Subject Top Page: Air Quality Index

Air Quality Index

This page last reviewed August 30, 2011


The Air Quality Index (AQI) (formerly known as the Pollutant Standards Index) was issued on July 23, 1999 by the U.S. EPA for daily air quality reporting to the public. The index is designed to provide accurate, timely and easily understandable information about daily levels of air pollution and ranges from 0 to 500. The higher the AQI value, the greater the level of air pollution and the greater the health concern. An AQI value of 100 generally corresponds to the national air quality standard for the pollutant, which is the level EPA has set to protect public health. The AQI reflects revisions to the primary health-based national ambient air quality standards for ground-level ozone and particulate matter issued by U.S. EPA in 1997. For more detailed information about the AQI, please visit the U.S. EPA's AirNow website.

For information about AQI levels in your area please visit the following links:


The intervals, color code assignment, and the terms describing the AQI are as follows:

AQI
Index Values
Health Categories Cautionary Statements for 8-Hour Ozone
0 to 50 Good None
51 to 100 Moderate Unusually sensitive people should consider limiting prolonged outdoor exertion.
101 to 150 Unhealthy for Sensitive Groups Active children and adults, and people with respiratory disease, such as asthma, should limit prolonged outdoor exertion.
151 to 200 Unhealthy Active children and adults, and people with respiratory disease, such as asthma, should avoid prolonged outdoor exertion; everyone else, especially children, should limit prolonged outdoor exertion.
201 to 300 Very Unhealthy Active children and adults, and people with respiratory disease, such as asthma, should avoid all outdoor exertion; everyone else especially children, should limit outdoor exertion.
301 to 500 Hazardous Everyone should avoid all outdoor exertion.

The Pollutant Standards Index (PSI) is still calculated daily for many major metropolitan areas of the United States with populations exceeding 200,000. The PSI converts measured pollutant concentration in a community's air to a number on a scale from 0 to 500. The number of 100, corresponds to the air quality standard established under the federal Clean Air Act. According to the U.S. EPA, a PSI level in excess of 100 means that a pollutant is in the unhealthy range on a given day, a PSI level at or below 100 means that a pollutant reading is in the satisfactory range.

The intervals and the terms describing the federal PSI air quality levels are as follows:

PSI
Index Values
Health Categories Further Comment
From 0 to 50 Good  
From 51 to 100 Moderate 100 = National Ozone Standard
From 101 to 199 Unhealthful 138 = Health Advisory - Athletes should avoid strenuous outdoor activities
From 200 to 299 Very Unhealthful 200 = Stage I Alert - Everyone should avoid strenuous outdoor activites
275 = Stage II Alert - Everyone should remain indoors
Over 300 Hazardous  

See also these Recommendations for Schools and Others on Poor Air Quality Days.
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