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The Minnesota Pollution Control Agency has extended its air quality alert for east central and southeast Minnesota until at least midnight Tuesday.

Wildfire smoke from Quebec and pollution from the Chicago area continue to linger, continuing the poor air quality alert for the state's east central and southeastern areas. The heaviest smoke was expected to be near Rochester and Winona, officials announced in the latest update.

But air quality was expected to improve Monday evening, when expected thunderstorms rumble into the state and help remove smoke particles from the air, officials said.

The MPCA warned of poor air quality from Hinckley to St. Cloud and Rochester, including the Twin Cities metro, on Sunday and Monday. Officials recommend that children, older adults and people with health issues limit physical exerting activities outside.

This is the sixth air quality alert in less than three weeks, according to the MPCA.

Sunday's air quality alert was an unusual warning for both ozone and particulate matter, said MPCA meteorologist Nick Witcraft. The ozone comes from emissions blown in from the Chicago area, Witcraft said, while wildfire smoke from Quebec accounts for the particulate matter.

A cold front expected late Monday could help clear some of the ozone and smoke, Witcraft said. But weather in recent weeks has been stagnant, said National Weather Service meteorologist Jake Beitlich, and could remain still for some days.

"There's no strong system that's going to change our weather pattern or push our air," he said.

The last three weeks have also been unusually dry, he said, with less than two-tenths of an inch of precipitation since May 15.