Atmospheric methane is an important greenhouse gas that is emitted from a diverse range of anthropogenic and natural sources. Quantifying and attributing methane emissions can provide information on the sources that are driving the increases in atmospheric methane concentrations and be used to guide mitigation policies. In this thesis, I use, develop and compare different approaches for attributing specific sources and quantifying emissions of methane in the UK. The work in this thesis uses carbon isotopes of methane and satellite observations of total methane columns (XCH4) from the TROPOSpheric Monitoring Instrument (TROPOMI) between 2018-2020.

Urban areas are hotspots of anthropogenic methane emissions, which are emitted from a number of different sources. I use in situ atmospheric methane and d13CH4 measurements made in central London to demonstrate that continuous measurements from a Picarro isotopic analyser can be used for methane source attribution of large pollution events. These measurements indicated a predominance of fossil methane in central London which was found to be underreported in the UK national emissions inventory. The utility of additional isotopic measurements of atmospheric D14CH4 is explored for the UK by developing a CH4-d13CH4-D14CH4
framework and using pseudo-data simulations. Pseudo-data indicate additional isotopic measurements of D14CH4 could improve the UK's methane source apportionment. A first analysis of TROPOMI methane measurements for the UK is also conducted. I conclude that TROPOMI XCH4 retrievals from 2018-2020 are not useful for informing on UK methane emissions and spatial variations due, in part, to the low data availability for the UK over this period.

My findings indicate that ground-based atmospheric measurements are more useful for constraining sector specific methane emissions and informing on regional differences than TROPOMI measurements for the UK. Whilst d13CH4 measurements are found to be valuable for source attribution, additional measurements of atmospheric D14CH4 could be used to improve the methane source constraint for the UK.