An air quality alert was in effect for most of the Chicago area Thursday due to wildfire smoke moving into the region from Canada.
Parts of northern Illinois and northwest Indiana were issued the alert, which is in effect until midnight, according to the National Weather Service.
The drop in air quality is due to wildfire smoke and unhealthy ozone pollutants, the weather service said. The area had previously been under an air quality alert for conditions unrelated to the wildfire smoke.
The Illinois Environmental Protection Agency triggered an Air Pollution Action Day and individuals were urged to limit prolonged outdoor activity and take more frequent breaks.
The Air Pollution Action Day alert is triggered when air pollution levels reach the “orange” or “unhealthy for sensitive groups” category on the national Air Quality Index.
Air-quality levels between 101 and 150 are unhealthy for sensitive groups like those with pre-existing respiratory conditions, babies, children and the elderly. Air-quality levels below 100 are considered healthy. Chicago’s Air Quality Index for Thursday reached 179, according to AccuWeather.
Canadian wildfire smoke has had a lingering effect on the Chicago area’s air quality over the last couple of years, including last June when the city’s air ranked among the worst in the world due to the smoke.
In a previous interview with the Sun-Times, retired WGN meteorologist Tom Skilling noted that lower air quality readings are coming from counties adjacent to Lake Michigan because of a temperature inversion that’s created when northeasterly winds bring cooler air that sits over the lake.
“Normally when you go up in the atmosphere, the temperature drops with height,” Skilling said. “When air is heated, it wants to rise and [when there’s a temperature inversion] you shut down the ability of that air to rise and ascend and cut down the vertical mixing of air that thins out air pollutants,” Skilling said.
