Photonucleation of water vapour in the presence of oxygen

The key role of oxygen in the formation of condensation nuclei in moist dust-free air by the action of ultraviolet light is discussed, and supported by showing that the photonucleation spectrum matches the absorption spectrum of liquid water saturated with oxygen. It is proposed that the phenomenon is due to the formation of charge-transfer complexes of molecular oxygen and water, H2O+O2−. A kinetic scheme is suggested.