During a hike in the Great Smoky Mountains National Park in 1995, Don Barger climbed Chilhowee Mountain hoping to gaze across the valley below. All he saw was a wall of gray haze.

An analysis of data from 1999 through 2023 shows 93% of parks and wilderness areas saw improved air quality on clear days.

The Great Smoky Mountains National Park ranked second overall, but it is the top park in the nation to see the categories of ...