Metro Denver and Fort Collins rank increasingly high on a notorious list that comes out each year — the worst U.S. cities for air pollution. Only the Los Angeles area and parts of California’s Central Valley now consistently outperform Colorado’s Front Range cities with their levels of ground-level ozone, which is linked to hospitalizations, ER visits and thousands of premature deaths. Metro Denver ranked eighth-worst for ozone, up from 10th in 2020 and 12th in 2019, according to a compilation of federal data by the American Lung Association.