Characteristic filtration lengths of fibrous filters collecting spherical submicrometer aerosol particles are calculated over a wide range of particle sizes and filtration operating parameters. The calculations were based upon the dispersion/reaction model for aerosol transport and filtration in porous filters, and were performed for spatially periodic models of fibrous arrays of circular cylinders in square arrays. Several orientations of the direction of mean air flow relative to the lattice axes were investigated. A comparison between our theoretical results, available experimental data, and the results of competitive filtration models, demonstrated the greater efficacy of our dispersion/reaction model in correlating characteristic filtration lengths of submicrometer particles possessing diameters less than 0.3-0.5 μm. The filtration rate of larger particles, governed primarily by the interception mechanism, is shown to be sensitive to the choice of the direction of the mean air flow relative to the axes of the periodic array.