Outdoor Air

Like the weather, air quality can change from day to day. The Illinois EPA issues daily air quality forecasts, based on the Air Quality Index (AQI), for 14 sectors in Illinois and posts the information at AIRNow.gov. The AQI is a color-coded system that classifies air quality from Good (Green) to Hazardous (Maroon). Because air quality can change as a result of changin weather conditions, long-range air quality forecasts are not posssible. Air quality forecasts are typically issued the afternoon prior but may be updated throughout the day if conditions warrant, similar to the weather.

Air quality forecasts are developed by Illinois EPA staff that monitor current weather, air quality conditions, and projected forecasts/models to determine what the air quality forecast is expected to be for the coming day.
In addition to air quality forecasts, real time air quality data is uploaded from Illinois EPA’s air monitoring network to the AirNow website for the public to see current conditions throughout the day.

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Air Quality Messages

Air Pollution Action Days

Beyond air quality forecasts, several regions throughout the United States have “Action Day” programs. Action Days are usually called when the Air Quality Index (AQI) registers in the unhealthy ranges. However, there is no current national requirement or threshold to issue such public service messages, resulting in different States/Agencies calling Action Days at different levels and by different names.

In Illinois, this program has historically been specific to only the Chicago Metropolitan Area (Cook and surrounding counties), and uses the term, “Air Pollution Action Day.” Such days are called when air quality is forecasted to be at or above the Orange or “Unhealthy for Sensitive Groups” category of the AQI for two or more consecutive days.
The Air Pollution Action Day program has been expanded to all 14 sectors where air quality is forecasted in Illinois.

Conditions that will trigger an Air Pollution Action Day/National Weather Service Air Quality Alert*":

Chicago Air Pollution Action Day = Air quality is forecasted to be at or above the Orange or “Unhealthy for Sensitive Groups” category of the AQI for two or more consecutive days for the Chicago Metropolitan Area (Cook and surrounding counties).
Statewide/Areawide Air Pollution Action Day = Air quality is forecasted to be at or above the Orange or “Unhealthy for Sensitive Groups” category on the AQI Statewide or in nearly all Illinois sectors.
Red Air Pollution Action Day - Air quality is forecasted to be at or above the Red or "Unhealthy" category on the AQI for any sector in Illinois.

*Historically, the National Weather Service has considered an "Action Day" forecast as an Air Quality Alert.