Ozone ring makes Everest rise riskier

The air around Tibetan plateau is thick with ozone, posing a medical danger to mountaineers, says a fresh study.

Not only is the air around the Tibetan plateau thin but it's also thick with ozone, posing a medical danger to mountaineers, says a new study by researcher at the University of Toronto.

The ring of ozone around the plateau, which rises 4,000 metres above sea level and includes such famous peaks as Mount Everest and K2, is as concentrated as the ozone found in heavily polluted cities -- and may put climbers at risk, a university release said.

These findings are published in a recent issue of the journal Geophysical Research Letters.

'Around the circumference of Tibet, there's a halo of very high levels of ozone,' said GW Kent Moore of the university and lead author of the study.

Ozone is a highly reactive gas that can cause coughing, chest pain and damage to the lining of the lungs.

Study co-author John Semple was initially interested in how weather changes at high altitude can have a medical impact on climbers. Along with Moore, he examined earlier data and found several studies that alluded to higher ozone levels.

'In meteorology, it's a fairly well known phenomenon that when you get storms, quite often, the tropopause -- which is the flexible boundary between the stratosphere and the troposphere -- descends,' Moore says.

'Its usual height might be 12 km, and it might descend to nine or 10 km. If you're on Mount Everest, you're eight or nine kilometres up. It might be that you're sometimes in the stratosphere.'

The stratosphere is where most of the ozone that protects the globe from the sun's ultraviolet rays can be found; for this reason stratospheric ozone is often referred to as 'good' as opposed to the ground-level ozone from pollution that is referred to as 'bad'.

When the tropopause descends, the ozone descends with it. 'Most people think about the mountains as one of the areas you can go to get clean air,' said Semple.

'It may be that when you're up high in the mountains that the good ozone actually becomes bad ozone -- because no matter where ozone comes from you don't want to breathe it.'

Semple climbed the Yeli Pass in Bhutan in the autumn of 2004 while collecting data on weather and atmospheric changes. He measured the levels of ozone between 3,000 and 5,000 metres above sea level and discovered that instead of falling (as pollutant levels normally do with altitude), ozone levels were rising.

He also found that while ozone levels were low over the centre of the Tibetan plateau, high levels of the gas could be found around the periphery of the plateau -- forming a halo.

The presence of such higher levels of ozone at extreme altitudes may add to the medical dangers faced by mountaineers.

'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.