30 Aug 2023
 | 30 Aug 2023
Status: this preprint is open for discussion and under review for Atmospheric Chemistry and Physics (ACP).

Estimation of the atmospheric hydroxyl radical oxidative capacity using multiple hydrofluorocarbons (HFCs)

Rona L. Thompson, Stephen A. Montzka, Martin K. Vollmer, Jgor Arduini, Molly Crotwell, Paul Krummel, Chris Lunder, Jens Mühle, Simon O'Doherty, Ronald G. Prinn, Stefan Reimann, Isaac Vimont, Hsiang Wang, Ray F. Weiss, and Dickon Young

Abstract. The hydroxyl radical (OH) largely determines the atmosphere’s oxidative capacity and, thus, the lifetimes of numerous trace gases, including methane (CH4). Hitherto, observation-based approaches for estimating the atmospheric oxidative capacity have primarily relied on using methyl chloroform (MCF), but as the atmospheric abundance of MCF has declined, the uncertainties associated with this method have increased. In this study, we examine the use of five hydrofluorocarbons (HFCs) (HFC-134a, HFC-152a, HFC-365mfc, HFC-245fa and HFC-32) in multi-species inversions, which assimilate three HFCs simultaneously, as an alternative method to estimate atmospheric OH. We find robust estimates of OH regardless of which combination of three HFCs are used in the inversions. Our results show that OH has remained fairly stable during our study period from 2004 to 2021, with variations of <2 % and no significant trend. Inversions including HFC-32 and HFC-152a (the shortest-lived species) indicate a small reduction in OH in 2020 (1.6 % ± 0.9 % relative to the mean over 2004–2021 and 0.6 ± 0.9 % lower than in 2019), but considering all inversions, the reduction was only 0.5 ± 1.1 % and OH was at a similar level to that in 2019.

Rona L. Thompson et al.

Status: open (until 11 Oct 2023)

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  • RC1: 'Comment on egusphere-2023-1917', Anonymous Referee #1, 30 Sep 2023 reply

Rona L. Thompson et al.

Rona L. Thompson et al.


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Short summary
The hydroxyl radical (OH) determines the atmospheric lifetimes of numerous species including methane. Since OH is very short-lived it is not possible to directly measure its concentration on scales relevant for understanding its effect on other species. Here, OH is inferred by looking at changes in hydrofluorocarbons (HFCs). We find OH levels have been fairly stable over our study period (2004 to 2021) suggesting that OH is not the main driver of the recent increase in atmospheric methane.