Air Quality Index – AQI

Air Quality Index – AQI – metric used by government agencies to inform the public about the quality of air

AQI, the acronym for Air Quality Index, is a metric used by government agencies to inform the public of the current air quality, or in other words, how pollutant it is or has become.  When the Air Quality Index increases, an increasing percentage of the public may experience severe adverse health effects.

Computation of AQI requires an air pollutant concentration over a specified averaging period obtained from an air monitor or model.  Air pollutants vary in potency, and the function of converting from air pollutant concentration to AQI varies by pollutant. Therefore, air quality index values are grouped into ranges.  Each range is assigned a descriptor, color code, and a standardized public health advisory.

AQI can increase due to an increase in air emissions or a lack of dilution of air pollutants.  Stagnant air, which is often caused by an anticyclone, temperature inversion, or low wind speed, lets air pollutants react with chemical reactions between air contaminants and hazy conditions.

When it is anticipated for the AQI to be elevated due to fine particle pollution, an agency or public health organization might:

  1. advise sensitive groups to avoid outdoor exertion, including the elderly, children, and those with respiratory or cardiovascular problems.
  2. Declare an “action day” to encourage voluntary measures to reduce air emissions, such as public transportation.
  3. Recommend the use of masks to keep fine particles from entering the lungs.

There are six measures:

  1. Good – 0 to 50 – air quality is considered satisfactory, and air pollution poses little to no risk.
  2. Moderate – 51 to 100 – air quality is acceptable.  However, there may be a moderate health concern for a minimal number of people who are unusually sensitive to air pollution for some pollutants.
  3. USG – 101 to 150 – although the general public is not likely to be affected at this AQI range, people with lung disease, older adults, and children are at greater risk of ozone exposure. In contrast, persons with heart and lung disease, older adults, and children are at greater risk from particles in the air.
  4. Unhealthy – 151 to 200 – everyone may begin to experience health effects members of sensitive groups may experience more serious health effects.
  5. Very Unhealthy – 201 to 300 – health alert: everyone may experience more serious health effects.
  6. Hazardous – 301 to 500 – health warnings of emergency conditions.  The entire population is more likely to be affected.

You can contact the Missouri Department of Natural Resources, American Lung Association, Missouri DNR, or the St. Louis Regional Air Partnership Forecasts for more information.