Ionic Air Purifier (aka. Ionizer)
An Ionizer / Ionic Air Purifier produces negatively charged "ions" - electronically charged air molecules which attract dust and other particles. This has a cleaning effect on the air as the particles which have clumped together fall from the air.
The fact that this works can be demonstrated - as dust can be seen to collect near an air ionizer after it has been switched on for a while. Ionizers are quiet in operation but recent research and consumer reports have claimed that ionizers do not perform anything like as well as HEPA Filters in cleaning the air. Also, they are believed to produce small amounts of ozone, a lung irritant. However, some believe that negative ions themselves have other health benefits and may counteract the positive ionization of the air caused by other electronic devices. Here at air-purifiers-online though, we have to say that we are bigger "fans" of HEPA filtration.... :)