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What is the air quality index (AQI)?

The air quality index, or AQI, is a measure describing the amount of particulate matter found in the air. Since this value can vary significantly over short periods of time, the AQI is typically reported for a given city at least once per day. The higher the AQI value, the greater the associated health concerns. Since a few different measures exist out there for characterizing the air quality, we will spare you the details of exactly how the number is calculated. It is worth paying attention to the AQI when you are considering traveling or relocating to new places. Some large cities have developed major ongoing problems with their air quality, and looking at a city’s recent AQI history is a useful indicator of the air quality you can expect to find.

The table below summarizes relevant ranges of AQI values used in the United States and their health implications.

Air Quality Index Level of Health Concern Color (AQI)
0-50 Good Green
51-100 Moderate Yellow
101-150 Unhealthy for Sensitive Groups Orange
151-200 Unhealthy Red
201-300 Very Unhealthy Purple
301-500 Hazardous Maroon


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