Testing radical assay by nitrite chemical entrapment (TRANCE)

尽管自由基的浓度极小，但它们在大气中发挥着关键作用。羟基自由基(OH)控制着包括许多重要温室气体在内的大多数大气污染物的氧化，而过氧化自由基(RO2)的性质和去向对对流层臭氧化学有重要影响。因此，全球化学模型准确地模拟羟基和过氧基的浓度是极其重要的。目前的自由基测量方法虽然灵敏、快速且得到了很好的验证，但它们都是庞大、昂贵和复杂的，因此对自由基的观测在空间和时间上都非常有限。这样做的一个结果是，全球模型中的氢氧化氢估算经常与长效示踪剂(例如甲基氯仿)进行检验，即使这些示踪剂本身的排放量不一定是准确知道的。此外，现有的测量过氧基的技术不能提供用于验证模型的单个有机RO2的测量。因此，如果有广泛的、长期的自由基测量来评估和改进模型，这将是巨大的好处，但这将需要小型的、易于部署的系统，而这些系统目前还不可用。羟基和过氧基几乎肯定在其他重要过程中起着关键作用，例如对极地对流层化学有很大影响的积雪的光化学诱导的排放。在积雪中进行详细的激进测量将极大地有助于理解这种化学作用，但目前还不可能。现有的动力学数据表明，通过与高浓度的NO反应，可以快速、定量地将小分子有机过氧基转化为稳定的有机亚硝酸盐。该项目将研究通过将有机过氧基转化为不同的有机亚硝酸盐化合物来量化有机过氧基的可行性，这些化合物可以通过高灵敏度的负离子气相色谱-质谱仪(NI-GCMS)进行测量。此外，如果允许OH与碳氢化合物反应生成不同的过氧基，那么亚硝酸盐转化法也提供了测量OH的机会。这种新的方法提供了比现有技术提供的更多关于单个有机过氧基的信息，应该能够同时测量OH和有机过氧基，并有可能同时测量氯和硝酸根。自由基转换和采样不同于分析仪器，分析仪器应该允许未来开发一种小型、低成本的采样设备，适合于测试全球化学模型所需的大规模部署，以及一种非常适合在积雪实验中测量自由基的采样系统。

Radicals play a pivotal role in the atmosphere even though their concentrations are extremely small. The hydroxyl radical (OH) controls the oxidation of most atmospheric pollutants, including many important greenhouse gases, whilst the nature and fate of peroxy radicals (RO2) has a major impact on tropospheric ozone chemistry. It is therefore extremely important that global chemistry models accurately simulate the OH and peroxy radical concentrations. Current radical measurement methods, whilst sensitive, fast and well proven, are large, expensive and complicated and therefore observations of radicals are very limited in space and time. A consequence of this is that OH estimations in global models are often tested against long-lived tracers (e.g. methyl chloroform) even though the emissions of these tracers themselves are not necessarily accurately known. Further, the existing techniques for measuring peroxy radicals are unable to provide a measure of individual organic RO2 with which to validate the models. Therefore it would be of immense benefit if there were extensive, long term measurements of radicals with which to assess and improve models, but this would need small, easily-deployable systems which are not currently available. Hydroxyl and peroxy radicals almost certainly play a key role in other important processes such as photochemically induced emissions from snowpacks which have a great influence on the chemistry of the polar troposphere. Detailed radical measurements within the snowpack would be hugely beneficial in understanding this chemistry, but are not currently possible. Currently available kinetic data suggests that small organic peroxy radicals can be converted rapidly and quantitatively into stable organic nitrites by reaction with high concentrations of NO. This project will examine the feasibility of quantifying organic peroxy radicals by this conversion into distinct organic nitrite compounds which can be measured by highly sensitive negative ion gas chromatography-mass spectrometry (NI-GCMS). Additionally, if OH is allowed to react with a hydrocarbon to produce a distinct peroxy radical, then the nitrite conversion method offers the opportunity to measure OH as well. This novel method offers more information on individual organic peroxy radicals than current technology affords, should be able to measure OH and organic peroxy radicals concurrently, and has the potential to also measure Cl and NO3 radicals. The radical conversion and sampling is distinct from the analysis instrument which should allow the future development of a small, low-cost sampling device suitable for the large scale deployments required to test global chemistry models, as well as a sampling system well suited to measuring radicals in snowpack experiments.