INFAMOS - a new method for speciated peroxy radical detection

国际社会对日益恶化的空气质量和不断变化的气候的反应是由数值模式的预测指导的。这些模型包含对未来自然过程和人类活动中微量气体和气溶胶排放量的估计，它们在大气中的扩散，以及它们在化学上转化为广泛的次生产物。对流层中的光氧化是非常复杂的，由短暂的自由基物种启动，在白天由羟基自由基主导，由氯原子贡献，在晚上由硝酸根或臭氧引起。快速的化学氧化循环去除了对人类和更广泛的环境有害的痕量物种。大气光氧化产生的许多次级产品也是直接有害的，例如臭氧、二氧化氮、酸和多功能有机分子，其中许多是低挥发性的，能够有效地分配到凝聚相，产生次级有机气溶胶，对气候和人类健康产生相关影响。测试空气质量或气候模型中使用的化学机制的准确性的最佳方法之一是将其在给定地点和时间对自由基物种的计算输出与在大气中进行的实际测量进行比较。自由基的寿命短，因此受化学而不是运输控制。大气中最简单的两种自由基是过氧化氢自由基，HO2，以及最小和最主要的有机过氧基CH3O2，它们是由OH与一氧化碳和甲烷反应直接形成的。它们与一氧化氮的反应构成了臭氧、呼吸刺激物和温室气体的唯一对流层原位来源。尽管HO2和CH3O2很重要，但它们都不是在大气中直接测量的，只有在采样后首先转换为OH后才能间接测定HO2。这项建议汇集了利兹的一个现场测量小组和牛津大学的一个腔增强光学光谱学小组的领先专业知识，以解决这一差距。总体目标是开发一种名为INFAMOS的新型直接激光光谱技术，该技术有可能测量现场HO2和CH3O2的浓度。将在利兹·希拉克大气室(容量2250升)中对INFAMOS与补充但间接的化学转化方法进行相互比较，该大气室的能力也将通过这项提议得到改善。这项新技术还将用于在Hirac对HO2和CH3O2进行直接、灵敏的测量，以研究几个关键大气反应的动力学和产物产率，这些反应的量化程度很低，结合使用主化学机理的速率理论计算和盒子建模。新开发的测量HO2或CH3O2的技术还将在其他领域具有潜在的好处，例如，理解能源领域的燃烧化学基础。

The international societal response to deteriorating air quality and the changing climate is guided by the predictions of numerical models. These models contain estimates of future emissions of trace gases and aerosols from natural processes and human activities, their dispersal throughout the atmosphere, and their chemical transformations into a wide range of secondary products.Photo-oxidation in the troposphere is highly complex, being initiated by short lived radical species, in the daytime dominated by the hydroxyl radical, with contributions from chlorine atoms, and at night by either the nitrate radical or ozone. Fast chemical oxidation cycles remove trace species which are harmful to humans and to the wider environment. Many secondary products produced by atmospheric photo-oxidation are also directly harmful, for example ozone, nitrogen dioxide, acids and multifunctional organic molecules, many of which are of low volatility and are able to partition effectively to the condensed phase, creating secondary organic aerosol, with associated impacts on climate and human health. One of the best ways to test the accuracy of a chemical mechanism used in an air quality or climate model is to compare its calculated output for radical species for a given location and time with actual measurements made in the atmosphere. Radicals are ideal for this purpose as their lifetimes are short, and hence are controlled by chemistry rather than by transport.Two of the simplest radicals in the atmosphere are the hydroperoxy radical, HO2, and the smallest and dominant organic peroxy radical, CH3O2, which are formed directly by the reactions of OH with carbon monoxide and methane. Their reaction with nitric oxide constitutes the only tropospheric in situ source of O3, a respiratory irritant and a greenhouse gas. Despite their importance, neither HO2 nor CH3O2 are measured directly in the atmosphere, with HO2 only being determined indirectly following conversion first to OH after sampling.This proposal brings together leading expertise from a field measurement group at Leeds and a cavity enhanced optical spectroscopy group at Oxford to tackle this gap. The overarching aim is to develop a novel and direct laser spectroscopic technique called INFAMOS which has the potential to measure the concentrations of HO2 and CH3O2 in the field. An intercomparison of INFAMOS with complementary, but indirect, chemical conversion methods will be carried out in the Leeds HIRAC atmospheric chamber (volume 2250 litres), whose capabilities will also be improved via this proposal. The new technique will also be used to make direct, sensitive measurements of HO2 and CH3O2 in HIRAC to study the kinetics and product yields for several key atmospheric reactions which are poorly quantified, in conjunction with rate theory calculations and box modelling using the Master Chemical Mechanism.The newly developed technique to measure HO2 or CH3O2 will also have potential benefits in other areas, for example to understand fundamentals of combustion chemistry in the energy sector.