Environmental Progress - Autumn 1996

Ozone Levels Exceed Federal Limits Three Times in Chicago Summer

High ozone events were linked to weekends and holidays

Ozone (smog) levels exceeded the federal health standard three times in the Chicago metropolitan area during the recently ended smog season. Data reported by the Partners for Clean Air coalition and the Illinois EPA showed that ozone levels exceeded the federal standard of 125 parts per billion (ppb) on June 27 and 28, and on July 6. The highest level during those days was 132 ppb., recorded on July 6.

The three high ozone days were linked to weekends and holidays, periods when more people are likely to be driving, barbecuing, mowing lawns or doing other outdoor chores using pollution-generating equipment.

Ozone is a respiratory irritant found in smog. It is formed when emissions from sources like industry, cars and household products combine with heat and sunlight on days with little wind and no precipitation. Ozone can cause health problems for some people, particularly children, the elderly and those with heart and respiratory conditions.

When air pollution levels are likely to be high, the Illinois EPA provides advance warnings to local weather forecasters, utilizing a new, color-coded air quality forecasting system. For example, the Illinois EPA calls a "code red" day when ozone could reach unhealthy levels.

On code red days, the Partners for Clean Air coalition declares an Ozone Action Day. On these days, the 250 Illinois partners among Chicago area businesses, industries and government agencies, voluntarily take action to reduce ozone by limiting employee travel, educating employees about ozone, or revising production schedules to reduce emissions.

Ozone Action Day alerts seek public help in reducing smog formation

Ozone Action Day alerts are also provided by the Partners for Clean Air to Chicago area news media, to inform the public about simple actions they can take to help prevent smog formation.

On high ozone days, certain health precautions are recommended. Children and the elderly should avoid outdoor activities, particularly between 11 a.m. and 7 p.m., and persons with heart or respiratory ailments such as emphysema, asthma or chronic bronchitis, should avoid all outdoor activities. If breathing becomes difficult, moving indoors is recommended.

Strenuous outdoor activities should be avoided by the general population on high ozone days.