AAAR 36th Annual Conference October 16 - October 20, 2017 Raleigh Convention Center Raleigh, North Carolina, USA
Abstract View
Atmospheric Mineral Aerosol Reaction (AMAR) Model for Simulation of Heterogeneous Photooxidation of SO2
ZECHEN YU, Myoseon Jang, Jiyeon Park, University of Florida
Abstract Number: 208 Working Group: Aerosol Chemistry
Abstract The photocatalytic uptake of SO2 corresponding to sulfate production on mineral dust particles is known to be much higher than that in the dark but is not fully considered by current models. In this study, the Atmospheric Mineral Aerosol Reaction (AMAR) model was developed to predict sulfate formation in the presence of airborne mineral dust particles under various environments. The SO2 oxidation reactions in three phases, including the gas phase, the inorganic salt aqueous phase, and the dust phase, are taken into account in this model. The kinetics of the dust chemistry is described as gas-particle partitioning process followed by surface reactions. The SO2 photooxidation is promoted by surface oxidants (e.g., OH radicals) that generated by the photoactive semiconducting metal oxides in dust particles (electron and hole theory). The photoactivation factor of dust particles to produce surface radicals was derived from the integration of the combination product of the dust absorbance spectrum and actinic flux of light sources. The kinetic parameters of dust chemistry were then leveraged using indoor chamber data for two different mineral dust particles, Arizona Test Dust (ATD) and Gobi Desert Dust (GDD). The AMAR model was evaluated using UF-APHOR chamber data, which was operated with ambient temperature and humidity under natural sunlight. After seven consecutive hours of photooxidation of SO2 in an outdoor chamber, the sulfate formation from dust phase was attributed to ~70% of total sulfate (60 ppb SO2, 290 μg m-3 ATD, and NOx less than 5 ppb). At high NOx concentration (>50 ppb of NOx), sulfate formation was suppressed by the competition between NO2 and SO2 that both consume the surface oxidants. The model derived in this study will provide a platform for the prediction of sulfate formation from the surface photochemistry of air-suspended mineral dust particles.