ACP Atmospheric Chemistry and Physics ACP 1680-7324 Copernicus GmbH Göttingen, Germany 10.5194/acp-11-8607-2011 The H<sub>2</sub>O-O<sub>2</sub> water vapour complex in the Earth's atmosphere Kasai Y. 1 Dupuy E. 1 Saito R. 1 4 Hashimoto K. 2 Sabu A. 2 Kondo S. 2 Sumiyoshi Y. 3 5 Endo Y. 3 National Institute of Information and Communications Technology, Nukui-kita, Koganei, Tokyo, 184-8795, Japan Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo, 192-0397, Japan Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, Komaba, Meguro-ku,Tokyo 153-8902, Japan present address: Japan Agency for Marine-Earth Science and Technology (JAMSTEC) Showa-machi, Kanazawa-ku, Yokohama-city, Kanagawa, 236-0001, Japan present address: Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University,4-2 Aramaki, Maebashi, Gunma 371-8510, Japan 23 08 2011 11 16 8607 8612 This is an open-access article ditributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. This article is available from http://www.atmos-chem-phys.net/11/8607/2011/acp-11-8607-2011.html The full text article is available as a PDF file from http://www.atmos-chem-phys.net/11/8607/2011/acp-11-8607-2011.pdf

Until recently, abundance estimates for bound molecular complexes have been affected by uncertainties of a factor 10–100. This is due to the difficulty of accurately obtaining the equilibrium constant, either from laboratory experiments or by statistical thermodynamic calculations. In this paper, we firstly present laboratory experiments that we performed in order to determine the molecular structure of H<sub>2</sub>O-O<sub>2</sub>. We also derive global abundance estimates for H<sub>2</sub>O-O<sub>2</sub> in the Earth's atmosphere. The equilibrium constant <i>K</i><sub>p</sub> evaluated using the "anharmonic oscillator approach" (AHOA) (Sabu et al., 2005) was employed: the AHOA explains well the structure of the complex obtained by the present experiment. The <i>K</i><sub>p</sub> calculated by this method shows a realistic temperature dependence. We used this <i>K</i><sub>p</sub> to derive global abundance estimates for H<sub>2</sub>O-O<sub>2</sub> in the Earth's atmosphere. The distribution of H<sub>2</sub>-O<sub>2</sub> follows that of water vapour in the troposphere and seems inversely proportional to temperature in the lower stratosphere. Preliminary estimates at the surface show amount of H<sub>2</sub>O-O<sub>2</sub> is comparable to CO or N<sub>2</sub>O, ranking water vapour complexes among the ten most abundant species in the boundary layer.

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