Air purifier

A Sharp FU-888SV Plasmacluster air purifier.
The same air purifier, cover removed.

An air purifier or air cleaner is a device which removes contaminants from the air in a room to improve indoor air quality. These devices are commonly marketed as being beneficial to allergy sufferers and asthmatics, and at reducing or eliminating second-hand tobacco smoke.

The commercially graded air purifiers are manufactured as either small stand-alone units or larger units that can be affixed to an air handler unit (AHU) or to an HVAC unit found in the medical, industrial, and commercial industries. Air purifiers may also be used in industry to remove impurities from air before processing. Pressure swing adsorbers or other adsorption techniques are typically used for this.


In 1830, a patent was awarded to Charles Anthony Deane for a device comprising a copper helmet with an attached flexible collar and garment. A long leather hose attached to the rear of the helmet was to be used to supply air, the original concept being that it would be pumped using a double bellows. A short pipe allowed breathed air to escape. The garment was to be constructed from leather or airtight cloth, secured by straps.[1]

In the 1860s, John Stenhouse filed two patents applying the absorbent properties of wood charcoal to air purification (patents 19 July 1860 and 21 May 1867), thereby creating the first practical respirator.[2]

A few years later, John Tyndall invented an improvement to the fireman's respirator, a hood that filtered smoke and noxious gas from air (1871, 1874).[3]

In the 1950s, HEPA filters were commercialized as highly efficient air filters, after being put to use in the 1940s in the United States' Manhattan Project to control airborne radioactive contaminants.[4][5]

The first residential HEPA filter was reportedly sold in 1963 by brothers Manfred and Klaus Hammes in Germany,[6] who created the Incen Air Corporation which was the precursor to the IQAir corporation.[citation needed]

Use and benefits of purifiers[]

Dust, pollen, pet dander, mold spores, and dust mite feces can act as allergens, triggering allergies in sensitive people. Smoke particles and volatile organic compounds (VOCs) can pose a risk to health. Exposure to various components such as VOCs increases the likelihood of experiencing symptoms of sick building syndrome.[7]


Joseph Allen, director of the Healthy Buildings program at Harvard's School of Public Health, recommends that school classrooms use an air purifier with a HEPA filter as a way to reduce transmission of COVID-19 virus, saying "Portables with a high-efficiency HEPA filter and sized for the appropriate room can capture 99.97 percent of airborne particles."[8]

However, one study from January 2021 suggests that operating air purifiers or air ventilation systems in confined spaces during their occupancy by multiple people leads or can lead to increased airborne virus transmission due to air circulation effects.[9][10]

Purifying techniques[]

An air purifier placed under a table

There are two types of air purifying technologies, active and passive. Active air purifiers release negatively charged ions into the air, causing pollutants to stick to surfaces, while passive air purification units use air filters to remove pollutants. Passive purifiers are more efficient since all the dust and particulate matter is permanently removed from the air and collected in the filters.[11]

Several different processes of varying effectiveness can be used to purify air. As of 2005, the most common methods were high-efficiency particulate air (HEPA) filters and ultraviolet germicidal irradiation (UVGI).[12]


Air filter purification traps airborne particles by size exclusion. Air is forced through a filter and particles are physically captured by the filter. Various filters exist notably including:

Other methods[]

Air purifier
A related technology relevant to air purification is photoelectrochemical oxidation (PECO) Photoelectrochemical oxidation. While technically a type of PCO, PECO involves electrochemical interactions among the catalyst material and reactive species (e.g., through emplacement of cathodic materials) to improve quantum efficiency; in this way, it is possible to use lower energy UVA radiation as the light source and yet achieve improved effectiveness.[17]

Consumer concerns[]

Other aspects of air cleaners are hazardous gaseous by-products, noise level, frequency of filter replacement, electrical consumption, and visual appeal. Ozone production is typical for air ionizing purifiers. Although a high concentration of ozone is dangerous, most air ionizers produce low amounts (< 0.05 ppm[citation needed]). The noise level of a purifier can be obtained through a customer service department and is usually reported in decibels (dB). The noise levels for most purifiers are low compared to many other home appliances.[citation needed] Frequency of filter replacement and electrical consumption are the major operation costs for any purifier. There are many types of filters; some can be cleaned by water, by hand or by vacuum cleaner, while others need to be replaced every few months or years. In the United States, some purifiers are certified as Energy Star and are energy efficient.

