The heterogeneous chemistry and photochemistry of ozone on oxide components of
mineral dust aerosol, including α-Fe2O3, TiO2, and α-Al2O3, at different relative humidities have been investigated using an environmental aerosol chamber. The rate and extent of ozone decomposition on these oxide surfaces are found to be a function of the nature of the surface as well as the presence of light and relative humidity. Under dark and dry conditions, only α-Fe2O3 exhibits catalytic decomposition toward ozone, whereas the reactivity of TiO2 and α-Al2O3 is rapidly quenched upon ozone exposure. However, upon irradiation, TiO2 is active toward O3 decomposition and α-Al2O3 remains inactive. In the presence of relative humidity, ozone decay on α-Fe2O3 subject to irradiation or under dark conditions is found to decrease. In contrast, ozone decomposition is enhanced for irradiated TiO2 as relative humidity initially increases but then begins to decrease at higher relative humidity levels. A kinetic model was used to obtain heterogeneous reaction rates for different homogeneous and heterogeneous reaction pathways taking place in the environmental aerosol chamber. The atmospheric implications of these results are discussed.