胶前体。本文将研究OH与苯和甲苯反应生成的过氧自由基的支化比，并得到从头计算的支持。3)我们实验室最近的工作已经确定了显着的CH 3CO自由基从乙醇的OH提取形成的碎片。如果得到证实，这将对PAN的形成产生重要影响。模型模拟表明，监测CO和CO2产量应确认在大气条件下存在或不存在化学活化的乙酰分解。4)OH +炔。乙炔是一种丰富的人类和生物质污染物，与OH的反应是其主要的大气去除过程。在O2存在下，存在两个生成乙二醛/OH和HCOOH/HCO的产物通道。乙二醛可以在相对长的波长下光解以产生2 HCO自由基，因此是重要的HOx源，但是相对不挥发，也已知是良好的气溶胶前体。大气中甲酸的收支受到很差的限制。5)OH +烯烃。乙烯氧化是欧洲O3形成的单一最大贡献者。该反应中的主要不确定性是最初形成的羟基过氧自由基与NO的反应速率和产物烷氧基自由基的命运。这两个问题都可以通过HIRAC中的产品研究来解决。作为提案的一部分，将为HIRAC提供温度控制，以模拟对流层的所有条件。该研究的一个要素将是一系列的OH，Cl和NO3反应通过相对和绝对技术构建温度依赖性结构活性关系（SAR）的系统研究（通过捆绑学生）。这样的SAR是至关重要的MCM的发展温度依赖的建模O3的形成和其他问题。

Chambers are a vital tool in understanding the chemistry of our atmosphere. They are an ideal vehicle to test proposed mechanisms under simplified, controlled but realistic conditions. The HIRAC (Highly Instrumented Reactor for Atmospheric Chemistry) chamber was constructed during grant NE/C513493/1 and contains several significant features: 1) Uniquely, for an indoor chamber, we can monitor OH and HO2 radicals directly using the FAGE technique. 2) As the chamber is of a stainless steel construction, it is possible to vary pressures over tropospherically relevant conditions. 3) Many important species can be measured by a variety of techniques. This allows us to investigate the possibility of systematic measurement errors. Concentrations of tropospheric ozone are predicted to rise with implications for climate change and air quality. The current proposal seeks to study a number of reactions that are important in determining ozone levels. The mechanims are complex and can only be unravelled via experimental measurements. HIRAC, with a range of complementary detection systems, is an ideal tool to tackle these systems. The reactions to be studied are: 1) Ozone/alkene reactions have been shown to be an important source of OH radicals especially at night. We propose to measure OH and co-product yields as a function of alkene structure in order to construct temperature and pressure dependent structure activity relationships. 2) OH + aromatics - The peroxy radical formed from the attack of OH on the aromatic ring and addition of O2 can react via two channels, either generating a phenol + HO2 (radical regeneration) or ring opening to give dicarbonyl species which are important radical and aerosol precursors. The branching ratio for peroxy radicals formed from reaction of OH with benzene and toluene will be investigated, supported by ab initio calculations. 3) Recent work in our laboratory has identified significant fragmentation of the CH3CO radical formed from OH abstraction of ethanal. If confirmed, this would have important implications for PAN formation. Modelling simulations shown that monitoring CO and CO2 yields should confirm the presence or absence of chemically activated acetyl decomposition under atmospheric conditions. 4) OH + alkynes. The reaction with OH is the major atmospheric removal process for acetylene, an abundant anthropogenic and biomass pollutant. In the prescence of O2, there are two product channels generating glyoxal/OH and HCOOH/HCO. Glyoxal can be photolysed at relatively long wavelengths to give 2HCO radicals and is hence an important HOx source but, being relatively involatile, is also known to be a good aerosol precursor. The atmospheric budget of formic acid is poorly constrained. 5) OH + alkenes. Ethene oxidation is the single largest contributor to European O3 formation. The major uncertainties in this reaction is the rate of reaction of the intially formed hydroxyperoxy radical with NO and the fate of the product alkoxy radical. Both issues can be addressed by product studies in HIRAC As part of the proposal temperature control will be provided for HIRAC to simulate all conditions of the troposphere. One element of the study will be a systematic study (through a tied studentship) of a range of OH, Cl and NO3 reactions via relative and absolute techniques to construct temperature dependent structure activity relationships (SAR). Such SAR are vital in the development of the MCM for temperature dependent modelling of O3 formation and other issues.