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- Title
Methane Source Attribution in the UK Using Multi‐Year Records of CH<sub>4</sub> and δ<sup>13</sup>C.
- Authors
Woolley Maisch, Ceres A.; Fisher, Rebecca E.; France, James L.; Lowry, David; Lanoisellé, Mathias; Bell, Thomas G.; Forster, Grant; Manning, Alistair J.; Michel, Sylvia E.; Ramsden, Alice E.; Yang, Mingxi; Nisbet, Euan G.
- Abstract
Isotopic measurements of atmospheric methane are valuable for the verification of bottom‐up atmospheric emissions inventories. The balance of sources in emissions inventories must be consistent with the δ13C‐CH4 isotopic record in the air. Long‐term records of both methane mole fraction and δ13C from five sites across the UK are presented, showing post‐2007 growth in CH4 and negative trend in δ13C, consistent with global background sites. Miller‐Tans analyses of atmospheric measurements identified that the δ13C signature of the methane source mix varied between −50.1 and −56.1‰, with less depleted δ13C signatures at sites receiving air from urban areas, consistent with an increased proportion of thermogenic sources. Isotopic signatures calculated for all sites are more enriched than those expected from the bottom‐up emissions inventory, suggesting that inventories for the UK either underestimate contributions of thermogenic/pyrogenic emissions or overestimate biogenic sources. Plain Language Summary: Methane is a powerful greenhouse gas. The UK has committed to net zero carbon emissions by 2050 and has signed the Global Methane Pledge, which aims to reduce methane emissions by 30% by 2030, compared to 2020 levels. This study analyses long‐term measurements of methane and its carbon isotope ratio (δ13C) collected by Royal Holloway, University of London, across five UK sites. The δ13C source signature value acts as a fingerprint, distinguishing between different sources of methane. Bulk regional isotopic source signatures for each site were calculated, showing that urban sites are dominated by thermogenic emissions (e.g., gas leaks) and rural sites by agricultural emissions (e.g., cattle). The data presented in this study are compared with data from the UK National Atmospheric Emissions Inventory (NAEI). According to the data that were collected by Royal Holloway, University of London, the NAEI underestimates the relative contribution of fossil fuel sources in the UK, such as gas from pipelines in domestic and industrial settings, or overestimates biogenic sources. This has important implications for the design of UK greenhouse gas reduction strategies. Key Points: Long‐term records of CH4 mole fraction and δ13C‐CH4 from five UK sites show an increase in CH4 and a decrease in δ13CThe Miller‐Tans method can be used to calculate bulk regional δ13C‐CH4 source signaturesThe relative contribution of thermogenic/pyrogenic emissions across the UK may be underestimated in inventories
- Subjects
UNITED Kingdom; GREENHOUSE gas mitigation; ATMOSPHERIC methane; EMISSION inventories; METHANE; GREENHOUSE gases
- Publication
Journal of Geophysical Research. Atmospheres, 2023, Vol 128, Issue 21, p1
- ISSN
2169-897X
- Publication type
Article
- DOI
10.1029/2023JD039098