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Quantifying fossil fuel methane emissions using observations of atmospheric ethane and an uncertain emission ratio [in review]

Ramsden, Alice E.; Ganesan, Anita L.; Western, Luke M.; Rigby, Matthew; Manning, Alistair J.; Foulds, Amy; France, James L. ORCID: https://orcid.org/0000-0002-8785-1240; Barker, Patrick; Levy, Peter; Say, Daniel; Wisher, Adam; Arnold, Tim; Rennick, Chris; Stanley, Kieran M.; Young, Dickon; O'Doherty, Simon. 2021 Quantifying fossil fuel methane emissions using observations of atmospheric ethane and an uncertain emission ratio [in review]. Atmospheric Chemistry and Physics Discussions. https://doi.org/10.5194/acp-2021-734

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Abstract/Summary

We present a method for estimating fossil fuel methane emissions using observations of methane and ethane, accounting for uncertainty in their emission ratio. The ethane:methane emission ratio is incorporated as a variable parameter in a Bayesian model, with its own prior distribution and uncertainty. We find that using an emission ratio distribution mitigates bias from using a fixed, potentially incorrect emission ratio and that uncertainty in this ratio is propagated into posterior estimates of emissions. A synthetic data test is used to show the impact of assuming an incorrect ethane:methane emission ratio and demonstrate how our variable parameter model can better quantify overall uncertainty. We also use this method to estimate UK methane emissions from high-frequency observations of methane and ethane from the UK Deriving Emissions linked to Climate Change (DECC) network. Using the joint methane-ethane inverse model, we estimate annual mean UK methane emissions of approximately 0.27 (95 % uncertainty interval 0.26–0.29) Tg per year from fossil fuel sources and 2.06 (1.99–2.15) Tg per year from non-fossil fuel sources, during the period 2015–2019. Uncertainties in UK fossil fuel emissions estimates are reduced on average by 15 %, and up to 35 %, when incorporating ethane into the inverse model, in comparison to results from the methane-only inversion.

Item Type: Publication - Article
Digital Object Identifier (DOI): https://doi.org/10.5194/acp-2021-734
UKCEH and CEH Sections/Science Areas: Atmospheric Chemistry and Effects (Science Area 2017-)
ISSN: 1680-7367
Additional Information. Not used in RCUK Gateway to Research.: Open Access paper - full text available via Official URL link.
NORA Subject Terms: Atmospheric Sciences
Date made live: 20 Oct 2021 11:30 +0 (UTC)
URI: http://nora.nerc.ac.uk/id/eprint/531277

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