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

在本提案中，我们的目标是实现对过氧化自由基行为的更好的机制理解，过氧化自由基是大气中间体的关键家族，对理解对流层挥发性有机化合物（VOCs）的氧化化学至关重要。全球每年有700万人死于空气污染。过氧化自由基化学控制着二次污染物臭氧、二氧化氮和二次有机气溶胶（SOA）的形成，而二次有机气溶胶是颗粒物（PM）的关键成分。2015年，暴露于直径小于2.5微米的PM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（自然界的清洁剂）的主要来源，对作物和生态系统有害，并且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（即通过化学氧化生成），其中大部分是SOA。然而，尽管它很重要，但对过氧自由基化学的了解仍然很少，在模型中也没有得到很好的体现，需要改进对机制的理解，以改进对空气污染的预测，并更好地评估拟议的干预措施和排放的长期变化的影响。为了解决这个问题，在本提案中，我们将开发新的仪器来测量过氧自由基，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实验。实地工作将包括参与UKRI/气象局战略优先基金清洁空气计划。我们将提供RO2的现场测量值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。大气中体积最小、含量最多的有机过氧自由基是甲基过氧（CH3O2），它是由羟基自由基与甲烷直接反应形成的。CH3O2与一氧化氮的反应是对流层臭氧最重要的原位来源之一。尽管它很重要，但CH3O2从未在大气中直接测量过，在本提案中，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、清洁的环境和污染的城市中心。较大的过氧自由基，统称为RO2，也是臭氧和二次有机气溶胶的重要前体，我们还将在野外测量RO2浓度的总和。由一系列自然或人为VOCs氧化产生的高度氧化分子（HOMs）是理解SOA如何形成的核心。过氧自由基是homs的重要组成部分，但homs类RO2的去除机制尚不明确。实地工作将通过有针对性的实验室研究得到加强，在实验室研究中，使用单个VOCs或VOCs混合物在一定范围的NOx下产生类似homo的RO2，以确定清除homo -RO2的动力学速率和产量。通过结合现场和室内研究，我们将进一步验证RO2转化的当前机制，以提高模型在一定NOx浓度范围内计算臭氧和二次有机气溶胶形成速率的能力。该提案汇集了来自利兹和曼彻斯特的领先互补专业知识，他们都在现场测量，气体和气溶胶过程的实验室室测量以及使用气体和耦合气体-气溶胶机制的数值模拟方面拥有丰富的经验。

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.