Climate Changed

Denver on Alert After Suffering Planet’s Worst Air Quality

Sloan’s Lake in central Denver, Colorado, on Aug. 9.

Photographer: RJ Sangosti/MediaNews Group/Getty Images

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Denver was under pollution alert Monday after suffering the worst air quality among the world’s major cities over the weekend -- and another round of smoke is in the forecast for Tuesday.

The Colorado capital was ranked No. 1 on the IQAir pollution index Saturday afternoon and slipped to No. 2 on Sunday as smoke from California wildfires blanketed the city at the base of the Rocky Mountains.