The Gibbs free energy, G, of ammonia (NH3) clusters is calculated by using ab initio molecular orbital methods. The free energy change, ΔG, for the formation of an NH3 cluster ion has a minimum near a cluster size of 5, which is the magic number for NH3 clusters. In ion-induced nucleation of NH3, the critical cluster size, n*, is smaller and ΔG at n* is lower, compared with homogeneous nucleation of NH3. The lowered ΔG results in an increase in the concentration of NH3 critical nuclei, which is the main cause of the increased nucleation rate in ion-induced nucleation of NH3.
Computer models were used to analyze the high concentration peaks of SO2 and NOx observed above the Osumi Strait on 14 December during the 1994 IGAC/APARE/PEACAMPOT aerial observation. On the basis of a mesoscale meteorological model and a Lagrangian particle model, it became clear that our aircraft encountered the pollution plume from the city of Kagoshima during the observation flights at 900 m and 300 m altitude, and that the plane grazed the volcanic plume from Mt. Sakurajima at the eastern ends of its flight tracks.