Several manufacturers are currently selling ozone generators as air cleaners. The companies manufacturing these devices state they are safe and effective at controlling indoor air pollution; however, for almost a century health professionals and health organizations such as the American Lung Association have challenged these claims.



Sellers of ozone-producing devices often use fanciful terms to describe ozone. It is referred to in such terms as "activated oxygen" or "pure air", which suggest that ozone is merely a healthy kind of oxygen. However, ozone is a toxic gas which has vastly different chemical and toxicological properties compared to oxygen.

Ozone is a molecule composed of three atoms of oxygen, as opposed to the oxygen we normally breath, which has two. The O2 molecule is stable and nonreactive, whereas the O3 molecule is unstable, tending to dissociate and produce an O2 molecule and one single ionized oxygen atom. This single atom acts as a "free radicle", that is, it reacts with other nearby substances and changes their chemical composition. It is this ability to combine with other substances that forms the basis of manufacturers' claims that it binds up organic particles in the air and removes them from circulation.

Unfortunately, the same chemical properties which allow ozone to react with organic material in the environment also give it the ability to react with similar organic material in the body, with potentially harmful health consequences. When inhaled, ozone can damage the lungs, and it is considered an undesirable substance that is a component of smog.

Inhalation of ozone at even low amounts can cause respiratory problems and throat irritation. In addition, ozone worsens chronic respiratory diseases such as asthma and impairs the body's natural ability to fight respiratory infections.

A generally accepted theory of aging states that the cells of the human body age both due to genetic factors (loss of cell telomeres) and oxidative damage by free radicals. People are encouraged to eat a diet high in antioxidants, and many take antioxidant supplements, precisely to avoid the kind of damage caused by reactive substances such as ozone.

Most people recover from acute exposure to ozone, but according to a 1996 EPA study, long-term exposure may cause permanent lung damage. The EPA regards ozone as an air pollutant and has formulated air quality standards to enable local officials to warn the public when ozone levels in urban areas are excessive. When ozone (and other air pollutants) are high, asthmatics and patients with chronic lung disease are encouraged to stay inside, and healthy people are told to refrain from strenuous outdoor exercise which raises their breathing rate in the toxic air. Since people are advised to avoid ozone in the outdoor environment, it is difficult to understand why anyone would buy a device to purposely produce it within their own homes.

The FDA requires ozone output of indoor medical devices to be less than 0.05 ppm. The Occupational Safety and Health Administration (OSHA) requires that workers' exposure to ozone not exceed an average concentration of more than 0.10 ppm for 8 hours. The National Institute of Occupational Safety And Health (NIOSH) recommends an upper limit of 0.10 ppm which should not be exceeded even briefly. EPA's National Ambient Air Quality Standard for ozone is a maximum 8 hour average outdoor concentration of 0.08 ppm.

The EPA coined the phrase "good up high -bad nearby" to differentiate between ozone in the upper and lower atmosphere. Stratospheric ozone in the upper atmosphere about 10 to 50km (32,000 to 164,000 feet) above Earth's surface helps filter out damaging ultraviolet solar radiation. This ozone layer is being decimated by CFC compounds used in refrigerators and coolant systems. After negotiation of an international treaty, the Montreal Protocol, CFC production was sharply limited beginning in 1987 and phased out completely by 1996, and a study by the American Geophysical Union shows the rate of stratospheric ozone destruction slowing.

Ozone Generators are ineffective in controlling indoor air pollution, because scientific evidence shows that at concentrations that do not exceed public health standards, ozone has little potential to remove indoor air contaminants, though it still has the longterm potential to cause lung irritation.

Vendors claim that ozone will render almost every chemical contaminant harmless through a chemical reaction whose only by-products are carbon dioxide, oxygen and water. This is false advertising for several reasons.

First, it takes months to years for ozone to react with many of the chemicals commonly found in indoor air (Boeniger, 1995); so for all practical purposes, this is useless. Also, ozone generators will not remove carbon monoxide (Salls, 1927; Shaughnessy et al., 1994) or formaldehyde (Esswein and Boeniger, 1994).

Secondly, in many cases where the reaction between the pollutants and ozone does occur readily, the by-products are as harmful or irritating as the original pollutants (Weschler et al., 1992a, 1992b, 1996; Zhang and Lioy, 1994).

For instance, a laboratory experiment was conducted which mixed ozone with chemicals from new carpet. Ozone did reduce many of the chemicals, including those which can produce "new carpet" odor. However, the reaction produced a variety of aldehydes, and the total concentration of organic chemicals in the air actually increased (Weschler, et. al., 1992b). Levels of irritating formic acid also rise (Zhang and Lioy, 1994).

Some of the byproducts of ozone reaction are themselves reactive and go on to produce further irritating and corrosive by-products (Weschler and Shields, 1996, 1997a, 1997b). Ozone producing devices turn an indoor environment into a seething chemical flask.

Third, ozone by itself does not remove airborne particles such as pollen and housedust. However, some ozone generators are manufactured with an "ion generator" or "ionizer" in the same unit to disperse negatively (and/or positively) charged ions into the air. These ions attach to particles in the air giving them a negative (or positive) charge so that the particles may attach to nearby surfaces such as walls or furniture, creating an undesirable grimy layer; or attach to one another and settle out of the air. In recent experiments, ionizers proved ineffective in removing dust, tobacco smoke, pollen or fungal spores compared to either high efficiency particle filters or electrostatic precipitators. (Shaughnessy et al., 1994; Pierce, et al., 1996).

Even at concentrations that greatly exceed public health standards, ozone is ineffective at cleaning the air. And unfortunately, there is evidence to suggest that in some circumstances ozone generating devices exceed tolerable output limits. Due to the varying brands and models of these machines, and the different room sizes in which they are eventually used, there can be great variation in the eventual concentration of ozone in the air.

In a study by Shaughnessy and Oatman (1991), a large ozone generator recommended by the manufacturer for spaces "up to 3,000 square feet," was placed in a 350 square foot room and run at a high setting. The ozone in the room quickly reached hazardous levels of 0.50 to 0.80 ppm, 5-10 times higher than public health limits.

In a 1995 EPA study, several different ozone generators were tested in a home environment, in rooms of various sizes, with doors alternately opened and closed, and with the central ventilation system fan alternately turned on and off. The results showed that some ozone generators, when run at maximum settings in a sealed room, frequently produced hazardous concentrations of 0.20 - 0.30 ppm. When the units were run at lesser settings, with interior doors opened, concentrations generally remained within public health standards.

Due to this wide variation in output and concentration, it is impossible for consumers to know how much ozone is actually in the air they are breathing; in many ordinary circumstances, ozone generators can produce toxic levels. At least one manufacturer is selling machines equipped with ozone sensors that turn the machine on and off in response to ambient ozone levels, in order to maintain levels of this entirely undesirable gas within a"safe" range. The EPA is currently conducting tests to evaluating the reliability of these sensors.