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This State Is Home to 4 of the 5 Most Polluted National Parks

News National Parks Activism
by Suzie Dundas Mar 25, 2024

A new report from the National Parks Conservation Association (NPCA) studied the most polluted national parks in the United States — and four of the five top offenders are in one of the “healthiest” states in the US: California.

In 2019, five of the most polluted parks were among the least visited: the report highlighted Sequoia and Kings Canyon, Mammoth Caves, Indiana Dunes, Guadalupe Mountains, and Everglades national parks. But this year, the organization rated the parks by how polluted they are, and California’s national parks are bearing the brunt of the damage.

polluted parks - sequoias in California

California’s parks stand to suffer the most, per the new polluted parks report. Photo: NPS /Sequoia National Park /Public Domain

In order, the top five most-polluted national parks were:

    1. Sequoia and King’s Canyon National Parks, California
    2. Joshua Tree National Park, California
    3. Mojave National Preserve, California (not technically a national park)
    4. Yosemite National Park, California
    5. Carlsbad Caverns National Park, New Mexico
    6. Death Valley National Park, California

The study looked at data for 399 parks, representing 93 percent of the units managed by the National Park Service (data wasn’t available for some of the newer parks in the system). Data were provided by NPS, and analyzed to look at three issues regarding air quality (unhealthy air, air that causes harm to nature, and haziness), as well as four issues related to climate change (wildfire, droughts, sea level rise, and invasive species). The latter four categories likely explain why California’s parks topped the list, as California prone to droughts, wildfires, and sea level rise.

Unhealthy air is defined as air that can cause harm when inhaled. Of the 399 parks studied, 42 percent fell into the “significant concern” category, while another 338 were considered to have “unsatisfactory” air quality. This is the category for which California’s parks above topped the list.

Hazy skies is similar, but relates more to how it impacts the guest experience. “Reduced visibility can detract from a person’s overall experience in parks or wilderness areas, muddying color and clarity and hindering the enjoyment of a place’s natural beauty,” writes the report. Only four parks were of significant concern, but 387 were considered moderate. The top offender was once again Sequoia and Kings Canyon National Parks, followed by Mammoth Cave (KY), Carlsbad Caverns (NM), Indiana Dunes (IN), and Hot Springs (AR) national parks.

Air that causes harm to nature is an extension of unhealthy air, but to a point where it’s causing harm to plants and animals. Per the report, this category is usually a combination of the effect of ozone on plants, and the impacts of harmful elemental deposits in soil, like sulfur. The finding found that 276 parks were of significant concern, while 110 were of moderate concern. Only six were of no concern.

KNPC fire in Sequoia - polluted parks california

California’s parks are at a high risk of damage form the effects of wildfire caused by climate change. Photo: NPS /Sequoia National Park /Public Domain

When it comes to climate change, the results are equally sobering. The report found that 113, or 28 percent, of parks are threatened by invasive species, 95 parks (or 23 percent) face wildfire threats, 75 parks face threats from droughts (18 percent) and another 48 parks, or 12 percent, face threats from rising sea levels. Sadly, five national parks face threats from at least three of these categories — and three of them (Lassen Volcanic, Yosemite, and Sequoia and Kings Canyon national parks) — are all in California.

The report does attempt to explain why California’s parks are suffering, and much of it comes down to their location near California’s agriculture regions. “The adverse air quality conditions in these parks are generated by vehicle emissions, industrial operations and agricultural activities in regions like the San Joaquin Valley of California,” write the authors, “one of the most polluted areas in the nation where residents are frequently exposed to unhealthy air.”

air pollution in national parks - carlsbad

Carlsbad Caverns was the only national park in the top five for air pollution that isn’t in California. Photo: NPS/Carlsbad Caverns National Park/Public Domain

According to Interim Campaigns Director for the Clean Air Program Natalie Levine, some of the reason California’s parks are hurting could be due to development in and around the Golden State. “National parks (and these five case study parks) are suffering the consequences from air pollution that travels from many miles away into the parks from industrial sources like coal plants, chemical and wood manufacturing, and oil and gas development and vehicles on a large collective scale,” she told Matador via email, “more than they are affected by in-park car traffic.”

Other important takeaways from the report include:

  • Roughly 90 percent of parks fall short of meeting recommended air quality standards.
  • “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.” (Based on NPS deciview data.)
  • The economic output of tourism from towns that are also threatened by poor air quality in parks equals roughly $50.3 billion.
  • Drought threatens some of the country’s most iconic species, like bison at Wind Cave National Park in South Dakota and the eponymous Saguaro cactus at Saguaro National Park in Arizona.
polluted parks - wind cave bison

The famous bison of Wind Cave. National Park are under threat from drought caused by climate change. Photo: NPS Photo/Kim Acker</>/Public Domain

But there’s some good news: NPCA’s analysis found that there have been slight improvements since the data was last complied in 2019. “The number of parks with significant concern levels in at least one of the air-quality conditions analyzed dropped from 96 percent to 70 percent,” reads the report. Those improvements were seen in two areas: unhealthy air, and hazy skies.

Aside from supporting climate-positive policy, there are immediate actions guests can take, says Levine of NPCA. “Immediate actions include sharing stories of going to parks on hazy or bad air quality days, learning more about your favorite park and the pollution sources that impact it, and advocating to your state and the federal government to hold those polluters accountable to clean up their air pollution,” she told Matador.

To learn what other actions national park visitors can take, visit the action page at

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