Vapor nucleation on PM2.5 from MSWI (municipal solid waste incineration) was modeled combined with the wetting abilities, compositions and surface characteristics of the particles. Nucleation characteristics of the fine particles were numerically studied. Results show that when the mass fraction of each salt is constant the free energy barrier of embryo formation is not influenced by the total mass of soluble salts in the particle. While the total mass of soluble salts does not change, the free energy barrier changes remarkably with the compositions of the Soluble salts in the particle. it is also found that the free energy barrier decreases with roughness of particle surfaces. Simulation results of the nucleation rate and the critical nucleation saturation indicate that both the compositions of the soluble salts and the Surface roughness dominate the activation of the PM2.5 from MSWI. (C) 2008 Elsevier B.V. All rights reserved