Dan Mitchinson: US correspondent on the air quality in Chicago worsening due to wildfire smoke - Heather du Plessis-Allan Drive

Wildfire smoke seeping into America's Midwest has made Chicago's air quality the worst in the world.

Many US cities have issued air quality alerts this month, urging residents to limit time outdoors.

US correspondent Dan Mitchinson says these wildfires are bad for businesses and people's health, especially when combined with the pollution from factories. 

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