The Minnesota Pollution Control Agency has issued an air quality alert for the Twin Cities and eastern and central Minnesota for Thursday from noon to 8 p.m.
Temperatures near 90 degrees, wildfire smoke drifting in from the west, and a sunny sky will result in elevated ozone and fine particles in the air that can create unhealthy conditions for people who are sensitive to air quality.
The worst conditions are expected during the afternoon and early evening in the Twin Cities area, St. Cloud, Hinckley, and the tribal nation of Mille Lacs.
The air will improve slightly, from an orange alert to a yellow alert level, when the sun sets, the agency said. But fine particles and ozone will still be elevated.
People most at risk include those with asthma or other breathing conditions, children and teenagers, and anyone doing heavy physical activity or sports outdoors.
People with those conditions may experience difficulty breathing deeply, shortness of breath, throat soreness, wheezing, coughing, or unusual fatigue.
Health officials said everyone should take some precautions when the air quality is bad: limit or postpone your physical activity, stay away from busy roads and wood fires.
Ozone is produced on hot, sunny days by a chemical reaction between volatile organic compounds and oxides of nitrogen. In order to reduce air pollution, state health officials recommend reducing activities such as driving, lighting backyard fires, and operating lawn mowers and other small engines.