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

Abstract

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 α-Fe₂O₃ particles were investigated. We found that NH₃ can promote the dissolution of α-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 α-Fe₂O₃ particles, which helps to improve the understanding of atmospheric processes involving NH₃, acidic gases, and mineral dust aerosols.