AirNow: Air Quality Index (AQI) Monitoring and Forecasts

The AQI translates air quality data into numbers and colors that help people understand when to take action to protect their health.

AirNow reports current and next-day forecasts for AQI conditions for over 400 cities, as well as nationwide and regional real-time ozone and particle pollution air quality maps, updated hourly, covering 46 states and part of Canada. Map and forecast data are collected using federal reference or equivalent monitoring techniques or techniques approved by the state, local, or tribal monitoring agencies. 

To maintain "real-time" maps, the data are displayed after the end of each hour. Although preliminary data quality assessments are performed, the data in AirNow are not fully verified and validated through the quality assurance procedures monitoring organizations used to officially submit and certify data on the EPA Air Quality System (AQS).