Smoke from dozens of Canadian wildfires will hang over the entire state of Minnesota until Friday morning, making air quality unhealthy for all and dangerous for those with asthma or heart conditions, according the Minnesota Pollution Control Agency (MPCA).

The smoke has been following a cold front, pushed by steady wind, from northern Alberta and northern Saskatchewan. It's expected to clear out of the state by 6 a.m. Friday, said David Brown, air quality meteorologist for the MPCA.

The fine particles and pollutants in the smoke can cause shortness of breath or heart palpitations. The MPCA recommends limiting outdoor exercise or exertion. Anyone with pre-existing conditions should be especially careful.

Air quality alerts for wildfire smoke have been increasing in recent years. Serious smoke plumes would typically impact Minnesota once every two or three years. They are now expected to develop just about every spring or summer, Brown said.

"Most of the time the smoke from a wildfire will get lofted almost immediately high into the atmosphere," he said. "But when there are especially warm sunny days where the fire is happening, that smoke will come down and reach the ground. The smoke has kind of been trapped near the ground as it traveled directly toward us."

Air quality alerts peaked around 2010 and 2011. That's when emissions from coal-fired power plants and vehicles had to meet new regulations. Many coal power plants were retired or replaced by natural gas, Brown said.

Air quality steadily improved throughout the state from 2011 until about 2019, when wildfires started to increase. Wildfires during the 2021 drought were particularly bad, with large plumes of heavy smoke covering the state.

Emissions have also been rising in recent years across the country, Brown said.

"Now with COVID [easing] and people getting back into travel and manufacturing picking up, we're starting to see generally increased emissions over the last couple years," he said.