Air quality index

Air Quality Index

When we breathe, we take in more than just air. On some days, there may be elevated levels of air pollution, specifically ozone and particulate matter, which change the outdoor air quality. Just like the weather, our air quality is forecasted every day. The daily air quality is assigned a category with a corresponding color. Also, there are actions we should take for each category.

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Daily air quality information is also available through the Chicago Air Quality hotline at 312.744.4365. For residents outside of the City of Chicago, the Air Pollution Hotline at 708.865.6320 provides daily air quality information for all sectors in the Chicago Metropolitan Area.

Air quality index for Chicago

Today, March 31, 2015



  1. Mar 31 Good
  2. Apr 1 Moderate
  3. Apr 2 Good


About the index colors

Think of the AQI as a yardstick that runs from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. AQI values below 100 are generally thought of as satisfactory. When AQI values are above 100, air quality is considered to be unhealthy-at first for certain sensitive groups of people, then for everyone as AQI values get higher.

0–50 Good
Air quality is considered satisfactory, and air pollution poses little or no risk.
51–100 Moderate
Air quality is acceptable; however, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.
101–150 Unhealthy for sensitive groups
Members of sensitive groups may experience health effects. The general public is not likely to be affected.
151–200 Unhealthy
Everyone may begin to experience health effects; members of sensitive groups may experience more serious health effects.
201–300 Very unhealthy
Health alert: everyone may experience more serious health effects.
301–500 Hazardous
Health warnings of emergency conditions. The entire population is more likely to be affected.