Advancing our understanding of peroxy radical chemistry in the atmosphere

这个项目的重点是更好地了解过氧基的化学，RO2，它是初级排放氧化后的关键中间体。例如，CH3O2是最简单的有机过氧基，是由甲烷氧化形成的，甲烷是一种重要的温室气体，但还没有测量到这种分子在大气中的浓度。过氧基与交通等工业排放的主要污染物NO迅速反应生成NO2，NO2在阳光下迅速光解，形成臭氧，对人类和生态系统有害。此外，更多官能化的挥发性有机化合物，例如芳香族和羰基物种的氧化，会导致更复杂的过氧基，可以经历新的和鲜为人知的化学，例如快速自氧化形成高度氧化的分子(HOMS)，这些分子具有较低的蒸汽压，并迅速凝聚形成SOA。然而，目前还没有对这些功能化RO2的测量，它们的动力学特征也很差，但它们构成了排放和有害二次颗粒物之间的关键联系。该项目结合了实地工作、实验室研究和数值模拟，有以下具体目标：(1)开发一种新的野外仪器，基于FAGE技术，首次测量大气中的CH3O2。我们已经开发出具有所需灵敏度和选择性的实验室原型。投产后，该仪器将被部署在清洁和污染环境中的协作实地活动中(如作为清洁空气计划的一部分)，以测量OH和HO2自由基、OH反应性(从大气中去除OH的速率)以及过氧化自由基的总和(使用ROxLIF方法测量)(2)利用我们的实验室设施，例如高度仪表化的大气化学反应器(Hirac)，其中可以在受控条件下对单个VOCs进行光氧化，将产生一系列过氧自由基并使用ROxLIF技术进行检测。重点将放在功能化RO2的产生上，以进一步发展它们的检测，在广泛的范围内研究NOx的化学动力学，这些化学动力学被假设为与简单RO2物种的化学动力学相似(但可能不是这样)，并探索通过自氧化和形成SO2与HOMS之间的联系。(3)对现场和实验室数据进行分析和解释，并进行数值模拟。该模型将包括包含17,000个反应和7,000个物种的主化学机理，并将用于计算过氧基的浓度，以便与测量结果进行比较。通过这种方式，可以定量地评估对RO2化学的了解程度。这项研究将导致在用于预测未来气候和空气质量变化的模型中改进化学氧化机制的表示。学生将受益于使用广泛的仪器(激光、光学、真空和气体处理、数据采集、电子学)和建模工具，并通过与专家调查人员合作，将获得高级技术培训并大大提高他们的技能基础。利兹FAGE仪器是国家大气科学中心的一部分。与利兹和其他地方的大气科学家还有进一步合作的余地。

The focus of this project is to better understand the chemistry of peroxy radicals, RO2, which are the critical intermediates following the oxidation of primary emissions. For example, CH3O2, the simplest organic peroxy radical, is formed from the oxidation of methane, an important greenhouse gas, yet there have been no measurements of the concentration of this molecule in the atmosphere. Peroxy radicals react quickly with nitric oxide, NO, a major emission from traffic and other industry, to form NO2, which is rapidly photolysed by sunlight leading to ozone formation, which is harmful to humans and ecosystems. In addition, oxidation of more functionalised volatile organic compounds, for example aromatic and carbonyl species, leads to more complex peroxy radicals, which can undergo novel and poorly understood chemistry, for example rapid autooxidation to form highly oxidised molecules (HOMs) which have low vapour pressures and rapidly condense to form SOA. However, there are no measurements of these functionalised RO2, and their kinetics are poorly characterised, yet they form the critical link between emissions and harmful secondary particulate matter.The project is a combination of fieldwork, laboratory studies and numerical modelling, and have the following specific objectives:(1) Development of a new field instrument, based on the FAGE technique, to make the first ever measurements of CH3O2 in the atmosphere. We have already developed a laboratory prototype with the required sensitivity and selectivity. Following commissioning, the instrument will be deployed in collaborative field campaigns in both clean and polluted environments (for example as part of the Clean Air Program) to make measurements alongside OH and HO2 radicals, OH reactivity (the rate at which OH is removed from the atmosphere) and the sum of peroxy radicals (measured using the ROxLIF method)(2) Making use of our laboratory facilities, for example the Highly Instrumented Reactor for Atmospheric Chemistry (HIRAC), in which individual VOCs can be photo-oxidised under controlled conditions, a range of peroxy radicals will be generated and detected using the ROxLIF technique. The focus will be on the generation of functionalised RO2, in order to further develop their detection, to study over a wide range of NOx their chemical kinetics, which are assumed in models to be similar to those of simple RO2 species (but may not be the case), and to explore the links with HOMs via autooxidation and the formation of SOA.(3) Perform analysis and interpretation of field and laboratory data and perform numerical modelling. The model will incorporate the Master Chemical Mechanism, which contains 17,000 reactions and 7,000 species, and will be used to calculate the concentrations of peroxy radicals for comparison with measurements. In this way it is possible to quantitatively evaluate how well the chemistry of RO2 is understood.The research will lead to an improved representation of chemical oxidation mechanisms in models that are used for the prediction of future changes in climate and air quality. The student will benefit from using a wide range of instrumentation (lasers, optics, vacuum and gas handling, data acquisition, electronics) and modelling tools, and by working with expert investigators will receive advanced technical training and enhance their skills base considerably. The Leeds FAGE instrumentation is part of the National Centre for Atmospheric Science. There is scope for further collaboration with atmospheric scientists in Leeds and elsewhere.