By Robert Roy Britt

LiveScience

Updated: 4:36 p.m. ET May 9, 2006

Here's how to create your own personal Stage 2 Smog Alert: Buy an indoor air purifier.

Using a popular process called ionization, the air cleaners can actually generate ozone levels in a room that exceed the worst smog days in Los Angeles, a new study finds.

The devices are popular in urban areas. They are touted as getting rid of dust, pollen and other airborne particles.

Ionic air purifiers, one type of these devices, are said to work by charging airborne particles and then attracting them to metal electrodes. They emit ozone as a byproduct of this ionization process.

In a small and poorly ventilated room, the ozone adds to existing ozone and creates potentially unhealthy concentrations.

"People operating air purifiers indoors are more prone to being exposed to ozone levels in excess of public health standards," said study leader Sergey Nizkorodov, a chemistry professor the University of California, Irvine.

The research, funded in part by the National Science Foundation, was announced today and is detailed in the Journal of the Air & Waste Management Association.

Ozone high in the atmosphere protects Earth from damaging ultraviolet radiation. Down here, it is called smog. Ozone can damage the lungs and cause shortness of breath and throat irritation, and it can also exacerbate asthma.

Nizkorodov and colleagues tested various air purifiers in homes, offices and cars. In many cases, ozone levels inside climbed above 90 parts per billion, exceeding California's basic safety threshold. In some cases, ozone soared higher than 350 parts per billion, which if measured outside would trigger a Stage 2 Smog Alert, an event that hasn't occurred in the Southern California coastal air basin since 1988.

California lawmakers are considering legislation to reduce emissions from indoor air purifiers. Meanwhile, both the state and the U.S. Environmental Protection Agency have issued advisories discouraging their use.

"These machines are insidious," said Barbara Riordan, acting chairperson of the California Air Resources Board (ARB), in a warning last year. "Marketed as a strong defense against indoor air pollution, they emit ozone, the same chemical that the ARB and … U.S. Environmental Protection Agency have been trying to eliminate from our air for decades. More chilling is that some people susceptible to the ill effects of ozone will eagerly bring these Trojan horses home."

Science does not even suggest the things do what they're purported to do.

An EPA fact sheet has this to say about air purifiers: "Available scientific evidence shows that at concentrations that do not exceed public health standards, ozone has little potential to remove indoor air contaminants. Some manufacturers or vendors suggest that ozone will render almost every chemical contaminant harmless by producing a chemical reaction whose only by-products are carbon dioxide, oxygen and water. This is misleading."