Wisconsinites breathed record-breaking levels of air pollution Thursday as wildfire smoke from northern Minnesota and Canada wafted across much of the Great Lakes region and the Northeast. Many monitoring stations across the state recorded pollution considered hazardous for the first time in at least 16 years — the span covered by most monitoring stations’ records.
As of 8 a.m. on Friday, Air Quality Index, or AQI, levels in Madison had peaked above 450 — far above the AQI’s 301 threshold for “hazardous” air quality, where everyone — not just sensitive groups — should take precautions to avoid breathing dangerous air.
Milwaukee’s AQI reached 644 earlier on Thursday — more than twice the hazardous threshold. Air quality deteriorated even further in northwestern Wisconsin, with the index reaching 967 along the Minnesota border earlier in the day.
Many Wisconsin communities, including Milwaukee, Waukesha, Odanah and Appleton, were still observing AQI over the 301 threshold Friday morning.
The index categories typically run only from zero to 500.
Thursday’s pollution surpassed levels once considered unprecedented. Before Canadian wildfire smoke pushed the AQI to record highs across Wisconsin in July 2023, cities including Madison, Milwaukee and Waukesha had not recorded an AQI above 200 since at least 2010, according to a Wisconsin Watch analysis of historical AQI data.
But wildfire smoke has elevated air pollution in Wisconsin each summer since 2023. Major cities have periodically recorded higher AQI readings around July, though Thursday’s levels were the first to surpass those recorded in 2023.
“This is a hazardous air quality episode that we have not experienced before,” Craig Czarnecki, air management outreach coordinator for the Wisconsin Department of Natural Resources, said in an email.
