Last week, Canadian wildfire smoke blanketed Wisconsin and caused the Air Quality Index to reach the unhealthy level for sensitive groups. Six days later, on July 31, the smoke appears to have a worse impact on the air.

A thick blanket of smoke from Canadian wildfires is pushing southward across the US, prompting air quality alerts across Wisconsin, Minnesota, Michigan, and Connecticut. Millions of residents are advised to reduce outdoor exposure as air pollution levels reach unhealthy to very unhealthy levels,