A recent Sunday morning trek to Mirror Lake in the Uinta National Forest, north of Park City, Utah, reveals crystal-clear mountain air; lush, green grass; majestic rock formations; and sparkling, cold waters in the glacial lake.
Not a sign of pollution.
America's national forests are an emerald treasure -- when not threatened by fire or the thick haze of air pollution.
The same cannot be said for many of the nation's national parks.
A new study by the National Parks Conservation Association says that one of Teddy Roosevelt's best ideas -- the National Park System -- is being threatened by air pollution.
One of every three of the parks is choking on pollution, the association says.
Of the 390 parks within the National Park System, 150 are located in places that fail to meet one or more national healthy-air standards.
"Millions of Americans will be escaping to the national parks Labor Day weekend for clean and healthy fun," the report said. "Unfortunately, many could find 'code red' air-quality conditions and hazy skies."
Air pollution is a lingering and insidious problem.
It makes it difficult for plants and animals to thrive, and puts the health of park visitors and staff at risk -- not to mention what it does to the scenic views.
"That's pollution out there on the horizon," said a visitor to California's Yosemite National Park earlier this summer. "That's why the sunset looks so reddish."
In fact, the red sky at dusk was created by tiny particulates in the smoke that had drifted near the park from a brush fire upwind.
Yosemite is not alone.
From Acadia National Park in Maine to the Cascades in Washington state, sulfur dioxide, nitrogen oxides, carbon dioxide and mercury can be found at air-monitoring stations in spite of a 30-year congressional mandate to restore clean air to the parks for this and future generations.
The Clean Air Act's 1990 acid-rain program made some progress in reducing the pollutants that fouled the air and contaminated park streams.
The Environmental Protection Agency's auto and power-plant emission limits also cut some of the smog and its damage to plants, trees and humans.
It appears, however, that more needs to be done especially now with the nation on the verge of an increase in the burning of coal, oil and natural gas.
At the Great Smoky Mountains National Park -- a perennial loser in the clean-air sweepstakes -- more than 30 species of trees are showing signs of ozone damage.
Even in the national parks of northwest Alaska, toxic air contaminates food that native people have relied on for generations.
Global warming is exacerbating the problem at the Blue Ridge Parkway in Virginia and North Carolina, where air pollution during the ever hotter summer months sometimes cuts visibility by a depressing 80 percent.
The slogan "America's Favorite Drive" might need a little rewriting.
Coal-fired electric utility power plants are the biggest culprits.
According to the Energy Information Administration, there are 3,200 power plants in the United States, the majority of them fueled by coal.
A General Accounting Office report says that together they emit 35 percent of the nation's carbon dioxide, 37 percent of its mercury, 23 percent of its nitrogen oxides, and 67 percent of its sulfur dioxide.
In parks that are downwind from one of these plants, such as Great Smoky Mountains, Mammoth Cave, and Shenandoah, visitors are bound to be affected by the dirty air.