This data collection has been generated in the framework of the Horizon Europe project PARIS with metrology support from Euramet's 21GRD04 isoMET for the optical measurements. Isotope ratios of 2H-CH4 to 1H-CH4 in air are relative to VSMOW. Isotope ratios of 13C-CH4 to 12C-CH4 in air are relative to VPDB. Document ch4-source-signatures-sampling-cluj.txt contains methane isotope ratio source signatures from samples taken during a mobile campaign in Cluj-Napoca (RO). The source signatures are established from repeated location samplings and background samples via the Keeling plot approach. Most of the data objects metadata contain a link to a descriptive peer reviewed publication. Please ensure that you contact the data owner(s) before considering data analysis and publication.