Charged liquid droplets or solid particles are widely used in industrial electrostatic processes, such as surface coating or painting, particle separation, scrubbing or two-stage electrostatic precipitation, improving their throughput or saving energy. The efficiency of these electrostatic processes can be further improved by maximizing the charge imparted to the particles and minimizing their loss while charging. This can be accomplished by charging the particles by an ionic current in alternating electric field. The paper deals with the alternating electric field charger in which the particles can be charged close to the theoretical Pauthenier limit. In this type of charger, the particles undergo oscillations and the number of particles precipitated on the electrodes is diminished, which was confirmed by the CCD camera recordings. An alternating electric field charger was constructed and mounted in a channel of cross section of 160 x 160 mm. Airborne MgO particles of mean diameter of 10 mum were charged in this charger up to 5 fC, and their specific charge was in the range of 1-3 mC/kg. (C) 2003 Elsevier B.V. All rights reserved.