The H₂O-O₂ water vapour complex in the Earth's atmosphere

Abstract. 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 H₂O-O₂. We also derive global abundance estimates for H₂O-O₂ in the Earth's atmosphere. The equilibrium constant K_p 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 K_p calculated by this method shows a realistic temperature dependence. We used this K_p to derive global abundance estimates for H₂O-O₂ in the Earth's atmosphere. The distribution of H₂-O₂ 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 H₂O-O₂ is comparable to CO or N₂O, ranking water vapour complexes among the ten most abundant species in the boundary layer.