Antje Hoheisel and Martina Schmidt present a 6-year time record of in situ methane and its carbon isotope composition δ(13C,CH4), measured with a cavity ring-down spectroscopy (CRDS) analyser in Heidelberg. The isotope data obtain information about seasonal variations and trends of CH4 emissions. The resulting source contributions are used to evaluate the CH4 emissions reported by two emission inventories: the Emissions Database for Global Atmospheric Research (EDGAR v6.0) and the inventory of the State Institute for the Environment Baden-Württemberg (LUBW). The mean isotopic carbon source signature for the Heidelberg catchment area shows an annual cycle. Comparison with emission inventories reveals that this cycle can only be partly explained by seasonal variations in the methane emissions from heating and that strong seasonal variations in biogenic emissions (waste water, landfills, or dairy cows) must contribute with stronger more in summer. Therefore, in situ CH4 isotope analyses at continental and urban monitoring stations make an important contribution to the verification and improvement of emission inventories.
Hoheisel, A. and Schmidt, M.: Six years of continuous carbon isotope composition measurements of methane in Heidelberg (Germany) – a study of source contributions and comparison to emission inventories, Atmos. Chem. Phys., 24, 2951–2969, 2024. https://doi.org/10.5194/acp-24-2951-2024