Articles | Volume 24, issue 22
https://doi.org/10.5194/acp-24-13001-2024
https://doi.org/10.5194/acp-24-13001-2024
Opinion
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26 Nov 2024
Opinion | Highlight paper |  | 26 Nov 2024

Opinion: Beyond global means – novel space-based approaches to indirectly constrain the concentrations of and trends and variations in the tropospheric hydroxyl radical (OH)

Bryan N. Duncan, Daniel C. Anderson, Arlene M. Fiore, Joanna Joiner, Nickolay A. Krotkov, Can Li, Dylan B. Millet, Julie M. Nicely, Luke D. Oman, Jason M. St. Clair, Joshua D. Shutter, Amir H. Souri, Sarah A. Strode, Brad Weir, Glenn M. Wolfe, Helen M. Worden, and Qindan Zhu

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Cited articles

Allen, D., Pickering, K. E., Bucsela, E., Van Geffen, J., Lapierre, J., Koshak, W., and Eskes, H.: Observations of lightning NOx production from Tropospheric Monitoring Instrument case studies over the United States, J. Geophys. Res.-Atmos., 126, e2020JD034174, https://doi.org/10.1029/2020JD034174, 2021. 
Allen, N. C. C., Abad, G. G., Bernath, P. F., and Boone, C. D.: Satellite observations of the global distribution of hydrogen dioxide (H2O2) from ACE, J. Quant. Spectrosc. Ra., 115, January 2013, 66–77, https://doi.org/10.1016/j.jqsrt.2012.09.008, 2013. 
Anderson, D. C., Duncan, B. N., Fiore, A. M., Baublitz, C. B., Follette-Cook, M. B., Nicely, J. M., and Wolfe, G. M.: Spatial and temporal variability in the hydroxyl (OH) radical: understanding the role of large-scale climate features and their influence on OH through its dynamical and photochemical drivers, Atmos. Chem. Phys., 21, 6481–6508, https://doi.org/10.5194/acp-21-6481-2021, 2021. 
Anderson, D. C., Follette-Cook, M. B., Strode, S. A., Nicely, J. M., Liu, J., Ivatt, P. D., and Duncan, B. N.: A machine learning methodology for the generation of a parameterization of the hydroxyl radical, Geosci. Model Dev., 15, 6341–6358, https://doi.org/10.5194/gmd-15-6341-2022, 2022. 
Anderson, D. C., Duncan, B. N., Nicely, J. M., Liu, J., Strode, S. A., and Follette-Cook, M. B.: Technical note: Constraining the hydroxyl (OH) radical in the tropics with satellite observations of its drivers – first steps toward assessing the feasibility of a global observation strategy, Atmos. Chem. Phys., 23, 6319–6338, https://doi.org/10.5194/acp-23-6319-2023, 2023. 
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Executive editor
Tropospheric OH plays a central role in the chemical degradation and formation of air pollutants and climate-relevant trace gases. Traditional direct measurements of the extremely short-lived OH radicals provide localised information on the OH budget. Due to the high technical complexity and scarcity of such measurements, they are practically unsuitable for mapping global spatio-temporal OH distributions. Budget analyses of long-lived tracers (e.g. methyl chloroform) that react exclusively with OH provide estimates of the global mean OH and its temporal variability, but lack spatial resolution. This forward-looking opinion paper discusses new ideas and proposals to constrain global chemical sources and sinks of tropospheric OH using satellite and suborbital observations. The proposed approaches promise a better understanding of the global OH budget at higher spatial and temporal resolution than has been possible to date.
Short summary
Trace gases emitted to or formed within the atmosphere may be chemically or physically removed from the atmosphere. One trace gas, the hydroxyl radical (OH), is responsible for initiating the chemical removal of many trace gases, including some greenhouse gases. Despite its importance, scientists have not been able to adequately measure OH. In this opinion piece, we discuss promising new methods to indirectly constrain OH using satellite data of trace gases that control the abundance of OH.
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