Abstract: Apparatus and method for generating and controlling flows of positive and negative air ions includes interposing isolated sets of electrodes in a flowing air stream to separately produce positive and negative ions. The rates of separated production of positive and negative ions are sensed to control ionizing voltages applied to electrodes that produce the ions. Variations from a balance condition of substantially equal amounts of positive and negative ions flowing in the air stream are also sensed to alter bias voltage applied to a grid electrode through which the air stream and ions flow.