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On clear days, Zion National Park visitors at Lava Point can see Mount Trumbull 70 miles to the south near the Grand Canyon.

Such days, however, are troublingly rare. Air pollution obscures Zion's vistas 80 percent of the time, according to the National Park Service (NPS).

The good news is that Utah can do something about this problem, which afflicts all of the state's "Mighty 5" national parks, by requiring further reductions in nitrogen-oxide emissions from two coal-fired power stations in central Utah, the service contends in comments submitted earlier this month to the Utah Department of Environmental Quality.

The bad news, according to the NPS, is the state Division of Air Quality won't take this step under proposed revisions to its plan to combat "regional haze." That compromises the breathtaking views Utah uses to advertise itself to the world, the service and other critics say.

"The state clearly values the importance of the five national parks in Utah and actively promotes national tourism, yet at the same time it appears unprepared to fulfill its legal requirements under the Clean Air Act and associated regulations to protect and enhance the very scenic views that attract millions of visitors to the parks every year," wrote Tammy Whittington, associate regional NPS director for resource stewardship and science.

Her remarks, submitted in April 2 letters to the Environmental Protection Agency and DEQ as part of a public comment process that closes next Friday, underscore the tension between two of Utah's key economic drivers: national parks tourism and low-cost energy.

Environmental advocates say Rocky Mountain Power (RMP), Utah's largest utility, should be required to install the best emission control retrofit technology, known as selective catalytic reduction, or SCR, at its Hunter and Huntington power stations in Emery County.

But Utah's air quality division has held that past upgrades that cost $588 million and the planned closure of RMP's aging Carbon Power Plant, which shut down last week, meet regional haze standards.

Developed as a component of the Clean Air Act, the regional haze rule is meant to protect 156 national parks and wilderness areas from visibility-impairing pollution by mandating upgrades at the nation's oldest and dirtiest power plants. Utah is the last state to comply with the rule, critics say.

But the state contends SCR retrofits would be cost prohibitive.

"You're talking in excess of $170 million per unit. They are custom retrofits; the actual cost would vary per unit. You get a better result by the work already done [on four units] at Hunter and Huntington and the Carbon closure than the regional haze rules requires," RMP spokesman Dave Eskelsen said. "If you add SCR to those units, you get a substantial expense to consumers with a marginal benefit to the regional haze quality."

The pollution over the parks comes from a variety of far-flung sources, most recently wildfires burning in Siberia, Eskelsen noted.

Advocates and parks officials see things differently.

Zion, Bryce Canyon and Utah's three other national parks were established to ensure citizens could enjoy geological wonders such Angels Landing, Delicate Arch, Observation Point, Yovimpa Point and Upheaval Dome.

"Clear, clean air is essential for that purpose," Whittington wrote. "Anthropogenic haze can render the inspirational landscapes of our national parks and their encompassing viewsheds to be colorless and bland."

Haze mars vistas at Utah's five national parks about three-fourths of the time, her comments said.

But Utah appears willing to sacrifice these values for the sake of cheap electrical power, according to Cory MacNulty of the National Parks Conservation Association. Air pollution threatens a critical piece of Utah's tourism economy and quality of life, MacNulty said. The five parks drew 7 million visitors last year, generating $730 million in activity, according to a recent study.

"They are putting national parks on cable channels, wrapping taxicabs in London. There is a huge push to get more visitors," MacNulty said. Preserving long-distance vistas is crucial to ensuring the parks' ability to draw people, MacNulty added.

SCR retrofits would reduce Hunter and Huntington nitrogen oxide emissions by 14,700 tons, or 86 percent, according to environmental groups. Last year the EPA rejected aspects of Utah's regional haze plan, but critics say the plan's latest revision is not much different than its flawed predecessor.

"They keep delaying and delaying and re-proposing the same plan," MacNulty said. "We have to have reductions that go much deeper than this plan to clean the air over our parks."