Air purifier

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

An air purifier is a device which removes contaminants from the air in a room. 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 such as CO2 from air before processing. Pressure swing adsorbers or other adsorption techniques are typically used for this.

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.[1] Air purifiers are becoming increasingly capable of capturing a greater number of bacterial, virus, and DNA damaging particulates.

Purifying techniques

Several different processes of varying effectiveness can be used to purify air.

High-efficiency particulate arrestance (HEPA) filters remove at most 99.97% of 0.3-micrometer particles and are usually more effective at removing larger particles. HEPA purifiers, which filter all the air going into a clean room, must be arranged so that no air bypasses the HEPA filter. In dusty environments, a HEPA filter may follow an easily cleaned conventional filter (prefilter) which removes coarser impurities so that the HEPA filter needs cleaning or replacing less frequently. HEPA filters do not generate ozone or harmful byproducts in course of operation.
Filter HVAC at MERV 14 or above are rated to remove airborne particles of 0.3 micrometers or larger. A high efficiency MERV 14 filter has a capture rate of at least 75% for particles between 0.3 to 1.0 micrometers. Although the capture rate of a MERV filter is lower than that of a HEPA filter, a central air system can move significantly more air in the same period of time. Using a high-grade MERV filter can be more effective than using a high-powered HEPA machine at a fraction of the initial capital expenditure. Unfortunately, most furnace filters are slid in place without an airtight seal, which allows air to pass around the filters. This problem is worse for the higher-efficiency MERV filters because of the increase in air resistance. Higher-efficiency MERV filters are usually denser and increase air resistance in the central system, requiring a greater air pressure drop and consequently increasing energy costs.
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.[13]

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 high concentration of ozone is dangerous, most air ionizers produce low amounts (< 0.05 ppm). 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. 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: CADR(Clean Air Delivery Rate); efficient area coverage; air changes per hour; the clean air delivery rate, which determines how well air has been purified; 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. 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.[16]

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.[17] 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.[18] IQAir, the educational partner of the American Lung Association, has been a leading industry voice against ozone-producing air cleaning technology.[19]

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.[20]

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.[21][22]

See also


  1. 1 2 H.M. Ang, M Tade, S Wang. (2007). "Volatile organic compounds in the indoor environment and photo-catalytic oxidation: state of the art". Environmental International 33: 694-705.
  5. 1 2 3 W.A. Zeltner, D.T. Tompkins. (2005). "Shedding light on photo catalysis". ASHRAE Transactions 3: 523-534.
  6. 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.
  7. Photocatalysis: Considerations for IAQ-Sensitive Engineering Designs, David J Branson, P.E.., Engineered Systems, April 2006
  8. , Formaldehyde Test Report: Genesis Air Populated Catalyst Panel RTI Report Number: A03230901 May 2009
  9. , Office VOC Mixture Test Report: Genesis Air Populated Catalyst Panel RTI Report Number: A03230902, May 2009
  10. "Study on Photocatalytic Oxidation (PCO) Raises Questions About Formaldehyde as a Byproduct in Indoor Air".
  11. "Residential Air Cleaners (Second Edition) - Indoor Air - US Environmental Protection Agency".
  12. The Application of Ultraviolet Germicidal Technology in HVAC Systems, Michael J. Taylor, Product Manager, Carrier Corporation, Syracuse, NY
  13. D. Y. Goswami. (2006). "Photoelectrochemical air disinfection" US Patent 7,063,820 B2.
  14. Ozone Generators: air cleaners intentionally designed to generate ozone
  15. Hogan, Jenny (4 February 2004). "Smog-busting paint soaks up noxious gases". New Scientist. London: Reed Business Information.
  16. 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.
  17. "Health Effects of Ozone in Patients with Asthma". US Environmental Protection Agency.
  18. "Consumer Reports Article: Not Acceptable: Ozone generators". Archived from the original on 2007-11-16. Retrieved 8 August 2013.
  19. Frank Hammes; President of IQAir. "Ozone: What Air Cleaner Advertisers Don't Tell You". Swede Clean.
  20. "Ozone Generators that are Sold as Air Cleaners". US Environmental Protection Agency.
  21. "AB 2276 Air Cleaner Regulation". Retrieved 2016-02-06.
  22. AB-2276 Ozone: indoor air cleaning devices., Act No. 2276 of 2006-09-29. Retrieved on 2016-02-06.

External links

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