Wildfire smoke puts Chicago among cities with worst air quality in the world

A new round of dense smoke has invaded the United States, specifically the Great Lakes region, as wildfires continue to munch through forests across Quebec and Ontario, with more than 3.7 million acres scorched over the last week in those provinces alone. Early Tuesday, Chicago air quality ranked the worst in the world among major cities.

As residents in Chicago awoke to smoke in the air, the city was joined by Minneapolis and Detroit in the top 10 with worst air quality, all dealing with Code Red conditions. Air quality was even worse in smaller cities, such as Grand Rapids, Michigan, where Code Purple has been reached, as it has in much of central lower Michigan.

Air quality alerts are in effect Tuesday for much of Minnesota, all of Wisconsin and Michigan, and parts of northern Indiana and Illinois.

The Air Quality Index (AQI) moves to Code Orange (unhealthy for sensitive groups) at a reading of 101. Code Red (unhealthy for everyone) starts at 151. Once reaching 201, it’s Code Purple (very unhealthy) and finally a Code Maroon (hazardous) begins at 301.

Wildfire smoke’s primary pollutant is often referred to as PM2.5. These are fine particles from burned organic matter, less than or equal to 2.5 microns in diameter. Something like microscopic soot.

The plume on Tuesday

A thick pall of smoke is draped from Quebec and Ontario to the southwest toward parts of the northern Midwest and Great Lakes region. The worst of it was centered over Lake Michigan and surrounding states Tuesday morning.

In Grand Rapids and surrounding areas, it was a mix of smoke and low clouds.

Up to Code Purple air quality values have been observed in Wisconsin, Michigan and northern Indiana so far, with an hourly 217 AQI and still climbing near Grand Rapids, observed at an Environmental Protection Agency monitor. The Canadian city of Sault Ste. Marie, on the international border of Michigan, reached a reading as high as 353 AQI overnight, which is Code Maroon – Code Purple was ongoing there after sunrise Tuesday.

Many more locations from eastern Minnesota to western Ohio were observing Code Red conditions. The thickest of the smoke plume had advanced as far east as Columbus and Cincinnati as of midmorning.

“Low visibility due to wildfire smoke will continue today. Consider limiting prolonged outdoor activities,” wrote the National Weather Service in Chicago.

Visibility in the city was down to two miles, with smoke reported in the observation from Chicago O’Hare International Airport. The Weather Service expects visibilities of 1 to 3 miles across the region for much of the day.

“You can literally smell the smoke in the air today in Chicago from the Canadian wildfires,” wrote a Twitter user.

For the rest of today, smoke continues to slowly move east and somewhat south. It should continue its focus on the lower Great Lakes and into the Midwest or Ohio Valley region. Some may be crossing the Appalachians and spilling eastward by late Tuesday.

Many such days

The number of Code Orange or greater days as a result of wildfire smoke continue to increase in the northeast quadrant of the United States, though they are comparatively minor when examined against areas immediately surrounding the sources of fire in Canada.

Many of these days also saw at least temporary spikes higher than Code Orange.

Much of western Wisconsin – in the thick again here – has already observed four or five Code Orange or higher 24-hour readings this month alone, and before the current wave. It’s a similar story near Detroit, with five in the city and up to seven or eight in nearby locations.

More than a dozen Code Orange or worse days have been tallied in June across the hardest-hit spots north of the border in Ontario and Quebec, especially north and northwest of Ottawa.

These bad air quality days may soon increase into the Northeast, as well. D.C. has seen two bad air days this month, both Code Red. Much of Pennsylvania, New Jersey and into Southern New England has piled up three such days, with a few locations at four or five.

While it is the case that AQI values in this plume are somewhat lower than earlier in the month – when hourly AQI values soared toward 400 in the Northeast Corridor – any values of Code Red or above are concerning for the general public.

Smoke’s future travel plans

This round of smoke, like one that smothered the Northeast from June 7-8, is moving into circulation via a crawling low-pressure area now over the eastern Great Lakes.

In general, winds blow from the east to the north of the low pressure center, pushing smoke westward from the source, before winds out of the north and northwest behind the center push smoke southward. As the low-pressure crawls east, so does the area of smoke it is carrying along with it.

Over the next several days, the low tracks through the Mid-Atlantic and offshore the East Coast. This trajectory would allow smoke to move eastward into the Mid-Atlantic and Northeast, but it has also been raining in the fire source regions, which has cut down on current emissions somewhat.

Even so, it seems a good bet that skies will turn milkier Wednesday and Thursday at the least. Some of the smoke may trickle into the region east of the Appalachians by late Tuesday.

High-level smoke may be common from the areas seeing it Tuesday and through the Mid-Atlantic and perhaps parts of the Southeast by Wednesday. Lower-level smoke is less widespread but may at least temporarily have a notable impact in any of the same locations, while tending to focus on the Ohio Valley to Mid-Atlantic region.

Potential for smoky skies could last into the weekend, although probably with lesser intensity over time as the pattern shifts slightly.