This study presents the experimental results of penetration of aerosol particles with diameters between 4.5 mn and 10 mu m through fibrous filters. Three particle size spectrometers: the TSI 3080 electrostatic classifier equipped with nano- or long differential mobility analyzer, and the TSI 3321 aerodynamic particle sizer, were used to measure nanometer, submicron, and micron-sized particles. NaCl aerosol particles were generated by using spray-drying methods. To eliminate electrostatic charges, filters were dipped in isopropanol for 5 min and allowed to dry. These dipped filters, along with controls of each filter type, were then tested to determine the aerosol penetrations in the size range of 4.5 nm-10 mu m. The experimental results demonstrated that almost all particles with sizes below 10 nm or exceeding 5 mu n were collected in the filters, and the filter charge density did not significantly affect the penetration values. The results also suggested that there is no thermal rebound of particles in the size range down to 4.5 nm in fibrous filters. (c) 2007 Elsevier Ltd. All rights reserved.