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, June 25, 2017



  1. Jun 25 Good
  2. Jun 26 Good
  3. Jun 27 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 50 generally corresponds to the national air quality standard for the pollutant, which is the level the U.S. EPA has set to protect public health. AQI values below 50 are generally thought of as satisfactory. When AQI values are above 50, air quality is considered to be unhealthy--at first for certain sensitive groups of people, then for everyone as AQI values get higher.

The air quality standards were recently tightened, therefore we may see more days in the yellow/orange category this summer.

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 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.
155–200 Unhealthy
Everyone may begin to experience health effects; members of sensitive groups may experience serious health effects.
201–300 Very unhealthy
Health alert: everyone may experience serious health effects.
301–500 Hazardous
Health warnings of emergency conditions. The entire population is likely to be affected.