DENVER— A federal appeals court has rejected Weld County’s attempt to delay steps to reduce pollution from the Colorado county’s oil and gas operations that contributes to asthma-causing smog in the Metro-Denver and Front Range region.

The area, which is home to 3.3 million people, has some of the worst air pollution in the world. That pollution is caused largely by fracking for oil and methane gas.

The federal appeals court decision late Tuesday rejected Weld County’s request that the court stay, or pause, the Environmental Protection Agency’s decision requiring the entire county to strengthen its pollution-reduction measures for ozone, commonly known as smog.

“The reality is that despite Colorado’s majestic beauty, it has dangerous levels of air pollution, and oil and methane gas wells are among the biggest culprits,” said Robert Ukeiley, a senior attorney at the Center for Biological Diversity. “For Colorado to have clean, clear air we need to move to renewable energy and increased electrification, and this ruling brings us closer to getting there.”

The Trump EPA failed to require that the region put additional protective measures in place. The Board of County Commissioners of Boulder County, the Center for Biological Diversity, the National Parks Conservation Association and the Sierra Club overturned that decision in the D.C. Circuit Court of Appeals.

Tuesday’s court ruling came after Weld County sued the EPA to try to keep northern Weld County, and its hundreds of pollution-producing oil and methane gas wells, from having to implement protective measures to reduce pollution. Weld County asked the court to put these protective measures on hold while the case was pending, but the court turned down that request.

“It’s unfortunate that Weld County officials are adamant about defending polluting industries rather than protecting people and the environment. We hope that this decision by the Court of Appeals paves the way for pollution reduction in Colorado,” said Ramesh Bhatt, chair of the conservation committee of the Colorado Sierra Club.

The court’s ruling will lead to reductions in the oil and gas smog pollution that not only triggers asthma attacks and other health problems but harms aspen trees and imperiled species like the Mexican spotted owl and obscures vistas in Rocky Mountain National Park.

“Rocky Mountain National Park remains a point of pride for Coloradans and its millions of visitors each year,” said Tracy Coppola, Colorado senior program manager at the National Parks Conservation Association. “But it’s no secret that this crown jewel is home to numerous problems tied to ozone pollution, including nitrogen deposition that exceeds 15 times the natural amount. Absent concrete measures like EPA’s recent decision to designate northern Weld County as an ozone nonattainment area, the future of the park’s fragile ecosystem and the health of Front Range communities remain at risk. We are thankful the stay was denied — because clean air is urgently needed.”