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Pollution reaching California’s Sierra Nevada has created the country’s most-polluted national parks, study says

A firefighter protects a sequoia tree as the Washburn Fire burns in Mariposa Grove in Yosemite National Park
Noah Berger
A firefighter protects a sequoia tree as the Washburn Fire burns in Mariposa Grove in Yosemite National Park, Calif., on Friday, July 8, 2022.

KINGS CANYON NATIONAL PARK, Calif. — A new study says Sequoia and Kings Canyon are tied as the most-polluted national parks in the country, posing an ecological threat to iconic giant sequoia trees enjoyed by millions of visitors each year.

The National Parks Conservation Association prepared a study titled “Polluted Parks” using data provided by the National Park Service. It found other California parks – Mojave, Joshua Tree and Yosemite – round out the country’s top-five most polluted.

Authors looked at factors such as air pollution, threat from climate change and visibility to make the determination.

“The borders on national parks are just lines on a map. They're not walls that protect the parks from this pollution,” said Mark Rose, who is the conservation group’s Sierra Nevada program manager.

Pollution at parks impacts views, nature, study says

On a clear day, Sequoia National Park visitors can see vistas stretching some 150 miles.

But smog and haze pollution sometimes cuts those sightlines by two-thirds, turning majestic Sierra summits into dingy gray smudges, particularly during the busier summer months.

And it’s not just tourist selfies that are impacted.

Ground-level ozone pollution harms a plant’s ability to photosynthesize at the same time climate change has led to more frequent and severe droughts. Drought-weakened trees are unable to defend themselves from infesting bark beetles, a leading cause of tree mortality across the forest.

A volunteer at Kings Canyon National Parks points to a dead tree in Grant Grove. A new study from the National Parks Conservation Association
Joshua Yeager
A volunteer at Kings Canyon National Parks points to a dead tree in Grant Grove. A new study from the National Parks Conservation Association says Sequoia and Kings Canyon are the nation's most-polluted national parks.

And when wildfire strikes, dried-out tree husks burn easily. In recent years that has contributed to unprecedented mega blazes that have killed up to a fifth of the world’s adult sequoia population in just over a decade.

Industrial and agricultural activity, as well as exhaust from vehicles traveling through the Central Valley below are behind the worrying concentrations of ozone and other pollutants within the parks, says Rose.

“Places like Los Angeles, Bakersfield and Fresno regularly rank as the most polluted cities in the country. It’s not a surprise that the same pollution impacting cities here in California is then making its way up to our national parks,” he added.

To combat pollution and its negative effects, the study advocates for more zero-emission vehicles on the road and for policy makers to speed up the state’s transition away from fossil fuels.

But Rose also pointed at regulators, noting the San Joaquin Valley air basin has been out of compliance with federal standards for decades. He argues there are benefits for everyone if pollution is reduced.

‘Not as fresh as you would think’

An air tanker flies over forest dropping fire retardant as a massive smoke cloud rises in the background.
Noah Berger
An air tanker drops retardant while trying to stop the Oak Fire from progressing in Mariposa County, Calif., on Sunday, July 24, 2022.

While recent winter storms have provided a respite from heavier air pollution, visitors and people living in the Sierra have started to take notice of the bad air.

Anthony Specchio said he frequently checks the air quality index.

He was surprised to see the readings in his remote mountain community of Badger are often similar to those found in heavily populated Southern California.

“We’re up in the mountains, and it looks all peaceful with trees and everything,” he said on a recent Sunday, standing below the 267-foot-tall General Grant tree. “People will come up and we’re like, ‘It’s actually not as fresh as you would think.’”

Others agreed that pollution is a problem but don’t see an easy solution.

Agriculture and the dairy industry are cornerstones of the San Joaquin Valley, and eliminating them would be a big blow to the local economy, says Anna Holt, a Miramonte native.

“California is such an agricultural state and it’s so essential to have these farms. It’s not really a problem I think can be fixed; we’ll just have to adapt,” she said outside a cafe on the road up to the park.

The National Park Service says it has implemented a number of programs to identify and curb pollution within its parks.

While the park service provided data used in the study, the agency didn’t review or have a hand in writing the publication, a spokesperson said.

Joshua Yeager is a Report For America corps reporter covering Kern County for KVPR.