Air ioniser

This photo shows the sterilisation effects of negative air ionization on a chamber aerosolised with Salmonella enteritidis. The left sample is untreated; the right, treated. Photo taken in a lab operated by the United States Department of Agriculture.

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 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 (balanced ion generator) used to neutralise static charge.

Russian scientist and inventor Alexander Chizhevsky produced the so called Chizhevsky Chandelier around 1918. This was the first modern air ioniser.

Ionic air purifiers

Air ioniser and purifier with its dust collection plates removed

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 (NHS) to research the effectiveness of anions for air purification.^[1] The SARS Pandemic fuelled the desire for personal ionisers in the Far East, 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 no specific standards for these devices. Notebook producers ASUS have now started to include air ionisers in their computers.^[2]

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, and ozone generators will produce gaseous ions of molecules other than ozone, because air consists of more elements than oxygen.

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,^[3] and has taken action against businesses that fail to comply with this regulation.^[4] Ozone is a highly toxic and extremely reactive gas.^[5] 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.^[6]

Consumer Reports court case

Consumer Reports, a non-profit U.S.-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 (among other products), sued Consumer's Union (the publishers of Consumer Reports) 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). 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 U.S. 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.^[7]

Negative ion treatment for seasonal affective disorder

Published research shows that high levels of negative ions are a useful treatment for Seasonal Affective Disorder^[8] if the negative ions are in sufficient density (quantity). Note that this is a separate issue from air cleaning claims or ozone generation that occurs in some devices that also generate negative ions.

Clinical research has been published through Columbia University, American Journal of Psychiatry/APA, 2006^[9] and Archives of General Psychiatry, Columbia University, and New York State Psychiatric Institute, 1998^[10] and Journal of Alternative Complementary Medicine, Columbia University 1995.^[11]

See also

• Electrostatic precipitator
• Humidifier
• Negative air ionization therapy
• Seasonal affective disorder
• Negative ion
• Nebuliser

References

1. ^ "Air ionizers wipe out hospital infections". The New Scientist. http://www.newscientist.com/article/dn3228-air-ionizers-wipe-out-hospital-infections.htm. Retrieved 2006-08-30. 
2. ^ http://www.asus.com/product.aspx?P_ID=0Tc42s23bOdbbvY5
3. ^ "TITLE 21—FOOD AND DRUGS; CHAPTER I—FOOD AND DRUG ADMINISTRATION DEPARTMENT OF HEALTH AND HUMAN SERVICES; SUBCHAPTER H—MEDICAL DEVICES". U.S. Food & Drug Administration (FDA) website. http://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/CFRSearch.cfm?FR=801.415. Retrieved 2006-08-30. 
4. ^ Kurtzweil P (1999). "Ozone generators generate prison terms for couple". FDA Consum 33 (6): 36–7. PMID 10628316. http://findarticles.com/p/articles/mi_m1370/is_6_33/ai_57800127/. 
5. ^ "Ozone: Good Up High, Bad Nearby". Environmental Protection Agency (EPA) Website. http://www.epa.gov/oar/oaqps/gooduphigh/bad.html. Retrieved 2006-08-30. 
6. ^ "Ozone Generators that are Sold as Air Cleaners: An Assessment of Effectiveness and Health Consequences". EPA Website. http://www.epa.gov/iaq/pubs/ozonegen.html. Retrieved 2006-08-30. 
7. ^ "Sharper Image pays $525,000 to end lawsuit against CU". Consumer Reports. 2006-08-06. http://www.consumerreports.org/cro/appliances/sharper-image-lawsuit-ends-505-air-purifier-ionic-air-cleaner.htm. 
8. ^ http://pn.psychiatryonline.org/cgi/content/full/42/1/25
9. ^ http://ajp.psychiatryonline.org/cgi/content/full/163/12/2126
10. ^ Archives of General Psychiatry, 1998. 1998;55:875–882
11. ^ . doi:10.1089/acm.1995.1.87. PMID 9395604. 

External links

• New Scientist – Air ionisers wipe out hospital infections
• Do "corona discharge" devices alleviate asthma?
• Overview of electrofilter precipitator
• NIOSH Immediate Danger to Life or Health (Ozone) Documentation
• Ionic Air Purifiers and Smog
• The Negative-Ion Myth
• Ionisers in the workplace information
• Air ion behaviour in ventilated rooms Indoor and Built Environment, 17 (2). pp. 173–182., Fletcher, L.A., Noakes, C.J., Sleigh, P.A., Beggs, C.B. and Shepherd, S.J. (2008)