Skip to main content

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. 
Sign-up to receive FREE Air Quality Forecasts and Alerts

Download the Free AIRNow App for iPhone and Android phones:
iPhone App | Android App

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. 

WHEN IS AN AIR POLLUTION ACTION DAY CALLED/ISSUED?

An Air Pollution Action Day will be issued the afternoon before and will run from issuance through the duration of the next calendar day.  Conditions that will trigger an Air Pollution Action Day are:

  1. 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); OR
  2. Air quality is forecasted to be at or above the Orange or “Unhealthy for Sensitive Groups” category on the AQI Statewide or in a majority of Illinois sectors.

Air Quality Alert

An Air Quality Alert is issued by the Illinois EPA when:

  1. An Air Pollution Action Day is issued by the Illinois EPA. Historically, the NWS has considered an Action Day forecast as an Air Quality Alert.  Therefore, future Air Quality Alerts will coincide with the NWS procedures.
  2. Air quality is forecasted to be at or above the Red or "Unhealthy" category on the AQI for any sector in Illinois.

*If Illinois EPA issues a special air quality statement, such as an Air Pollution Action Day and/or an Air Quality Alert, it is provided to the National Weather Service (NWS) for distribution through their channels, which includes news meteorologists, weather apps, etc.

Additional Resources

Illinois Department of Public Health - Air Quality

Air Quality Guide for Particle Pollution

Air Quality Guide for Ozone Pollution

Subscribe to Free Air Quality Forecasts & RealTime Alerts

Download the Free AIRNow App for iPhone and Android phones:
iPhone App | Android App