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Air purifiers Filtering the claims
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Most people buy air purifiers to ease asthma or allergies. But despite product claims, there's little definitive medical evidence that air purifiers help relieve respiratory symptoms. Some may pose a threat even to healthy users.

Electrostatic precipitators are the most heavily promoted air purifiers, accounting for about half of the models sold. Oreck and Sharper Image versions are best sellers, despite their lackluster air-cleaning performance in our tests. Electrostatic precipitators trap particles by applying an electrical charge to them as they pass through the unit and depositing them on plates or filters. The process creates some ozone as a byproduct.

While ozone in the upper atmosphere protects us from the sun's ultraviolet rays, ground-level ozone is an irritant that can aggravate asthma and lessen lung function.

Another type of purifier, ozone generators, are a growing part of the market. They create large amounts of ozone by design and claim to use it to purify the air. We rated two such models Not Acceptable because in our latest tests they reached up to 20 times the voluntary ozone standard based on the limit set by the U.S. Food and Drug Administration for medical devices. The FDA, though, doesn't consider air purifiers a medical device. And the ozone emissions of home air purifiers aren't regulated by any federal agency. But as we went to press, California banned ozone generators for most uses, effective 2010.

Air purifiers that draw air through fabric filters are among those that do the best job of removing dust and smoke from the air without producing any ozone. Top-rated models such as the Whirlpool Whispure, $230, performed better at their lowest, quietest speeds than many others did at their higher, noisier settings. But simple steps such as those mentioned in Improving your air quality could improve air quality enough so that you don't need a purifier. Other findings and issues:

Ozone is a growing concern. No standard exists for acceptable indoor ozone levels generated by a nonmedical device. Underwriters Laboratories (UL) certifies electrostatic precipitators using the FDA limit of 50 parts per billion. But that limit is under scrutiny.

"Fifty parts per billion is by no means universally accepted in the scientific community as being a low enough benchmark for ozone," says Richard Shaughnessy, Ph.D., director of the University of Tulsa's Indoor Air Research Program and the author of an analysis prepared for the Consumer Product Safety Commission on research pertaining to the current limit. A recent study of outdoor air in 98 urban areas, led by Michelle L. Bell, assistant professor of environmental health at Yale University, indicated that even low levels of ground-level ozone were associated with increased risk of premature death.

Ozone has other risks. Studies increasingly suggest that ozone creates other irritants as it reacts with household products such as scented cleaners and air fresheners. Among these irritants are formaldehyde, a carcinogen; acrolein, a toxic irritant found in cigarette smoke; and ultrafine particles. "Picture ultrafine particle behavior the way you see cigarette smoke behave in a lighted room," says Charles J. Weschler, Ph.D., a researcher at the University of Medicine and Dentistry of New Jersey. "They hang in the air for a long time. The concern is how easily the ultrafine particles are inhaled before they can settle."

Germ-cleaning claims are oversold. Many air purifiers claim to rid your home of airborne bacteria and viruses in addition to dust, pollen, and smoke. We ran tests on five portable air purifiers that made those claims. While our tests confirmed that they reduce germs in the air, so should any air purifier that effectively removes dust and smoke.

Still, germ removal isn't a good reason to buy an air purifier. "The limited effectiveness of the home air purifiers may give people a false sense of security," says Edward J. Septimus, M.D., an infectious-disease expert at Methodist Hospital in Houston. "Stick with the basics instead: Wash your hands with soap and water for at least 15 seconds and cover your mouth and nose when you sneeze and cough."

Ozone testing is in flux. Even the UL ozone test is under review as UL and industry and consumer groups, including Consumers Union, the nonprofit publisher of Consumer Reports, search for a better way to measure the ozone some purifiers emit."You can get any results you want depending on how you run the current UL test," says Shaughnessy, who is on the committee revising the standard.

In the past we used the UL ozone test, among others. But because of concerns about the UL approach, we tested ozone-producing air purifiers using our own test in an airtight, unfurnished room. While that won't exactly reproduce the levels in your home, given the increasing concerns about even low levels of ozone, it's useful to have this worst-case scenario of ozone buildup in a room.

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