DENVER— A federal appeals court today rejected an attempt by commissioners in Colorado’s Weld County to let some oil and gas operations off the hook for their contribution to asthma-causing smog in the Denver and Front Range region.

The U.S. Court of Appeals for the D.C. Circuit ruled that the Environmental Protection Agency properly included northern Weld County in the smog clean-up zone. Today’s decision confirms that companies operating thousands of oil and gas wells in the area must reduce ozone pollution known to be a major cause of the region’s chronic smog problem.

“For far too long Big Oil has forced millions of Coloradans to breathe filthy air,” said Robert Ukeiley, a senior attorney at the Center for Biological Diversity. “With this ruling oil and fracked gas operators have to reduce dangerous asthma-causing smog pollution that harms people’s health and fouls the wild places that make Colorado so special.”

The court ruling requires common sense reductions in oil and gas smog pollution that triggers asthma attacks, damages aspen trees and imperiled species like the Mexican spotted owl, and obscures vistas in Rocky Mountain National Park.

The Clean Air Act sets science-based national ambient air-quality standards that are designed to protect public health and the environment. All areas that violate air-quality standards for smog and contribute to those violations must be included in the designated smog clean-up zone.

The current ozone nonattainment area where smog must be cleaned up under the Clean Air Act stretches along the Front Range, from Castle Rock in the south to Fort Collins and Greeley in the north and west into Rocky Mountain National Park.

“This court decision is also a victory for the millions of visitors to Rocky Mountain National Park who will be a step closer to once again getting to enjoy unobscured views from its many mountain peaks,” said Ukeiley.