Atmospheric methane (CH₄) and its isotopic composition trends over the last decades are explained by various flux scenarios, from tropical wetland emission increases through to reductions in global hydroxyl (OH). In this study, we develop a modeling framework to assess the potential usefulness of clumped isotope measurements to distinguish between the main drivers of change in the CH₄ burden. We model interhemispheric differences of 0.12‰ and 0.38‰ and seasonal cycles of 0.02‰–0.04‰ and 0.21‰–0.32‰ for Δ¹³CH₃D and Δ¹²CH₂D₂, respectively, which is insignificant relative to the uncertainty of measurements that could eventually be made. We show, however, that measurements of Δ¹²CH₂D₂ specifically could provide constraints for understanding trends in the global total source and sink magnitudes, which has not been possible with the current sets of observables. Changes in OH concentration of 10% developed across three decades result in a difference of up to 2‰ in Δ¹²CH₂D₂, which would be observable given current measurement uncertainty limits. For this type of global-scale analysis, we show that measurements of Δ¹³CH₃D would be unlikely to provide additional useful information. We suggest an emphasis should now be on developing the methods to make measurements from ambient air samples, followed by measurements of Δ¹³CH₃D and Δ¹²CH₂D₂ from sampling at clean Northern and Southern Hemisphere sites, combined with more accurate and precise laboratory measurements of the clumped kinetic isotope effects relevant for the atmospheric sinks.

中文翻译：

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聚集同位素在限制全球大气甲烷收支方面的潜力

过去几十年的大气甲烷 (CH ₄ ) 及其同位素组成趋势可以通过各种通量情景来解释，从热带湿地排放的增加到全球羟基 (OH) 的减少。在这项研究中，我们开发了一个建模框架来评估聚集同位素测量的潜在用途，以区分 CH ₄负荷变化的主要驱动因素。对于 Δ ¹³ CH ₃ D 和 Δ ¹² CH ₂ D _2，我们模拟了 0.12‰ 和 0.38‰ 的半球差异和 0.02‰–0.04‰ 和 0.21‰–0.32‰ 的季节周期，分别相对于最终可能进行的测量的不确定性而言是微不足道的。然而，我们表明，对 Δ ¹² CH ₂ D _{2 的}测量特别可以为理解全球总源和汇量级的趋势提供限制，而这在当前的一组可观测值中是不可能的。三个十年间 OH 浓度的 10% 变化导致 Δ ¹² CH ₂ D ₂的差异高达 2‰，鉴于当前的测量不确定性限制，这将是可以观察到的。对于这种类型的全球尺度分析，我们表明 Δ ¹³ CH _{3 的}测量值D 不太可能提供额外的有用信息。我们建议现在重点应该放在开发从环境空气样本中进行测量的方法，然后是在干净的北半球和南半球地点采样的 Δ ¹³ CH ₃ D 和 Δ ¹² CH ₂ D ₂的测量，结合更准确和与大气汇相关的聚集动力学同位素效应的精确实验室测量。