An air cleaning device for separating airborne particles from a flow of air is provided. The air cleaning device comprises a separating unit and an ionizing unit arranged to charge airborne particles present in the flow of air and transmit at least a major part of the charged particles towards the separating unit. The ionizing unit comprises at least one collector electrode and at least one emitter electrode. The separating unit is arranged to attract at least some of the charged particles so as to separate them from the flow of air. Further, the at least one collector electrode is shaped so as to conduct at least a portion of the flow of air and has a spherically curved inner surface and the emitter electrode is centered with respect to the spherically curved inner surface of the collector electrode.