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© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 18 Dec 2018

Research article | 18 Dec 2018

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Estimates of sub-national methane emissions from inversion modelling

Sarah Connors1,a, Alistair J. Manning2, Andrew D. Robinson1, Stuart N. Riddick1,b, Grant L. Forster3, Anita Ganesan4, Aoife Grant5, Stephen Humphrey3, Simon O'Doherty5, Dave E. Oram3, Paul I. Palmer6, Robert L. Skelton7, Kieran Stanley5, Ann Stavert5,c, Dickon Young5, and Neil R. P. Harris8 Sarah Connors et al.
  • 1Centre for Atmospheric Science, University of Cambridge, Cambridge, UK
  • 2Met Office, Exeter, UK
  • 3National Centre for Atmospheric Science (NCAS), School of Environmental Sciences, University of East Anglia, Norwich, UK
  • 4School of Geographical Sciences, University of Bristol
  • 5School of Chemistry, University of Bristol, Bristol, UK
  • 6School of GeoSciences, University of Edinburgh, Edinburgh, UK
  • 7Department of Engineering, University of Cambridge, Cambridge, UK
  • 8Centre for Environmental and Informatics, Cranfield University, Cranfield, UK
  • anow at: Université Paris Saclay, Paris, 91120, France
  • bnow at: Department of Civil and Environmental Engineering, Princeton University, NJ 08540, USA
  • cnow at: CSIRO, Oceans and Atmosphere, Aspendale, Australia

Abstract. Methane is a strong contributor to global climate change, yet our current understanding and quantification of its sources and their variability is incomplete. There is a growing need for comparisons between emission estimates produced using bottom-up inventory approaches and top-down inversion techniques based on atmospheric measurements, especially at higher spatial resolutions. To meet this need, this study presents using an inversion approach based on the Inversion Technique for Emissions Modelling (InTEM) framework and measurements from four sites in East Anglia, United Kingdom. Atmospheric methane concentrations were recorded at 1–2 minute time-steps at each location within the region of interest. These observations, coupled with the UK Met Office's Lagrangian particle dispersion model, NAME (Numerical Atmospheric dispersion Modelling Environment), were used within InTEM2014 to produce methane emission estimates for a 1-year period (June 2013–May 2014) in this eastern region of the UK (~ 100 × 150 km) at high spatial resolution (up to 4 × 4 km). InTEM2014 was able to produce realistic emissions estimates for East Anglia, and highlighted potential areas of difference from the UK National Atmospheric Emissions Inventory (NAEI). As this study was part of the UK Greenhouse gAs Uk and Global Emissions (GAUGE) project, observations were included within a national inversion using all eleven measurement sites across the UK to directly compare emission estimates for the East Anglia Region. Results show similar methane estimates for the East Anglia region. Methane emissions from Norfolk and Suffolk show good agreement with the estimates in NAEI, with differences of ~ 5 %. Larger differences are found for Cambridgeshire where our estimate is 22.5 % lower than that of NAEI. The addition of the EA sites within the national inversion system enabled finer spatial resolution and a decrease in the associated uncertainty for that area. Further development of our approach to include a more robust analysis of the methane concentration in the air entering this region and the uncertainty associated with the resulting emissions would strengthen this inverse method. Nonetheless, our results show there is value in high spatial resolution measurement networks and the resulting inversion emission estimates.

Sarah Connors et al.
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Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Sarah Connors et al.
Sarah Connors et al.
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Publications Copernicus
Short summary
Methane is an important greenhouse gas & reducing its emissions is a vital part of climate change mitigation to limit global temperature increase to 1.5 °C or 2.0 °C. This paper explains a way to estimate emitted methane over a sub-national area by combining measurements & computer dispersion modelling in a so-called inversion technique. Compared with the current national inventory, our results show lower emissions for Cambridgeshire, possibly due to waste sector emission differences.
Methane is an important greenhouse gas & reducing its emissions is a vital part of climate...