Role of NH3 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-Fe2O3, α-Al2O3, CaO, and MgO) in the evolution of NO3-, SO42-, and NH4+ has been established. It was found that the promotion effect of NH3 was more favorable for the formation of NO3- (or SO42-) and NH4+ on acidic α-Fe2O3 and α-Al2O3 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 Fe2O3 owing to its unique redox chemistry. However, the opposite was found on basic CaO and MgO for the formation of SO42- and NO3-. Under equivalent concentration conditions, the two synergistic effects did not further strengthen on Fe2O3, CaO and MgO due to a competition effect. In NH3-rich situation, a synchronous increase of SO42-, NO3-, and NH4+ occurred on Fe2O3. On acidic Al2O3, the favorable adsorption of NH3 on the surface as well as the existence of NO2 with an oxidizing capability synergistically promoted the formation of SO42-, NO3-, and NH4+.