POLYGRAM: POLYisotopologues of GReenhouse gases: Analysis and Modelling

迄今为止，温室气体二氧化碳（CO2）和甲烷（CH4）是造成近期和持续气候变化的最大因素。在所有已知的温室气体（不包括水蒸气）中，二氧化碳和甲烷在大气中的浓度最高，并且正在迅速上升。二氧化碳的问题尤其严重，因为它的含量非常高（大约是甲烷的200倍），而且一旦排放到大气中，其中大部分将在那里停留数百年。然而，相比之下，CH4在大气中的寿命只有10年左右，但它是一种比CO2强得多的温室气体——也就是说，对于大气中等量的CO2和CH4， CH4捕获热辐射的效率是CO2的70倍（在20年的时间周期内）。随着《巴黎协定》的批准，全世界都致力于避免危险的气候变化，而最明显的方法就是减少二氧化碳和甲烷的排放。我们如何知道减排政策是否有效？哪些国家或地区达到了减排目标？自然CO2和CH4通量如何响应极端天气事件？碳循环的哪些方面仍未得到解决？例如，尽管经过了几十年的研究，科学家们仍然不确定为什么甲烷的排放量目前在上升。为了回答这些问题，我们需要能够测量和量化二氧化碳和甲烷的排放和浓度，并有能力分别量化自然和人为来源。我们目前这样做的能力非常有限，特别是对于甲烷，它有各种各样的自然和人为来源。如果我们不能确定减缓政策的有效性，那么我们预测气候变化影响的能力将受到巨大不确定性的影响。“多同位素”是一种非常有前途的区分不同源排放的新工具。组成CO2和CH4分子的化学元素(碳(C)、氧（O)和氢(H)）可以有不同的质量，称为同位素。不同的源可能有不同的同位素“指纹”或“特征”（因为源反应过程可能倾向于更轻或更重的分子），因此测量同位素特征是深入了解源的有用方法。几十年来，同位素测量一直是例行公事；然而，在这个项目中开发的最先进的技术将使我们能够测量含有多种稀有同位素的分子。例如，大多数碳的相对原子质量是12，而氢的相对原子质量是1。C和H的稀有同位素的质量分别为13和2。常规测量的CH4同位素物包括12CH4、13CH4和12CH3D（其中“D”表示质量为2的重H原子）。而CH4的多同位素物包括13CH3D和12CH2D2——这些测量难度要大得多，但可以为了解源排放和汇提供宝贵的信息。POLYGRAM（温室气体的多同位素：分析和建模）将利用激光光谱分析和高分辨率同位素比质谱法的最新进展，推动二氧化碳和CH4多同位素测量能力的前沿。除了这些具有挑战性的技术发展之外，我们将建立一个小型的全球大气采样网络，以检查多同位素的纬度和纵向变化，这将有助于我们限制CO2和CH4的总体全球预算。我们将开展实地活动，以确定多同位素源特征，例如，来自湿地、牛和垃圾填埋场的甲烷，以及来自植物光合作用和呼吸作用以及化石燃料燃烧的二氧化碳。我们将进行实验室实验，以估计甲烷同位素物在大气中被氧化和破坏时的反应速率。最后，我们将对这两种气体进行大气输送模拟，以更好地解释和理解测量结果。

The greenhouse gases carbon dioxide (CO2) and methane (CH4) are by far the biggest contributors to recent and ongoing climate change. Of all the known greenhouse gases (excluding water vapour), CO2 and CH4 have the highest concentrations in the atmosphere and they are rising rapidly. CO2 is particularly problematic because there is so much of it (about 200 times more than CH4) and because once emitted to the atmosphere, much of it will stay there for several hundred years. Whereas, by comparison, CH4 only has a lifetime in the atmosphere of about ten years, but it is a much more potent greenhouse gas than CO2 - that is, for equal amounts of CO2 and CH4 in the atmosphere, CH4 will trap heat radiation about 70 times more effectively than CO2 (over a 20-year time period).With the ratification of the Paris Agreement, the world has committed to avoiding dangerous climate change and the most obvious way to do this is by reducing emissions of CO2 and CH4. How will we know if emission mitigation policies are effective? Which nations or regions are meeting their emissions reduction targets? How will natural CO2 and CH4 fluxes respond to extreme weather events? And which aspects of the carbon cycle remain unsolved? For example, despite decades of study, scientists are still not sure why CH4 emissions are currently rising. To answer these questions we need to be able to measure and quantify CO2 and CH4 emissions and concentrations, and have the ability to separately quantify natural and manmade sources. Our current abilities to do so are severely limited, especially for CH4, which has a diverse array of natural and manmade sources. If we cannot determine the effectiveness of mitigation policies, then our ability to predict climate change impacts will be compromised by large uncertainties.'Polyisotopologues' are one very promising new tool for distinguishing between different source emissions. The chemical elements that make up CO2 and CH4 molecules (carbon (C), oxygen (O) and hydrogen (H)) can have different masses, called isotopes. Different sources can have different isotopic 'fingerprints' or 'signatures' (because source reaction processes may favour a lighter or heavier molecule), thus measuring isotopic signatures is a useful way to gain insight into sources. Isotopic measurements have been made routinely for several decades; whereas the state-of-the-art technology developed in this project would allow us to measure molecules with more than one rare isotope. For example, most C has a relative atomic mass of 12 and H a mass of 1. The rarer isotopes of C and H have masses of 13 and 2, respectively. Isotopologues of CH4, which are measured routinely, include 12CH4, 13CH4 and 12CH3D (where 'D' represents the heavy H atom with mass 2). Whereas polyisotopologues of CH4 include 13CH3D and 12CH2D2 - these are far more challenging to measure, yet could provide invaluable insight into source emissions and sinks.POLYGRAM (POLYisotopologues of GReenhouse gases: Analysis and Modelling) will push the frontiers for both CO2 and CH4 polyisotopologue measurement capability using the latest advances in laser spectroscopic analysis and very high-resolution isotope ratio mass spectrometry. In addition to these challenging technological developments, we will establish a small global atmospheric sampling network to examine latitudinal and longitudinal variations in polyisotopologues, which will help us to constrain overall global budgets of CO2 and CH4. We will carry out field campaigns to determine polyisotopologue source signatures, for example, of CH4 from wetlands, cattle and landfills, and of CO2 from plant photosynthesis and respiration, and from fossil fuel burning. We will conduct laboratory experiments to estimate the reaction rates for CH4 isotopologues when they are oxidised and destroyed in the atmosphere. Finally, we will carry out atmospheric transport modelling for both gases to better interpret and understand the measurements.