13 Improved method for mobile characterisation of δ CH4 source signatures and its application in Germany Antje Hoheisel1, Christiane Yeman1,2, Florian Dinger1,3, Henrik Eckhardt1, and Martina Schmidt1 1Institute of Environmental Physics, Heidelberg University, Heidelberg, Germany 2Laboratory of Ion Beam Physics, ETH Zurich, Zurich, Switzerland (now) 3Max-Planck Institute for Chemistry, Mainz, Germany Correspondence: Antje Hoheisel (
[email protected]) 13 Abstract. The carbon isotopic signature (δ CH4) of several methane sources in Germany (around Heidelberg and in North Rhine-Westphalia) were characterised. Mobile measurements of the plume of CH4 sources are carried out using a cavity ring- down spectrometer (CRDS). To achieve precise results a CRDS analyser, which measures methane (CH4), carbon dioxide 13 12 (CO2) and their C to C ratios, was characterised especially with regard to cross sensitivities of composition differences of 13 5 the gas matrix in air samples or calibration tanks. The two most important gases which affect δ CH4 are water vapour (H2O) and ethane (C2H6). To avoid the cross sensitivity with H2O, the air is dried with a nafion dryer during mobile measurements. C2H6 is typically abundant in natural gases and thus in methane plumes or samples originating from natural gas. A C2H6 13 correction and calibration are essential to obtain accurate δ CH4 results, which can deviate up to 3‰ depending on whether a C2H6 correction is applied. 10 The isotopic signature is determined with the Miller-Tans approach and the York fitting method. During 21 field campaigns 13 the mean δ CH4 signatures of three dairy farms (−63.9±0.9‰), a biogas plant (−62.4±1.2‰), a landfill (−58.7±3.3‰), a wastewater treatment plant (−52.5±1.4‰), an active deep coal mine (−56:0 ± 2:3‰) and two natural gas storage and gas compressor stations (−46.1±0.8‰) were recorded.