08 Nov 2023
 | 08 Nov 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Six years of continuous carbon isotope composition measurements of methane in Heidelberg (Germany) – a study of source contributions and comparison to emission inventories

Antje Hoheisel and Martina Schmidt

Abstract. δ(13CH4) and the mole fraction of CH4 have been measured continuously since April 2014 using a cavity ring-down spectroscopy (CRDS) analyser in Heidelberg, Germany. This 6-year time series shows an increasing trend of (6.8±0.3) nmol mol-1 a-1 for the CH4 mole fraction between 2014 and 2020. δ(13CH4) decreases by (-0.028±0.002) ‰ a-1 over this time period.

In this study, seasonal variations and trends of CH4 emissions in the catchment area of Heidelberg are analysed using three approaches by applying the Miller-Tans method to atmospheric measurements on different time scales. The mean δ13C isotopic source signature for the Heidelberg catchment area is (-52.5±0.3) ‰ (moving Miller-Tans approach). In all three approaches, there is no significant trend in the monthly mean source signature over the last six years. However, more depleted source signature values occur in summer. This annual cycle in 13C-CH4 sources, with a peak-to-peak amplitude of -6.2 ‰ can only be partially explained by seasonal variations in CH4 emissions from heating. Additional seasonal variations probably occur in biogenic CH4 emissions from waste water, landfills or dairy cows.

Furthermore, the source contributions derived from atmospheric measurements are used to evaluate the CH4 emissions reported by two emission inventories: the Emissions Database for Global Atmospheric Research (EDGARv6.0) and the inventory of the State Institute for the Environment Baden-Württemberg (LUBW – Landesanstalt für Umwelt Baden-Württemberg). The mean δ(13CH4) source signature determined from the LUBW inventory agrees well with the result from atmospheric measurements. However, the signature determined from EDGARv6.0 data is less depleted by about 7 ‰. Thus, EDGARv6.0 seems to overestimate CH4 emissions from more enriched sources.

Antje Hoheisel and Martina Schmidt

Status: open (until 20 Dec 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2023-2079', Anonymous Referee #1, 24 Nov 2023 reply
  • RC2: 'Comment on egusphere-2023-2079', Anonymous Referee #2, 04 Dec 2023 reply

Antje Hoheisel and Martina Schmidt

Antje Hoheisel and Martina Schmidt


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Short summary
In Heidelberg, Germany, methane and its stable carbon isotope composition have been measured continuously with a cavity ring-down spectroscopy (CRDS) analyser since April 2014. These six-year time series are analysed with the Miller-Tans method for the isotopic composition of the sources, as well as seasonal variations and trends in methane emissions. The source contributions derived from atmospheric measurements were used to evaluate global and regional emission inventories of methane.