HEPA technology is used in portable air purifiers as it removes common airborne allergens. The US Department of Energy has requirements manufacturers must pass to meet HEPA requirements. The HEPA specification requires removal of at least 99.97% of 0.3 micrometers airborne pollutants. Products that claim to be "HEPA-type", "HEPA-like", or "99% HEPA" do not satisfy these requirements and may not have been tested in independent laboratories.

Air purifiers may be rated on a variety of factors, including Clean Air Delivery Rate (which determines how well air has been purified); efficient area coverage; air changes per hour; energy usage; and the cost of the replacement filters. Two other important factors to consider are the length that the filters are expected to last (measured in months or years) and the noise produced (measured in decibels) by the various settings that the purifier runs on. This information is available from most manufacturers.

Potential ozone hazards[]

As with other health-related appliances, there is controversy surrounding the claims of certain companies, especially involving ionic air purifiers. Many air purifiers generate some ozone, an energetic allotrope of three oxygen atoms, and in the presence of humidity, small amounts of NOx. Because of the nature of the ionization process, ionic air purifiers tend to generate the most ozone.[citation needed] This is a serious concern because ozone is a criteria air pollutant regulated by health-related US federal and state standards. In a controlled experiment, in many cases, ozone concentrations were well in excess of public and/or industrial safety levels established by US Environmental Protection Agency, particularly in poorly ventilated rooms.[21]

Ozone can damage the lungs, causing chest pain, coughing, shortness of breath and throat irritation. It can also worsen chronic respiratory diseases such as asthma and compromise the ability of the body to fight respiratory infections—even in healthy people. People who have asthma and allergy are most prone to the adverse effects of high levels of ozone.[22] For example, increasing ozone concentrations to unsafe levels can increase the risk of asthma attacks.

Due to the below average performance and potential health risks, Consumer Reports has advised against using ozone producing air purifiers.[23] IQAir, the educational partner of the American Lung Association, has been a leading industry voice against ozone-producing air cleaning technology.[citation needed]

Ozone generators used for shock treatments (unoccupied rooms) which are needed by smoke, mold, and odor remediation contractors as well as crime scene cleanup companies to oxidize and permanently remove smoke, mold, and odor damage are considered a valuable and effective tool when used correctly for commercial and industrial purposes. However, there is a growing body of evidence that these machines can produce undesirable by-products.[24]

In September 2007, the California Air Resources Board announced a ban of indoor air cleaning devices which produce ozone above a legal limit. This law, which took effect in 2010, requires testing and certification of all types of indoor air cleaning devices to verify that they do not emit excessive ozone.[25][26]

Industry and markets[]

As of 2015, the United States residential air purifier total addressable market was estimated at around $2 billion per year.[27]

See also[]


