Photochemistry of mineral dust surface as a potential atmospheric renoxification process

The nitrate formation on dust particles is considered as a sink for atmospheric NOy (such as HNO3). However mineral dust is shown here to be an effective photocatalyst for transformation of nitrate anions into NO and NO2, without involving its photolysis. The photodecomposition of NO3− at the surface of synthetic mineral dust samples of SiO2, TiO2, mixed TiO2‐SiO2 and authentic sand doped with 6% NO3− was studied by means of a flow‐tube at 298 K with UV‐illumination in the 340–420 nm range at relative humidities between 5 and 80%. Both NO and NO2 are observed during irradiation of films composed of either mixed TiO2‐SiO2, pure TiO2 and authentic minerals from the Sahara. The relative humidity strongly affects the concentration of NOx released into the gas phase. The photoinduced nitrate conversion into NOx is discussed as being a potential renoxification process of the atmosphere.