Testing radical assay by nitrite chemical entrapment (TRANCE)

自由基在大气中起着关键作用，尽管它们的浓度非常小。羟基自由基（OH）控制着大多数大气污染物的氧化，包括许多重要的温室气体，而过氧自由基（RO2）的性质和命运对对流层臭氧化学有重大影响。因此，全球化学模型准确模拟OH和过氧自由基浓度是极其重要的。目前的自由基测量方法虽然灵敏、快速、成熟，但体积大、成本高、复杂，因此对自由基的观察在空间和时间上都非常有限。这样做的一个后果是，全球模型中的氢氧根估计常常是针对长寿命示踪剂（例如甲基氯仿）进行测试的，尽管这些示踪剂本身的排放量不一定是准确知道的。此外，现有的测量过氧自由基的技术无法提供单个有机RO2的测量来验证模型。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，但这需要小型的、易于部署的系统，目前还没有。羟基和过氧自由基几乎肯定在其他重要过程中起关键作用，如积雪光化学诱导的辐射，对极地对流层的化学有很大影响。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反应，但目前还不可能。现有的动力学数据表明，少量的有机过氧自由基与高浓度的NO反应可快速定量地转化为稳定的有机亚硝酸盐。本项目将研究通过转化为不同的有机亚硝酸盐化合物来定量有机过氧自由基的可行性，这些化合物可以通过高灵敏度负离子气相色谱-质谱法（NI-GCMS）进行测量。此外，如果OH与碳氢化合物反应产生不同的过氧自由基，那么亚硝酸盐转化方法也提供了测量OH的机会。这种新方法提供了比现有技术更多的关于单个有机过氧自由基的信息，应该能够同时测量OH和有机过氧自由基，并且也有可能测量Cl和NO3自由基。自由基转换和采样与分析仪器不同，这将允许未来开发一种小型，低成本的采样设备，适用于测试全球化学模型所需的大规模部署，以及一种采样系统，非常适合测量积雪实验中的自由基。

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.