Discovering reasons for global atmospheric methane growth using deuterium isotopes

使用氘同位素发现全球大气甲烷增长的原因

• 批准号: NE/V00090X/1
• 负责人: Anna Jones
• 金额: $ 14.13万
• 依托单位: British Antarctic Survey
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2021
• 资助国家: 英国
• 起止时间: 2021 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FV00090X%2F1
• 关键词: Discovering; reasons; global; atmospheric; methane

This proposal is to measure and model deuterium/hydrogen (D/H) isotope ratios in methane, to constrain the uncertainties in the global methane budget. Measurement will include 1) Field campaigns to determine isotopic source signatures; 2) time series from remote stations in both hemispheres; and 3) modelling to extract global budgets and causes of change. Atmospheric methane is growing rapidly. Its mixing ratio has risen 80 ppb (over 4% of total burden) since 2007. Growth accelerated in 2014 (13 ppb/yr) and has continued to be high since (7 to 10 ppb/yr). This high methane growth was unexpected and presents one of the greatest immediate challenges to the Paris Agreement. The reasons behind renewed methane growth since 2007 and acceleration in 2014 are not understood. Was it caused by increased emissions, and if so from which sources, or by declining OH, the main sink of methane? Is growth a feedback from climate change, the warming feeding warming? Or is it a direct consequence of human activities? Mixing ratio measurements alone are inadequate to solve the methane budget, though geographic foci indicate the main driving factors are in the tropics and low northern latitudes. Isotopologues (variations in the relative amounts of 12CH4, 13CH4 and 12CH3D) identify and discriminate between source and sink changes. After two centuries of becoming more 13C-rich, methane has shifted 'light' (more 12C-rich) since 2007. The C-isotope change gives insight into the main driving factors behind growth, but more information is needed to fully understand the reasons for interannual variability and continued methane growth. The greatest need is to measure H-isotopes, which provide extremely powerful discriminants of methane sources and sinks.A new technical advance in measuring H-isotopes in methane in ambient air permits this project. A new rapid multiple-sample high-precision mass spectrometric system, which radically cuts the per-sample cost of measurement was installed in late 2019 and was a major goal of NERC's MOYA highlight project. It will allow thousands of ambient air samples per year to be analysed for H-isotopes.Currently only very few labs worldwide make this challenging measurement and source isotopic signatures and time series of ambient air measurements are sparse. The new work will reinstate a global two-hemisphere network, measuring time series in the Arctic, northern mid-latitudes, tropics, southern mid-latitudes, and Antarctica. D/H isotopic signatures of the major sources will be characterised: wetlands, waste, biomass burning, fossil fuel, ruminants and rice agriculture. Field campaigns will focus on tropical Africa, East Asia and S America, with high emissions of methane, but very few measurements of methane isotopic signatures. Results will give regional source signatures for the source types.Modelling will use the new measurements and source signatures to constrain the global methane budget. Combining time series measurements of methane mole fraction and 13C/12C and D/H in methane with improved source signatures will determine latitudinal gradients and temporal trends, Numerical modelling using the UM-UKCA chemical transport model will use D/H as a key discriminant, to test the various hypotheses and identify the causes of methane's rise.The new rapid multi-sample system, which permits us to go from studying methane in 2D (mixing ratio + C-isotopes) to 3D (adding H-isotopes), is a very radical advance in solving the methane budget problem. Understanding why methane is rising is critical to driving mitigation policy to attain the Paris Agreement's goals. This project will lead to a major improvement in understanding the global methane budget, and help shape decisions on strategies needed to stabilise and reduce methane.

该提案旨在测量和模拟甲烷中的氘/氢 (D/H) 同位素比率，以限制全球甲烷预算的不确定性。测量将包括 1) 确定同位素源特征的现场活动； 2）来自两个半球远程站的时间序列； 3) 建模以提取全球预算和变化原因。大气中的甲烷正在迅速增长。自 2007 年以来，其混合比已上升 80 ppb（超过总负荷的 4%）。2014 年增长加速（13 ppb/年），此后一直保持较高水平（7 至 10 ppb/年）。甲烷的高增长是出乎意料的，也是《巴黎协定》面临的最大的直接挑战之一。 2007 年以来甲烷重新增长以及 2014 年加速增长背后的原因尚不清楚。是由排放量增加引起的吗？如果是，是由哪些来源引起的，还是由甲烷主要汇 OH 的减少引起的？增长是气候变化、气候变暖、喂养变暖的反馈吗？还是人类活动的直接后果？尽管地理焦点表明主要驱动因素位于热带地区和北纬低纬度地区，但仅混合比测量不足以解决甲烷预算问题。同位素体（12CH4、13CH4 和 12CH3D 相对量的变化）可识别和区分源和汇的变化。经过两个世纪以来，甲烷的 13 C 含量越来越丰富，自 2007 年以来，甲烷已转变为“轻质”（更加富含 12 C）。C 同位素的变化使人们能够深入了解增长背后的主要驱动因素，但需要更多信息才能充分理解其原因年际变化和持续的甲烷增长。最大的需求是测量氢同位素，它为甲烷源和汇提供了极其有力的判别依据。测量环境空气中甲烷中氢同位素的新技术进步使得该项目得以实现。 NERC MOYA 亮点项目的主要目标是于 2019 年底安装了新型快速多样品高精度质谱系统，该系统从根本上降低了每个样品的测量成本。它将允许每年对数千个环境空气样本进行 H 同位素分析。目前，全球只有极少数实验室进行这项具有挑战性的测量，并且源同位素特征和环境空气测量的时间序列很少。这项新工作将恢复全球两半球网络，测量北极、北部中纬度地区、热带、南部中纬度地区和南极洲的时间序列。主要来源的 D/H 同位素特征将被描述：湿地、废物、生物质燃烧、化石燃料、反刍动物和水稻农业。实地活动将集中在热带非洲、东亚和南美洲，这些地方的甲烷排放量很高，但甲烷同位素特征的测量却很少。结果将给出源类型的区域源特征。建模将使用新的测量值和源特征来限制全球甲烷预算。将甲烷摩尔分数、13C/12C 和 D/H 的时间序列测量与改进的源特征相结合，将确定纬度梯度和时间趋势，使用 UM-UKCA 化学输运模型的数值建模将使用 D/H 作为关键判别式，测试各种假设并确定甲烷上升的原因。新的快速多样本系统使我们能够从二维研究甲烷（混合比+ C-同位素）到 3D（添加 H-同位素），是解决甲烷预算问题的一个非常根本的进步。了解甲烷排放量上升的原因对于推动缓解政策以实现《巴黎协定》的目标至关重要。该项目将大大提高对全球甲烷预算的了解，并帮助制定稳定和减少甲烷所需的战略决策。