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Model simulations of atmospheric methane (1997--2016) and their evaluation using NOAA and AGAGE surface and IAGOS-CARIBIC aircraft observations

Zimmermann, Peter. H. and Brenninkmeijer, Carl. A. M. and Pozzer, Andrea and Jöckel, Patrick and Winterstein, Franziska and Zahn, Andreas and Houweling, Sander and Lelieveld, Jos (2020) Model simulations of atmospheric methane (1997--2016) and their evaluation using NOAA and AGAGE surface and IAGOS-CARIBIC aircraft observations. Atmospheric Chemistry and Physics (ACP), 20 (9), pp. 5787-5809. Copernicus Publications. doi: 10.5194/acp-20-5787-2020. ISSN 1680-7316.

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Official URL: https://www.atmos-chem-phys.net/20/5787/2020/


Methane (CH4) is an important greenhouse gas, and its atmospheric budget is determined by interacting sources and sinks in a dynamic global environment. Methane observations indicate that after almost a decade of stagnation, from 2006, a sudden and continuing global mixing ratio increase took place. We applied a general circulation model to simulate the global atmospheric budget, variability, and trends of methane for the period 1997–2016. Using interannually constant CH4 a priori emissions from 11 biogenic and fossil source categories, the model results are compared with observations from 17 Advanced Global Atmospheric Gases Experiment (AGAGE) and National Oceanic and Atmospheric Administration (NOAA) surface stations and intercontinental Civil Aircraft for the Regular observation of the atmosphere Based on an Instrumented Container (CARIBIC) flights, with > 4800 CH4 samples, gathered on > 320 flights in the upper troposphere and lowermost stratosphere. Based on a simple optimization procedure, methane emission categories have been scaled to reduce discrepancies with the observational data for the period 1997–2006. With this approach, the all-station mean dry air mole fraction of 1780 nmol mol−1 could be improved from an a priori root mean square deviation (RMSD) of 1.31 % to just 0.61 %, associated with a coefficient of determination (R2) of 0.79. The simulated a priori interhemispheric difference of 143.12 nmol mol−1 was improved to 131.28 nmol mol−1, which matched the observations quite well (130.82 nmol mol−1). Analogously, aircraft measurements were reproduced well, with a global RMSD of 1.1 % for the measurements before 2007, with even better results on a regional level (e.g., over India, with an RMSD of 0.98 % and R2=0.65). With regard to emission optimization, this implied a 30.2 Tg CH4 yr−1 reduction in predominantly fossil-fuel-related emissions and a 28.7 Tg CH4 yr−1 increase of biogenic sources. With the same methodology, the CH4 growth that started in 2007 and continued almost linearly through 2013 was investigated, exploring the contributions by four potential causes, namely biogenic emissions from tropical wetlands, from agriculture including ruminant animals, and from rice cultivation, and anthropogenic emissions (fossil fuel sources, e.g., shale gas fracking) in North America. The optimization procedure adopted in this work showed that an increase in emissions from shale gas (7.67 Tg yr−1), rice cultivation (7.15 Tg yr−1), and tropical wetlands (0.58 Tg yr−1) for the period 2006–2013 leads to an optimal agreement (i.e., lowest RMSD) between model results and observations.

Item URL in elib:https://elib.dlr.de/134942/
Document Type:Article
Title:Model simulations of atmospheric methane (1997--2016) and their evaluation using NOAA and AGAGE surface and IAGOS-CARIBIC aircraft observations
AuthorsInstitution or Email of AuthorsAuthor's ORCID iD
Zimmermann, Peter. H.MPI für Chemie, MainzUNSPECIFIED
Brenninkmeijer, Carl. A. M.MPI für Chemie, MainzUNSPECIFIED
Pozzer, AndreaMPI für Chemie, Mainzhttps://orcid.org/0000-0003-2440-6104
Jöckel, PatrickDLR, IPAhttps://orcid.org/0000-0002-8964-1394
Winterstein, FranziskaDLR, IPAhttps://orcid.org/0000-0002-2406-4936
Zahn, AndreasMPI für Chemie, MainzUNSPECIFIED
Houweling, SanderSRON, Utrecht, Niederlandehttps://orcid.org/0000-0002-6189-1009
Lelieveld, JosMPI für Chemie, Mainzhttps://orcid.org/0000-0001-6307-3846
Date:14 May 2020
Journal or Publication Title:Atmospheric Chemistry and Physics (ACP)
Refereed publication:Yes
Open Access:Yes
Gold Open Access:Yes
In ISI Web of Science:Yes
Page Range:pp. 5787-5809
Publisher:Copernicus Publications
Keywords:EMAC, MESSy, Methane, hydroxyl radical, CARIBIC, IAGOS atmospheric methane, modelling
HGF - Research field:Aeronautics, Space and Transport
HGF - Program:Space
HGF - Program Themes:Earth Observation
DLR - Research area:Raumfahrt
DLR - Program:R EO - Earth Observation
DLR - Research theme (Project):R - Atmospheric and climate research, R - Project Climatic relevance of atmospheric tracer gases, aerosols and clouds
Location: Oberpfaffenhofen
Institutes and Institutions:Institute of Atmospheric Physics > Earth System Modelling
Deposited By: Jöckel, Dr. Patrick
Deposited On:15 May 2020 17:16
Last Modified:15 May 2020 17:16

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