.

Chapters

0:00 Introduction
0:59 How do air purifiers work?
1:43 Effectiveness of air purifiers
2:40 Best practices when using purifiers



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]

In 1871, the physicist John Tyndall wrote about his invention, a fireman's respirator, as a result of a combination of protective features of the Stenhouse's respirator and other breathing devices.[3] This invention was later described in 1875.[4]

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.[5][6]

The first residential HEPA filter was reportedly sold in 1963 by brothers Manfred and Klaus Hammes in Germany,[7] who created the Incen Air Corporation which was the precursor to the IQAir corporation.[citation needed]
Use and benefits

Dust, pollen, pet dander, mold spores,[8] 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.[9]
COVID-19
See also: Impact of the COVID-19 pandemic on public transport § Research and development
A Sharp FU-888SV Plasmacluster air purifier.
The same air purifier, cover removed.

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."[10]

One fluid dynamic modelling study from January 2021 suggests that operating air purifiers or air ventilation systems in confined spaces, such as an elevator, during their occupancy by multiple people leads to air circulation effects that could, theoretically, enhance viral transmission.[11] However, real-life testing of portable HEPA/UV air filters in COVID-19 wards in hospital demonstrated complete elimination of air-borne SARS-CoV-2.[12] Interestingly this report also showed a significant reduction in other bacteria, fungal and viral bioaerosol, suggesting that portable filters such as this may be able to prevent not only nosocomial spread of COVID-19 but also other hospital-acquired infections.
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.[13] 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).[14]
Filtration

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: