Nitrate formation and iron dissolution in the heterogeneous reactions of NH₃ on nano -Fe₂O₃

Ammonia (NH3), the most common alkaline gas in the atmosphere, participates in heterogeneous reactions on the surface of aerosols and produces ammonium (NH4+). While most previous studies have focused on the effect of NH3 on the heterogeneous reactions of other gases on mineral dust aerosols, little research has been done on the heterogeneous reactions of NH3 influenced by acidic gases. Here, the effects of sulfur dioxide (SO2), formic acid, acetic acid and acrylic acid on the heterogeneous reaction of NH3 on the surface of nano alpha-Fe2O3 particles were investigated. We found that NH3 can promote the dissolution of alpha-Fe2O3 through NH3-Fe complexation and be oxidized to NO3-, while the addition of acidic gas inhibits the NH3-Fe complex formation and converts it into physical adsorption. SO2 promoted the conversion of NH3 to NH4+, while weakly inhibiting the oxidation of NH3 to NO3- by competing for oxidation sites under light conditions. Organic acids, on the other hand, inhibited the heterogeneous conversion of NH3, and strongly competed for oxidation sites under light conditions, significantly reducing NO3- production. This study reveals the various influences of acidic gases on NH3 heterogeneous reactions on alpha-Fe2O3 particles, which helps to improve the understanding of atmospheric processes involving NH3, acidic gases, and mineral dust aerosols.