About the AQI and NowCast

The Air Quality Index (AQI) reports daily air quality information. It is calculated for five of the six major criteria air pollutants regulated by the federal Clean Air Act: Ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide. EPA established national ambient air quality standards for each pollutant to protect public health. 

The AQI is a national index and the value and colors are the same across the United States. The higher the AQI value, the greater the level of air pollution and health risk.

An AQI of 100 is the level set by EPA for each pollutant to protect public health. An AQI above 100 is considered unhealthy for certain sensitive groups. As AQI increases, air quality becomes unhealthy for the general public. For more information on AQI health precautions, visit our Air Quality Forecasts page and EPA’s AirNow pages.

DEQ collects hourly air quality data from over 30 monitoring stations and converts the information into a real-time Air Quality Index (AQI) known as NowCast. NowCast takes a weighted average of the hourly air quality data and provides a real-time AQI. It uses a longer average during periods of stable air quality and a shorter average when air quality is rapidly changing such as during a wildfire. NowCast is designed to respond to current conditions and help people make real-time health-based decisions.