A Kinetic Study of Ozone Decomposition on Illuminated Oxide Surfaces

The heterogeneous chemistry and photochemistry of ozone on oxide components of mineral dust aerosol, including alpha-Fe(2)O(3), TiO(2), and alpha-Al(2)O(3), 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 alpha-Fe(2)O(3) exhibits catalytic decomposition toward ozone, whereas the reactivity of TiO(2) and alpha-Al(2)O(3) is rapidly quenched upon ozone exposure. However, upon irradiation, TiO(2) is active toward O(3) decomposition and alpha-Al(2)O(3) remains inactive. In the presence of relative humidity, ozone decay on alpha-Fe(2)O(3) subject to irradiation or under dark conditions is found to decrease. In contrast, ozone decomposition is enhanced for irradiated TiO(2) 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.