INFAMOS - a new method for speciated peroxy radical detection

国际社会对空气质量恶化和气候变化的反应以数值模式的预测为指导。这些模型包括对自然过程和人类活动产生的微量气体和气溶胶的未来排放量、它们在整个大气中的扩散以及它们向各种各样的二次产物的化学转化的估计。对流层中的光氧化是高度复杂的，由短命的自由基引起，白天由羟基自由基主导，氯原子起作用，晚上由硝酸盐自由基或臭氧起作用。快速的化学氧化循环去除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二次产物也是直接有害的，例如臭氧、二氧化氮、酸和多功能有机分子，其中许多挥发性低，能够有效地分解到凝聚相，产生二次有机气溶胶，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内对自由基的计算输出与大气中的实际测量结果进行比较。自由基是实现这一目的的理想选择，因为它们的寿命很短，因此是由化学而不是由运输来控制的。大气中最简单的两种自由基是氢氧自由基HO2和最小且占主导地位的有机过氧自由基CH3O2，它们是由OH与一氧化碳和甲烷直接反应形成的。它们与一氧化氮的反应构成了对流层中臭氧的唯一原位来源，臭氧是一种呼吸刺激物和温室气体。尽管HO2和CH3O2很重要，但它们都不能在大气中直接测量，HO2只能在采样后先转化为OH后间接测定。该提案汇集了利兹大学现场测量小组和牛津大学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称为INFAMOS的新型直接激光光谱技术，该技术有可能在现场测量HO2和CH3O2的浓度。将在利兹HIRAC大气室（容量2250升）中对INFAMOS与互补但间接的化学转化方法进行相互比较，其能力也将通过这项建议得到改善。这项新技术还将用于直接、灵敏地测量HIRAC中的HO2和CH3O2，以研究几个关键的大气反应的动力学和生成量，这些反应很难量化，同时结合速率理论计算和使用主化学机制的盒子模型。新开发的测量HO2或CH3O2的技术也将在其他领域有潜在的好处，例如了解能源部门燃烧化学的基本原理。

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.