Wildfire smoke triggers another bad air quality warning in Minnesota through Thursday

Commuters who walked outside Tuesday morning and smelled something burning weren't imagining it: Canadian smoke has again descended on Minnesota.

The Minnesota Pollution Control Agency issued another warning of bad air quality until midnight Thursday.

Forecasters warned that the air quality index would reach the orange category, or unhealthy for sensitive groups, across the southern third of the state and the northeastern edge, roughly from the Twin Cities up through the Arrowhead region.

Shortly before 10 a.m., hourly air quality index readings in the central Twin Cities had reached the red category, meaning air is unhealthy for everyone to breathe, according to the Environmental Protection Agency and the private company Purple Air.

MPCA issues its alerts based on 24-hour averages, but David Brown, an air quality forecaster for the agency, said readings may spike higher at various points throughout the day.

Brown said two plumes have combined to make the sky hazy on Tuesday — ground-level smoke from just north of the border in Ontario was mixing with the edge of a much larger plume from Quebec, which is lingering over a large swath of the Great Lakes region.

It's been a challenging event to forecast, he said. "With this particular event the smoke models haven't been handling this ground-level smoke very well. They keep indicating things will clear out, but it keeps building and building," Brown said.

Experts advise to stay indoors during days when lung-damaging fine particles from smoke foul the air, or to wear a well-fitted N95 mask if it's necessary to be outdoors.

So far, the agency has warned Minnesota residents about poor air from smoke or ozone for 26 days in 2023.

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