Articles | Volume 18, issue 2
Atmos. Chem. Phys., 18, 901–920, 2018
Atmos. Chem. Phys., 18, 901–920, 2018

Research article 25 Jan 2018

Research article | 25 Jan 2018

Inverse modelling of European CH4 emissions during 2006–2012 using different inverse models and reassessed atmospheric observations

Peter Bergamaschi1, Ute Karstens2,3, Alistair J. Manning4, Marielle Saunois5, Aki Tsuruta6, Antoine Berchet5,7, Alexander T. Vermeulen3,8, Tim Arnold4,9,10, Greet Janssens-Maenhout1, Samuel Hammer11, Ingeborg Levin11, Martina Schmidt11, Michel Ramonet5, Morgan Lopez5, Jost Lavric2, Tuula Aalto6, Huilin Chen12,13, Dietrich G. Feist2, Christoph Gerbig2, László Haszpra14,15, Ove Hermansen16, Giovanni Manca1, John Moncrieff10, Frank Meinhardt17, Jaroslaw Necki18, Michal Galkowski18, Simon O'Doherty19, Nina Paramonova20, Hubertus A. Scheeren12, Martin Steinbacher7, and Ed Dlugokencky21 Peter Bergamaschi et al.
  • 1European Commission Joint Research Centre, Ispra (Va), Italy
  • 2Max Planck Institute for Biogeochemistry, Jena, Germany
  • 3ICOS Carbon Portal, ICOS ERIC, University of Lund, Lund, Sweden
  • 4Met Office Exeter, Devon, UK
  • 5Laboratoire des Sciences du Climat et de l'Environnement (LSCE-IPSL), CEA-CNRS-UVSQ, Université Paris-Saclay, 91191 Gif-sur-Yvette, France
  • 6Finnish Meteorological Institute (FMI), Helsinki, Finland
  • 7Swiss Federal Laboratories for Materials Science and Technology (Empa), Dübendorf, Switzerland
  • 8Energy research Centre of the Netherlands (ECN), Petten, the Netherlands
  • 9National Physical Laboratory, Teddington, Middlesex, TW11 0LW, UK
  • 10School of GeoSciences, The University of Edinburgh, Edinburgh, EH9 3FF, UK
  • 11Institut für Umweltphysik, Heidelberg University, Heidelberg, Germany
  • 12Center for Isotope Research (CIO), University of Groningen, Groningen, the Netherlands
  • 13Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado, Boulder, CO, USA
  • 14Hungarian Meteorological Service, Budapest, Hungary
  • 15Research Centre for Astronomy and Earth Sciences, Geodetic and Geophysical Institute, Sopron, Hungary
  • 16Norwegian Institute for Air Research (NILU), Kjeller, Norway
  • 17Umweltbundesamt, Messstelle Schauinsland, Kirchzarten, Germany
  • 18AGH University of Science and Technology, Krakow, Poland
  • 19Atmospheric Chemistry Research Group, University of Bristol, Bristol, UK
  • 20Voeikov Main Geophysical Observatory, St. Petersburg, Russia
  • 21NOAA Earth System Research Laboratory, Global Monitoring Division, Boulder, CO, USA

Abstract. We present inverse modelling (top down) estimates of European methane (CH4) emissions for 2006–2012 based on a new quality-controlled and harmonised in situ data set from 18 European atmospheric monitoring stations. We applied an ensemble of seven inverse models and performed four inversion experiments, investigating the impact of different sets of stations and the use of a priori information on emissions.

The inverse models infer total CH4 emissions of 26.8 (20.2–29.7) Tg CH4 yr−1 (mean, 10th and 90th percentiles from all inversions) for the EU-28 for 2006–2012 from the four inversion experiments. For comparison, total anthropogenic CH4 emissions reported to UNFCCC (bottom up, based on statistical data and emissions factors) amount to only 21.3 Tg CH4 yr−1 (2006) to 18.8 Tg CH4 yr−1 (2012). A potential explanation for the higher range of top-down estimates compared to bottom-up inventories could be the contribution from natural sources, such as peatlands, wetlands, and wet soils. Based on seven different wetland inventories from the Wetland and Wetland CH4 Inter-comparison of Models Project (WETCHIMP), total wetland emissions of 4.3 (2.3–8.2) Tg CH4 yr−1 from the EU-28 are estimated. The hypothesis of significant natural emissions is supported by the finding that several inverse models yield significant seasonal cycles of derived CH4 emissions with maxima in summer, while anthropogenic CH4 emissions are assumed to have much lower seasonal variability. Taking into account the wetland emissions from the WETCHIMP ensemble, the top-down estimates are broadly consistent with the sum of anthropogenic and natural bottom-up inventories. However, the contribution of natural sources and their regional distribution remain rather uncertain.

Furthermore, we investigate potential biases in the inverse models by comparison with regular aircraft profiles at four European sites and with vertical profiles obtained during the Infrastructure for Measurement of the European Carbon Cycle (IMECC) aircraft campaign. We present a novel approach to estimate the biases in the derived emissions, based on the comparison of simulated and measured enhancements of CH4 compared to the background, integrated over the entire boundary layer and over the lower troposphere. The estimated average regional biases range between −40 and 20 % at the aircraft profile sites in France, Hungary and Poland.

Short summary
European methane (CH4) emissions are estimated for 2006–2012 using atmospheric in situ measurements from 18 European monitoring stations and 7 different inverse models. Our analysis highlights the potential significant contribution of natural emissions from wetlands (including peatlands and wet soils) to the total European emissions. The top-down estimates of total EU-28 CH4 emissions are broadly consistent with the sum of reported anthropogenic CH4 emissions and the estimated natural emissions.
Final-revised paper