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Wisconsin Natural Resources magazine

Wisconsin Natural Resources magazine

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Wisconsin is working aggressively to revise and improve air quality regulations for new and existing businesses. © Sherry Sanford
Wisconsin is working aggressively to revise and improve air quality regulations for new and existing businesses.

© Sherry Sanford

December 2004

Air Quality Index

Linking air quality to health concerns

Natasha Kassulke

Air Quality Index

How concerned should you be about the air you will breathe while walking, running or biking today? There is a colorful tool to tell you.


The Department of Natural Resources and the EPA use the Air Quality Index (AQI) to provide timely and easy to understand information on whether air pollution levels pose a health concern. Some newspapers and TV stations in Wisconsin provide AQI information, along with The Weather Channel and USA Today.

An "Ozone Action Day" is called when the forecast indicates that ground-level ozone concentration could reach unhealthy levels the next day, and actions are recommended to help prevent ozone. Air quality health advisories are issued when conditions have reached levels that are considered unhealthy for sensitive groups.

Air quality varies from place to place and, like the weather, from day to day. Air quality is measured by a network of monitors that daily record concentrations of major pollutants at more than a thousand locations across the country.

For each of these pollutants, EPA has established national air quality standards to protect against harmful health effects. Ozone and particle pollution (PM) are of significant concern in Wisconsin. Ozone is likely to have the highest value on a hot summer day, while PM might be highest on a cold, still winter night.

The AQI numerical index runs from 0 to 500 and is also expressed on a color-coded scale.

"The higher the AQI value, the greater the level of pollution and the greater the health danger," explains Lloyd Eagan, director of DNR's Bureau of Air Management. "AQI values below 100 are generally considered satisfactory. AQI values above 100 move into the level of being unhealthy, at first for certain sensitive groups of individuals and as the values get higher, increasingly unhealthy for more people."

It's like a stop-and-go light. Green means go, yellow is caution and red means stop.

To access the AQI report in Wisconsin call 1-866-DAILY AIR (1-866-324-5924). Or visit Air Now.


AQI 0 to 50
"Good" – GREEN

AQI 51 to 100
"Moderate" – YELLOW

AQI 101 to 150
"Unhealthy for sensitive groups" – ORANGE

AQI 151 to 200
"Unhealthy" – RED

AQI 201 to 300
"Very unhealthy" – PURPLE

AQI 301 to 500
"Hazardous" – MAROON

AQI values above 200 are very infrequent and above 300 are extremely rare in the United States.