Development and First Deployment of an Innovative Airborne δ13C(CH4) In Situ Measurement Setup

• Main Author: Waldmann, Paul
• Format: Thesis
• Language: English
• Published: 2023
• Subjects: Atmosphärische Spurenstoffe; Arctic
• Online Access: https://elib.dlr.de/193673/; https://elib.dlr.de/193673/1/MA_Waldmann_final.pdf

This thesis introduces an innovative in situ airborne system for the measurement of the stable carbon isotope ratio of methane emitters, called MIRACLE (measurement of methane stable carbon isotope ratio by airborne implementation of a cavity ring down laser spectrometer). A conventional Picarro greenhouse gas analyser was used for the measurement of methane and the methane carbon isotope ratio aboard the research aircraft HALO during the CoMet 2.0 Arctic campaign. Precise δ13C(CH4) measurements were achieved by the supplement of a new type of sample collector to the analyser, which makes it possible to take up to six gas samples in a short time, for an extended period of subsequent analysis. The extended measurement period allows analysis with a δ13C(CH4) 1σ uncertainty of 0.34 ‰ aboard the aircraft. The MIRACLE instrument was tested for contamination of the samples but showed no distortion of the methane concentration or the isotope ratio. For two of the successful research flights of the campaign, the isotopic signatures of the target areas were analysed using the data of MIRACLE, in order to highlight the measurement uncertainties of the instrument and to discuss the results in the context of the literature. The δ13C(CH4) signature of the lake Winnipeg wetland area was found to be -61.95 ± 2.56‰, which is in accordance with comparable studies. The δ13C(CH4) signature of a biomass burning fire plume was found to be -35.33 ± 8.58‰, also consistent with the literature. The MIRACLE instrument combines the advantages of high precision δ13C(CH4) measurements, which were previously only possible under stable laboratory conditions, with the in situ, real time data analysis and large-scale sampling of secluded areas, due to the airborne deployment.