Tracing Sources of Atmospheric Methane Using Clumped Isotopes

Here we use a box model to evaluate how much additional data from Δ12CH2D2 and Δ13CH3D may add to understanding the temporal trend in atmospheric methane, and specifically, whether they may differentiate the contributions of fossil fuel and microbial sources. EDGAR (Emissions Database for Global Atmospheric Research) provides high-quality constraints on methane fluxes from major anthropogenic sources, and different versions of EDGAR reflect uncertainty in understanding of the apportionment of these fluxes over the past few decades. We used two versions of EDGAR and also considered another model of fossil fuel flux to build four different scenarios for anthropogenic source fluxes for our box model. EDGAR does not include wetland emissions and those are calculated (a free variable) to close the flux balance needed by the model. Each scenario broadly follows one of four parameterizations of anthropogenic source fluxes to obtain an estimate of the composition and evolution of Δ12CH2D2 and Δ13CH3D through time.

本研究采用箱式模型（box model），评估Δ12CH2D2与Δ13CH3D的额外数据可在多大程度上增进学界对大气甲烷时间演变趋势的认知，尤其可用于判断这些数据能否区分甲烷的化石燃料源与微生物源贡献。全球大气研究排放数据库（Emissions Database for Global Atmospheric Research）为主要人为源的甲烷通量提供了高质量约束，而EDGAR的不同版本则反映了近数十年来学界对这些通量分配认知的不确定性。本研究选用EDGAR的两个版本，并额外考虑了另一种化石燃料通量模型，为箱式模型构建了四种不同的人为源通量情景。EDGAR未纳入湿地排放项，该部分以自由变量形式进行计算，以闭合模型所需的通量平衡条件。每种情景大致遵循四种人为源通量参数化方案之一，以估算Δ12CH2D2与Δ13CH3D随时间的组成及演变过程。