National Parks Conservation Association (ARA) - Every year, millions of Americans look forward to autumn and the opportunity to take in the beautiful fall foliage. As deciduous trees across the country begin to shed their leaves, "leaf peeping," as it is known, becomes a pastime of many travelers.

The national parks offer a serene setting and unmatched views to enjoy this majestic transformation. Our parks preserve hundreds of tree species, which, into November, vibrantly paint the mountains and hillsides and fields with fresh shades of red, orange, yellow and purple.

"Visitors come from miles away each year to experience fall foliage in our national parks. It is truly a spectacular time of year," says Mark Wenzler, director of Clean Air and Climate Programs for the National Parks Conservation Association. "Unfortunately, many of the trees people come to see face threats like air pollution, most of which is caused by exhaust from coal-fired power plants and automobiles. It is essential we do everything we can to protect our national parks for our children and grandchildren to enjoy, as well."

Here are a few national park sites beloved for their brilliant fall foliage, but also facing air pollution issues:

Although nearing the completion of this year's season, Acadia National Park in Maine is well-known for its beautiful fall foliage. Timing varies each year, but peak colors are typically seen in early to mid-October. The park offers nearly 40,000 acres of Maine coastline for visitors to explore the remarkable foliage and views. Leaf peepers come to see the bright yellow birch leaves, the deep red maple foliage, and the orange hue of the white ash. At an elevation of 1,530 feet, Cadillac Mountain allows visitors to enjoy fall foliage at the highest point along the North Atlantic seaboard.

Despite the undeniable beauty throughout the park, Acadia's forests are threatened by harmful air pollution. To reduce pollution from your car, consider carpooling in the fall, as the park's shuttle system stops operating after Columbus Day. For more information about fall foliage at Acadia National Park, please see: http://www.nps.gov/acad/planyourvisit/.

Great Smoky Mountains National Park (Tennessee, North Carolina) usually experiences a fall foliage season that lasts several weeks. Park trees change colors at various times, depending mostly on elevation. At mid and lower-level elevations, the color display typically reaches peak between mid-October and early November. The park attracts leaf peepers, who want a glimpse of the nearly 100 native tree species, most of which are deciduous. Some of the more vibrant trees include hickories, sugar maple, scarlet oak, sweetgum and red maple.

The fall foliage display at Great Smoky Mountains remains one of the best in the country, but park forests face air pollution threats like acid rain, which weakens trees by damaging the leaves and limiting the nutrients available to them. Visitors might consider alternative transportation options to lessen their own impact at the park, as automobile emissions are a contributor to air pollution. At Cades Cove, one of the more congested areas of the park, NPCA has partnered with the nonprofit Cades Cove Heritage Tours to offer a guided shuttle service for visitors. For more information about fall foliage at Great Smoky Mountains, please visit www.nps.gov/grsm/planyourvisit.

Mammoth Cave National Park in Kentucky is known for its extensive cave system -- the longest in the world. However, visitors have ample opportunity to explore other features of this national park, as well. Mammoth Cave preserves the forested Kentucky hills, which offer numerous trails for hikers to explore and observe the vibrant fall foliage. Oak, tulip poplar and sassafras are among the trees that scatter park forests and attract leaf peepers annually.

Unfortunately, the park's beloved deciduous trees are threatened by acid rain year-round. Consider carpooling to the park, and using park trails to explore its changing forests. Mammoth Cave offers trails for every level of hiker. For an updated webcam shot of fall foliage at the park, please visit http://nature.nps.gov/air.

Each of these parks is downwind of dozens of coal-fired power plants, which are the major cause of acid rain and ozone which damage their trees. Fortunately, many electric utilities are now offering their customers the choice of green energy alternatives to coal, like wind and solar power. After returning from your fall leaf peeping trip, consider switching to green energy to help protect the beautiful scenery you just enjoyed.

For additional information about reducing your own carbon footprint to help protect our national parks, as well as the tools to actually do so, visit the new interactive Do Your Part! for Climate Friendly Parks Web site, sponsored by the National Parks Conservation Association in support of the National Park Service's Climate Friendly Parks program at www.doyourpartparks.org.

Courtesy of ARAcontent