AQI Guide

The Air Quality Index (AQI) was designed by the EPA to provided a standardized, national method of measuring air quality.  It classifies air quality concentrations as good, moderate, unhealthy for sensitive groups, unhealthy, very unhealthy and hazardous, based on a scale of 0-500.  Each category is color-coded to help make the categories easy to understand.

The U. S. Environmental Protection Agency's color-coded scale for rating air quality1:

Air Quality Rating Air Quality Index Number


Good 0-50  Green   Air quality is good and poses little to no health risks.
Moderate 51-100  Yellow 

 Air quality is acceptable.  It may cause a moderate health concern
 for a small number of people who are unusually sensitive to pollutants.

Unhealthy for Sensitive Groups 101-150  Orange

Members of sensitive groups may experience health effects.
The general public is not likely to be affected.

Unhealthy for General Population 151-200  Red 

 Everyone may experience health effects.  Sensitive groups may
 experience more serious health effects.

Very Unhealthy 201-300  Purple

 Health warnings of emergency conditions.  The entire populations is
 likely affected.

Hazardous >300  Maroon  Health alert. Everyone is likely to experience serious health effects.


1Information from