An Illinois Air Pollution Action Day is declared when weather conditions are such that widespread ozone and or particulate levels are expected to be at or above the Unhealthy for Sensitive Groups (USG) category of the Air Quality Index for all or almost all of Illinois.

National Weather Service officials called an air quality alert in effect until midnight as well as a beach hazard warning.

Air quality alerts issued Thursday in Illinois because of Canadian wildfire smoke marked the latest bout in an increasingly common summer occurrence. The alert covers 34 Illinois counties designated as having unhealthy air for all residents.