Characterization and Quantification of Offshore Methane Emissions using Airborne in situ Measurements of Methane, Ethane and Methane Isotopologues

• Main Author: Pühl, Magdalena Maria Theresia
• Format: Thesis
• Language: English
• Published: 2024
• Subjects: Atmosphärische Spurenstoffe; Antarctic; Antarc*
• Online Access: https://elib.dlr.de/212541/; https://elib.dlr.de/212541/1/Puehl_Magdalena_Dissertation.pdf; https://edoc.ub.uni-muenchen.de/34698/

Methane (CH4) is the second-most important long-lived anthropogenic greenhouse gas after carbon dioxide and, because of its short lifetime, is an attractive target for rapid emission reduction. Atmospheric CH4 mole fractions have almost tripled since preindustrial times due to human activity. A concurrent decline in the 13CH4/12CH4 isotopic ratio of CH4 (expressed as δ13C(CH4)) since 2007 points to a significant change in CH4 sources and sinks, since those vary in their δ13C(CH4) signatures. So far, the understanding of the underlaying drivers is insufficient, which hampers both prioritizing mitigation actions and predicting future CH4 trends. This dissertation aims at a more detailed characterization of anthropogenic CH4 emissions using airborne in situ measurement methods. Thereby, the focus is on the sector of offshore fossil fuel production, which is understudied so far. Driven by the hypothesis that emission inventories using generic scaling methods are not able to estimate emissions with sufficient accuracy, airborne measurement data gathered around offshore installations is analyzed and compared with different inventory data. Moreover, it is investigated, whether emissions can be better characterized by using the latest airborne laser spectroscopy methods. To this end, an existing direct laser absorption spectrometer is adapted for the high-resolution and continuous airborne measurement of the tracers C2H6 and δ13C(CH4), and deployed on research aircraft to study offshore emissions. The first part presents the analyses of an airborne study conducted by the British Antarctic Service (BAS) in the southern North Sea in 2019. CH4 emission rates from offshore gas installations were derived by applying the well-established mass balance method. They were then compared with direct operator-reporting, estimates from regional point source inventories and a globally gridded inventory, which uses national reported emissions in the framework of the United Nations Framework Convention on Climate Change (UNFCCC) and ...