Air Quality Index (AQI)

What is the Air Quality Index?

The Air Quality Index (AQI) is a standardized method of reporting air pollution values. The AQI converts the measured pollutant concentration in a community's air to a number on a scale of 0 to 500. The most important number on this scale is 100, since this number corresponds to the standard established under the Clean Air Act. Currently, the AQI reported on this web site by the Saint Louis Regional Clean Air Partnership is for ground-level ozone only.

What does the AQI do?

AQI figures enable the public to determine whether air pollution levels in a particular location are good, moderate, unhealthful, or worse.

How do I read the AQI values?

In St. Louis, the air quality forecast reports air pollution values in the following way:

Forecast AQI Range Weather Conditions Health Information
0 - 50 AQI Cool summer temperatures, windy and/or cloudy, recent rain or cool front None
51 - 100 AQI Temperatures mid 70's or above, light winds, sunny skies Very sensitive individuals, people with respiratory disease should limit prolonged exertion outdoors
(Unhealthy for sensitive groups)
101 - 150 AQI Temperatures 80's or above, very light winds, sunny skies, hazy, hot HEALTH NOTICE: Sensitive children and adults and people with respiratory disease, such as asthma, should limit prolonged, moderate exertion outdoors.
151- 200 AQI Hazy, hot (90's) and humid HEALTH ADVISORY: Sensitive individuals, people with respiratory disease should avoid exertion outdoors. Others should limit prolonged or vigorous outdoor exercise


What happens when AQI levels are high?

Air pollution readings of 151 or above indicate the presence of a Red Air Quality day. On Red days, children, seniors and other sensitive populations, including those with respiratory disease, should avoid exertion outdoors and limit their time outdoors. When a Red day is forecasted, the American Lung Association in Missouri asks that businesses and St. Louis residents modify their behaviors to help reduce the emissions that lead to ozone pollution. This voluntary modification of behaviors is important year-round, but is especially critical when air quality conditions deteriorate.

Click here to review air quality data.