UV Air Purifiers

There are a number of manufacturers of air purifiers who have begun to include a UV stage in their products. This is done so that the air purifiers address the concerns of those who are concerned about microorganisms such as bacteria and viruses. The at-risk very old and very young are typically the population for which UV air purifiers are purchased. Therefore these air purifiers are often seen in nursing homes or day care centers.

Ultraviolet or UV light has a shorter wavelength than violet light which has the shortest wavelength in the visible spectrum. Thus UV is in visible to the human eye. The UV spectrum has been divided into three categories: 380–315 nm which is called UVA and was used in the “Backlights” of the 70s, 315–280 nm which is called UVB, and <280 nm which is called UVC and the range which kills microorganisms. UVA, UVB, and UVC can all cause damage to the eyes and also cause skin cancer.

UV is effective in killing organisms such as bacteria and viruses. It achieves this by disturbing the DNA of the organism at a molecular level. There are two wavelengths of UV light that are best absorbed and thus most effective at killing microorganisms. These are 185 nm and 265 nm. This means that for a UV lamp to be effective killing microorganisms it must emit energy in or around one of those wavelengths.

Keeping track of bulb life is critical. The bulbs will continue to “light” with the violet color which is a side effect of the bulb technology after they have stopped emitting in the UVC range. So when you start using your UV based air purifiers or put in new bulbs it is critical that you write the date in permanent marker on the bottom of the air purifier so that you will not forget. Then calculate the life of the bulbs based on the air purifiers manufacturer's recommendations and write the change date on you calendar.

While UV technology is excellent at destroying viruses and bacteria it should not be employed without a particulate filter system ahead of the lamps.  Without a particulate filter system too many microorganisms may be shaded from the light by particulates.  Therefore, most air purifiers that employ UV start by filtering the air with HEPA and activated carbon and use the UV as a final stage of filtration.

Ted Zajac, Jr.
MSE Johns Hopkins University