  1. ^ Newton, William; Partington, Charles Frederick (1825). "Charles Anthony Deane - 1823 patent". Newton's London Journal of Arts and Sciences. W. Newton. 9: 341.
  2. ^ "Stenhouse, John". Dictionary of National Biography. 54. 1885–1900.
  3. ^ Ian Taggart History of air-purifying type gas-masks in the 19th-century Archived 2013-05-02 at the Wayback Machine. John Tyndall (1871), Fireman's Respirator, and John Tyndall (1874). "On Some Recent Experiments with a Fireman's Respirator". Proceedings of the Royal Society of London. 22 (148–155): 359–361. doi:10.1098/rspl.1873.0060. JSTOR 112853. S2CID 145628172.
  4. ^ Ogunseitan, Oladele (2011-05-03). Green Health: An A-to-Z Guide. SAGE. p. 13. ISBN 9781412996884.
  5. ^ Gantz, Carroll (2012-09-21). The Vacuum Cleaner: A History. McFarland. p. 128. ISBN 9780786493210.
  6. ^ White, Mason (2009-05-01). "99.7 Per Cent Pure". Architectural Design. 79 (3): 18–23. doi:10.1002/ad.883.
  7. ^ a b Wang, Shaobin; Ang, H.M.; Tade, Moses O. (2007). "Volatile organic compounds in indoor environment and photocatalytic oxidation: State of the art". Environment International. 33 (5): 694–705. doi:10.1016/j.envint.2007.02.011. PMID 17376530. Archived from the original on 2019-12-28. Retrieved 2019-12-12.
  8. ^ Daily, Laura (October 19, 2020). "Can an air purifier help protect you against the coronavirus?". Washington Post. Retrieved October 19, 2020. I checked in with two of the top experts on indoor air quality: Joseph Allen, director of the Healthy Buildings program at the Harvard T.H. Chan School of Public Health, and Richard Corsi, dean of the Maseeh College of Engineering and Computer Science at Portland State University. In the fight against the coronavirus, both have championed the cause of placing portable air cleaners equipped with HEPA filters in school classrooms.
  9. ^ "Air purifiers may do more harm than good in confined spaces with airborne viruses". Retrieved 13 February 2021.
  10. ^ Dbouk, Talib; Drikakis, Dimitris (1 January 2021). "On airborne virus transmission in elevators and confined spaces". Physics of Fluids. 33 (1): 011905. doi:10.1063/5.0038180. ISSN 1070-6631. Retrieved 13 February 2021.
  11. ^ "Types and Function of Air Filters | Air Filtration System For Home, Office and Car". Official Blog Updates - Honeywell Air Purifiers. 2017-09-04. Retrieved 2018-02-12.
  12. ^ "Air Cleaning Technologies". Ontario Health Technology Assessment Series. 5 (17): 1–52. 2005-11-01. ISSN 1915-7398. PMC 3382390. PMID 23074468.
  13. ^ Roza, Da; A, R. (1982-12-01). "Particle size for greatest penetration of HEPA filters - and their true efficiency". Cite journal requires |journal= (help)
  14. ^ a b c W.A. Zeltner, D.T. Tompkins. (2005). "Shedding light on photocatalysis". ASHRAE Transactions 3: 523-534.
  15. ^ Ao, C. H.; Lee, S. C. (2004). "Combination effect of activated carbon with TiO2 for the photodegradation of binary pollutants at typical indoor air level". Journal of Photochemistry and Photobiology A: Chemistry. 161 (2–3): 131. doi:10.1016/S1010-6030(03)00276-4. hdl:10397/17192.
  16. ^ "Residential Air Cleaners (Second Edition) - Indoor Air - US Environmental Protection Agency". 2014-07-03.
  17. ^ US patent 7063820B2, Goswami, D. Y., "Photoelectrochemical air disinfection", issued 2006-06-20 
  18. ^ "Residential Air Cleaners: A Technical Summary, 3rd ion". US-EPA. 402-F-09-002. July 2018.
  19. ^ "Archived copy". Archived from the original on 2010-01-04. Retrieved 2010-01-27.CS1 maint: archived copy as title (link)
  20. ^ Hogan, Jenny (4 February 2004). "Smog-busting paint soaks up noxious gases". New Scientist. London: Reed Business Information.
  21. ^ Britigan, Nicole; Alshawa, Ahmad; Nizkorodov, Sergey A. (May 2006). "Quantification of Ozone Levels in Indoor Environments Generated by Ionization and Ozonolysis Air Purifiers". Journal of the Air & Waste Management Association. 56 (5): 601–610. doi:10.1080/10473289.2006.10464467. ISSN 1047-3289. PMID 16739796.
  22. ^ "Health Effects of Ozone in Patients with Asthma". US Environmental Protection Agency. Archived from the original on 2011-06-08.
  23. ^ "Consumer Reports Article: Not Acceptable: Ozone generators". Archived from the original on 2007-11-16. Retrieved 8 August 2013.
  24. ^ "Ozone Generators that are Sold as Air Cleaners". US Environmental Protection Agency. 2014-08-28.
  25. ^ "AB 2276 Air Cleaner Regulation". Retrieved 2016-02-06.
  26. ^ "AB-2276 Ozone: indoor air cleaning devices.". Act No. 2276 of 29 September 2006. Retrieved 2016-02-06.
  27. ^ "U.S. Residential Air Purifiers Market Poised to Surge from USD 2.02 Billion in 2015 to USD 2.72 Billion by 2021 – ZionMarketResearch.Com". CNBC. 2016-08-30. Archived from the original on 2019-04-14. Retrieved 2019-04-14.

External links[]