New contributions of measurements in Europe to the global inventory of the stable isotopic composition of methane

Recent climate change mitigation strategies rely on the reduction of methane (CH4) emissions. Carbon and hydrogen isotope ratio (delta C-13(CH4) and delta H-2(CH4)) measurements can be used to distinguish sources and thus to understand the CH4 budget better. The CH4 emission estimates by models are sensitive to the isotopic signatures assigned to each source category, so it is important to provide representative estimates of the different CH4 source isotopic signatures worldwide. We present new measurements of isotope signatures of various, mainly anthropogenic, CH4 sources in Europe, which represent a substantial contribution to the global dataset of source isotopic measurements from the literature, especially for delta H-2(CH4). They improve the definition of delta C-13(CH4) from waste sources, and demonstrate the use of delta H-2(CH4) for fossil fuel source attribution. We combined our new measurements with the last published database of CH4 isotopic signatures and with additional literature, and present a new global database. We found that microbial sources are generally well characterised. The large variability in fossil fuel isotopic compositions requires particular care in the choice of weighting criteria for the calculation of a representative global value. The global dataset could be further improved by measurements from African, South American, and Asian countries, and more measurements from pyrogenic sources. We improved the source characterisation of CH4 emissions using stable isotopes and associated uncertainty, to be used in top-down studies. We emphasise that an appropriate use of the database requires the analysis of specific parameters in relation to source type and the region of interest. The final version of the European CH4 isotope database coupled with a global inventory of fossil and non-fossil delta C-13(CH4) and delta H-2(CH4) source signature measurements is available at .https://doi.org/10.24416/UU01-YP43IN (Menoud et al., 2022a).

Automated summary

This study provides a better method for estimating CH4 emission sources by measuring the isotope signatures of different sources and presents a new global database. The results indicate that microbial sources are well described, while there is significant variability in the isotope compositions of fossil fuel sources, requiring careful selection of weighting criteria.