Hundreds of school districts and universities around the country rushed to invest in new electronic air cleaning systems in the last two years to help alleviate COVID concerns. But in many cases, those investments turned out to be doing more harm than good.

Why it matters: In some cases, the efforts to keep kids and teachers safe in schools may not be as effective as claimed. In other cases, the air cleaning systems could be exposing them to the harmful toxins ozone and formaldehyde, experts warn…

Matthew Johnson, professor of chemistry at the University of Copenhagen and co-founder of air quality tech firm AirLabs, said he recommends schools stay away from products that boast the use of ionization, plasma, dry hydrogen peroxide, or ultraviolet rays, he said.

In the example of ionization devices, the Environmental Protection Agency warns the devices have the “potential to generate ozone and other potentially harmful by-products indoors.”