The rational design of filtration process should be based on reliable predictions of the dependence on the effluent concentration and on the pressure drop variations with time for a given set of the operating conditions, i.e. particle concentration and size, filter packing density, size of filter element, gas velocity, etc. The pattern of filling of the internal space with the porous structure of fibrous filters strongly influences the behavior of the filter at the stage of non-steady-state filtration. The cellular automata probabilistic model extended to the lattice-Boltzmann approach was used for description of the local structures of deposited particles forming clusters on the surface of a single fibre of the filter. The fractal dimension of deposited structure and its local porosity were calculated for the Peclet number ranging from 0.5 to 10. The results of calculations show that deposits, for which diffusion is a controlling mechanism of deposition, have higher fractal dimension, are strongly branched and are distributed around the filter fibre. Deposits obtained for the conditions related to the higher Peclet numbers are situated at the front of the fibre and are more regular than those obtained for diffusion-controlled deposition. The pressure drop of the aerosol flow through a loaded fibre increases more. rapidly, during loading, for diffusion-controlled deposition than that for the higher contribution of convection during the deposition process. (C) 2003 Elsevier Science Ltd. All rights reserved.