This measure, based on data from the Environmental Protection Agency, evaluates states on the number of days the Air Quality Index in counties was not rated “good.” U.S. News calculated a ...

The EPA measures regional air quality index (AQI) by how hazardous it is to the general public. Discover the AQI in your city by searching below.

It comprises two measures: the number of days with an air quality index below a certain threshold and the number of violation points against drinking water systems in each state. Learn more about ...

Please refer to the AirNow information on wildfires to learn how and why the United States Environmental Protection Agency (EPA) applies a correction factor to PurpleAir data to estimate the air ...