Air purifiers

Before you buy an air purifier, try some simple, common-sense steps to reduce indoor air pollution. Begin by vacuuming often, banning smoking indoors, minimizing use of candles and wood fires, and using exhaust fans in kitchen, bath, and laundry areas. Test your home for radon gas, which can cause lung cancer (test kits cost about $15). Don't store chemicals, solvents, glues, or pesticides in your house. Minimize the risk of deadly carbon monoxide gas by properly maintaining and venting heating equipment, wood stoves, fireplaces, chimneys, and vents--and by installing carbon-monoxide alarms on all levels of your home. And don't idle your car, run fuel-burning power equipment, or light a barbecue grill in your garage, basement, or in confined spaces near your home.

The better air purifiers do especially well at filtering pollutant particles such as dust, tobacco smoke, and pollen. Volatile organic compounds (VOCs) and other types of gaseous pollutants, however, are another matter. Some portable models with carbon pre-filters are claimed to filter VOCs, known respiratory irritants that arise from adhesives, paints, and cleaning products. But the Environmental Protection Agency warns that such filters are specific to certain gaseous pollutants, not for others, and that no air purifiers are expected to remove all gaseous pollutants found in the typical home. Carbon filters also must be replaced often, typically every 3-6 months, or they stop working--and can even, when full, release trapped pollutants back into the air. The safer course: Heed strict product-label warnings such as "use only in well-ventilated spaces."

Air-purifier models with an electrostatic precipitator remove pollutant particles by charging them as they pass through and collecting them on an oppositely charged metal plate or filter. In the process, they produce some ozone as a byproduct. You'll also find dedicated ozone generators, which produce relatively large amounts of this gas by design. While ozone in the upper atmosphere protects us from the sun's ultraviolet rays, ground-level ozone is an irritant that can worsen asthma and compromise your ability to fight respiratory infections. We believe that air purifiers that emit even small amounts of ozone are a poor choice if someone in your household has pulmonary problems or allergy symptoms. We also suggest that you avoid dedicated ozone generators entirely, given their high ozone emissions.

The very best portable models we tested were effective at cleaning the air of dust, smoke, and pollen at their highest or lowest speed. For whole-house purifiers, our recommended models did best at filtering dust and pollen without impeding the airflow of forced-air heating and cooling systems. The worst models weren't terribly effective at any speed.