Air pollution: Sources and sinks of carbon monoxide in the atmosphere

一氧化碳（CO）是空气污染的主要来源。它是由机动车辆燃烧化石燃料和燃烧植物作为燃料产生的，如农业废物或野火。许多政府已经制定了减少CO排放的政策。例如，英国的CO排放量估计在1990年至2017年期间下降了80%，这主要归功于欧盟范围内的机动车排放标准。 本计画将以放射性碳为示踪剂，探讨一氧化碳的源与汇。放射性碳（14 C）是化石燃料碳源的一种强有力的示踪剂，因为化石燃料已经储存在地下很长时间，它们已经失去了所有的14 C放射性衰变。通过测量CO中的14 C（14 CO），可以在区域尺度上确定化石燃料与CO生物源的比例。这是一项新技术，将作为该奖学金的一部分开发，这将可能导致减少空气污染政策的验证方法。 14 C的测量还可以提供有关大气中CO的清除（汇）的信息，这是通过与羟基自由基（OH）反应发生的。了解与OH反应的变化不仅对CO很重要，而且对许多其他也与OH反应的化合物也很重要，包括甲烷。OH被称为大气的“真空吸尘器”或“清洁剂”。14 CO可以提供关于OH的信息，因为14 CO主要是通过宇宙成因辐射以空间和时间变化的速率产生的，这是相当众所周知的，特别是在最近宇宙成因产量估计有所改善之后。因此，在大尺度上观察到的14 CO变化可以提供关于OH变化的信息，否则很难观察到。这种技术在过去已经被使用[Manning et al. Nature 2005，doi：10.1038/nature 03900]，但它需要用改进的模型进行更新。

Carbon monoxide (CO) is a major contributor to air pollution. It is produced by the burning of fossil fuels in motor vehicles and the burning of vegetation for fuel, as agricultural waste, or in wildfires. Many governments have enacted policies to reduce the emissions of CO. For example, CO emissions in the UK are estimated to have declined 80% between 1990 and 2017, largely attributed to EU-wide emission standards for motor vehicles. This project will investigate the sources and sinks of CO by using radiocarbon as a tracer. Radiocarbon (14C) is a powerful tracer of fossil fuel sources of carbon because fossil fuels have been stored underground so long they have lost all their 14C to radioactive decay. By measuring 14C in CO (14CO), the fraction of fossil fuel vs biogenic sources of CO can be determined on regional scales. This is a new technique that will be developed as part of this studentship, which will potentially lead to methods for verification of policies for reducing air pollution. Measurements of 14C can also provide information on the removals (sinks) of CO in the atmosphere, which occur through reaction with the hydroxyl radical (OH). Understanding variations in the reaction with OH is important not just for CO but for many other compounds that also react with OH including methane. OH has been called the "vacuum cleaner" or "detergent" of the atmosphere. 14CO can provide information on OH because 14CO is mainly produced via cosmogenic radiation at spatially- and temporally-varying rates which are reasonably well-known, particularly after recent improvements in cosmogenic production estimates. Therefore, observed variations in 14CO over large scales can provide information on the variation in OH, which is otherwise very difficult to observe. This technique has been used in the past [Manning et al. Nature 2005, doi: 10.1038/nature03900], but it needs updating with improved models.