The COVID-19 pandemic has increased awareness of the importance of clean air. UV light air purifiers or “sterilization lamps” have been touted as being able to kill 99.9% of viruses, including COVID. But what exactly are UV purifiers and do they live up to the hype?
What is the technology behind UV purifiers?
UV light, or ultraviolet light, is a form of electromagnetic light that is invisible to the naked eye. The main source of UV light is the sun.
There are three types of UV light: UV-A, UV-B, and UV-C. UV-A light has the largest wavelength, ranging from 315-400nm and UV-C light has the shortest wavelength, from 100-280nm.
Because UV-C light has the shortest wavelength, it also has the most energy and is the most effective at destroying viruses and other microbes.
Even though UV-C light has been used for killing germs for over 50 years, scientists are only now beginning to understand how it works so well.
DNA is made of up 4 nucleotides: adenine (A), thymine (T), guanine (G), and cytosine (C). When UV light hits DNA, it knocks an electron loose and causes two T molecules or two C molecules to bond together, creating errors in the strings of DNA. Fortunately, humans have some genetic self-repair mechanisms to minimize UV destruction, but SARS viruses, the viruses that cause coronaviruses, do not.
Although the genetic material of the COVID virus is made up of RNA, not DNA , the effect of UV-C is essentially the same: UV causes genetic damage and the virus is destroyed.
How safe are UV purifiers?
It’s questionable. The biggest issue with UV purifiers is that they emit varying levels of ozone. Even very small amounts of ozone in the air may result in chest pain, coughing, shortness of breath, and throat irritation.
The UV-C radiation itself is also a concern if improperly handled.
Dan Arnold, a scientist at UV Light Technology in the UK warns of the dangers of UV-C purifiers for home use.
“It can take hours to get sunburn from UVB, but with UVC it takes seconds. If your eyes are exposed… you know that gritty feeling you get if you look at the sun? It’s like that times 10, just after a few seconds.” he said.
Special training and equipment are required to use UVC technology safely. In fact, The World Health Organization (WHO) has issued a warning against people using UV light to sterilize their hands or any other part of their skin.
How effective are UV purifiers?
Not very. Microbes have to spend some time in front of the UV light before they’re destroyed. The EPA explains that microbes must be exposed to the light “on the order of minutes and hours rather than the few seconds typical of most UVGI air cleaners.”
Air takes less than a second to filter through purifiers, not nearly enough time to destroy the coronavirus.
Another factor to consider is that, while the UV light may destroy the virus given sufficient time, it can’t do it if the virus is covered by dust or soil, or embedded in a porous surface Because of these concerns, the CDC only recommends UV disinfection in ductwork or pointed at the ceiling in infectious wards, and cautions against using them in place of an air filter.
What’s the alternative?
It’s no coincidence that most UV purifiers also contain HEPA filters. Although the standard for HEPA filters is that they need to be able to filter out 99.95% or more of all particles which are 0.3 microns in diameter, they are actually capable of filtering out particles of almost any size.