Low-pressure chemical and photochemical reactions of oxides of nitrogen on alumina taken as a model substance for mineral dust in relation to air pollution

The interaction of γ-Al2O3, taken as a model substance of tropospheric mineral dust, with N2O, NO and NO2 has been studied using kinetic and temperature-programmed desorption (TPD) mass-spectrometry in presence and absence of UV irradiation. At low surface coverages (<0.001 ML), adsorption of N2O and NO2 is accompanied by dissociation and chemiluminescence, whereas adsorption of NO does not lead to appreciable dissociation. Upon UV irradiation of Al2O3 in a flow of N2O, photoinduced decomposition and desorption of N2O take place, whereas in a flow of NO, only photoinduced desorption is observed. Dark dissociative adsorption of N2O and NO and photoinduced N2O dissociation apparently occur by a mechanism involving electron capture from surface F- and F+-centers. Photoinduced desorption of N2O and NO may be associated with decomposition of complexes of these molecules with Lewis acid sites, V-centers or OH-groups. TPD of N2O and NO proceeds predominantly without decomposition, while NO2 partially decomposes to NO and O2.