Once again, smoke from Canadian wildfires envelops many American cities

For the second time this month, massive plumes of smoke from hundreds of out-of-control Canadian wildfires are polluting much of America's air.

Among the major U.S. cities now experiencing poor air quality are St. Louis, Milwaukee, Cincinnati, and Chicago, while entire states have also issued air quality alerts, according to the National Weather Service. These are Delaware, Illinois, Indiana, Iowa, Maryland, Michigan, New York, and Wisconsin. Parts of Kansas, Minnesota, Missouri, North Carolina, Ohio, Pennsylvania, and Virginia also have alerts. In the cities of Chicago, Cleveland, Detroit, Indianapolis, Milwaukee, Pittsburgh, and Davenport, Iowa, air quality was in the "very unhealthy" range, according to airnow.gov.

Between 80 million and 120 million people are affected by this poor air quality, according to an analysis by the National Weather Service and CNN. In some locations, residents have been asked to stay inside and run their air conditioning or to wear N95 masks if they need to go outside, according to CNN.

Smoke concentration may increase over New York City on Thursday, CNN reported. City police and firefighters planned to distribute masks, Mayor Eric Adams said. Levels were expected to be higher around the state than in the city.