Laramie, Wy – A new Park Service study shows air quality is worsening at Yellowstone National Park.
The study compiled air-quality trends dating back to 1995 at national parks across the country.
One pollutant on the rise in Yellowstone is ground-level ozone. It can cause respiratory problems and threaten plant health.
But the Park Service says the levels in Yellowstone don't exceed any national standards and are NOT high enough to pose a risk.
Still, Yellowstone had more categories in which air quality was getting worse than any other park in the country.
Other air-quality categories that worsened at Yellowstone were ammonium, sulfates and nitrates. Two categories measuring visibility showed improvements.