Understanding Hygroscopic Nucleation of Sulfate Aerosols: Combination of Molecular Dynamics Simulation with Classical Nucleation Theory

We present a combined molecular dynamics (MD) and classical nucleation theory (CNT) approach to address many issues regarding the nucleation of inorganic aerosols. By taking parameters from MD simulations, we find the CNT predicts fairly reasonable free-energy profiles for the hygroscopic nucleation of aerosols. Moreover, we find that the ionization of sulfates can play a key role in stabilizing aqueous clusters and that both the size of the critical nucleus and the nucleation barrier can be significantly lowered by the H₂SO₄ and NH₄HSO₄, whereas the effect of NH₃ on nucleation is negligible. NH₄HSO₄ provides stronger enhancement effect to aerosol formation than H₂SO₄. In view of the consistency between the theoretical prediction and experimental observation, the combination of MD simulation and CNT appears to be a valuable approach to gain deeper understanding of how aerosol nucleation is affected by different chemical species.