(NH₄)₂SO₄ heterogeneous nucleation and glycerol evaporation of (NH₄)₂SO₄-glycerol system in its dynamic efflorescence process

Using the FTIR-ATR technique, we investigated the heterogeneous nucleation process of aqueous (NH₄)₂SO₄ binary droplets and (NH₄)₂SO₄/glycerol ternary droplets. From the red shift of δ-NH₄⁺ with a linearly declining relative humidity (RH), the ERHs of pure (NH₄)₂SO₄ droplets and mixed (NH₄)₂SO₄/glycerol droplets with different organic-inorganic ratio (OIR) of 1:4, 1:2 and 1:1 ranges from ∼51.9 to ∼34.9%, ∼49.8 to ∼33.0%, ∼48.0 to ∼30.6% and ∼43.7 to ∼25.2%, respectively. From the changing absorbance of δ-NH₄⁺ band, we determined the heterogeneous nucleation rates of crystalline (NH₄)₂SO₄ in the pure and mixed droplets. The interfacial tension between an (NH₄)₂SO₄ critical nucleus and surrounding (NH₄)₂SO₄ solution was determined using classical nucleation theory and experimental data to be 0.031 ± 0.002 J m⁻². Evaporation of glycerol in (NH₄)₂SO₄/glycerol ternary droplets are also studied to be restrained by participation of (NH₄)₂SO₄. Determined vapour pressure of glycerol is on the same magnitude with results from previous studies.