Enhancement in aerosol filtration by synthesizing carbon nanostructures including nanofibers within nickel sintered metal microfibrous matrices/filter media was studied. An improvement in filtration performance observed in the quality factor (-ln(1 - E)/Delta P) analysis was attributed to wall slip flow over nanofibers. The wall slip flow contributed to high filtration efficiency and a low rise in pressure drop. The effect of varying quantities of carbon nanostructures and their effects on matrices of various pore sizes were also studied. Three different diameters of nickel microfibers (4, 8 and 12 mu m) were used to prepare filter media to study the effects of carbon nanofiber synthesis on filter media of different pore sizes. The synthesis condition was chosen for uniform synthesis in the 3-dimensional structure of the matrix and to prevent only 2-dimensional surface deposition. The quantity of nanostructures was changed by varying the synthesis time. Two competing effects were seen as the quantity of nanostructures increased: an increase in filtration efficiency due to nanostructures and an increase in pressure drop due to the decrease in the mean pore diameter of the filter media. For 4 mu m matrices, which had a small initial mean pore diameter, the benefit of an increase in filtration efficiency was outweighed by the decrease in the mean pore diameter. This study shows that carbon nanostructure synthesis leads to significant improvement in the performance of filter media with large initial pore size because the pore diameters do not reduce significantly with synthesis. (C) 2011 Elsevier B.V. All rights reserved.