A simple bimodal particle dynamics model was proposed to describe a particle system undergoing simultaneous particle formation, coagulation, coalescence, and surface growth. We extended our previous bimodal model, which used two discrete modes, to account for the surface growth of nonspherical particles. Surface reaction from TiCl4 was considered and its effects on the formation and growth of TiO2 particles were investigated. Simulation results of the present bimodal model considering surface growth showed very good agreement with those of the moving sectional model for the growth of spherical TiO2 in the literature. Surface growth of TiO2 aggregates was also simulated by using this bimodal model and a new design diagram indicating the significance of surface reaction of TiCl4 was proposed. (C) 2004 Elsevier Inc. All rights reserved.