Air Quality Index – AQI

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

AQI, acronym for Air Quality Index, is a metric used by government agencies to inform the public 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 used to convert from air pollutant concentration to AQI varies by pollutant.  Air quality index values are grouped into ranges.  Each range is assigned a describor, color code and a standardized public health advisory.

AQI can increase due to an increase in air emissions or from a lack of dilution of air pollutants.  Stagnant air often caused by an anticyclone, temperature inversion or low wind speed lets air pollutants chemical reaction 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, elderly, children and those with respiratory or cardiovascular problems.
  2. declare an “action day” to encourage voluntary measures to reduce air emissions, such as using public transportation.
  3. recommend the use of masks to keep fine particles from entering into the lungs.

There are six measures:

  1. Good – 0 to 50 – air quality is considered satisfactory and air pollution posses little to no risk.
  2. Moderate – 51 to 100 – air quality is acceptable.  However, for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution.
  3. USG – 101 to 150 – although general public is not likely to be affected at this AQI range, people with lung disease, older adults and children are at a greater risk from exposure to ozone, whereas persons with heart and lung disease, older adults and children are at greater risk from the presence of 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.

For more information you can contact the Missouri Department of Natural Resources, American Lung Assocation, Missouri DNR, or the St. Louis Regional Air Partnership Forecasts.