Brasseur, G. 

Gaubert, B.

English

MPG.PuRe

RESEARCH HIGHLIGHT National Science Review 12: nwaf347, 2025 https://doi.org/10.1093/nsr/nwaf347Advance access publication 21 August 2025 EARTH SCIENCES The atmospheric oxidizing capacity and the methane budget Guy P. Brasseur1 , ∗ and Benjamin Gaubert 2 T(hp2gagwwgiob(wwacttrtoHtitccCviaos1smlqvations [6 ], ozone profile observations and model simulations (e.g. [7 ,8 ]). The paper by Chen et al. [9 ] specifi- cally addresses the question of the 2020 methane anomaly. From a detailed inves- tigation based on data analysis and mod- eling, the Westlake University researchers conclude that the global mean OH con- centration was ∼4% lower in 2020 compared to 2018–2019 (2.4% in the Northern Hemisphere and 5.7% in the Southern Hemisphere). The authors inferred the tropospheric concentration of OH for each season and for six lati- tude bands using an inversion algorithm that assimilates satellite (MOPITT) observations of the CO column. The explanation proposed by Chen et al. [9 ] for this 2020 anomaly refers to forcing mechanisms that are differ- ent in the two hemispheres. South of the equator, the reduction in OH is at- tributed to an anomalous increase in the CO concentration resulting from the in- tense Australian wildfires, thereby facil- itating a rapid methane growth. North of the equator, the OH decrease is at- tributed to the large decrease in NOx emissions observed during the COVID- 19 pandemic, and hence a reduced re- cycling of OH. From an inverse analy- sis of methane satellite data, the authors determined that the observed 27 TgCH4 a−1 increase in the methane burden, rel- ative to years 2018–2019, results from a 17 TgCH4 a−1 increase in surface emis- sions, and an 18 TgCH4 a−1 reduction in the atmospheric loss by OH, which is partly compensated by an 8 TgCH4 a−1 in- crease in the loss, due to enhancement of the methane concentration. The study by Chen et al. [9 ] highlights the strong link that exists between the variations and trends in the atmospheric abundance of some climate-relevant at- mospheric constituents, such as methane, and air pollutants such as CO, NOx and ozone. This highlights the need to include the influence of chemical processes in cli- mate simulations and projections. An im- portant extension of the study performed by Chen et al. [9 ] would be to assess how the exceptional situation of 2020 changed the relative contribution of dif- ferent chemical processes to the OH pro- duction and destruction rates. Improved quantification of the methane budget can only be achieved by reducing uncertainty in the OH budget, through analyzing processes with chemistry-climate models and innovative use of chemical observa- tional datasets. Conflict of interest statement. None declared. Guy P. Brasseur1 , ∗ and Benjamin Gaubert 2 1 NSF National Center for Atmospheric Research (NSF NCAR), USA and Max Planck Institute for Meteorology, Germany and 2 NSF National Center for Atmospheric Research (NSF NCAR), USA ∗Corresponding author . E-mail: brasseur@ucar.eduREFERENCES 1. Nisbet EG, Manning MR, Dlugokencky EJ et al. Glob Biogeochem Cycle 2023; 37 : e2023GB007875. 2. Feng L, Palmer PI, Parker RJ et al. Atmos ChemPhys2023; 23 : 4863–80. 3. Szopa S, Naik V, Adhikary B et al. Short-lived cli- mate forcers. In Masson-Delmotte V, Zhai P, Pirani A et al. (eds.). Contribution of Working Group I to the Sixth Assessment Report of the Intergovern- mental Panel on Climate Change . Cambridge: Cam- bridge University Press, 2021, 817–922. ©CwDownloaded from https://academic.oup.com/nsr/article/12/9/nwaf347/8239277 by guest on 13 October 2025he increase in atmospheric methane CH4 ) is of concern because this green- ouse gas has a high global warming otential. After an 8-year pause (20 0 0–007) in the atmospheric methane rowth trend and a resumption that has ccelerated since 2007, a surge in the lobal atmospheric methane burden as observed in 2020, 2021 and 2022, ith an unprecedently high atmospheric rowth rate. Analysis of the methane sotopic content [1 ], as well as satellite bservations (e.g. [2 ]) led to the attri- ution of the resumed methane growth post 2007) to microbial emissions, hich are predominantly from tropical etlands, with contributions from waste nd agricultural activity. Earth system models with interactive hemistry and inversion method estima- ions from methyl-chloroform observa- ions currently disagree on the tempo- al trends in the hydroxyl radical (OH), he chemical species responsible for 90% f atmospheric methane oxidation [3 ]. owever, there is a growing consensus hat the global OH inter-annual variabil- ty is < 4% [4 ]. The OH radical is primarily formed hrough ozone (O3 ) photolysis and ‘recy- led’ with nitrogen oxides’ (NOx) photo- atalytic cycles, while it is destroyed by H4 , carbon monoxide (CO) and many olatile organic species. This has led to an ncreased interest in characterizing OH t a shorter temporal scale from satellite bservational proxies of OH sources and inks of such species [5 ]. The COVID- 9 pandemic provides an excellent case tudy to apply such techniques with onths-long hemispheric scale anoma- ies in O3 levels and NOx emissions, as uantified by assimilated satellite obser- The Author(s) 2025. Published byOxford University Press on behalf of China Science Publishing &Media Ltd. This is anOpen Access article distributed under the terms of the Creativeommons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original ork is properly cited. Natl Sci Rev, 2025, Vol. 12, nwaf347456789© ss on  Ope  C .org/l butio  wDownloaded from https://academic.oup.com/nsr/article/12/9/nwaf347/8239277 by guest on 13 October 2025. Montzka SA, Krol M, Dlugokencky E et al. Science2011; 331 : 67–9. . Duncan BN, Anderson DC, Fiore AM et al. AtmosChem Phys 2024; 24 : 13001–23. The Author(s) 2025. Published by Oxford University Preommons Attribution License ( https://creativecommonsork is properly cited. . Miyazaki K, Bowman K, Sekiya T et al. Sci Adv2021; 7 : eabf7460. . Bouarar I, Gaubert B, Brasseur GP et al. GeophysRes Lett 2021; 48 : e2021GL094204.  behalf of China Science Publishing & Media Ltd. This is anicenses/by/4.0/), which permits unrestricted reuse, distriPage 2 of 2. Gaubert B, Bouarar I, Doumbia T et al. JGR Atmos2021; 126 : e2020JD034213. . Chen W, Zhang Y, Liang R. Natl Sci Rev 2025; 12 : nwaf232. n Access article distributed under the terms of the Creativen, and reproduction in any medium, provided the original

The atmospheric oxidizing capacity and the methane budget

http://hdl.handle.net/21.11116/0000-0011-F3B3-0

The atmospheric oxidizing capacity and the methane budget

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