Role of NH 3 in the Heterogeneous Formation of Secondary Inorganic Aerosols on Mineral Oxides.

In this work, a relationship between the role of NH3 and the properties of mineral oxides (α-Fe2 O3 , α-Al2 O3 , CaO, and MgO) in the evolution of NO3 - , SO4 2- , and NH4 + has been established. It was found that the promotion effect of NH3 was more favorable for the formation of NO3 - (or SO4 2- ) and NH4 + on acidic α-Fe2 O3 and α-Al2 O3 due to acid-base interactions between NO2 with NH3 or between SO2 and NH3 , while this effect was weaker on basic CaO and MgO possibly due to their basic nature. The acid-base interaction (NO2 /SO2 with NH3 ) overpowered the redox reaction (SO2 with NO2 ) on Fe2 O3 owing to its unique redox chemistry. However, the opposite was found on basic CaO and MgO for the formation of SO4 2- and NO3 - . Under equivalent concentration conditions, the two synergistic effects did not further strengthen on Fe2 O3 , CaO and MgO due to a competition effect. In NH3 -rich situation, a synchronous increase of SO4 2- , NO3 - , and NH4 + occurred on Fe2 O3 . On acidic Al2 O3 , the favorable adsorption of NH3 on the surface as well as the existence of NO2 with an oxidizing capability synergistically promoted the formation of SO4 2- , NO3 - , and NH4 + .