@article{b33dc527e6e64fd69c5ad501ba03db0c,
title = "Interlaboratory comparison of δ13C and δd measurements of atmospheric CH4 for combined use of data sets from different laboratories",
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.",
author = "Taku Umezawa and Brenninkmeijer, {Carl A.M.} and Thomas R{\"o}ckmann and {Van Der Veen}, Carina and Tyler, {Stanley C.} and Ryo Fujita and Shinji Morimoto and Shuji Aoki and Todd Sowers and Jochen Schmitt and Michael Bock and Jonas Beck and Hubertus Fischer and Michel, {Sylvia E.} and Vaughn, {Bruce H.} and Miller, {John B.} and White, {James W.C.} and Gordon Brailsford and Hinrich Schaefer and Peter Sperlich and Brand, {Willi A.} and Michael Rothe and Thomas Blunier and David Lowry and Fisher, {Rebecca E.} and Nisbet, {Euan G.} and Rice, {Andrew L.} and Peter Bergamaschi and Cordelia Veidt and Ingeborg Levin",
note = "Funding Information: Acknowledgements. We thank Morimasa Sato for measurements at TU. We thank Owen Sherwood for his contribution in setting up the INSTAAR measurement system and Ken Masarie and John Mund, who developed software enabling data comparisons from co-located samples measured by INSTAAR, RHUL and NIWA. We thank Paul Quay (UW) for isotopic CH4 data and intercalibration information and Doaa Teama for isotopic measurements at PDX. We thank C{\'e}lia Sapart for helpful information about the past intercomparison. Part of this work at NIES was supported by the Environment Research and Technology Development Fund (2-1710) of the Ministry of the Environment, Japan and Environmental Restoration and Conservation Agency. Funding for work at PDX was provided by the US National Science Foundation (Atmospheric and Geospace Sciences Grant 0952307). CH4 isotope ice core work at UB received funding from the European Research Council under the European Union{\textquoteright}s Seventh Framework Programme (FP7/2007-2013) ERC grant agreement no. 226172 and the Swiss National Science Foundation (grant no. 200020_159563 & 20020_172506). NIWA{\textquoteright}s isotope measurements are funded under the Climate and Atmosphere Research Programme CAAC1804 (2017/18 SCI). We are grateful to the referee Sergey Assonov and one anonymous referee for their insightful and constructive comments for improving this paper. Publisher Copyright: {\textcopyright} Author(s) 2018. This work is distributed under the Creative Commons Attribution 4.0 License.",
year = "2018",
month = mar,
day = "2",
doi = "10.5194/amt-11-1207-2018",
language = "English (US)",
volume = "11",
pages = "1207--1231",
journal = "Atmospheric Measurement Techniques",
issn = "1867-1381",
publisher = "Copernicus Gesellschaft mbH",
number = "2",
}