An air ioniser is a device that uses high voltage to ionise air molecules. Negative
ions, or anions, are particles with one or more extra electrons, 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. Another type of air ioniser is the ESD ioniser used to neutralise static charge.
In 2002, Cecil Alfred 'Coppy' Laws was credited with being the inventor of the domestic air
ioniser in an obituary in The Independent newspaper.
Air ionisers have been used to eliminate the occurrence of Acinetobacter infections as
well as reduce static electricity buildup in electronics.
Ionic air purifiers
Air ionisers are used in air purifiers. 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 and ceilings. To increase the efficiency of this process, some commercial
products provide such surfaces within the device. The frequency of nosocomial infections
in British hospitals prompted the National Health Service to research the effectiveness
of anions for air purification, finding that repeated airborne acinetobacter infections
in a ward were eliminated by the installation of a negative air ioniser—the infection
rate fell to zero. The SARS Pandemic fuelled the desire for personal ionisers in the Far
East, including Japan. There are no specific standards for these devices.
Ions versus ozone Ionisers should not be confused with ozone
generators, even though both devices operate in a similar way. Ionisers use electrostatically
charged plates 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.
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 humans and animals that the FDA in the United States explicitly demands ozone
therapy not be used as medical treatment, and has taken action against businesses that
fail to comply with this regulation. Ozone is a highly toxic and extremely reactive gas.
A higher daily average than 0.1 ppm is not recommended and can damage the lungs and olfactory
bulb cells directly. Consumer Reports court case
Consumer Reports, a non-profit US-based product-testing magazine, reported in October 2003 that air
ionisers do not perform to high enough standards compared to conventional HEPA filters. The
exception was a combination unit that used a fan to move air while ionizing it. In response
to this report, The Sharper Image, a manufacturer of air ionisers, sued Consumer's Union for
product defamation. Consumer Reports gave the Ionic Breeze and other popular units a
"fail" because they have a low Clean Air Delivery Rate. CADR measures the amount of filtered
air circulated during a short period of time, and was originally designed to rate media-based
air cleaners. The Sharper Image claimed that this test was a poor way to rate the Ionic
Breeze, since it does not take into account other features, such as 24-hour a day continuous
cleaning, ease of maintenance, and silent operation. The US District Court for the Northern
District of California subsequently struck down The Sharper Image's complaint and dismissed
the case, reasoning that The Sharper Image had failed to demonstrate that it could prove
any of the statements made by Consumer Reports were false. The Court's final ruling in May
2005 ordered The Sharper Image to pay US $525,000 for Consumer Union's legal expenses.
Electrostatic neutralizer in electronics Air ionisers are sometimes used in electronic
work environments to eliminate the buildup of potentially damaging static charges on
insulators or conductors. This is sometimes necessary when ground straps cannot be used.
Notebook computer producer ASUS included an integrated air ioniser in the N51Vf laptop.
See also Dehumidifier
Electrostatic precipitator Humidifier
Nebuliser References
External links New Scientist – Air ionizers wipe out hospital
infections Do "corona discharge" devices alleviate asthma?
NIOSH Immediate Danger to Life or Health Documentation Ionic Air Purifiers and Smog
The Negative-Ion Myth Air ion behavior in ventilated rooms Indoor
and Built Environment, 17. pp. 173–182., Fletcher, L.A., Noakes, C.J., Sleigh, P.A.,
Beggs, C.B. and Shepherd, S.J.