The Department of Natural Resources is warning of fine particle pollution across east-central Iowa that could be harmful to people with certain health conditions.
The DNR says high levels were found Tuesday morning in Cedar Rapids, Clinton, Davenport, Iowa City, Muscatine and Waterloo.
Vehicles and other combustion sources emit fine particles, and stagnant air doesn't allow the particles to disperse, causing pollution levels to increase.
Officials recommend that people in east-central Iowa limit prolonged outdoor activity if they have respiratory problems or heart disease.
A cold air mass with westerly winds is expected to enter the area early Wednesday, causing pollution levels to drop.