Heterogeneous Photo-oxidation of SO2 in the Presence of Two Different Mineral Dust Particles: Gobi and Arizona Dust

Abstract

The impact of authentic mineral dust particles sourced from the Gobi Desert (GDD) on the kinetic uptake coefficient of SO2 was studied under varying environments (humidity, O3, and NOx) using both an indoor chamber and an outdoor chamber. There was a significant increase in the kinetic uptake coefficient of SO2 (ΥSO4(2-),light) for GDD particles under UV light compared to the value (ΥSO4(2-),dark) under dark conditions at various relative humidities (RH) ranging from 20% to 80%. In both the presence and absence of O3 and NOx, ΥSO4(2-),light and ΥSO4(2-),dark) greatly increased with increasing RH. The resulting ΥSO4(2-),light of GDD particles was also compared to that of Arizona Test Dust (ATD) particles. The ΥSO4(2-),light 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 semi-conductive metals in dust particles and partially by hygroscopic properties.