In addition to thin air and sub-zero temperatures, climbers scaling Mount Everest face another challenge. Mountains in the Tibetan plateau where Everest is located contains levels of ozone as high as that of heavily polluted cities.
"Around the circumference of Tibet, there's a halo of very high levels of ozone," said Kent Moore, a physicist at the University of Toronto and lead author of a new report on the discovery.
Ozone is a colorless and highly corrosive molecule. It's made up of three oxygen atoms instead of the usual two that are crucial to breathable air.
Most of the Earth's ozone is found in the stratosphere, from about 8 to 30 miles above the planet's surface. Mount Everest is 5.5 miles high at its peak.
Ozone in the stratosphere helps protect the globe from the Sun's ultraviolet rays. But closer to the ground, where it is produced when auto emissions and other pollutants interact with sunlight, ozone is a major component of smog.
If inhaled, ozone can cause coughing, chest pain and damage to the lining in the lungs.
Higher, higher …
In autumn last year, John Semple, a plastic surgeon from the University of Toronto and a researcher in the new study, collected data on ozone concentrations while climbing the Yeli Pass in Bhutan. He found that concentrations of the gas increased the higher he went.
"Most people think about the mountains as one of the areas you can go to get clean air," Semple said. "It may be that when you're up high in the mountains that the good ozone actually becomes bad ozone—because no matter where the ozone comes from you don't want to breathe it."
To explain Semple's findings, Moore examined satellite measurements of ozone above the plateau between 1997 and 2004. He found that while ozone levels were low over the center of the Tibetan plateau, a concentrated ring was evident around the edges, where the mountains are located.
The scientists think they've seen the first planet-wide example of a curious phenomenon common to rivers and other flows of fluid.
River of air
When moving fluid comes into contact with a submerged object, it forks in two and flows around the object. But if the fluid is moving in a circle and rotating, something strange happens: the submerged object creates a "cylinder" of still water that extends from the top to the bottom of the fluid, well above the physical height of the object.
This "virtual" cylinder is known as a Taylor column and can disrupt the flow of water just as if it were a physical column.
The atmosphere has its own rivers of air, which scientists treat as a fluid moving in a circular motion due to the rotation of the Earth. Moore believes the Tibetan plateau is acting like a submerged object, creating what is essentially a Taylor column that extends from the surface of the planet up into the stratosphere where it disrupts the flow of ozone.
"As far as we know, this is the first one that's ever been found in the atmosphere," Moore said.
The ozone levels documented in the study are not enough to cause a significant change in the lungs but could exacerbate medical dangers faced by mountaineers, the researchers said.
"We can only imagine that hypoxia [lack of oxygen] and the rate of hyperventilation that people have at extreme altitudes would actually make the effects of ozone worse," Semple said.
The findings were detailed in a recent issue of the journal Geophysical Research Letters.
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