An air ioniser (or negative ion generator) is a device that uses high voltage to ionise (electrically charge) air molecules. Negative ions, or anions, are particles with one or more extra electron, conferring a net negative charge to the particle. Cations are positive ions missing one or more electrons, resulting in a net positive charge. Most commercial air purifiers are designed to generate negative ions.
Air ionisers are used in air purifiers to remove particles from the air. Airborne particles are attracted to the electrode in an effect similar to static electricity. These ions are de-ionised by seeking earthed conductors, such as walls, ceilings, tables, computers or other surfaces. They are not eliminated but rather removed from the air by becoming stuck to surfaces, potentially contaminating those surfaces.
The SARS epidemic of 2003 fuelled the desire for personal ionisers in East Asia, including Japan (where many products have been specialised to contain negative ion generators, including toothbrushes, refrigerators, air conditioners, air cleaners, and washing machines). There are however no specific standards for these devices or any evidence that these devices are actually beneficial.
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