Air purifier

These devices are commonly marketed as being beneficial to allergy sufferers and asthmatics, and at reducing or eliminating second-hand tobacco smoke.

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.

[9] 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.

[12] 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.

[13] The researchers found an association between the deployment of air purifying devices and reduced nosocomial transmission of SARS-CoV-2 but the size of the effect and uncertainty around it were high.

Many air purifiers generate some ozone, an energetic allotrope of three oxygen atoms, and in the presence of humidity, small amounts of NOx.

[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.

[43] Ozone can damage the lungs, causing chest pain, coughing, shortness of breath and throat irritation.

[44] Due to the below average performance and potential health risks, Consumer Reports has advised against using ozone producing air purifiers.

[46] Ozone generators are used by cleanup contractors on unoccupied rooms to oxidize and permanently remove smoke, mold, and odor damage, and are considered a valuable and effective industrial tool.

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.