The discrete vortex method coupled with the particle-tracking and moment methods have been used to calculate the trajectories of individual nano and fine particles undergoing the coagulation and dispersion in a round jet. The results show that the Stokes number plays an important role in the dispersion of fine particles. The radial dispersion of fine particles for the wavenumher of 5 is the largest when an azimuthal perturbation is introduced to its flow. However, the width of particle dispersion is not always proportional to the amplitude of the azimuthal perturbation. As the round jet flow develops, the mass concentration of nanoparticles within the jet core decreases continuously. The number concentration of nanoparticle decreases rapidly near the jet exit, then decreases slowly in the far field until an asymptotic state is attained. Both the polydispersity and diameter of nanoparticle increase, the rate of increase for the former is the largest near the jet exit, and the largest particles are found near the jet core. The particle diameter is relatively constant across the width of the jet within and outside the jet core except the region near the interface of the jet and the outside. The standard deviation of nanoparticle size distribution increases at the jet exit. approaching slowly at an asymptotic value in the jet core. The minimum and maximum of standard deviation appear between the jet core and edge, and at the jet centerline, respectively. The region of mixing of nanoparticles becomes narrower, however. the particle number concentration grows with increasing Schmidt number. The particle size increases along the radial direction with increasing Damkohler number, and the standard deviation does not change when the Damkohler number is monotonous. (C) 2006 Elsevier Ltd. All rights reserved.