A sonic jet bipolar ionizer has been designed and tested. Ion production rates and characteristics of particulate contaminants were studied as a function of design parameters (i.e., electrode material, and orifice plate material) and of operating conditions (i.e., electrode to orifice distance, pressure, electrode voltage). In the optimized design particle generation by electrode or plate sputtering was eliminated, while particle generation by chemical reaction and subsequent gas to particle conversion was reduced to low levels. The ionizer provided a high output of bipolar ions at rates that ensured balanced operation and low charge neutralization times. An aerosol neutralizer using the corona ionizer was designed and tested with singly charged monodisperse aerosols. The equilibrium charge distribution of the aerosol was measured using an electrical mobility classification technique, and was found to be in good agreement with theoretical predictions.