Ionic air purifiers

Ionic air purifiers use an electrically charged plate to produce negative gas ions that particulate matter sticks to (in an effect similar to static electricity). Many ionisers are sold as air purifiers, but in this regard they are very inefficient. They will clean the air to a small degree, by charging dust and smoke particles which will then be attracted to a neutral or positively charged surface. Heavier combined particles may precipitate (fall) out of the air should two smaller particles of different charge clump together.

The use of negative ions continues to be a less accepted mainstream therapy in Eastern Europe and the Far East than in Western Europe or the United States , although problems with nosocomial infections (hospital acquired "super-bugs") have led the National Health Service (NHS) in the UK to do extensive research into the effect of negative ions on this area of hygiene. Recent SARS outbreaks have fueled the desire for personal ionisers in the far east, including Japan (where many products have been specialized to contain negative ion generators, including toothbrushes, refrigerators and washing machines). There are no specific standards for these devices, and though a few may have some benefit, most will be at best useless, at worst harmful.

 Air purifier criticisms

Criticisms of ionisers as air purifiers include:

• Cleaning range, as portable units are typically built to clean one room only.
• All the affected airborne particles ultimately wind up on surfaces close to the ioniser, making the area immediately surrounding the ioniser dirty and reducing the unit efficiency as the high voltage emitter is slowly covered in dirt. Overall cleaning efficiency roughly on par with the static charge from the front of a powered-up CRT TV screen. 
• Companies or individuals who sell (or support the use of) air ionizing devices claim additional, less easily substantiated effects, including:
  • Generation of ozone as a beneficial byproduct.
  • Creation of an ionic wind, caused by the repulsion of similarly charged ions near the electrodes.
  • Negative ions producing a general feeling of well-being  (and positive ions producing a feeling of decreased well-being), an effect duplicated in thunderstorms, waterfalls, cathode ray tubes found in televisions and computer monitors.

 Ions vs ozone

Ionisers should not be confused with ozone generators, even though both devices operate in a similar way. Ionisers use an electrostatically charged plate to produce positively or negatively charged gas ions that particulate matter sticks to (in an effect similar to static electricity). Ozone generators are optimised to attract an extra oxygen ion to an O₂ molecule, using either a corona discharge tube or UV light. Even the best ionisers will produce a small amount of ozone, and ozone generators will produce gaseous ions of molecules other than ozone (unless fed by pure oxygen, not air). 

Ozone, is claimed by some alternative medicine proponents to be relatively harmless to humans, but this is a demonstrable fallacy. Ozone is a highly toxic and extremely reactive gas. A higher daily average than 0.1 ppm (0.2 mg/m³) is not recommended and can damage the lungs and olfactory bulb cells directly. At high concentrations, ozone can also be toxic to air-borne bacteria, and may destroy or kill these sometimes infectious organisms. However, the needed concentrations are toxic enough to man and animal that the FDA explicitly demands ozone therapy not be used as medical treatment, and has taken action against businesses that fail to comply with this regulation