People with chronic respiratory issues are being advised to limit prolonged outdoor activity.
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Smoke from the raging wildfires in the western U.S. and Canada has created poor air quality, resulting in "elevated ozone levels and fine particles."
RELATED: Wildfire smoke casts haze over Chicago skies, impacting air quality
While most of the smoke is aloft, some is also making it to ground level and affecting our Air Quality Index, also called the AQI.
"What you have to know about the AQI is that 100 is the level where unsafe starts to happen, where the air is labeled unhealthy," said Brian Urbaszewski, director of environmental health programs at Respiratory Health Association. "And that can be from ozone/smog, it could be from fine particulate matter, like soot. It could be from any number of air pollutants as well."
The alert is for the Chicago metropolitan area counties in Illinois, NSW tweeted Sunday.
Officials say anyone with pulmonary or respiratory diseases, such as asthma, should consider reducing their activity level or shorten the amount of time they are active outdoors.
"When you hit that 100 level and you're exceeding federal air quality health standards, it's really at the point where people, especially with chronic diseases, lung and heart conditions, should really take it easy, stay indoors," Urbaszewski said.
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The haze in Chicago also extends east to Boston and New York City, and thinner smoke stretches all the way south to the border with Mexico!
RELATED: Wildfires produced up to half of pollution in US West, according to study
For more information, visit airnow.gov.
The video featured is from a previous report.