The proceeded ammonia release from ammonium nitrate owing to sodium malonate addition: Dependence of RH, acidity and surfactant

The gas-particle partition of ammonia has strong effect on size, composition and hygroscopic property of atmospheric aerosols. However, how chemical reaction drives ammonia evaporation from particle is not well known. In this work, ammonium depletion is used to characterize the ammonia liberation from aqueous ammonium nitrate and sodium malonate/ammonium nitrate aerosols. The addition of sodium malonate promotes more ammonia liberation owing to inter-ingredients reaction. As the relative humidity (RH) decreases, ammonia release is enhanced. Moreover, NH₃ evaporation is also impacted by aerosol acidity. At pH 1.93, malonate is directly converted into hydrogen malonate and malonic acid via protonation. Under the neutral/alkaline condition, higher pH is beneficial for component reactions. When cetyltrimethylammonium bromide is added into mixed aerosols, NH₃ evaporation becomes slow. These results can provide a new perspective on the evolution mechanism of NH₃–NH₄⁺ buffer pairs for multicomponent aerosols.