Preprints
https://doi.org/10.5194/acp-2021-734
https://doi.org/10.5194/acp-2021-734

  15 Sep 2021

15 Sep 2021

Review status: this preprint is currently under review for the journal ACP.

Quantifying fossil fuel methane emissions using observations of atmospheric ethane and an uncertain emission ratio

Alice E. Ramsden1, Anita L. Ganesan1, Luke M. Western2, Matthew Rigby2, Alistair J. Manning3, Amy Foulds4, James L. France5, Patrick Barker4, Peter Levy6, Daniel Say2, Adam Wisher2, Tim Arnold7,8, Chris Rennick7, Kieran M. Stanley9, Dickon Young2, and Simon O'Doherty2 Alice E. Ramsden et al.
  • 1School of Geographical Sciences, University of Bristol, Bristol, UK
  • 2School of Chemistry, University of Bristol, Bristol, UK
  • 3Met Office Hadley Centre, Exeter, UK
  • 4School of Earth and Environmental Sciences, University of Manchester, Manchester, UK
  • 5Department of Earth Sciences, Royal Holloway, University of London, Egham, UK
  • 6UK Centre for Ecology and Hydrology, Edinburgh, UK
  • 7National Physical Laboratory, Teddington, UK
  • 8School of Geosciences, University of Edinburgh, Edinburgh, UK
  • 9Institute for Atmospheric and Environmental Science, Goethe University Frankfurt, Frankfurt am Main, Germany

Abstract. 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.

Alice E. Ramsden et al.

Status: open (until 13 Nov 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Alice E. Ramsden et al.

Data sets

EDGAR v5.0 methane inventory Team EDGAR https://edgar.jrc.ec.europa.eu/dataset_ghg50

MOYA FAAM aircraft observations FAAM Team https://catalogue.ceda.ac.uk/uuid/dd2b03d085c5494a8cbfc6b4b99ca702

UK Greenhouse Gas Model Peter Levy https://github.com/NERC-CEH/ukghg

Methane observations from UK DECC network sites Daniel Say, Adam Wisher, Tim Arnold, Chris Rennick, Kieran Stanley, Dickon Young, Simon O'Doherty https://catalogue.ceda.ac.uk

Methane observations from AGAGE Mace Head site Daniel Say, Adam Wisher, Tim Arnold, Chris Rennick, Kieran Stanley, Dickon Young, Simon O'Doherty http://agage.mit.edu/data

Model code and software

Tracer inverse model Alice E Ramsden https://doi.org/10.17605/OSF.IO/VH8ND

Alice E. Ramsden et al.

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Short summary
Quantifying methane emissions from different sources is a key focus of current research. We present a method for estimating sectoral methane emissions that uses ethane as a tracer for fossil fuel methane. By incorporating variable ethane:methane emission ratios into this model, we produce emissions estimates with improved uncertainty characterisation. This method will be particularly useful for studying methane emissions in areas with complex distributions of sources.
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