Wildfire smoke from Quebec and pollution from the Chicago area have led to another air quality alert for a swath of eastern Minnesota, with the alert in place until at least 9 a.m. Monday.

The Minnesota Pollution Control Agency has warned of poor air quality from Hinckley to St. Cloud to Rochester, including the Twin Cities metro, on Sunday and Monday. Children, older adults and people with health issues are warned to limit their time outside Sunday and Monday.

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

Unusually, said pollution control agency meteorologist Nick Witcraft, Sunday’s air quality alert is a warning for both ozone and particulate matter. 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 later 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.