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.

这一提议是为了测量甲烷中的重氢(D/H)同位素比率并对其进行建模，以限制全球甲烷预算中的不确定性。测量将包括1)确定同位素来源特征的实地活动；2)来自两个半球偏远站点的时间序列；以及3)提取全球预算和变化原因的模型。大气中的甲烷正在迅速增长。自2007年以来，其混合比例上升了80 ppb(占总负担的4%以上)。增长在2014年加速(13ppb/年)，此后一直保持较高水平(7ppb/年至10ppb/年)。甲烷的高增长出乎人们的意料，是《巴黎协定》面临的最大直接挑战之一。自2007年以来甲烷再次增长和2014年甲烷加速增长背后的原因尚不清楚。它是由排放增加引起的吗？如果是的话，是来自哪个来源，还是由于甲烷的主要汇--OH的减少？增长是气候变化的反馈吗？气候变暖导致气候变暖？或者它是人类活动的直接后果？混合比测量本身不足以解决甲烷收支问题，尽管地理焦点表明主要驱动因素在热带和北纬较低的地区。同位素(12CH4、13CH4和12CH3D的相对数量的变化)识别和区分源和汇的变化。经过两个世纪变得更富含13C的甲烷，自2007年以来，甲烷已经变得“轻”(更富含12C)。碳同位素的变化有助于洞察甲烷增长背后的主要驱动因素，但需要更多信息才能充分理解甲烷年际变化和持续增长的原因。最大的需求是测量氢同位素，它为甲烷的来源和汇提供了极其强大的判别式。在测量环境空气中甲烷的氢同位素方面的新技术进步使这一项目成为可能。一种新的快速多样品高精度质谱学系统于2019年底安装，它从根本上降低了每个样品的测量成本，这是NERC莫亚亮点项目的主要目标。它将允许每年对数千个环境空气样本进行氢同位素分析。目前，世界上只有极少数实验室进行了这项具有挑战性的测量，并且环境空气测量的来源同位素特征和时间序列稀少。这项新工作将恢复一个全球双半球网络，测量北极、北中纬度、热带、南中纬度和南极洲的时间序列。将描述主要来源的D/H同位素特征：湿地、废物、生物质燃烧、化石燃料、反刍动物和水稻农业。实地活动将集中在甲烷排放量较高的热带非洲、东亚和S美洲，但很少测量到甲烷同位素特征。结果将给出来源类型的地区性来源特征。建模将使用新的测量和来源特征来限制全球甲烷预算。将甲烷摩尔分数和甲烷中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化学传输模型的数值模拟将使用D/H作为关键判别式，以检验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2D(混合比+C同位素)研究甲烷到3D(添加H同位素)，这是解决甲烷预算问题的一个非常根本的进步。了解甲烷为什么会上升，对于推动缓解政策以实现《巴黎协定》的目标至关重要。该项目将极大地改善对全球甲烷预算的理解，并有助于制定稳定和减少甲烷所需战略的决策。