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.

Today, he said, he can see some 50 miles (80 kilometers) across that same valley to the Cumberland Mountains.

A 26-year-old federal regulation known as the regional haze rule has helped cut down on pollution over national parks, wilderness areas and tribal reservations, restoring some of the nation’s most spectacular natural vistas for outdoor lovers like Barger. But conservationists fear those gains may be lost after President Donald Trump’s administration announced in March the rule is among dozens of landmark environmental regulations that it plans to roll back.

“It means a promise that was made to the American public is lost,” Barger, 74, said. “More and more generations of people are going to grow up as ignorant as I was, not realizing what I’m missing and not seeing.”

Congress pushes to clean air over parks, wilderness areas

Haze forms when small particles of air pollution, such as sulfur dioxide or nitrogen oxides, scatter and absorb sunlight, blurring views and decreasing visibility.

Congress amended the Clean Air Act in 1977 to make restoring and maintaining visibility a goal for 156 national parks, wilderness areas, wildlife refuges and tribal reservations across 36 states. That includes places like the Great Smoky Mountains National Park in North Carolina and Tennessee; Grand Canyon National Park; Glacier National Park; and the Boundary Waters Canoe Area Wilderness.

After years of drafting and litigation, the U.S. Environmental Protection Agency adopted regulations known as the regional haze rule in 1999 to implement the amendments.

The rule calls for attaining natural visibility conditions by the year 2064 and mandates that states come up with plans that include limitations on emissions, compliance schedules and monitoring strategies. Older facilities that emit pollution, such as coal-fired power plants, must adopt mitigation technology such as scrubbers or shut down periodically to decrease overall annual emissions.

A work in progress

The states’ plans have been plagued with delays as the EPA approves parts of them and rejects others. For example, two big oil- and coal-producing states, North Dakota and Wyoming, and industry groups filed petitions in federal court in January seeking review of EPA decisions rejecting their plans, according to the Harvard Law School’s Environmental and Energy Law Program.

The rule works in conjunction with other federal antipollution regulations, but it’s been crucial in clearing the skies over national parks and wilderness areas.

An Associated Press analysis of data from a nationwide network of monitoring sites from 1999, when the rule was implemented, through 2023 shows 93% of the parks and wilderness areas have seen improved air quality on clear days. No parks or wilderness areas have seen any notable worsening in visibility.

Visibility in the Great Smoky Mountains National Park was twice as good on a typical clear day in 2023 as it was in 1999, marking the biggest improvement among the national parks.

The EPA estimates that between 2007 and 2018 the rule has cut 500,000 tons of sulfur dioxide and 300,000 tons of nitrous oxides annually. The average visual range has increased from 90 miles to 120 miles (144 kilometers to 193 kilometers) in some western parks and from 50 to 70 miles (80 kilometers to 112 kilometers) in some eastern parks, according to the Harvard program.

‘Most consequential day of deregulation’

Trump’s EPA administrator, Lee Zeldin, announced March 12 that the agency would look to roll back 31 landmark environmental regulations, including the regional haze rule. Zeldin called the announcement the “most consequential day of deregulation in American history” and said in an essay published in the Wall Street Journal that the administration is “driving a dagger through the heart of climate-change religion.”

Asked for comment on the regional haze rule, the EPA said they want to better account for pollution from outside the U.S. and from natural sources and avoid unnecessary burdens for states and industry.

Has the rule hurt energy producers?

In a cost-benefit analysis of the rule before it took effect, the EPA found it would cost energy producers up to $98 billion by 2025 while providing about $344 billion in benefits such as health care savings.

Producers argue that the haze rule has done its job and it doesn’t make sense to continue to impose costs on them.

“This is a matter of diminishing returns,” said Jonathan Fortner, interim president and CEO of the Lignite Energy Council, which advocates for North Dakota’s coal industry. “The air is clean, the data proves it, and the science backs that up. The rule’s being misapplied, not because we disagree with clean air goals, but because we’re already there.”

Two federal properties in North Dakota are subject to the rule, the Lostwood National Wildlife Refuge and Theodore Roosevelt National Park. The AP analysis found both sites have seen dramatic visibility improvements over the five years from 2019 to 2023.

EPA officials did not respond to an AP request for a list of power plants that have closed due to the regional haze rule. A number of energy industry groups did not return repeated requests for comment, including the U.S. Energy Association and the National Utility Contractors Association.

What’s next for the parks?

Advocates of the rule say eliminating it could lead to reduced tourism and the economic boom visitors bring to national park regions. The National Park Service estimates 325 million people visited national parks in 2023, spending $26.4 billion in gateway communities.

Nothing appears likely to change overnight. Conservationists expect the Trump administration to pursue a rollback through language revisions in the rule, a process that would require a public comment period and would likely trigger court challenges that could last years.

“I’ve watched the Great Smoky Mountains National Park emerge from the chemical haze that once enshrouded it and was getting worse,” Barger said. “It’s just this visceral sense of place. We had lost it entirely. The Clean Air Act is working and it’s a work in progress. You have to stay with it or it doesn’t work.”

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Associated Press Science Writer Seth Borenstein contributed to this report.

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