Interlaboratory comparison of δ13C and δD measurements of atmospheric CH 4 for combined use of data sets from different laboratories

Umezawa, Taku; Brenninkmeijer, Carl A. M.; Röckmann, Thomas; van der Veen, Carina; Tyler, Stanley C.; Fujita, Ryo; Morimoto, Shinji; Aoki, Shuji; Sowers, Todd; Schmitt, Jochen; Bock, Michael; Beck, Jonas; Fischer, Hubertus; Michel, Sylvia E.; Vaughn, Bruce H.; Miller, John B.; White, James W. C.; Brailsford, Gordon; Schaefer, Hinrich; Sperlich, Peter; Brand, Willi A.; Rothe, Michael; Blunier, Thomas; Lowry, David; Fisher, Rebecca E.; Nisbet, Euan G.; Rice, Andrew L.; Bergamaschi, Peter; Veidt, Cordelia; Levin, Ingeborg

We report results from a worldwide interlaboratory comparison of samples among laboratories that measure (or measured) stable carbon and hydrogen isotope ratios of atmospheric CH 4 ( δ13C-CH 4 and δD-CH 4). 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-CH 4 and δD-CH 4 measurements among data sets reported from different laboratories; the differences among laboratories at modern atmospheric CH 4 level spread over ranges of 0.5 ‰ for δ13C-CH 4 and 13 ‰ for δD-CH 4. The intercomparison results summarized in this study may be of help in future attempts to harmonize δ13C-CH 4 and δD-CH 4 data sets from different laboratories in order to jointly incorporate them into modelling studies. However, establishing a merged data set, which includes δ13C-CH 4 and δD-CH 4 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-CH 4 and δD-CH 4 data sets.

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Umezawa, Taku / Brenninkmeijer, Carl A. M. / Röckmann, Thomas / et al: Interlaboratory comparison of δ13C and δD measurements of atmospheric CH4 for combined use of data sets from different laboratories. 2018. Copernicus Publications.

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