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St.
Louis Regional Clean Air Partnership
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 4 Warn Aircast® reports the air pollution values in the following way:
| Gateway Aircast® | AQI Range | Weather Conditions | Health Information |
| Green (Good) |
0 - 50 AQI | Cool summer temperatures, windy and/or cloudy, recent rain or cool front | None |
| Yellow (Moderate) |
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 |
| Orange (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. |
| Red (Unhealthy) |
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 above 100 AQI will trigger preventive action by the American Lung Association of Missouri or other local officials. On days where levels are forecasted to be Orange or Red, above 100 AQI, the American Lung Association and the St. Louis Regional Clean Air Partnership issue an Air Quality Alert. This could include health advisories for citizens or susceptible individuals to limit certain activities and potential restrictions on industrial activities. During air quality alerts, we ask both businesses and people in St. Louis to modify their behaviors so we can reduce our emissions that lead to ozone air pollution.
Click here to review air quality data.
About Air Pollution Subcategories
Air Pollution Basics
• What is Ozone?
• Sources of Ozone
• Ozone Formation
Health Effects of Ozone
• St. Louis Population with
Lung Disease
• How Healthy Adults are
Affected by Ozone
• Tips for Exercisers
• Ozone & Hospital
Admissions
Local Air Quality
• St. Louis Monitor Map
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