Unhealthy parks

get in line

The line that sometimes forms at the entrance to Arches National Park in Utah/NPS photo

Alaska may be the last bastion of heart-healthy national parks, according to a study out this week warning that visiting a national park in the Lower 48 states could be bad for your cardio-vascular system.

Visitor traffic to Outside parks has helped to boost air pollution to a level “statistically indistinguishable from the 20 largest U.S. metropolitan areas,” the scientists reported in a study published at Science Advances.

The study goes on to warn that “35 percent of all national park visits occur when ozone levels are elevated.”

Alaska parks escape the problem given that most of them aren’t road accessible, and the few that are have very limited road access. The big exception is highly popular Denali National Park and Preserve, but most visitors there are restricted to buses.

Alaska parks remains free of the crush of humanity and the traffic jams for which some Outside parks have become infamous. Yosemite National Park in California welcomed a record 5 million guests in 2016, and “that spike in attendance is causing more cars to creep along the valley floor,” ABC30 in Fresno reported in May.

“Bob and Pat McNulty traveled from Georgia to see Yosemite for the first time, but say because of the traffic, this trip might also be their last.

“‘I knew Yosemite is the most congested park; we’ve been to most of them, but I was shocked this early in May it’s already this bad,’ said Bob.”

Worse than the traffic

Crowding and traffic, according to Ivan Rudick from Cornell, and David Keiser and Gabriel Lade from Iowa State, might be the lesser of the issues with over-flowing parks.

They estimate 284 million visitor days in parks since 1990 “occurred when ozone exceeded the 55-part per billion (ppb) “moderate”, air quality index threshold. Nearly 9 percent of visitor days (77 million visitor days) occurred at parks when ozone levels exceeded 70 ppb. A large body of evidence finds that ozone exposure increases hospitalization rates, respiratory symptoms, and mortality. These adverse effects from exposure are greater during exercise.”

So if you’re going to a national park in the Lower 48 during the peak of the season, don’t breathe the air. Or at least don’t go on the sort of hike that requires you to breathe large amounts of the air.

A “visitor day” is one visitor spending one day in the park. Yosemite visitation peaked at more than 5 million in 2016. Denali visitation peaked last year at 643,000 – about an eighth the number of people in a park eight times bigger than Yosemite.

Denali was the only Alaska park included in the sample of air quality in 33 parks. The sample, according to the study authors, provided “broad coverage across the United States and include(d) the largest and most heavily visited parks in the NPS system such as Acadia, Great Smoky Mountains, Yellowstone, and Yosemite.”

The study somewhat inexplicably found that cities have been doing a better job of cleaning up their air than parks.

From 1990 to 2014, the scientists concluded, major metropolitan areas were able to reduce their bad air days by 66 percent from 53 days per year to 18 while the reduction in the parks was but 41 percent “from 27 to 16 days per year.”

“Summertime ozone concentrations and the average number of unhealthy ozone days are nearly identical in national parks and metropolitan areas starting in the 2000s,” the study says.

“Ozone pollution at the national park with the highest average ozone concentrations, Sequoia National Park, follows a similar trend in exceedance days as the metropolitan area with the highest ozone concentrations, Los Angeles. Notably, exceedance days at Sequoia have surpassed those in Los Angeles in all but two years since 1996.”

The study makes it clear some parks are worse than others for bad air, and some times of year are worse than others for bad air, and some bad air days are natural.

Blame the trees, too

“…Both cars and vegetation produce volatile organic compounds (VOCs),” the study’s authors concede. “Both are chemical precursors to ozone.”

Great Smoky Mountain National Park got its name from the Smoky Mountains of East Tennessee and Western North Carolina. The mountains were so named for the smoky haze that regularly hangs over them as a result of high emissions of VOCs from coniferous trees, which emit terpenes – a compound from which turpentine is made – and deciduous trees, which emit isoprenes – a compound that used to produce rubber.

“We tend to think of VOCs as an indoor air quality problem, being released when people paint, clean, or spray pesticides, or as the unhealthy smog that hangs over cities,” Laura Narajano observes at the website of the National Aeronautics and Space Administration (NASA). “Yet scientists estimate that trees and plants emit about two-thirds of the VOCs currently in the air. So if these compounds are already prevalent, why are they a problem? The natural VOCs produced by trees are not as toxic to human health as those emitted by paint and pesticides, which can cause headaches and irritate our eyes and lungs. However, once in the atmosphere, all VOCs react with other airborne chemicals to form air pollution.”

The scientists controlled for nature by monitoring air quality upwind from the parks. “We did not include parks for which we could not construct a measure of upwind ozone concentrations,” they noted.

When they corrected for natural conditions, they found most of the pollution in the parks was caused by humans.