By STEVE KARNOWSKI, Associated Press

MINNEAPOLIS (AP) — Smoke from Canadian wildfires carried another day of poor air quality south of the border to the Midwest, where conditions in parts of Minnesota, Wisconsin and Michigan were rated “very unhealthy” Tuesday.

The fires have forced more than 27,000 Canadians in three provinces to flee their homes, and the smoke has even reached Europe.

The smell of smoke hung over the Minneapolis-St. Paul area on Tuesday morning despite rain that obscured the full measure of the dirty air. The Minnesota Pollution Control Agency issued an alert for almost the entire state into Wednesday, but the Twin Cities area got the worst of it in the Midwest on Tuesday.

“As the smoke continues to move across the state Tuesday, air quality will slowly improve from northwest to southeast for the remainder of the alert area,” the agency said. “The smoke is expected to leave the state by Wednesday at noon.”

The Iowa Department of Natural Resources warned that air quality in a band from the state’s southwest corner to the northeast could fall into the unhealthy category through Thursday morning. The agency recommended that people, especially those with heart and lung disease, avoid long or intense activities and to take extra breaks while doing strenuous actions outdoors.

Smoky conditions that have reached the U.S. periodically in recent weeks extended as far east Tuesday as Michigan, west into the Dakotas and Nebraska, and as far to the southeast as Georgia.

Conditions at ground level are unhealthy

The U.S. Environmental Protection Agency’s AirNow map showed a swath of red for “unhealthy” conditions across the eastern half Minnesota into western Wisconsin and northern Iowa. The map also showed purple for “very unhealthy” across much of the Minneapolis-St. Paul metropolitan area, where the Air Quality Index numbers of 250 and were common, though conditions started to improve slightly by late morning.

The Air Quality Index — AQI — measures how clean or polluted the air is, focusing on health effects that might be experienced within a few hours or days after breathing polluted air. It is based on ground-level ozone, particle pollution, carbon monoxide, sulfur dioxide, and nitrogen dioxide. Particulates are the main issue from the fires

The index ranges from green, where the air quality is satisfactory and air pollution poses little or no risk, to maroon, which is considered hazardous. That level comes with health warnings of emergency conditions where everyone is more likely to be affected, according to AirNow.

While Minnesota officials warned on Monday that conditions in the northwest part of the state could reach the maroon category on Tuesday, conditions there were generally yellow, or moderate. There were a few scattered locations in the Twin Cities area that temporarily hit maroon on Tuesday morning. But by midday Tuesday, most of the remaining maroon spots in the region were on the Upper Peninsula of Michigan.

Hospitals are seeing more patients with respiratory symptoms

Hennepin Healthcare, the main emergency hospital in Minneapolis, has seen a slight increase in visits by patients with respiratory symptoms aggravated by the dirty air.

Dr. Rachel Strykowski, a pulmonologist, said there is usually a bit of a delay before patients come in, which is unfortunate because the sooner those patients contact their doctors, the better the outcome. Typical symptoms, she said, include “increase in shortness of breath, wheezing, maybe coughing a bit more, and flares of their underlying disease, and that’s usually COPD and asthma.”

What happens, Strykowski said, is that the fine particulate matter from the wildfire smoke triggers more inflammation in patients’ airways, aggravating their underlying medical conditions.

Strykowski noted that this is usually a time those patients can go outside and enjoy the summer weather because there are fewer triggers, so the current ones forcing them to stay inside can feel “quite isolating.”

People can protect themselves by staying indoors or by wearing N95 masks, she said. Strykowski added that they must be N95s because the cloth masks many people used during the COVID-19 pandemic don’t provide enough filtration.

The Canadian fire situation

Canada is having another bad wildfire season, and more than 27,000 people in three provinces have been forced to evacuate. Most of the smoke reaching the American Midwest has been coming from fires northwest of the provincial capital of Winnipeg in Manitoba.

Winnipeg hotels opened Monday to evacuees. More than 17,000 Manitoba residents have been displaced since last week, including 5,000 residents of the community of Flin Flon, nearly 400 miles (645 kilometers) northwest of Winnipeg. In neighboring Saskatchewan, 2,500 residents of the town of La Ronge were ordered to flee Monday, on top of more than 8,000 in the province who had been evacuated earlier.

In Saskatoon, where the premiers of Canada’s provinces and the country’s prime minister met Monday, Saskatchewan Premier Scott Moe said all of Canada has come together to help the Prairie provinces.

Two people were killed by a wildfire in mid-May in Lac du Bonnet, northeast of Winnipeg.

Canada’s worst-ever wildfire season was in 2023. It choked much of North America with dangerous smoke for months.

The smoke reaches Europe

Canada’s wildfires are so large and intense that the smoke is even reaching Europe, where it is causing hazy skies but isn’t expected to affect surface-air quality, according the European climate service Copernicus.

The first high-altitude plume reached Greece and the eastern Mediterranean just over two weeks ago, with a much larger plume crossing the Atlantic within the past week and more expected in coming days, according to Copernicus.

“That’s really an indicator of how intense these fires are, that they can deliver smoke,” high enough that they can be carried so far on jet streams, said Mark Parrington, senior scientist at the service.

The fires also are putting out significant levels of carbon pollution — an estimated 56 megatonnes through Monday, second only to 2023, according to Copernicus.

Associated Press writers Tammy Webber in Fenton, Michigan, and Scott McFetridge in Des Moines, Iowa, contributed to this report.