This work demonstrated that an electrostatic precipitator (ESP), originally designed for dust collection, could become a nanoparticle generator under specific operating conditions. A lab-scale wire-plate positive ESP was built for measuring aerosol penetration and generation rate. The carrier air was filtered by activated charcoal, silica gel and HEPA filters to remove potential contaminants. The data, obtained in both power-on and power-off modes, were utilized to calculate penetration and generation rate of aerosol. The results showed that air temperature appeared to have a strong effect on ESP nanoparticle generation. At temperature above 37 C and flow rate below 9 L/min, the nanoparticle penetration of ESP exceeded 100%, indicating that the ESP was generating aerosol particles. Sputtering on the corona discharger appeared to be the key mechanism of aerosol generation. The ozone concentration increased with increasing corona current. The ESP reached a maximum number concentration at the electric field strength of 4.8 kV/cm when the air flow and temperature were fixed at 6 L/min and 40 C, respectively. The particle size ranged from 5 to 40 nm, with a mode around 12 nm. Elementary components of the discharge wire were detected on the filter samples collected downstream the ESP and ground plates, indicating that nanoparticles were generated from the discharge wire. (C) 2012 Elsevier Ltd. All rights reserved.