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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Atmos. Chem. Phys., 16, 12477-12493, 2016
https://doi.org/10.5194/acp-16-12477-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
05 Oct 2016
Global tropospheric hydroxyl distribution, budget and reactivity
Jos Lelieveld, Sergey Gromov, Andrea Pozzer, and Domenico Taraborrelli Max Planck Institute for Chemistry, Atmospheric Chemistry Department, P.O. Box 3060, 55020 Mainz, Germany
Abstract. The self-cleaning or oxidation capacity of the atmosphere is principally controlled by hydroxyl (OH) radicals in the troposphere. Hydroxyl has primary (P) and secondary (S) sources, the former mainly through the photodissociation of ozone, the latter through OH recycling in radical reaction chains. We used the recent Mainz Organics Mechanism (MOM) to advance volatile organic carbon (VOC) chemistry in the general circulation model EMAC (ECHAM/MESSy Atmospheric Chemistry) and show that S is larger than previously assumed. By including emissions of a large number of primary VOC, and accounting for their complete breakdown and intermediate products, MOM is mass-conserving and calculates substantially higher OH reactivity from VOC oxidation compared to predecessor models. Whereas previously P and S were found to be of similar magnitude, the present work indicates that S may be twice as large, mostly due to OH recycling in the free troposphere. Further, we find that nighttime OH formation may be significant in the polluted subtropical boundary layer in summer. With a mean OH recycling probability of about 67 %, global OH is buffered and not sensitive to perturbations by natural or anthropogenic emission changes. Complementary primary and secondary OH formation mechanisms in pristine and polluted environments in the continental and marine troposphere, connected through long-range transport of O3, can maintain stable global OH levels.

Citation: Lelieveld, J., Gromov, S., Pozzer, A., and Taraborrelli, D.: Global tropospheric hydroxyl distribution, budget and reactivity, Atmos. Chem. Phys., 16, 12477-12493, https://doi.org/10.5194/acp-16-12477-2016, 2016.
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Short summary
The self-cleaning capacity of the atmosphere is controlled by hydroxyl (OH) radicals in the troposphere. There are primary and secondary OH sources, the former through the photodissociation of ozone, the latter through OH recycling. We used a global model, showing that secondary sources are larger than assumed previously, which buffers OH. Complementary OH formation mechanisms in pristine and polluted environments, connected through transport of ozone, can maintain stable global OH levels.
The self-cleaning capacity of the atmosphere is controlled by hydroxyl (OH) radicals in the...
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