Ozone-free electrostatic precipitators incorporating an array of electrospray wick charged aerosol ionization sources were built and tested. The particle ionization and collection efficiencies were independently measured for airborne particles as a function of air flow rate, electric field magnitude, and particle size. The results indicate that, while particle ionization efficiencies near 100% can be achieved using the electrospray ionization method, the number of elemental charges deposited onto a given particle depends strongly on the particle diameter and for submicron particles is very low. High overall particle collection efficiency, therefore, requires a carefully designed precipitation region where the maximum particle collection time, associated with the particles with the lowest mobility, is less than the residence time within the collector. (C) 2008 Elsevier Ltd. All rights reserved.