By Sid Perkins
Think heading to the mountains guarantees crisp, clean air? Think again: Recent observations on Mount Everest suggest that that Asian peak is often bathed in unhealthy levels of ozone — possibly one reason that climbers sometimes have such tremendous difficulty breathing there.
In 2005, climbers in one group scaling Mount Everest — with a height of 8,848 meters, it’s the world’s tallest peak — carried portable ozone monitors. On May 18, the team took readings at elevations between 6,400 and 7,500 m, says Kent Moore, an atmospheric scientist at the University of Toronto.
At 7,500 m, ozone concentrations measured 70 parts per billion (ppb). In the United States, exposure to ground-level ozone at levels higher than 75 ppb for more than eight hours violates air quality standards set by the Environmental Protection Agency.
Weather patterns for the days preceding May 18, 2005, suggest that the ozone bathing Mount Everest had descended from the stratosphere, which is the second-lowest layer of Earth’s atmosphere. Moore and colleague John Semple reported January 15 in Phoenix at the annual meeting of the American Meteorological Society. When faster-than-average portions of the jet stream blast past the mountain, stratospheric air can spill over Everest in episodes lasting a couple of days, Moore notes. In 2006, during a similar event, another team of climbers measured ozone levels around 100 ppb.
But the stratosphere isn’t the mountain’s only source of ozone: On May 30, 2005, climbers measured 50-ppb concentrations of the gas at the summit. Meteorological data suggest that in this case the ozone drifted to the area from the southwest, within polluted air masses from India and other parts of southern Asia. Similarly, in 2008, climbers measured ozone concentrations of 120 ppb in air wafting to the region from southern. Weather patterns in the region suggest that such pollution-laden air may swaddle the peak for lengthy periods, Moore notes.
Regardless of its source, ozone may be aggravating breathing problems among climbers on Everest, Moore and Semple speculate. Most people who climb the peak spend weeks in the region — much of that time at various high-altitude base camps to become acclimated to the thin, low-oxygen air — so a climber’s exposure to ozone could be both prolonged and substantial.
