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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/acp-2020-308
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2020-308
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 24 Apr 2020

Submitted as: research article | 24 Apr 2020

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This preprint is currently under review for the journal ACP.

On the role of trend and variability of hydroxyl radical (OH) in the global methane budget

Yuanhong Zhao1, Marielle Saunois1, Philippe Bousquet1, Xin Lin1,a, Antoine Berchet1, Michaela I. Hegglin2, Josep G. Canadell3, Robert B. Jackson4, Makoto Deushi5, Patrick Jöckel6, Douglas Kinnison7, Ole Kirner8, Sarah Strode9,10, Simone Tilmes11, Edward J. Dlugokencky12, and Bo Zheng1 Yuanhong Zhao et al.
  • 1Laboratoire des Sciences du Climat et de l'Environnement, LSCE-IPSL (CEA–CNRS–UVSQ), Université Paris-Saclay, 91191 Gif-sur-Yvette, France
  • 2Department of Meteorology, University of Reading, Earley Gate, Reading RG6 6BB, United Kingdom
  • 3Global Carbon Project, CSIRO Oceans and Atmosphere, Canberra, Australian Capital Territory 2601, Australia
  • 4Earth System Science Department, Woods Institute for the Environment, and Precourt Institute for Energy, Stanford University, Stanford, CA 94305, USA
  • 5Meteorological Research Institute, 1-1 Nagamine, Tsukuba, Ibaraki, 305-0052, Japan
  • 6Deutsches Zentrum für Luft- und Raumfahrt (DLR), Institut für Physik der Atmosphäre, Oberpfaffenhofen, Germany
  • 7Atmospheric Chemistry Observations and Modeling Laboratory, National Center for Atmospheric Research, 3090 Center Green Drive, Boulder, CO, 80301, USA
  • 8Steinbuch Centre for Computing, Karlsruhe Institute of Technology, Karlsruhe, Germany
  • 9NASA Goddard Space Flight Center, Greenbelt, MD, USA
  • 10Universities Space Research Association (USRA), GESTAR, Columbia, MD, USA
  • 11National Center for Atmospheric Research, Boulder, CO, USA
  • 12Global Monitoring Division, NOAA Earth System Research Laboratory, Boulder, CO
  • anow at: Climate and Space Sciences and Engineering, University of Michigan, Ann Arbor, MI 48109, USA

Abstract. Decadal trends and interannual variations in the hydroxyl radical (OH), while poorly constrained at present, are critical for understanding the observed evolution of atmospheric methane (CH4). Through analyzing the OH fields simulated by the model ensemble of the Chemistry–Climate Model Initiative (CCMI), we find (1) the negative OH anomalies during the El Niño years mainly corresponding to the enhanced carbon monoxide (CO) emissions from biomass burning and (2) a positive OH trend during 1980–2010 dominated by the elevated primary production and the reduced loss of OH due to decreasing CO after 2000. Both two-box model inversions and variational 4D inversions suggest that ignoring the negative anomaly of OH during the El Niño years leads to a large overestimation of the increase in global CH4 emissions by up to 10 Tg yr−1 to match the observed CH4 increase over these years. Not accounting for the increasing OH trends given by the CCMI models leads to an underestimation of the CH4 emission increase by ~ 23 Tg yr−1 from 1986 to 2010. The variational inversion estimated CH4 emissions show that the tropical regions contribute most to the uncertainties related to OH. This study highlights the significant impact of climate and chemical feedbacks related to OH on the top-down estimates of the global CH4 budget.

Yuanhong Zhao et al.

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Short summary
Decadal trends and variations in the OH are critical for understanding the atmospheric CH4 evolution. We quantify the impacts of OH trends and variations on the CH4 budget by conducting CH4 inversions on decadal-scale with an ensemble of OH fields. We find the negative OH anomalies due to enhanced fires can reduce the optimized CH4 emissions by up to 10 Tg yr−1 during El Niño years, and the positive OH trend from 1986 to 2010 results in ~ 23 Tg yr−1 additional increase in optimized CH4 emissions.
Decadal trends and variations in the OH are critical for understanding the atmospheric CH4...
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