Weeks after wildfire smoke from fires burning in Canada blanketed much of the East Coast with hazy, orange skies and unsafe air quality, parts of the Midwest were startled Tuesday as Chicago and Detroit saw the worst air quality in the world.

Thick smoke clogged the sky in Chicago early Tuesday, with a gray haze limiting visibility, and a faint burning smell filled the air as residents commuted to work. In downtown Detroit, smoke could be seen lingering over the skyline and the National Weather Service issued an air quality advisory for the city until Wednesday night.

Chicago and Detroit held the top two rankings for worst air quality in the world, according to IQAir’s Air Quality Index. The two Midwest metropolitans alternated between the “unhealthy” and “very unhealthy” categories through Tuesday.

Unhealthy levels of pollutants from the smoke spread across parts of the Great Lakes Region surrounding Chicago, including most of Wisconsin and parts of Michigan, Illinois, Indiana, and Ohio, according to tracker AirNow.gov.

Meanwhile, more smoky air is headed back New Yorkers’ way. Gov. Kathy Hochul warned air quality is expected to reach unhealthy levels in parts of western and central New York and eastern Lake Ontario on Wednesday and Thursday.