The Air Quality Index (AQI), formerly the Pollutant Standards Index (PSI), is a uniform system developed by U.S. EPA to enable the public to determine whether air quality levels in a particular location are good, moderate, unhealthful, or worse. The AQI is used as an information tool to advise the public-- it is often presented along with the weather report in local newspapers. The AQI describes the general health effects associated with different pollution levels, as well as whatever precautionary steps may need to be taken if air pollution levels rise into the unhealthful range.
NOTE: In June 2000, EPA updated the PSI index and renamed it Air Quality Index (AQI). The AQI includes a new health risk category (unhealthy for sensitive groups) and two additional pollutants: ozone averaged over 8 hours, and fine particulate matter (PM 2.5).
WHAT DO AQI VALUES MEAN?
The AQI measures five criteria air pollutants (particulate matter, sulfur dioxide, carbon monoxide, nitrogen dioxide, and ozone), and converts the measured pollutant concentrations in a community's air to a number on a scale of 0 to 500. The intervals on the AQI scale relate to the potential health effects of the daily concentrations of each of these five pollutants. The most important number on this scale is 100, since this number corresponds to the National Ambient Air Quality Standard established under the Clean Air Act. A AQI level in excess of 100 means that a pollutant is in the unhealthful range on a given day; a AQI level at or below 100 means that a pollutant reading is in the satisfactory range.
The following table was constructed by the EPA to identify health effects associated with different levels of air pollution, along with the cautionary statements that would be appropriate if air pollution in a community were to fall into one of the "unhealthful" categories on the AQI scale:
General Health Effects and Cautionary Statements
|Up to 50
||None for the general population.
|50 to 100
||Few or none for the general population.
|100 to 200
||Mild aggravation of symptoms among susceptible
people, with irritation symptoms in the
||Persons with existing heart or respiratory ailments should reduce physical
exertion and outdoor activity. General population should reduce vigorous
|200 to 300
||Significant aggravation of symptoms and decreased exercise tolerance in
persons with heart or lung disease; widespread symptoms in the healthy
||Elderly and persons with existing heart or lung disease should stay indoors
and reduce physical activity. General population should avoid vigorous
||Early onset of certain diseases in addition to significant aggravation
of symptoms and decreased exercise tolerance in healthy persons. At AQI
levels above 400, premature death of ill and elderly persons may result.
Healthy people experience adverse symptoms that affect normal activity.
||Elderly and persons with existing diseases should stay indoors and avoid
physical exertion. At AQI levels above 400, general population should
avoid outdoor activity. All people should remain indoors, keeping
windows and doors closed, and minimize physical exertion.
More on the Air Quality Index. More on the relationship between PSI and the new Air Quality Index.