Heterogeneous Photo-oxidation of SO in the Presence of Two Different Mineral Dust Particles: Gobi and Arizona Dust.

The impact of authentic mineral dust particles sourced from the Gobi Desert (GDD) on the kinetic uptake coefficient of SO was studied under varying environments (humidity, O, and NO) using both an indoor chamber and an outdoor chamber. There was a significant increase in the kinetic uptake coefficient of SO (γ) for GDD particles under UV light compared to the value (γ) under dark conditions at various relative humidities (RH) ranging from 20% to 80%. In both the presence and the absence of O and NO, γ and γ greatly increased with increasing RH. The resulting γ of GDD particles was also compared to that of Arizona Test Dust (ATD) particles. The γ values of GDD were 2 to 2.5 times greater than those of ATD for all RH levels. To understand the photocatalytic act of dust particles, both GDD and ATD were characterized for the metal element composition of fresh particles, the aerosol acidity of aged particles, and the hygroscopic properties of both fresh and aged particles. We conclude that the difference in the formation of sulfate between GDD and ATD particles is regulated mainly by the quantity of the semiconductive metals in dust particles and partially by hygroscopic properties.