Ultra Violet Light For Air Handling Systems? Question about ultraviolet light in air purifiers or air cleaners

We get asked this question a lot. Here is Professor Thad Godish's reply
What are the potential benefits and pitfalls to installing a ultra-violet light system in a residential air handling system? Will it indeed improve indoor air quality or is it another snake oil- like cure-all in disguise? - Curious in Talahassee

A number of vendors of air cleaners and air cleaning systems include ultraviolet (UV) lights in their product and intensively promote them as further improving indoor air quality. Unfortunately, such use is intuitive at best and is unlikely to have beneficial effects in most indoor applications. Indeed it has the potential for causing some unintentional and unwanted side effects.
Ultraviolet lights have been demonstrated to be an effective control measure for controlling disease germs for which such control is necessary. It is particularly effective in killing airborne bacterial cells that cause tuberculosis (TB) and is used in a number of cases in TB isolation wards and other medical care facilities. The use of UV light as an air- cleaning tool in such environments is both justified and desirable.
In most other cases potential exposures to highly infectious bacteria and viruses are quite low with little need for disinfection by an air cleaning system. In the case of cold and flu viruses in homes, offices and school buildings, exposures from coughing and sneezing from infected individuals occurs even before they (viruses) reach the air cleaning system that could in theory kill them.
To produce UV light one must use systems with a high voltage potential. Such systems produce ozone as a by-product. Indeed UV lights are used as a source of ozone for purposes of reducing algal growth in fish aquaria.
Ozone is toxic to humans even at very low concentrations. Exposures above background levels (20 ppbv) should be avoided (though peak concentrations in polluted outdoor air in cities such as Houston and Los Angeles may reach 120-160 ppbv).
Ozone is a potent bleaching agent. It has been reported to have caused blue carpeting to turn green in some of the Gulf states.
Ozone attacks and degrades rubber products and soft plastics producing ozone cracking. As such, it is undesirable to have above- background levels in either residential or non-residential buildings.
The use of UV lights in most air cleaning systems is in fact a snake-oil kind of thing.
Contributed by Professor Thad Godish.