A computational, three-dimensional approach to investigate the behavior of diesel soot particles in the micro-channels of a wall-flow, porous-ceramic particulate filter is presented. Particle size examined is in the PM2.5 range. The flow field is simulated with a finite-volume Navier-Stokes solver and the Ergun equation is used to model the porous material. The permeability coefficients were obtained by fitting experimental data. Particle flow, dispersion, deposition and wall-particle interactions are investigated tracking large swarms of 2 and 0.2 mu m diameter particles in a Lagrangian frame of reference. Particle dynamics included rarefied gas hypotheses (the Knudsen number being larger than unity) and bounce/capture models based on impact kinetic energy loss. The influence of gas molecules-particle interaction on overall particle behavior is also examined by including Brownian motion and partial slip in particle equation of motion. Simulations help to highlight three-dimensional non-uniform particle deposition, mainly due to flow distribution in the micro-channel. All particles deposit onto the porous filter wall following the distribution of the through-wall velocity. The larger, 2 mu m, particles show a larger tendency to deposit at the end of the filter. Due to the flow contraction at the inlet, virtually no particle deposit in the inlet section of the filter. Reasons for the scarce influence on particle deposition due to particle-flow slip and Brownian motion are given. (c) 2005 Elsevier Ltd. All rights reserved.