These Are the Most Polluted National Parks

Five California sites made the top ten list for unhealthiest air, according to a new report

Hazy sunset with mountains
Air pollution can obscure miles of scenery at Joshua Tree National Park in California and other sites. NPS / Robb Hannawacker

America’s national parks may conjure up visions of pristine wilderness and clear skies. But many of these protected public landscapes are suffering from air pollution and facing threats stemming from human-caused climate change, according to a new report from the National Parks Conservation Association (NPCA).

Founded in 1919, the NPCA is an advocacy group that aims to protect and enhance the country’s national parks. This month, it released its latest “Polluted Parks” report, which includes an analysis of air quality data collected by 399 national parks across the country in 2021. The report also explores how four climate change-related threats—drought, sea level rise, invasive species and wildfires—are affecting national parks.

The group finds that 98 percent of parks suffer from visible haze pollution, while 96 percent are grappling with ozone pollution that could be harmful to human health.

Though national parks are protected from development, air pollution “knows no bounds,” says Ulla Reeves, interim director for NPCA’s clean air program, in a statement. Greenhouse gases and particles waft into national parks from nearby cities, highways, factories, ports, warehouses and other sources.

In the atmosphere, ozone helps protect Earth’s surface from the sun’s ultraviolet radiation. But when it forms near the ground—from a chemical reaction caused by sunlight, heat and pollutants—it irritates the lungs and can cause coughing, inflammation, sore throat and pain while breathing, among other issues.

Air pollution not only makes it harder for people to breathe (particularly those with asthma and other respiratory conditions), but it can also harm plants and animals. Nitrogen and sulfur deposits can make water more acidic, while excess nitrogen can also contribute to toxic algae blooms. Ozone pollution, meanwhile, can stunt the growth of trees and weaken plants, per the report.

Hazy skies also obscure the views of the national parks’ natural beauty: The report found that on average, visitors miss out on roughly 50 miles of scenery because of air pollution.

Four of the nation’s parks with the unhealthiest air are in California: Sequoia and Kings Canyon National Park, Joshua Tree National Park, Mojave National Preserve and Yosemite National Park, according to the report. Another California site, Death Valley National Park, also made the top ten list.

“It’s not a surprise that air pollution is a problem in California—I think people know this,” Reeves tells the Los Angeles Times’ Lila Seidman. “But we see that the sequoias and the Joshua trees and all of these places are really having an outsized experience of air pollution and climate threats.”

The other national parks on the list are Carlsbad Caverns National Park and White Sands National Park in New Mexico, Indiana Dunes National Park in Indiana, Guadalupe Mountains National Park in Texas and Rocky Mountain National Park in Colorado.

The report also finds that 57 percent of national parks are facing at least one threat stemming from climate change that could permanently alter its ecosystems, with many parks grappling with multiple issues at the same time. Fourteen parks are dealing with three of the four threats identified in the report.

Invasive species were the most prevalent issue, affecting 113 parks, followed by wildfire (95 parks), drought (75 parks) and sea level rise (48 parks). At Shenandoah National Park in Virginia, for example, warmer winters are making it easier for pests like the hemlock woolly adelgid to thrive and proliferate. These invasive insects are attacking the park’s eastern hemlocks.

“Without intervention, there is a very real possibility that this insect pest could eliminate eastern hemlocks from Shenandoah's ecosystem,” according to the national park.

Meanwhile, Everglades National Park in Florida is contending with rising sea levels, which are causing saltwater to infiltrate the park’s freshwater marshes and mangrove forests. And Wind Cave National Park in South Dakota is suffering from more frequent and severe drought conditions, which increase the risk of wildfire and put stress on the park’s buffaloes.

The report also offers potential solutions for safeguarding national parks, such as allocating funding for improved air monitoring instruments and enacting stricter emissions standards for power plants, oil and gas operations and vehicles.

The National Park Service (NPS) was not involved in the creation of the new report. Scott Clemans, an NPS spokesman, tells LAist’s Kevin Tidmarsh that the federal agency is “actively working” to respond to climate change through a variety of programs.

Mark Rose, the NPCA’s Sierra Nevada program manager, tells SFGATE’s Sam Mauhay-Moore that the poor conditions in California’s parks are particularly concerning.

The new report, he adds, is “certainly a wake-up call for our state.”

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