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 (CH 4) emissions. Carbon and hydrogen isotope ratio (δ13 C CH4 and δ2 H CH4) measurements can be used to distinguish sources and thus to understand the CH 4 budget better. The CH 4 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 CH 4 source isotopic signatures worldwide. We present new measurements of isotope signatures of various, mainly anthropogenic, CH 4 sources in Europe, which represent a substantial contribution to the global dataset of source isotopic measurements from the literature, especially for δ2 H CH4. They improve the definition of δ13 C CH4 from waste sources, and demonstrate the use of δ2 H CH4 for fossil fuel source attribution. We combined our new measurements with the last published database of CH 4 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 CH 4 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 CH 4 isotope database coupled with a global inventory of fossil and non-fossil δ13 C CH4 and δ2 H CH4 source signature measurements is available at 10.24416/UU01-YP43IN. [ABSTRACT FROM AUTHOR]