Browsing by Author "Turnbull, J"

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    Compatibility of atmospheric 14CO2 measurements: comparing the heidelberg low-level counting facility to international accelerator mass spectrometry (AMS) laboratories
    (Cambridge University Press, 2016-09-19) Hammer, S; Friedrich, R; Kromer, B; Cherkinsky, A; Lehman, SJ; Meijer, HAJ; Nakamura, T; Palonen, V; Reimer, RW; Smith, AM; Southen, JR; Szidat, S; Turnbull, J; Uchida, M
    Combining atmospheric Δ14CO2 data sets from different networks or laboratories requires secure knowledge on their compatibility. In the present study, we compare Δ14CO2 results from the Heidelberg low-level counting (LLC) laboratory to 12 international accelerator mass spectrometry (AMS) laboratories using distributed aliquots of five pure CO2 samples. The averaged result of the LLC laboratory has a measurement bias of –0.3±0.5‰ with respect to the consensus value of the AMS laboratories for the investigated atmospheric Δ14C range of 9.6 to 40.4‰. Thus, the LLC measurements on average are not significantly different from the AMS laboratories, and the most likely measurement bias is smaller than the World Meteorological Organization (WMO) interlaboratory compatibility goal for Δ14CO2 of 0.5‰. The number of intercomparison samples was, however, too small to determine whether the measurement biases of the individual AMS laboratories fulfilled the WMO goal. © 2016 by the Arizona Board of Regents on behalf of the University of Arizona
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    Initial results of an intercomparison of AMS-based atmospheric 14CO2 measurements
    (Cambridge University Press, 2016-02-16) Miller, J; Lehman, SJ; Wolak, C; Turnbull, J; Dunn, G; Graven, H; Keeling, RF; Meijer, HAJ; Aerts-Bijma, AT; Palstra, SWL; Smith, AM; Allison, CE; Southon, J; Xu, XM; Nakazawa, T; Aoki, S; Nakamura, T; Guilderson, TP; LaFranchi, B; Mukai, M; Terao, Y; Uchida, M; Kondo, M
    This article presents results from the first 3 rounds of an international intercomparison of measurements of Δ14CO2 in liter-scale samples of whole air by groups using accelerator mass spectrometry (AMS). The ultimate goal of the intercomparison is to allow the merging of Δ14CO2 data from different groups, with the confidence that differences in the data are geophysical gradients and not artifacts of calibration. Eight groups have participated in at least 1 round of the intercomparison, which has so far included 3 rounds of air distribution between 2007 and 2010. The comparison is intended to be ongoing, so that: a) the community obtains a regular assessment of differences between laboratories; and b) individual laboratories can begin to assess the long-term repeatability of their measurements of the same source air. Air used in the intercomparison was compressed into 2 high-pressure cylinders in 2005 and 2006 at Niwot Ridge, Colorado (USA), with one of the tanks "spiked" with fossil CO2, so that the 2 tanks span the range of Δ14CO2 typically encountered when measuring air from both remote background locations and polluted urban ones. Three groups show interlaboratory comparability within 1‰ for ambient level Δ14CO2. For high CO2/low Δ14CO2 air, 4 laboratories showed comparability within 2‰. This approaches the goals set out by the World Meteorological Organization (WMO) CO2 Measurements Experts Group in 2005. One important observation is that single-sample precisions typically reported by the AMS community cannot always explain the observed differences within and between laboratories. This emphasizes the need to use long-term repeatability as a metric for measurement precision, especially in the context of long-term atmospheric monitoring. © 2013 by the Arizona Board of Regents on behalf of the University of Arizona.