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Read the label carefully when buying air 'purifiers'. They are not all created as equals.

Designed to clean the air in your home, some models actually add to indoor air pollution by emitting ozone, the most harmful component of smog.

"Over the last 20 years, billions of dollars have been spent in this country to reduce levels of smog and its main ingredient, ozone. Ironically, ozone generators are being marketed heavily as a means to 'purify' indoor air," reports the California Department of Health Services.

What's more, the American Lung Association says too few studies are available to offer real conclusive evidence about the benefits of any of the appliances, which are more aptly called air cleaners because they remove particulates rather than add purity. Even silicon chip companies' so-called "clean rooms" and surgical operation rooms don't have "pure" air.

Instead of relying solely upon air cleaners to remove pollutants from the air in your home, the American Lung Association and others recommend controlling the source as the front line in the war against bad air.

Even non-ozone emitting air cleaners are second string -- at best.

"As an adjunct to effective source control and adequate ventilation, highly efficient air cleaners can be useful in further reducing levels of certain indoor air pollutants," according to the association's report Residential Air Cleaning Devices.

As for ozone, in the upper atmosphere (stratospheric ozone) it is naturally occurring and environmentally beneficial. It shields the Earth's surface from ultraviolet light. A hole in the ozone removes some of that protection. Ozone at ground level, however, is a harmful air pollutant regulated by federal and state air quality standards which allow a range of 80 parts (of ozone) per billion (parts of air) per hour to 120 parts per billion (ppb) per hour.

Once ground level ozone exceeds those limits, people begin to be threatened by the potential of a variety of negative health effects. Children, especially asthmatics, are most at risk.

Health and air quality officials from the Environmental Protection Agency, California's health services department and similar agencies, say:

  • Ozone can cause eye, nose, throat and lung irritation.
  • Moderate levels of ozone can irritate the eyes, nose, throat, and lungs.
  • Ozone can cause significant temporary decreases in lung capacity in healthy, exercising adults.
  • Some asthmatic individuals are especially susceptible to ozone toxicity, which includes constricting airways.
  • Short-term exposures can cause increased sensitivity to airborne allergens and other irritants, and it can impair the body's immune system.
  • Summertime ozone episodes in the northeastern U.S. lead to a 10 to 20 percent increase in hospital admissions and emergency room visits.
  • Human population studies of long-term exposures to low-level ozone indicate that it may lead to permanent reduction in lung capacity; animal studies have shown chronic high-level exposures can cause lasting structural damage in the lungs.

Naturally produced ozone and the ozone produced by some air cleaners is identical, despite some manufacturer's claims to the contrary, says the EPA.

Air cleaners most likely to produce ozone may even say so and come with warnings advising those with a respiratory disease to consult with a physician about sensitivity to very low ozone.

These so-called ozone generators use a chemical modification process to "clean" the air and have been marketed with misleading claims that ozone removes air contaminants from indoor air by oxidizing airborne gases, and even particulates, to carbon dioxide and water vapor. The problem is, they leave ozone in their air "cleaning" wake.

Electronic filters, generally marketed as electronic air cleaners, electrostatic precipitators and ionizers can also produce ozone, either as a by-product of use or intentionally.

Health and air quality officials concede none of the air filters have been linked to harmful effects, but question the wisdom of attempting to clean the air by using an appliance that generates even a small amount of potentially deadly ozone.

They also say that controlling the source of dirty air is the best path to cleaner air. However, if you insist on buying an air cleaner, consider HEPA (high efficiency particle arrestance) air cleaners and other models that do not produce ozone.

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