Particle dispersion and deposition over a square cylinder in a channel flow has been investigated numerically Two-dimensional fluid flow computations were performed using lattice Boltzmann method (LBM), while a Lagrangian description was used for simulation of spherical, solid particles immersed in the flow Computational simulations were performed for Reynolds numbers of 120 and 200, where unsteady vortex shedding forms behind the square cylinder Good agreement was observed between present fluid flow simulations and earlier numerical works This instantaneous flow field was used to evaluate particle trajectories Transport and deposition of 0.01-10 mu m particles were studied The forces considered in the equation of particle motion were drag, the Saffman lift, gravity and Brownian forces The simulation results show that the Brownian diffusion affects the deposition rate of ultrafine particles on the front and the back sides of the block. Motion of particles behind the obstacle is greatly influenced by the vortex shedding. (c) 2009 Elsevier Ltd. All rights reserved