Browsing by Author "Graven, H"

Now showing 1 - 2 of 2
  • Thumbnail Image
    Item
    Global fossil methane emissions constrained by multi-isotopic atmospheric methane histories.
    (American Geophysical Union, 2025-02-28) Fujita, T; Graven, H; Zazzeri, G; Hmiel, B; Petrenko, VV; Smith, AM; Michel, SE; Morimoto, S
    The global CH4 budget of sources and sinks is highly uncertain, particularly the emissions from specific sources such as fossil fuels (FF) or agriculture. Here, we estimate plausible global CH4 source and sink scenarios using historical observations and simulations of atmospheric CH4 mole fraction and its stable isotopic (δ13C-CH4, δD-CH4) and radiocarbon (Δ14C-CH4) composition, combining constraints from all these tracers for the first time. We employ a one-box model along with a Monte Carlo particle filter technique, explicitly exploring the impact of each isotopic constraints and uncertainties in prior CH4 source and sink parameters on posterior sectorial source fractions. We find our posterior anthropogenic FF emissions at the global scale are 30% lower than previous isotope-based studies. Our analysis suggests previous δ13C-CH4-based studies are potentially biased because the current database-derived estimate of the global mean biogenic δ13C-CH4 source signature is too low and/or current sink-weighted total carbon kinetic isotope effect is underestimated. We find modern atmospheric Δ14C-CH4 data constrains lower global FF emissions after 1980s, which is contrary to the most recent finding that utilized atmospheric Δ14C-CH4 data, but supported by an independent estimate of global nuclear 14CH4 emissions. Our multi-isotopic constraints align with CH4-only inversion results, while reducing their uncertainties with greater robustness against different prior emission scenarios. We find strong constraints not only on FF emissions but also other key sources and sinks, showing that long-term multi-isotopic observations are critical for refining the global CH4 budget and developing effective CH4 emission mitigation strategies. © 2025. The Author(s). This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.
  • No Thumbnail Available
    Item
    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.