Most of southern Minnesota south of a line from Ortonville to St. Cloud and Cambridge has been placed in an air quality alert until 9 p.m. Friday because of unhealthy particles brought to the Midwest by wind carrying smoke from Canadian wildfires.
The explanation from the Minnesota Pollution Control Agency is complicated, but it all leads to a simple result: the air quality is unhealthy for sensitive groups, including people with lung disease, asthma, heart disease, children and older adults.
People who are active outside are encouraged to limited prolonged exertion, the National Weather Service says.
Any thunderstorms that develop Friday afternoon and evening will help improve the air quality.
Here's the full air quality alert explanation from the weather service.
"Air quality is expected to worsen Friday to unhealthy levels. Wildfires in northern Alberta, Canada have produced large amounts of pollutants, including smoke, nitrogen oxides (NOx), and volatile organic compounds (VOCs) which have been carried by the winds into the region over the past several days. Sunny skies and hot temperatures will cause these pollutants to react in the air to produce high levels of ground level ozone. Air Quality Index (AQI) values are expected to climb into the low 100s today in the alert area. This is considered unhealthy for sensitive groups. Ozone concentrations will be the lowest in the morning hours Friday, and will gradually rise midday through the afternoon. Air quality will improve Friday evening into the weekend, with thunderstorms expected on Friday evening and cooler air moving in on Saturday."