Photochemistry of mineral dust surface as a potential atmospheric renoxification process

The nitrate formation on dust particles is considered as a sink for atmospheric NO(y) (such as HNO(3)). However mineral dust is shown here to be an effective photocatalyst for transformation of nitrate anions into NO and NO(2), without involving its photolysis. The photodecomposition of NO(3)(-) at the surface of synthetic mineral dust samples of SiO(2), TiO(2), mixed TiO(2)-SiO(2) and authentic sand doped with 6% NO(3)(-) 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 NO(2) are observed during irradiation of films composed of either mixed TiO(2)-SiO(2), pure TiO(2) 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. Citation: Ndour, M., P. Conchon, B. D'Anna, O. Ka, and C. George (2009), Photochemistry of mineral dust surface as a potential atmospheric renoxification process, Geophys. Res. Lett., 36, L05816, doi: 10.1029/2008GL036662.