Subject Top Page: Air Quality Index

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This page last reviewed November 29, 2007

The U.S. EPA has replaced its Pollutant Standards Index (PSI) with its new Air Quality Index (AQI) in order to incorporate the new Federal ozone and PM2.5 standards. The index is designed to provide accurate, timely and easily understandable information about daily levels of air pollution.

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. This new index 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 much more detailed information, about the AQI and AQI levels in your area, please visit the U.S. EPA's AirNow website.

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

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Air Quality Index Overview

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