Inter-model comparison of global hydroxyl radical (OH) distributions and their impact on atmospheric methane over the 2000–2016 period

Zhao, Yuanhong; Saunois, Marielle; Bousquet, Philippe; Lin, Xin; Berchet, Antoine; Hegglin, Michaela I.; Canadell, Josep G.; Jackson, Robert B.; Hauglustaine, Didier; Szopa, Sophie; Stavert, Ann R.; Abraham, N. L.; Archibald, A. T.; Bekki, Slimane; Deushi, Makoto; Jöckel, Patrick; Josse, B.; Kinnison, Douglas E.; Kirner, Oliver; Marécal, Virginie; O’Connor, Fiona M.; Plummer, David A.; Revell, Laura E.; Rozanov, Eugene; Stenke, Andrea; Strode, Sarah A.; Tilmes, Simone; Dlugokencky, Edward J.; Zheng, Bo

doi:10.5194/acp-19-13701-2019

Cited by 66 publications

(58 citation statements)

References 108 publications

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“…Here we continue our former studies (Zhao et al, 2019(Zhao et al, , 2020, in which we have quantified the impact of OH on top-down estimates of CH 4 emissions during the 2000s. This work aims to better understand the production and loss processes of OH and quantitatively assess their influence on the temporal changes in the CH 4 lifetime and the global CH 4 budget on a decadal scale since the 1980s.…”

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confidence: 61%

“…One of the barriers to understanding atmospheric CH 4 changes is the CH 4 sink, which is mainly the chemical reaction with the hydroxyl radical (OH; Saunois et al, 2016Saunois et al, , 2017Saunois et al, , 2020Zhao et al, 2020) that determines the tropospheric CH 4 lifetime. The burden of atmospheric OH is determined by complex and coupled atmospheric chemical cycles influenced by anthropogenic and natural emissions of multiple atmospheric reactive species and also by climate change (Murray et al, 2013;Turner et al, 2018;Nicely et al, 2018), making it difficult to diagnose OH temporal changes from a single process.…”

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confidence: 99%

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

et al. 2020

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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 ± 3 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 ± 9 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.

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confidence: 61%

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

et al. 2020

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“…Differences between transport models affect the chemical removal of CH 4 , leading to different chemical loss rates, even with the same OH distribution. However, uncertainties in the OH distribution and magnitude (Zhao et al, 2019) are not considered in our study, while it could contribute to a significant change in the chemical sink and then in the derived posterior emissions through the inverse process (Zhao et al, 2020). The chemical sink represents more than 90 % of the total sink, the rest being attributable to soil uptake (38 [27-45] Tg CH 4 yr −1 ).…”

Section: Global Budget Of Total Methane Sinksmentioning

confidence: 99%

“…-Integrate the aforementioned different potential OH chemical fields, also including inter-annual variability, to assess the impact on the methane budget following Zhao et al (2020).…”

