Column by Niko Kommenda
July 14, 2025
America’s national parks are wildly popular. Last year, they had more than 330 million visits, a number close to the entire population of the United States.
If you ask online what the U.S. “does better than any other country,” national parks emerge as one of the top answers, alongside its cultural diversity or the universal availability of iced drinks.
I still remember my first visit to Shenandoah National Park in Virginia, where I got lost in the thick undergrowth before climbing a boulder to see the Blue Ridge Mountains flatten into rolling hills and farmland underneath me.
Having experienced such stunning views just hours from D.C., I was surprised when in May the Trump administration paused air quality monitoring at all national parks — although the decision was quickly reversed.
Beyond public health, air quality protections help preserve the scenic vistas that define the country’s national parks.
Since 1999, the Environmental Protection Agency has required states to reduce human-caused “visibility impairments” in national parks and wilderness areas.
While haze levels have declined in most parks in the past quarter century, some sources of pollution have proved difficult to tackle. And in parts of the country, more intense wildfires are threatening to reverse the trend.
Here, you can look up trends for sites with the most complete data. “Very bad” visibility, defined here as less than 20 miles, signals an increase in particles no larger than one-thirtieth the size of a human hair. Once inhaled, these fine particles can infiltrate the heart and lungs, causing serious illness.
Not all national parks have air quality sensors. The charts and rankings presented here excluded a small number of sites with a lot of gaps in their records.
When haze monitoring at national parks was introduced 40 years ago, sites in the eastern U.S. reported the worst numbers. That’s partly because the area is home to some of the biggest and densest urban areas in the country. But one specific industry has had an outsize impact on pollution in protected areas: coal power.
Bill Wade, who spent 32 years at the Park Service and retired in 1997, was superintendent for Shenandoah National Park in the 1990s, when the region ran largely on coal and power companies were trying to expand their footprint.
“There were times when you could drive down [Skyline Drive in Shenandoah] and stop at any one of the 40 turnouts and you could not see the valley floor on either side,” he said in an interview.
Air quality monitoring inside the park became a crucial tool to push for stricter controls on new coal operations.
“We were successful in modifying the permit conditions in a number of plants,” Wade said. In practice, this meant that operators had to install scrubbers or catalytic converters similar to the one you might find in your car.
As the region became less reliant on coal for electricity, its national parks and wilderness areas saw steep improvements in visibility and healthier air for visitors.
The rising threat of wildfires
In the West, where other sources of pollution dominate, the trends are less clear.
Some of California’s most famous parks such as Yosemite, Sequoia and Kings Canyon are situated downwind from the state’s largest cities, busy highways and industrial-scale agriculture, all of which spew fine particles in the air.
From July to October, wildfires add to the mix, bringing brief but intense spikes in pollution. Smoke from large fires can cause yellow haze thousands of miles from where it rises into the atmosphere.
“You don’t have to be anywhere near a fire, or even in the same country, to experience substantial negative impacts,” said Marshall Burke, an associate professor and air quality expert at Stanford University.
Burke’s research has found that increased wildfire activity is stalling or even reversing air quality improvements all over the country. The effects are not limited to national parks, but remote areas are often hit hardest because they are closer to multiple active fires, Burke said.
Wildfires have always occurred in the American West, and until the early 20th century, the landscape was adapted to keep most blazes contained. “They would come through and burn the underbrush and leaf litter but not burn down the big trees,” Burke said.
But over the next 100 years, forest managers aimed to suppress as many fires as possible, leading to more fuel that could ignite in a blaze. This decision, in combination with a hotter and drier climate, paved the way for an era of megafires with record amounts of smoke.
Ranking national parks by their average haze levels from 2019 to 2023, four out of the 10 most polluted sites are in California.
In contrast, the region with best average visibility is the Southwest, where there is less fuel for fires to burn and parks lie farther away from large cities and industrial centers.
While air quality monitoring at the parks continues for now, the Park Service has lost around 13 percent of its staff since January, according to the National Parks Conservation Association, an advocacy group.
“Among the people that are being lost are many of the professional scientific and research people,” said Wade, the retired park superintendent. “It isn’t just the park rangers that run the visitor centers.”
Asked for comment, the Park Service said in a statement that its air quality program will “continue to operate within its budget while collecting critical data across the country.”
Next year, the Trump administration is planning to cut the service’s budget by $1.2 billion, according to its proposed budget. That would cut the agency’s funds by 38 percent but save less than 0.1 percent of the total federal budget.
Phil Francis, another former Park Service official with a career spanning four decades, said the role of the agency goes beyond allowing visitors to tour protected areas.
“Their job is to conserve the natural and cultural resources so as to leave them unimpaired forever,” he said. “These are special places, amazing places.”
If some areas were to lose their protected status entirely, Francis added, “it seems to me we would be violating the very basic reason the national parks were created.”