Ozone adsorption and decomposition on metal oxides is of wide interest in technology and in atmospheric chemistry. Here, ozone-adsorption-induced band bending is observed on Ti- and Fe-oxide model surfaces under dry and humid conditions. Photoelectron spectroscopic studies indicate the effect of charge transfer to O3, which limits the surface coverage of the precursor to decomposition reactions. This is also consistent with the negative pressure dependence observed in previous studies. These results contribute to our fundamental understanding of ozone adsorption and decomposition mechanisms on metal oxides of environmental and technological relevance.