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Abstract

Continuous measurements of the greenhouse gases CO2 and CH4, along with their isotopologues 13CO2 and 13CH4, are the basis for estimating the atmospheric CO2 and CH4 fluxes on high temporal resolution and for identifying their sources and sinks. The Cavity Ring-Down Spectrometer (CRDS) G2201-i measures 12CO2, 13CO2, 12CH4, 13CH4, and H2O continuously and simultaneously in a gas sample. In this thesis, the CRDS G2201-i has been installed in Heidelberg for routine ambient air analysis and for measurements of highly concentrated CH4 samples. It has been characterised and thoroughly tested in terms of accuracy, precision, and compatibility. It was found, that for accurate results, the internal water vapour correction is insufficient, which makes a preceding drying necessary. Furthermore, an instrumental non-linearity in the CO2 and CH4 concentrations was observed. Nevertheless, a single-point calibration yields CO2 and CH4 concentrations which are compatible to other routine instruments (i.e. Fourier Transform InfraRed spectrometer (FTIR) and gas chromatograph) in Heidelberg within the World Meteorological Organization recommendations. The delta13CO2 results of CRDS, FTIR, and the mass spectrometer in Heidelberg are compatible for cylinder measurements. For continuous ambient air measurements a systematic offset of Delta(delta13CO2)_{CRDS-FTIR} = (0.07+-0.11) per mil was observed.