Section: Future Developments Missing Elements and Remaining Uncertamentioning

confidence: 99%

The Global Methane Budget 2000–2017

Saunois

Stavert

Poulter

et al. 2020

Earth Syst. Sci. Data

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Abstract. Understanding and quantifying the global methane (CH4) budget is important for assessing realistic pathways to mitigate climate change. Atmospheric emissions and concentrations of CH4 continue to increase, making CH4 the second most important human-influenced greenhouse gas in terms of climate forcing, after carbon dioxide (CO2). The relative importance of CH4 compared to CO2 depends on its shorter atmospheric lifetime, stronger warming potential, and variations in atmospheric growth rate over the past decade, the causes of which are still debated. Two major challenges in reducing uncertainties in the atmospheric growth rate arise from the variety of geographically overlapping CH4 sources and from the destruction of CH4 by short-lived hydroxyl radicals (OH). To address these challenges, we have established a consortium of multidisciplinary scientists under the umbrella of the Global Carbon Project to synthesize and stimulate new research aimed at improving and regularly updating the global methane budget. Following Saunois et al. (2016), we present here the second version of the living review paper dedicated to the decadal methane budget, integrating results of top-down studies (atmospheric observations within an atmospheric inverse-modelling framework) and bottom-up estimates (including process-based models for estimating land surface emissions and atmospheric chemistry, inventories of anthropogenic emissions, and data-driven extrapolations). For the 2008–2017 decade, global methane emissions are estimated by atmospheric inversions (a top-down approach) to be 576 Tg CH4 yr−1 (range 550–594, corresponding to the minimum and maximum estimates of the model ensemble). Of this total, 359 Tg CH4 yr−1 or ∼ 60 % is attributed to anthropogenic sources, that is emissions caused by direct human activity (i.e. anthropogenic emissions; range 336–376 Tg CH4 yr−1 or 50 %–65 %). The mean annual total emission for the new decade (2008–2017) is 29 Tg CH4 yr−1 larger than our estimate for the previous decade (2000–2009), and 24 Tg CH4 yr−1 larger than the one reported in the previous budget for 2003–2012 (Saunois et al., 2016). Since 2012, global CH4 emissions have been tracking the warmest scenarios assessed by the Intergovernmental Panel on Climate Change. Bottom-up methods suggest almost 30 % larger global emissions (737 Tg CH4 yr−1, range 594–881) than top-down inversion methods. Indeed, bottom-up estimates for natural sources such as natural wetlands, other inland water systems, and geological sources are higher than top-down estimates. The atmospheric constraints on the top-down budget suggest that at least some of these bottom-up emissions are overestimated. The latitudinal distribution of atmospheric observation-based emissions indicates a predominance of tropical emissions (∼ 65 % of the global budget, < 30∘ N) compared to mid-latitudes (∼ 30 %, 30–60∘ N) and high northern latitudes (∼ 4 %, 60–90∘ N). The most important source of uncertainty in the methane budget is attributable to natural emissions, especially those from wetlands and other inland waters. Some of our global source estimates are smaller than those in previously published budgets (Saunois et al., 2016; Kirschke et al., 2013). In particular wetland emissions are about 35 Tg CH4 yr−1 lower due to improved partition wetlands and other inland waters. Emissions from geological sources and wild animals are also found to be smaller by 7 Tg CH4 yr−1 by 8 Tg CH4 yr−1, respectively. However, the overall discrepancy between bottom-up and top-down estimates has been reduced by only 5 % compared to Saunois et al. (2016), due to a higher estimate of emissions from inland waters, highlighting the need for more detailed research on emissions factors. Priorities for improving the methane budget include (i) a global, high-resolution map of water-saturated soils and inundated areas emitting methane based on a robust classification of different types of emitting habitats; (ii) further development of process-based models for inland-water emissions; (iii) intensification of methane observations at local scales (e.g., FLUXNET-CH4 measurements) and urban-scale monitoring to constrain bottom-up land surface models, and at regional scales (surface networks and satellites) to constrain atmospheric inversions; (iv) improvements of transport models and the representation of photochemical sinks in top-down inversions; and (v) development of a 3D variational inversion system using isotopic and/or co-emitted species such as ethane to improve source partitioning. The data presented here can be downloaded from https://doi.org/10.18160/GCP-CH4-2019 (Saunois et al., 2020) and from the Global Carbon Project.

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“…Measurements of the ratio of NO to nitrogen dioxide (NO 2 ) in the upper troposphere (UT) frequently cannot be reconciled with models (Cohen et al, 2000;Silvern et al, 2018). Zhao et al (2019) show that differences in background NO at the single pptv level are responsible for differences in global modeled OH on the order of 50%. The ability to measure atmospheric NO at very low mixing ratios and with low uncertainty will be crucial to address these and other questions in atmospheric chemistry research for the foreseeable future.…”

Section: Introductionmentioning

confidence: 99%

Single-photon laser-induced fluorescence detection of nitric oxide at sub-parts per trillion mixing ratios

Rollins¹,

Rickly²,

Gao³

et al. 2020

Preprint

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Abstract. We describe a newly developed single-photon laser-induced fluorescence sensor for measurements of nitric oxide (NO) in the atmosphere. Rapid tuning of a narrow-band laser on and off of a rotationally resolved NO spectral feature and detection of the red-shifted fluorescence provides for interference-free direct measurements of NO with a detection limit of 1 pptv for 1 second of integration, or 0.3 pptv for 10 seconds of integration. The instrument was deployed on the NASA DC-8 aircraft during the NASA FIREX-AQ experiment during July–September of 2019 and provided more than 140 hours of NO measurements over 22 flights, demonstrating the ability of this instrument to operate routinely and autonomously. Comparisons with a seasoned chemiluminescence sensor during FIREX-AQ in a variety of chemical environments provides validation and confidence of the accuracy of this technique.

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Inter-model comparison of global hydroxyl radical (OH) distributions and their impact on atmospheric methane over the 2000–2016 period

Cited by 66 publications

References 108 publications

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

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

The Global Methane Budget 2000–2017

Single-photon laser-induced fluorescence detection of nitric oxide at sub-parts per trillion mixing ratios

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