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Air pollution afflicts nearly all of U.S. national parks, 33 at city-like levels

If you’re planning to visit Sequoia this summer, best check for smog alerts; on many days the ozone is as bad as L.A.’s.

A giant chainsaw carved bust of naturalist John Muir
A giant chainsaw carved bust of naturalist John Muir is seen in Lemon Cove near the entrance to Sequoia National Park.
REUTERS/Lucy Nicholson

Air pollution being highly mobile, it should come as no surprise to learn that it drifts into U.S. national parks.

Still, it’s kind of a stunner to learn that 96 percent of the areas set aside as America’s most beautiful and ecologically important places bear a “significant” burden of bad air for at least part of the year. For many, this includes stretches where levels of lung-irritating ozone are above the federal safety maximums set for urban areas.

This is the fresh finding of the National Parks Conservation Association in a report issued last week. NPCA obviously has much love for the park systems and, as you might reasonably expect, the realities beneath that summary number are complex, covering impairments that range widely in type and degree.

But if your initial reaction is a bit skeptical, as mine was, consider that summertime ozone levels at Sequoia National Park often rival the situation in Los Angeles. That is some serious smog, hard on the lungs of healthy humans even if they’re not on a vigorous hike up the Watchtower trail.

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Indeed, Sequoia and 86 other parks regularly exceed the U.S. Environmental Protection Agency’s health standard for ozone, posting a five-year average value above 70 parts per billion. This places them, as NPCA points out, on the same footing as the nation’s most ozone-afflicted large cities — or would, except that the ozone numbers are falling in many of those cities as work to comply with EPA regulations; because parks don’t generate their own smog, they lack for options to actively reduce it, apart from restricting vehicle traffic.

As it stands today, the association says, “33 of America’s most-visited national parks are as polluted as our 20 largest cities.”

A credible base in data

The analysis and commentary here are the association’s but the underlying research and data come from a wide array of credible research sources, from EPA to the National Climate Assessments, from management studies in the Department of the Interior to papers published in an array of medical, environmental and public-health journals.

NPCA chose to categorize those findings on air pollution’s impacts in four dimensions:

Health, where monitoring shows air officially classified as unhealthy for humans to breathe, mostly because of ozone.

Nature, referring to air pollution that damages sensitive species and habitat; here the culprits include ozone and an array of other pollutants, including sulfur and nitrogen compounds.

Visibility, where long-distance views are truncated by the haze of dirty air (again, primarily ozone).

Climate, where scientific study has shown that global warming is having a significant impact on such factors as precipitation, temperature and wildfire patterns (and sea level, in the case of the Harriet Tubman Underground Railroad National Historical Park on Maryland’s Eastern Shore).

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The association’s analysis ranked these impacts in four quantitative categories: significant concern, moderate concern, little to no concern, no data available. Moderate to significant impacts were the norm across the 417 parks, monuments, historic sites, lakeshores, preserves and other units of the National Park Service; a distinct minority of parks, like 20 percent, had lesser problems.

And while the 96 percent figure I’ve cited above is sort of an aggregate — the portion of parks with a significant impact in any one of the four dimensions — the extent of problems in each component category was so great that averaging them wouldn’t have produced a dramatically different overall figure:

  • 85 percent of the parks had problems with unhealthy air. That’s 354 parks and other sites, 87 of them with significant impacts and 267 with moderate problems. Examples:

In 2018, four parks — Sequoia, Kings Canyon and Joshua Tree National Parks and Mojave National Preserve—had unhealthy air for most park visitors and rangers to breathe for more than two months of the year, mostly in the summer months. These are among our nation’s most polluted national parks. Much of  the air pollution in these parks comes from vehicles and the agriculture industry in the San Joaquin Valley — one of the most polluted areas in the nation — where residents are frequently exposed to unsafe air.

  • 88 percent, or 368 sites, had problems with air pollution harming sensitive species and habitat (283 significant, 85 moderate).

At Rocky Mountain National Park, flowering plants are being replaced by grasses. The park’s high-elevation environment is highly vulnerable to nitrogen because of the ecosystem’s shallow soils and short growing seasons. Additionally, the increase in nitrogen, which results from increased pollution from oil and gas development in the region, can change the types of plants that grow on the tundra. As levels of nitrogen increase, grasses take over footprints of alpine flowers and reduce habitat for some animals at Rocky Mountain National Park.

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  • 89 percent, or 370 sites, are experiencing visibility impairments (304 moderate, 66 significant).

On average, visitors to national parks miss out on 50 miles of scenery because of air pollution—a distance equivalent to the length of Rhode Island. … Yosemite, Everglades, Acadia and Joshua Tree national parks are just a few of our nation’s greatest wild places that experience widespread effects from air pollution even if sometimes they don’t appear to be polluted.

(Also, BTW, is Great Smoky Mountains National Park, where the haze over the ridges is  heavier than ever, and rather a different hue from the days when the blanketing was natural mist.)

  • 80 percent, or 335 sites, are showing climate impacts of significant concern (none listed for moderate concern.)

Everglades National Park is part of a unique subtropical peatland environment that requires excess fresh water to support the myriad life that thrives there. Because water depth means a healthy, thriving ecosystem and drives essential peat accumulation, rising sea levels — of even just a few centimeters — can inundate freshwater habitats. As a result, rare tropical orchids and herbs, pine forests, and freshwater marshes are at risk that in turn support many species of wildlife, birds and amphibians.

In Mt. Rainier National Park, melting of the Nisqually glacier is directly responsible for infrastructure damage along the park’s historic Nisqually Road. As the glacier retreats, it leaves behind boulders, sediment and debris that washes more easily downstream during storms, tearing apart the river banks that form the base of the road.


The full report, “Polluted Parks: How America Is Failing to Protect Our National Parks, People and Planet from Air Pollution,” is available here without charge.