(CNN) Denver experienced the worst air quality of any city in the world for several hours Saturday as heavy smoke from raging western wildfires polluted the city. IQAir, a Swiss air quality technology company, determined that Denver's air was the most polluted early Saturday at an Air Quality Index of 167. The measurement is by US standards, where a higher number indicates poorer air quality. Later on Saturday, the city of Johannesburg, South Africa, moved to the top spot with a US AQI of 178. Smoke from western wildfires obscures the skyline of Denver on August 7, 2021.

Source: CNN August 08, 2021 10:18 UTC