Joshua Tree National Park is among the hundreds of sites across the country being significantly impacted by air pollution, according to a report that was released Tuesday.

The National Parks Conservation Association's report identifies Joshua Tree, along with the Mojave National Preserve and Sequoia and Kings Canyon national parks, as sites with the worst air quality. It indicates those parks often struggle with air that's unhealthy to visitors and comparable to conditions in densely populated citieslike Los Angeles.

"When people think of iconic parks like Joshua Tree or the Grand Canyon, they think of unspoiled landscapes and scenic views. I think they would be shocked to know that these are actually some of our most polluted national parks," said Theresa Pierno, NPCA president and CEO.

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Attempts to reach Joshua Tree officials for comment have been unsuccessful.

Researchers evaluated 417 national parks and preserves and targeted four categories of potential impact. Results showed:

85% of parks have air that is unhealthy to breathe at times

89% of parks suffer from haze pollution

80% of parks are negatively impacted by climate change

88% of parks' soils and waters are affected by air pollution that impacts sensitive species and habitat

Joshua Tree had significant levels of concerns in the first three categories, while Sequoia and Kings Canyon fell into all four categories, according to the report.

Overall, 96 percent of the nation's parks are affected by air pollution.

“The poor air quality in our national parks is both disturbing and unacceptable," Pierno said.

Southern California's air pollution remains above legal levels and has been blamed for illnesses. A recent study found that more than 100,000 Americans die each year from illnesses caused by air pollution, which causes $886 billion in hospital stays and other expenses.

Most live in polluted valleys in the Golden State and the NPCA report singles out the San Joaquin Valley as one of the most polluted areas in the nation.

The Coachella Valley's air quality is most affected by smog and soot blown inland from diesel trucks, trains and cars in coastal Los Angeles. A recent Desert Sun investigation identified other local sites as cause for pollution in the Coachella Valley.

Previous reporting from Desert Sun reporter Janet Wilson was used in this story

Desert Sun reporter Colin Atagi covers crime, public safety and road and highway safety. He can be reached at Colin.Atagi@desertsun.com or follow him at @tdscolinatagi.