A vast plume of toxic smoke from hundreds of Canadian wildfires has spread across the U.S. Midwest, Mid-Atlantic, and Northeast, placing more than 109 million Americans under air quality alerts as of July 18, 2026. AirNow data showed Air Quality Index readings reaching a hazardous 361 in Chicago and Detroit on Friday, indicating dangerous conditions for all residents. Baltimore and Washington, D.C., recorded very unhealthy levels, while Philadelphia, Cleveland, and New York City also faced significantly degraded air. State and local agencies, including Pennsylvania’s Department of Environmental Protection, issued emergency alerts warning of serious health risks from elevated fine particulate pollution.

Prepared by Olivia Bennett and reviewed by editorial team.