Overview
- Multiple 911 calls from central Illinois through northwest Indiana to the Wisconsin border reported a chemical- or burning-like smell beginning late Saturday into Sunday.
- Fire departments in Algonquin–Lake in the Hills and Pleasant Prairie said the odor seemed to originate from well south of their communities, though no definitive source has been found.
- The Illinois Environmental Protection Agency said Tuesday it is investigating odor complaints around greater Chicagoland, and Chicago’s health department has acknowledged the reports.
- Meteorologists pointed to a possible temperature inversion trapping pollution near the surface as a plausible explanation, a theory that remains unconfirmed.
- By Monday afternoon the smell had dissipated in some areas and call volume declined; officials advised using 911 only for emergencies and seeking medical care only if symptomatic, while a BP refinery in northwest Indiana said it saw no link to its operations.