Air purifier

An air purifier is a device which removes contaminants from air. Air purifiers are commonly marketed as being particularly beneficial to allergy sufferers and asthmatics, and at reducing second-hand tobacco smoke.

Use 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.H.M. Ang, M Tade, S Wang. (2007). "Volatile organic compounds in the indoor environment and photocatalytic oxidation: state of the art". Environmental International 33: 694-705.] Air purifiers are used to reduce the concentration of these airborne contaminants and are especially useful for people who suffer from allergies and asthma. They also reduce the need for frequent household cleaning. Air purifiers use a small amount of electrical energy, causing a small amount of expense and environmental effect.

Purifying techniques

Several different processes of varying effectiveness can be used to purify air. Different processes may remove different contaminants, so there is advantage in using more than one process in a purifier.

* Filter-based purification traps airborne particles by size exclusion. Air is forced through a filter and particles are physically captured by the filter. :HEPA filters can, by definition, remove at least 99.97% of 0.3-micrometer particles, and are usually more effective for particles which are larger or slightly smaller. They are effective down to 0.01 micrometers in many cases, but become very ineffective for particles smaller than 0.01 micrometer. 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 does not need to be changed or cleaned frequently. HEPA filters do not generate ozone or other harmful byproducts.

:Filter for HVAC at MERV 13 or above can remove airborne particles of 0.3 micrometers or larger. A medium efficiency MERV 13 has a capture rate of 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.

* Activated carbon is a highly porous material that can absorb volatile chemicals on a molecular basis, but does not remove larger particles. It is important to note that the absorption process when using activated carbon must reach equilibrium thus it may be difficult to completely remove contaminants. Activated carbon is merely a process of changing contaminants from a gaseous phase to a solid phase, when aggravated or disturbed contaminants can be regenerated in indoor air sources.C.H. Ao, S.C. Lee. (2004). “Combination effect of activated carbon with TiO2 for the photo degradation of binary pollutants at typical indoor air level”. Journal of Photochemistry and Photobiology 161: 131-140.] Activated carbon can be used at room temperature and has a long history of commercial use.It is normally used in conjunction with other filter technology, especially with HEPA. * Photocatalytic Oxidation (PCO) is an emerging technology in the HVAC industry that has great potential for application toward improvement of indoor air quality. However, there also is evidence that in practical applications, PCO may substantially increase the amount of formaldehyde in indoor air. [ [http://allergyclean.com/news/uvpcoformaldehyde.htm Photocatalytic Oxidation (PCO) Produces Formaldehyde as a Byproduct in Indoor Air] ] In addition to the prospect of IAQ benefits, it has the added potential for limiting the introduction of unconditioned air to the building space, thereby presenting an opportunity to achieve energy savings over classical prescriptive designs. As with other advanced technologies, sound engineering principles and practices should be employed by the HVAC designer to ensure proper application of the technology. Photocatalytic oxidation systems are able to completely oxidize and degrade organic contaminants. For example, Volatile Organic Compounds found low concentrations within a few hundred ppmv or less are the most likely to be completely oxidized.W.A. Zeltner, D.T. Tompkins. (2005). “Shedding light on photo catalysis”. ASHRAE Transactions 3: 523-534.] However, the system must run for a relatively longer to completely oxidize contaminants. (PCO) uses short-wave ultraviolet light (UVC), commonly used for sterilization, to kill 99.9% of bacteria and virusesFact|date=April 2007. Independent research confirms its effectiveness against molds, bacteria, and virusesFact|date=April 2007. UVC in-duct units can be mounted to an existing forced-air HVAC system. PCO is not a filtering technology, as it does not trap or remove particles. It is sometimes coupled with other filtering technologies for air purification. To remove VOCs present in larger concentrations a system that combines photocatalytic oxidation and some other form of air purification may be necessary.UV sterilization bulbs must be replaced about once a year; [ [http://www.americanultraviolet.com/uvc/faq/index.htm American Ultraviolet Company] ] manufacturers may require periodic replacement as a condition of warranty. Photocatalytic Oxidation systems often have high commercial costs.

*Ionizer purifiers use charged electrical surfaces or needles to generate electrically charged ions. Ions attach to airborne particles which are then electrostatically attracted to a charged collector plate. This mechanism produces trace amounts of ozone and other oxidants as by-products. Most ionizers produce less than 0.05 ppm of ozone, an industrial safety standard. There are two major subdivisions: the fanless ionizer and fan-based ionizer. Fanless ionizers are noiseless and use little power, but are less efficient at air purification. Fan-based ionizers clean and distribute air much faster. Permanently mounted home and industrial ionizer purifiers are called electrostatic precipitators
* Ozone generators produce ozone, and are sometimes sold as whole house air cleaners. Unlike ionizers, ozone generators are designed to produce significant amounts of ozone, a strong oxidant gas which can oxidize many other chemicals. The only safe use of ozone generators is in unoccupied rooms, utilising "shock treatment" commercial ozone generators that produce over 3000 mg of ozone per hour. Restoration contractors use these types of ozone generators to remove smoke odors after fire damage, musty smells after flooding, mold (including toxic molds), and the stench caused by decaying flesh which cannot be removed by bleach or anything else except for ozone. However, it is not healthy to breathe ozone gas, and one should use extreme caution when buying a room air purifier that also produces ozone.

