May 11, 2006 -- You can create dangerous smog levels in your own home with an ozone-generating air purifier.
The finding comes from a study of ozone-emitting air purifiers by Sergey A. Nizkorodov, PhD, and colleagues at the University of California, Irvine. The researchers studied 13 air purifiers known to give off small and large amounts of ozone, a major ingredient in air pollution.
Included in the study were several ionic air purifiers made by The Sharper Image, including the popular Ionic Breeze Quadra. These machines produce detectable levels of ozone. But they did not emit dangerous levels of ozone, except when a Quadra model intended for a large room was tested in a tiny bathroom.
Ozone generators, however, were a different story. As they are designed to do, they put a lot of ozone into indoor spaces. The devices quickly caused ozone buildups to levels that would trigger severe smog alerts for outdoor air.
"If I put one in my office, I can generate a stage 2 ozone level if I want to," Nizkorodov tells WebMD. "This is the problem -- right now it is not controlled. Air purifiers that make ozone above a certain rate should be banned. The public should not be allowed to buy them."
Ozone is great in the upper atmosphere, where it protects the Earth from harmful radiation. Ground-level ozone, however, isn't our friend. According to the American Lung Association, ozone exposure may lead to premature death, shortness of breath, chest pain when inhaling deeply, and wheezing and coughing. High ozone levels irritate the lung and make asthma worse.
The Nizkorodov study, funded by the National Science Foundation, appears in the May issue of the Journal of the Air & Waste Management Association.
Ozone Generators vs. Ionic Air Purifiers
It's easy for consumers to be confused. Three basic kinds of devices call themselves air purifiers. None is foolproof. Consumer Reports has found that "even the best air cleaners could be a frivolous investment."
There's no ozone emission from air purifiers that use only high-efficiency particulate air filters (HEPA filters) to cleanse the air. Ionizing air purifiers, because of their electric charge, do create ozone. Consumer Reports has warned that they may give off potentially harmful ozone levels.
"There are plenty of ionic air purifiers; only a small fraction make ozone," Nizkorodov says.
Mark Connelly, senior director of appliances and home improvement for Consumer Reports, oversees the magazine's air-cleaner tests.
"You don't want to say that anything that generates ozone is bad," Connelly tells WebMD. "A printer produces ozone, but just because printers sit on people's desks doesn't mean they should be taken off the market. But the people who buy air purifiers are most susceptible to the problems they create. You buy it to make things better, and it ends up making things worse for you."
Whatever ozone comes from ionic air purifiers pales in comparison to the amount produced by ozone-generating air purifiers. These machines make ozone for one reason: That's what they are designed to do.
"Ozone is a very effective way of disinfecting water -- and some believe it is also possible to do this in the air," Nizkorodov says. "Unfortunately, at the concentrations you need to destroy germs and pollutants, the ozone levels are so high you cannot safely use it."
In a small bathroom, the UCI researchers found that one ozone generator, the EZ-COM Air Purifier, took only a half hour to build up ozone to a smog level that would force school closings if detected in a city's air. In a 1,250-square-foot office, the device took about a half hour to build ozone to smog levels that would trigger unsafe air alerts.
By contrast, the Sharper Image Ionic Breeze Quadra model -- an ionic air purifier, not an ozone generator -- built ozone to a maximum level of 40 parts per billion (ppb) in a large office. The FDA considers medical devices safe if they emit less than 50 ppb of ozone. The World Health Organization considers eight-hour ozone levels of 60 ppb to be acceptable.
The Quadra did make the air unsafe when used in a small bathroom -- not the products' intended use, says Sharper Image spokeswoman Suzie Stephens.
"Sharper Image products were included in the study and, in fact, met all safety standards for ultra-low trace ozone emissions when the appropriate-sized models were used in the manufacturer-recommended room sizes," Stephens tells WebMD. "Why they chose to place the unit in a room size for which it is clearly not intended nor used is inexplicable."
Stephens worries that the UCI study sows confusion by testing ionic air purifiers alongside ozone generators. Indeed, she points to news reports on the study that confused Sharper Image products with ozone generators.
"The study found that ozone generators, not ionic air purifiers when used appropriately, can generate potentially unsafe levels of ozone indoors," Stephens says. "None of the Sharper Image air purifiers are ozone generators."
Government Action on the Way?
While Consumer Reports has been critical of ionic air purifiers -- including explicit criticism of the Sharper Image Ionic Breeze Professional with OzoneGuard -- it is far less worried about these devices than about ozone generators.
"We slammed ozone generators back in 1992 -- but they are still being marketed to unsuspecting people," he says. "Those people most susceptible to harm are cranking ozone into their lungs. Ozone generators should be regulated first and foremost."
There's already a bill before the California legislature to regulate these devices. And the California Air Resources Board will meet on May 25 to update its recommendation on ozone generators.
Nizkorodov says he thinks California will set a limit on how much ozone a device will be allowed to generate. He guesses the limit will be between 10 and 100 milligrams of ozone per hour -- and his bet is on the lower limit.
His study found that the Sharper Image Ionic Breeze Quadra puts out 2.2 milligrams of ozone per hour -- far below the lowest limit California is likely to set.
On the other hand, ozone generators fail the test. The EZ-COM Air Purifier put out 68 mg/hour, while the Air-Zone XT-400 put out a whopping 220 mg/hour.