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

Zhao, Yuanhong; Saunois, Marielle; Bousquet, Philippe; Lin, Xin; Hegglin, Michaela I.; Canadell, Josep G.; Jackson, Robert B.; Deushi, Makoto; Jöckel, Patrick; Kinnison, Douglas E.; Kirner, Oliver; Strode, Sarah A.; Tilmes, Simone; Zheng, Bo

doi:10.5194/acp-2020-308

Cited by 7 publications

(17 citation statements)

References 36 publications

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“…The ENSO signal is weak during the early 2000s, resulting in small interannual variations of tropospheric OH burden (Zhao et al, 2019). The mechanisms of OH variations related to ENSO and their impacts on the CH 4 budget need to be explored by inversions, but over a longer time period than this study (e.g., 1980-2010Zhao et al, 2020).…”

Section: Conclusion and Discussionmentioning

confidence: 96%

“…One way can be to build semi-empirical OH fields by combining atmospheric chemistry models, observation-based meteorological data, and chemical species concentrations (e.g., NO x , CO, VOCs, etc.) as initiated in Spivakovsky et al (2000); another way is conducting a multispecies variational inversion of OH (e.g., Zheng et al, 2019) with hydrofluorocarbon (HFC) species (Liang et al, 2017), formaldehyde (Wolfe et al, 2019), CH 4 (Zhang et al, 2018;Maasakkers et al, 2019), or CO (Zheng et al, 2019). In addition, as suggested by Prather et al (2017), OH inversion would benefit from including in the prior data the responses of [OH] to variations of the precursor emissions (e.g., biomass burning and lighting) using the uncertainties estimated by 3D models.…”

Section: Conclusion and Discussionmentioning

confidence: 99%

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Influences of hydroxyl radicals (OH) on top-down estimates of the global and regional methane budgets

et al. 2020

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Abstract. The hydroxyl radical (OH), which is the dominant sink of methane (CH4), plays a key role in closing the global methane budget. Current top-down estimates of the global and regional CH4 budget using 3D models usually apply prescribed OH fields and attribute model–observation mismatches almost exclusively to CH4 emissions, leaving the uncertainties due to prescribed OH fields less quantified. Here, using a variational Bayesian inversion framework and the 3D chemical transport model LMDz, combined with 10 different OH fields derived from chemistry–climate models (Chemistry–Climate Model Initiative, or CCMI, experiment), we evaluate the influence of OH burden, spatial distribution, and temporal variations on the global and regional CH4 budget. The global tropospheric mean CH4-reaction-weighted [OH] ([OH]GM-CH4) ranges 10.3–16.3×105 molec cm−3 across 10 OH fields during the early 2000s, resulting in inversion-based global CH4 emissions between 518 and 757 Tg yr−1. The uncertainties in CH4 inversions induced by the different OH fields are similar to the CH4 emission range estimated by previous bottom-up syntheses and larger than the range reported by the top-down studies. The uncertainties in emissions induced by OH are largest over South America, corresponding to large inter-model differences of [OH] in this region. From the early to the late 2000s, the optimized CH4 emissions increased by 22±6 Tg yr−1 (17–30 Tg yr−1), of which ∼25 % (on average) offsets the 0.7 % (on average) increase in OH burden. If the CCMI models represent the OH trend properly over the 2000s, our results show that a higher increasing trend of CH4 emissions is needed to match the CH4 observations compared to the CH4 emission trend derived using constant OH. This study strengthens the importance of reaching a better representation of OH burden and of OH spatial and temporal distributions to reduce the uncertainties in the global and regional CH4 budgets.

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Section: Conclusion and Discussionmentioning

confidence: 96%

Section: Conclusion and Discussionmentioning

confidence: 99%

Influences of hydroxyl radicals (OH) on top-down estimates of the global and regional methane budgets

et al. 2020

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“…There are many proposed reasons for this "missing" reactivity, such as short-lived VOCs that were not measured (Kovacs et al, 2003) or in the rainforests some mixture of unidentified biogenic emissions and photooxidation products (Edwards et al, 2013;Nölscher et al, 2016). An improved understanding of OH temporal variation is vital to understanding key aspects of atmospheric chemistry, such as interannual to decadal variability in methane (Turner et al, 2019;Zhao et al, 2020). Studies using MCF observations in combination with box-model analyses show similar annual OH anomalies between 1995 and 2010, with a broadly negative anomaly of -6 to 0 % between 1995 and 1999, a positive anomaly of 0 to 6 % between 1999 and 2007 and a negative anomaly of -5 to 0 % between 2007 and 2010 (Montzka et al, 2011;Rigby et al, 2017;Turner et al, 2017;Patra et al, 2021).…”

