Denver Has Worst Air Quality In The World: Report

DENVER, CO — Denver had the worst air quality in the world Saturday, according to the IQAir pollution ranking.

The city has shifted into the top 10 several times over the past week, but a massive plume of wildfire smoke drifted into the city Saturday and pushed Denver into the No. 1 spot.

The smoke, which is coming from wildfires in California and the West Coast, triggered air quality alerts across Colorado.

"People with heart or lung disease, older adults, and children should avoid prolonged or heavy exertion on Saturday; everyone else should reduce prolonged or heavy exertion on Saturday," the Colorado Department of Public Health and Environment said in an alert for the Front Range.

Visibility in Denver was rated in the agency's air quality report as 'extremely poor.' The smoke is expected to last through at least Sunday morning, according to the alert.

Salt Lake City was briefly ranked No.4 on the IQAir list Saturday afternoon, and by 3 p.m., Denver had moved into the No. 2 spot, behind Johannesburg, South Africa.

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The smoke combined with high ozone in Denver Saturday, worsening the air quality. Dozens of action day alerts for ozone have been issued for metro Denver and Boulder so far this summer.

Ozone pollution, often called smog, forms when gases that come out of tailpipes and smokestacks, among other sources, come into contact with sunlight. Ozone is "one of the most dangerous and widespread pollutants in the U.S.," the lung association said.

Ozone can damage people's airways, make their lungs more susceptible to infection and aggravate lung diseases, according to the U.S. Environmental Protection Agency.