New field measurements and mechanistic understanding of peroxy radicals (PEROXY)

在这项提议中，我们的目标是更好地从机制上理解过氧基的行为，过氧基是大气中间体的一个关键家族，对于理解挥发性有机化合物(VOCs)的对流层氧化化学至关重要。暴露在空气污染中每年导致全球700万人死亡。过氧基化学控制二次污染物臭氧、二氧化氮和二次有机气溶胶的形成，二次有机气溶胶是颗粒物(PM)的关键成分。2015年，暴露在直径小于2.5微米的颗粒物中导致全球420万人死亡，英国2.9万人死亡。对流层臭氧也是一种重要的温室气体(辐射强迫约为二氧化碳的25%)，是羟基自由基(天然洗涤剂)的主要来源，对农作物和生态系统有害，只能通过过氧自由基的反应产生。很大一部分PM本质上是次要的(即通过化学氧化产生)，其中大部分是SOA。然而，尽管过氧基化学很重要，但人们对其了解很少，也没有在模型中很好地表示，需要改进机制理解，以改进对空气污染的预测，并更好地评估拟议干预措施的影响和排放的长期变化。为了解决这个问题，在这项建议中，我们将开发新的仪器来测量过氧基，在清洁和污染的环境中进行实地研究，并进行有针对性的实验室室内实验。实地考察工作将包括参与英国皇家国际研究院/英国气象局战略优先基金清洁空气计划。我们将提供RO2的现场测量作为模型计算的目标，并提供RO2过程的新动力学数据作为模型的输入。大气中最小和最丰富的有机过氧基是甲基过氧基(CH3O2)，它是由羟基自由基与甲烷反应直接生成的。CH3O2与一氧化氮的反应构成了对流层中最重要的原位臭氧来源之一。尽管CH3O2很重要，但它从未在大气中直接测量过，在这项提议中，我们将首次开发一种现场仪器来进行测量，并将其部署在偏远、清洁的环境和受污染的城市中心。更大的过氧基，也称为RO2，也是臭氧和次级有机气溶胶的重要前体，我们还将测量现场RO2浓度的总和。由一系列自然或人为VOCs氧化而来的高氧化分子(HOMS)是理解SOA形成的关键。过氧自由基是HOM的重要组成部分，但HOM类RO2的去除机理尚不清楚。现场工作将通过有针对性的实验室室内研究来补充，其中单个VOCs或混合的VOCs被用来在一定范围的NOx下产生类Hom的RO2，以确定清除Hom-RO2物种的动力学速率和产量。利用这种现场和室内研究的组合，我们将进一步验证当前RO2转化机制的代表性，以提高模型计算一系列NOx浓度范围内臭氧和二次有机气溶胶形成速率的能力。这项提议汇集了来自利兹和曼彻斯特小组的领先的互补专业知识，这两个小组在现场测量、气体和气溶胶过程的实验室室内测量、以及使用气体和气体-气溶胶耦合机制的数值模拟。

In this proposal we aim to achieve a better mechanistic understanding of the behaviour of peroxy radicals, a key family of atmospheric intermediates, central to understanding the tropospheric oxidation chemistry of volatile organic compounds (VOCs). Exposure to air pollution kills 7 million people worldwide per year. Peroxy radical chemistry controls the formation of the secondary pollutants ozone, nitrogen dioxide and secondary organic aerosol (SOA), a key component of particulate matter (PM). Exposure to PM less than 2.5 micrometres in diameter led to 4.2 million deaths globally in 2015 and 29,000 in the UK. Tropospheric ozone is also an important greenhouse gas (radiative forcing ~25% that of carbon dioxide), is the main source of the hydroxyl radical (nature's detergent), is harmful to crops and ecosystems, and is only generated via reactions of peroxy radicals. A large proportion of PM is secondary in nature (i.e. generated via chemical oxidation), with much of this being SOA.However, despite its importance, peroxy radical chemistry remains poorly understood and not well represented in models, and improved mechanistic understanding is required to improve prediction of air pollution and to provide better assessment of the impact of proposed interventions and long term changes in emissions. To address this problem, in this proposal we will develop novel instrumentation to measure peroxy radicals, conduct field studies in clean and polluted environments and carry out targeted laboratory chamber experiments. The fieldwork will include participation in the UKRI/Met Office Strategic Priority Fund Clean Air Programme. We will provide field measurements of RO2 as a target for model calculations, and new kinetic data for RO2 processes as input for models.The smallest and most abundant organic peroxy radical in the atmosphere is methyl peroxy (CH3O2), which is formed directly by the reaction of the hydroxyl radical with methane. Reaction of CH3O2 with nitric oxide constitutes one of the most important tropospheric in situ sources of ozone. Despite its importance, CH3O2 has never been measured directly in the atmosphere, and in this proposal we will develop a field instrument to do so for the first time, and deploy it in both remote, clean environments and polluted urban centres. Larger peroxy radicals, together known as RO2, are also important precursors to ozone and secondary organic aerosol, and we will also measure the sum of RO2 concentrations in the field.Highly oxidised molecules (HOMs) deriving from the oxidation of a range of natural or anthropogenic VOCs are central to understanding how SOA forms. Peroxy radicals form an important component of HOM, however the removal mechanisms of HOM-like RO2 are highly uncertain. The fieldwork will be augmented by targeted laboratory chamber studies where individual VOCs or mixes of VOCs are used to generate HOM-like RO2 under a range of NOx, in order to determine kinetic rates and yields for the scavenging of HOM-RO2 species.Using this combination of field and chamber studies, we will further validate the representation of current mechanisms for RO2 transformations, to improve the ability of models to calculate formation rates of ozone and secondary organic aerosol over a range of NOx concentrations.This proposal brings together leading complementary expertise from groups in Leeds and Manchester who both have considerable experience in field measurements, laboratory chamber measurements of gas and aerosol processes, and numerical modelling using gas and coupled gas-aerosol mechanisms.