Promoted Activity of Surface Hydroxyls on γ-Al₂O₃ Mineral Dust with the Coexistence of SO₂ and NH₃

Abstract

Sulfate and ammonium formed on mineral dust can be mutually accelerated through the heterogeneous reactions of coexisting SO 2 and NH 3 . However, little is known about the underlying mechanism, especially the pivotal reactive sites. Using combined Born−Oppenheimer molecular dynamics simulations and density functional theory calculations, the results show that, compared to that of SO 2 or NH 3 alone on the γ-Al 2 O 3 surface, the increased level of formation of sulfate and ammonium can be attributed to the promoted activity of the surface-bridged hydroxyl with the coexistence of SO 2 and NH 3 . In the specific mechanism, the O and H of the surface-bridged hydroxyl group are attacked by the adjacent SO 2 and NH 3 , respectively, which directly enhances the formation of absorbed sulfite and ammonium, and indirectly facilitates the production of sulfate by oxidation of atmospheric O 2 . The proposed mechanisms can be broadly applied to other aluminum-based suspended dust particles, such as kaolinite, montmorillonite, and clay dust.