CHICAGO —  Wildfire smoke from Canada has brought air quality levels to unhealthy levels in Chicago and much of the Midwest.

Chicago currently has the worst air quality in the world right now.

An Air Quality Alert has been issued for the Chicago area and Northwest Indiana though Wednesday night. Counties include Cook, DuPage, Will, Grundy, Kane, Kankakee, Kendall, La Salle, Lake and McHenry in Illinois.

People with heart or lung disease, older adults, children and teens should avoid strenuous outdoor activities, keep outdoor activities short. Others should choose less strenuous activities limit active time outdoors.

The thick haze shrouding Chicago cut Tuesday morning visibilities to 2 to 3 miles.

Full forecast details and more at the WGN Weather Center blog

The Illinois EPA is reporting air quality in Chicago at unhealthful levels, levels first reached in Chicago at 4 p.m. Monday and which have continued through the night and morning.

Latest warnings and watches from the National Weather Service.

The smoke has been “mixed” down to the surface–due, in part, to showers the past 24 hours–and it’s possible to smell the smoke in many areas.

Here’s what EPA says about such levels: “Unhealthy (Red): 151-200 AQI is considered unsafe and anyone could experience negative health effects from pollution in the air.”

It is recommended in such conditions that those with respiratory consider limiting outdoor exposure and exertion during the period of elevated pollution levels.

Air Quality an Issue Throughout Illinois

Morning measurements indicate unhealthful air qualities are being noted not only across the Chicago area–but also west to Rockford and south to Peoria.

Fifteen of the past 30 days have seen air qualities affected by Canadian smoke and the build-up of other pollutants exacerbated by lake breezes which bring a layer of cooler air, which past measurements have put at a depth of around 2,000 feet creating a meteorological condition known as a TEMPERATURE INVERSION. During periods of temperature inversions, instead of temperatures falling with height as they usually do–a set up in which air is encouraged to “mix” vertically, a process which thins out pollution concentrations—temps hold steady or even rise with height through the 2,000 ft. deep layer. This essentially traps smoke and pollutants in the lower levels and leads to the unhealthful air quality.

Here’s a 52 hour national weather service animated computer model smoke forecast

More from Tom Skilling on his Facebook page here.