Much of eastern Wisconsin is breathing unhealthy air on Thursday, as the Wisconsin Department of Natural Resources warns that ground-level ozone will reach harmful levels from Green Bay south to the Illinois line — part of a broader bout of summer smog spreading across the Great Lakes and Ohio Valley.
Where and When the Advisory Applies
The Wisconsin DNR issued an Air Quality Advisory for ozone running from noon until 11 p.m.
Thursday across 21 counties spanning southeast, east-central and northeast Wisconsin — including Milwaukee, Racine, Kenosha, Sheboygan, Fond du Lac, Appleton, Oshkosh and Green Bay.
Most of the region is forecast to reach the “Orange,” or Unhealthy for Sensitive Groups, level. But forecasters warned that conditions could be worse right along the shoreline: “Red,” or Unhealthy for everyone, ozone is possible within the lake breeze from Sheboygan south to Kenosha. A breezy south-southwest flow was expected to keep that pocket of dirtier air pinned near the lakefront rather than pushing it far inland.
The Lake Breeze That Traps the Ozone
The lakefront geography that makes Wisconsin’s shoreline so pleasant in summer is also what concentrates its pollution. On warm, sunny days, a cool lake breeze develops off Lake Michigan and pushes inland, and it can carry a dense ribbon of ozone with it. According to coverage from WKOW, those elevated concentrations on Thursday were expected to stay confined to that narrow lake-breeze zone…