Section: Introductionmentioning

confidence: 99%

“…He et al, (2020) found negative anomalies of -5 to 0 % between 1995 and 2005 and then positive anomalies of 0 to 4 % between 2005 and 2017. A study by Zhao et al, (2020) found a multi-model mean increase of 0.7 ×10 5 molecule cm -3 between 1980 and 2010, equivalent to around 0.1-0.5 % yr -1 , with the greatest rate of increase in the final decade (2000)(2001)(2002)(2003)(2004)(2005)(2006)(2007)(2008)(2009)(2010). The OH increase from 2000-2010 was predominantly due to that in the primary production term (O( 1 D) + H2O) though also to a decrease in the CO sink term (OH + CO).…”

Section: Introductionmentioning

confidence: 99%

Investigating the Global OH Radical Distribution Using Steady-State Approximations and Satellite Data

Pimlott

Pope

Kerridge

et al. 2022

Preprint

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Abstract. We present a novel approach to derive indirect global information on the hydroxyl radical (OH), one of the most important atmospheric oxidants, using state-of-art satellite trace gas observations (key sinks and sources of OH) and a steady-state approximation (SSA). This is a timely study as OH observations are predominantly from spatially sparse field and infrequent aircraft campaigns, so there is a requirement for further approaches to infer spatial and temporal information on OH and its interactions with important climate (e.g. methane, CH4) and air quality (e.g. nitrogen dioxide, NO2) trace gases. Due to the short lifetime of OH (~1.0 s), SSAs of varying complexities can be used to model its concentration and offer a tool to examine the OH budget in different regions of the atmosphere. Here, we use the well-evaluated TOMCAT three-dimensional chemistry transport model to identify atmospheric regions where different complexities of the SSAs are representative of OH. In the case of a simplified SSA (S-SSA), where we have observations of ozone (O3), carbon monoxide (CO), CH4 and water vapour (H2O) from the Infrared Atmospheric Sounding Interferometer (IASI) on-board ESA’s MetOp-A satellite, it is most representative of OH between 600 and 700 hPa (though suitable between 400–800 hPa) within ~20 % of TOMCAT modelled OH. The same S-SSA is applied to aircraft measurements from the Atmospheric Tomography Mission (ATom) and compares well with the observed OH concentrations within ~30 % yielding a correlation of 0.78. We apply the S-SSA to IASI data spanning 2008–2017 to explore the global long-term inter-annual variability of OH. Relative to the 10-year mean, we find that global annual mean OH anomalies ranged from −3.1 % to +4.4 %, with the largest spread in the tropics between −7.0 % and +7.7 %. Investigation of the individual terms in the S-SSA over this time period suggests that O3 and CO were the key drivers of variability in the production and loss of OH. For example, large enhancement in the OH sink during the positive 2015/2016 ENSO event was due to large scale CO emissions from drought induced wildfires in South East Asia). The methodology described here could be further developed as a constraint on the tropospheric OH distribution as further satellite data becomes available in the future.

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“…Nonetheless, we can hypothesize. For example, El Niño years (high MEI) are associated with more wildfires, resulting in higher CO emissions which could suppress OH concentrations (Zhao et al, 2020;Nguyen et al, 2020). La Niña years (low MEI) are associated with increased convection over the Pacific, increased lightning NO x production and by extent increased OH recycling (Turner et al, 2018 regionally (Oman et al, 2011).…”

Section: That Variability In [Oh]mentioning

confidence: 99%

Improving estimates of the atmospheric oxidative capacity and Amazon fire emissions

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The composition of the air outside, the atmosphere, is the end-result of complex chemistry, dynamical transport and emissions of gases. Anthropogenic activity, such as fossil fuel combustion, refrigeration and large-scale deforestation, contributes to a rapidly changing composition of the atmosphere, often with adverse effects: air quality issues, global warming and depletion of stratospheric ozone are some of the most complex and impactful problems that society has to face. Many gases are removed from the atmosphere through the process of oxidation and the primary atmospheric oxidant is the hydroxyl radical (OH). Gases removed by OH include important pollutants, such as the potent greenhouse gas methane (CH 4) and urban pollutants such as CO and NO x. Therefore, the oxidation capacity of the atmosphere, as determined by the "cleansing-agent" OH, is an important quantity that is central to this thesis.

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

Cited by 7 publications

References 36 publications

Influences of hydroxyl radicals (OH) on top-down estimates of the global and regional methane budgets

Influences of hydroxyl radicals (OH) on top-down estimates of the global and regional methane budgets

Investigating the Global OH Radical Distribution Using Steady-State Approximations and Satellite Data

Improving estimates of the atmospheric oxidative capacity and Amazon fire emissions

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