Consumer concerns

When selecting air purifiers, consumers are influenced by several factors besides cleaning ability. These include possible hazardous gaseous by-products, noise level, frequency of filter replacement, electrical consumption, and visual appeal. Ozone production is typical for ionizing purifiers and has received much attention recently. Although high concentration of ozone is dangerous, most ionizers produce low amounts of ozone (<0.05 ppm). The noise level of a purifier can be obtained easily 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 and are not expected to cause hearing loss. However, purifiers are expected to operate over long periods of time. Therefore, even a moderate level of noise can be disturbing to some people. Frequency of filter replacement and electrical consumption are the major operation costs for any purifier. There are many different 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. Some purifiers are certified as ENERGY STAR® and are energy efficient.

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

Other factors that buyers consider when purchasing an air purifier are: the area coverage; the Air Changes Per Hour, which indicates how frequently the air purifier can exchange all the air in a given room; the Clean Air Delivery Rate, which determines how well air has been purified; energy usage; and the cost of the replacement filters. [http://www.achooallergy.com/air-purifier-buying-guide.asp]

Air ionizers and ozone

As with all health-related appliances, there is some controversy surrounding the claims of certain companies, specifically involving ionic air purifiers. Particularly, some ionic air purifiers generate ozone, an energetic allotrope of three oxygen atoms, and in the presence of humidity, small amounts of NOx (laughing gas). Ironically, people who have asthma and allergy are most prone to the adverse effects of high levels of ozone.N Britigan, A Alshawa, S.A. Nizkorodov. (2006)."Quantification of ozone levels in indoor environments generated by ionization and ozonolysis air purifiers," Journal of the Air and Waste Management Association 56: 601-610.] 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 have advised against using ozone producing air purifiers. [ [http://www.consumerreports.org/cro/appliances/heating-cooling-and-air/air-cleaners/air-purifiers-sub/ozone-generators/ozone-generators-not-acceptable.htm Consumer Reports Article: Not Acceptable: Ozone generators] ]
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 however considered a valuable and effective tool when used correctly. Ozone, unlike other harsh chemicals used to clean odors, will revert back to O2 (oxygen) after about 30-40 minutes and will not leave behind any residue or harsh byproducts.

In September, 2007, the California Air Resources Board announced a ban of in-home ozone producing air purifiers. This law, which will take effect in 2009, will require testing and certification of all types of air purifiers to verify that they don't generate too much ozone. This ban does not affect shock treatment ozone generators however. Studies indicate that some ionic air purifiers produce ozone at 3.3 to 4.3 mg ^-1^. [S.A. Grinshpun, G Mainelis, M Tunov, A Adhikari, T Reponen, K Willeke. (2005). “Evaluation of ionic air purifiers for reducing aerosol exposure in confined indoor spaces”. Indoor Air 15: 235-245.] Ozone generators used for shock treatments on the other hand produce over 3000 mg/h, the amount of ozone needed to create a "shock treatment" over a 6 hour period in a 100-200 sq. ft room. The ozone generators which are subject to this ban use cermic Mica plates that produce 300-400 mg/h of ozone and are intended to be used indoors in occupied rooms.

References

<8. Dave Branson PE April 2006. "Photocatalysis: Considerations for IAQ-Sensitive Engineering Designs": http://www.genesisair.com/documents/PhotocatalysisIAQSensitive.pdf><9. Amy K.Swinford, DVM,MS,Dipl. ACVM. "The Capability of the Genesis Air 2002B.mil to Remove and Neutralize High Concentrations of Airborne Biological Contaminants" http://www.genesisair.com/documents/AmySwinfordSummaryGA2002BmilDugwayReport.pdf >

See also

* Air filter
* Air ioniser
* Electrostatic precipitator
* Ozone generator
* HEPA

External links

* [http://www.aircleaningspecialistsonline.com Air Cleaners Air Cleaner] Industrial Air Cleaner, Industrial Air Cleaners, Commercial Air Cleaner, Commercial Air Cleaners
* [http://www.aham.org/ AHAM] Association of Home Appliance Manufacturers
* [http://www.cadr.org/ CADR.org] Information on Clean Air Delivery Rate by AHAM
* [http://www.eh.doe.gov/techstds/standard/std3020/std3020.pdf DOE HEPA Filter Standards] (pdf) HEPA filter specifications for DOE contractors
* [http://www.epa.gov/iaq/pubs/ozonegen.html EPA report on the effectiveness of ozone generators]
* [http://www.epa.gov/iaq/pubs/insidest.html EPA report on indoor air quality]
* [http://www.eh.doe.gov/techstds/standard/std3020/std3020.pdf DOE HEPA Filter Standards] (pdf) HEPA filter specifications for DOE contractors