Virtual 3-D geometries resembling the internal microstructure of electrospun fibrous materials are generated in this work to simulate the pressure drop and collection efficiency of nanofibrous media when challenged with aerosol particles in the size range of 25 to 1000 nm. In particular, we solved the air flow field in the void space between the fibers in a series of 3-D fibrous geometries with a fiber diameter in the range of 100 to 1000 nm and a Solid Volume Fraction (SVF) in the range of 2.5 to 7.5%, using the Fluent CFD code, and simulated the flow of large and fine particles through these media using Lagrangian and Eulerian methods, respectively. Particle collection due to interception and Brownian diffusion, as well as the slip effect at the surface of nanofibers, has been incorporated in the CFD calculations by developing customized C++ subroutines that run in the Fluent environment. Particle collection efficiency and pressure drop of the above fibrous media are calculated and compared with analytical/empirical results from the literature. The numerical simulations presented here are believed to be the most complete and realistic filter modeling published to date. Our simulation technique, unlike previous studies based on oversimplified 2-D geometries, does not need any empirical correction factors, and can be used to directly simulate pressure drop and efficiency of any fibrous media. (C) 2010 Elsevier B.V. All rights reserved.