The National Weather Service issued an air quality alert Saturday afternoon for the Chicago area.
The alert came after the Illinois Environmental Protection Agency declared an air pollution action day, the weather service said. An air pollution action day is announced when widespread ozone or particulates are observed to be at or above healthy levels for people sensitive to the conditions.
That so-called "action day" was extended through the Memorial Day holiday by the EPA.
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Active children and adults, especially those with pulmonary or respiratory diseases like asthma, were advised to limit their outdoor activity, the weather service said. The general public will not likely be affected by the conditions.
The air quality alert will remain in effect until midnight Tuesday, the weather service said. The alert includes McHenry, Lake, Kane, DuPage, Cook, Kendall, Grundy and Will counties.