The hydroxyl radical is the predominant atmospheric oxidant1, responsible for removing a wide range of trace gases, including greenhouse gases, from the atmosphere. Determination of trends and variability in hydroxyl radical concentrations2,3 is critical to understanding whether the ‘cleansing’ properties of the atmosphere are changing. The variability in hydroxyl radical concentrations on annual to monthly timescales, however, is difficult to quantify. Here we show records of carbon monoxide containing radiocarbon (14CO), which is oxidized by hydroxyl radicals4,5, from clean-air sites at Baring Head, New Zealand, and Scott Base, Antarctica, spanning 13 years. Using a model study, we correct for known variations in production of 14CO (refs 6, 7), allowing us to exploit this species as a diagnostic for short term changes in hydroxyl radical concentrations. We find no significant long-term trend in hydroxyl radical concentrations but provide evidence for recurring short-term variations of around ten per cent persisting for a few months. We also find decreases in hydroxyl radical concentrations of up to 20 per cent, apparently triggered by the eruption of Mt Pinatubo in 1991 and by the occurrence of extensive fires in Indonesia in 1997.
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C. Brenninkmeijer helped to establish the 14CO measurement programme and R. Sparks, G. Brailsford and A. Gomez helped with the measurements and analysis used. This work was supported by the New Zealand Foundation for Research Science and Technology and Antarctica New Zealand. M.M. thanks S. Solomon for her support in completing this work.
Reprints and permissions information is available at npg.nature.com/reprintsandpermissions. The authors declare no competing financial interests.
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Manning, M., Lowe, D., Moss, R. et al. Short-term variations in the oxidizing power of the atmosphere. Nature 436, 1001–1004 (2005). https://doi.org/10.1038/nature03900
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