Large quantities of mineral dust particles are frequently ejected into the atmosphere through the action of wind. The surface of dust particles acts as a sink for many gases, such as sulfur dioxide. It is well known has been postulated that under most conditions, sulfur dioxide may undergo reactions on dust particle surfaces leading to the production of sulfate ions. It is known that light-driven reactions on dust particles containing TiO2 or Fe(III) oxides produce OH radicals from water. These radicals can convert SO2 adsorbed onto the particles into H2SO4, which stays on the parti-cles. In this presentation, for specific atmospheric conditions, we provide evidence for an alternate pathway in which a series of reactions under solar ultraviolet light produces first gaseous sulfuric acid as an intermediate product before surface-bound sulfate. Metal oxides present in mineral dust act as atmospheric photocatalysts promoting the formation of gaseous OH radicals, which initiate the conversion of SO2 to H2SO4 in the vicinity of dust particles. Under low dust conditions, this process may leads to nucleation events in the atmosphere. To simulate such conditions, we shone light into a flow tube containing low concentrations of dust, along with water vapor and SO2, and monitored the particle concentrations inside the tube. Low dust concentrations are necessary for new particle nucleation; high dust concentrations would provide enough surface area for sulfuric acid to adsorb onto the dust, instead of nucleating aerosol. These findings are supported by recent field observa-tions near Beijing and Lyon.