Articles | Volume 11, issue 2
Atmos. Meas. Tech., 11, 1207–1231, 2018
Atmos. Meas. Tech., 11, 1207–1231, 2018

Research article 02 Mar 2018

Research article | 02 Mar 2018

Interlaboratory comparison of δ13C and δD measurements of atmospheric CH4 for combined use of data sets from different laboratories

Taku Umezawa1,2, Carl A. M. Brenninkmeijer1, Thomas Röckmann3, Carina van der Veen3, Stanley C. Tyler4,5, Ryo Fujita6, Shinji Morimoto6,7, Shuji Aoki6, Todd Sowers8, Jochen Schmitt9, Michael Bock9, Jonas Beck9, Hubertus Fischer9, Sylvia E. Michel10, Bruce H. Vaughn10, John B. Miller10, James W. C. White10, Gordon Brailsford11, Hinrich Schaefer11, Peter Sperlich11, Willi A. Brand12, Michael Rothe12, Thomas Blunier13, David Lowry14, Rebecca E. Fisher14, Euan G. Nisbet14, Andrew L. Rice15, Peter Bergamaschi16, Cordelia Veidt17, and Ingeborg Levin17 Taku Umezawa et al.
  • 1Max Planck Institute for Chemistry, Atmospheric Chemistry Department, 55128 Mainz, Germany
  • 2Center for Environmental Measurement and Analysis, National Institute for Environmental Studies, Tsukuba 305-8506, Japan
  • 3Institute for Marine and Atmospheric research Utrecht, Utrecht University, Utrecht, the Netherlands
  • 4Earth System Science Department, University of California, Irvine, USA
  • 5Chemistry Department, Norco College, Norco, CA 92860, USA
  • 6Center for Atmospheric and Oceanic Studies, Graduate School of Science, Tohoku University, Sendai, Japan
  • 7National Institute of Polar Research, Tokyo, Japan
  • 8The Earth and Environmental Systems Institute, Pennsylvania State University, University Park, Pennsylvania 16802, USA
  • 9Climate and Environmental Physics, Physics Institute and Oeschger Center for Climate Change Research, University of Bern, 3012 Bern, Switzerland
  • 10Institute of Arctic and Alpine Research, University of Colorado Boulder, Boulder, Colorado, USA
  • 11National Institute of Water and Atmospheric Research, Wellington 6021, New Zealand
  • 12Max Planck Institute for Biogeochemistry, 07745 Jena, Germany
  • 13Centre for Ice and Climate, University of Copenhagen, Copenhagen, Denmark
  • 14Department of Earth Sciences, Royal Holloway, University of London, Egham, UK
  • 15Department of Physics, Portland State University, Portland, OR 97207, USA
  • 16European Commission Joint Research Centre, Institute for Environment and Sustainability, Ispra (Va), Italy
  • 17Institute for Environmental Physics, Heidelberg University, 69120 Heidelberg, Germany

Abstract. We report results from a worldwide interlaboratory comparison of samples among laboratories that measure (or measured) stable carbon and hydrogen isotope ratios of atmospheric CH4 (δ13C-CH4 and δD-CH4). The offsets among the laboratories are larger than the measurement reproducibility of individual laboratories. To disentangle plausible measurement offsets, we evaluated and critically assessed a large number of intercomparison results, some of which have been documented previously in the literature. The results indicate significant offsets of δ13C-CH4 and δD-CH4 measurements among data sets reported from different laboratories; the differences among laboratories at modern atmospheric CH4 level spread over ranges of 0.5 ‰ for δ13C-CH4 and 13 ‰ for δD-CH4. The intercomparison results summarized in this study may be of help in future attempts to harmonize δ13C-CH4 and δD-CH4 data sets from different laboratories in order to jointly incorporate them into modelling studies. However, establishing a merged data set, which includes δ13C-CH4 and δD-CH4 data from multiple laboratories with desirable compatibility, is still challenging due to differences among laboratories in instrument settings, correction methods, traceability to reference materials and long-term data management. Further efforts are needed to identify causes of the interlaboratory measurement offsets and to decrease those to move towards the best use of available δ13C-CH4 and δD-CH4 data sets.

Short summary
Isotope measurements are useful for separating different methane sources. However, the lack of widely accepted standards and calibration methods for stable carbon and hydrogen isotopic ratios of methane in air has caused significant measurement offsets among laboratories. We conducted worldwide interlaboratory comparisons, surveyed the literature and assessed them systematically. This study may be of help in future attempts to harmonize data sets of isotopic composition of atmospheric methane.