Indoor Ozone
What about indoor ozone levels?
Indoor ozone concentrations vary widely--from less than 10 percent of the outdoor level to 80 percent of the outdoor level. This large variation is caused by many factors such as air infiltration or exchange rate of the structure, interior air circulation, interior surface composition (e.g., rugs, draperies, furniture, etc.) and reaction with other indoor air compounds. In situations where there is an indoor ozone source, such as ozone-generating air cleaners, indoor ozone concentrations have been reported to range between 0.12 to 0.80 ppm.
While the indoor ozone sources (e.g. ozone generators, electrostatic air cleaners, photocopiers, and laser printers) can be responsible for higher concentrations indoors, outdoor ozone appears to be the major source of indoor ozone. In general, it is safer to be indoors on high ozone days unless there is an ozone-generating device like an air cleaner present.
Should I be concerned about air cleaners generating indoor ozone?
The NC State Health Director has issued several warnings, alerting consumers that certain types of indoor air cleaners can generate potentially harmful concentrations of ozone. These air cleaning devices are known as ozone generating air purifiers. They are also marketed as "energized or activated oxygen" or "pure air" devices.
The ozone generated by such devices is the same chemical that is responsible for the outdoor air pollution warnings issued in North Carolina during summer months. The manufacturers of ozone-generating devices provide room-sizing guidelines and some units are equipped with ozone limiting sensors. However, controlled studies have shown that ozone concentrations from some of these devices can exceed acceptable public health standards. Independent research on ozone has shown that at concentrations below public health standards, the effectiveness of ozone to control indoor air pollutants is limited. A detailed summary on the ozone generator issue may be found at the United States Environmental Protection Agency's (EPA) Indoor Air Quality Web Site.
The North Carolina Department of Health and Human Services (NCDHHS) has serious concerns about ozone exposures from these devices. The EPA and industrial hygienists with the NCDHHS advise the public to use other proven methods for controlling indoor air pollution. These methods include eliminating or controlling pollutant sources, increasing outdoor air ventilation, and using proven methods of air cleaning. For more information on indoor air quality issues, including ozone generators, please contact the Occupational and Environmental Epidemiology Branch at (919) 733-3410.
- Ozone Home Page
- The Basics
- The Symptoms
- Protecting Yourself
- Indoor Ozone
- If You're Serious about Ozone
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Page last updated on Tuesday, 25-Nov-03 10:17:45