Ozone hole over Tibet

a large hole may be developing in the ozone layer over the Qinghai-Tibet Plateau, says a Chinese study. The area of depleted ozone appears to be spread over 2.5 million-sq km, which is almost three-fourth the size of India, says the study published in a recent issue of the Chinese journal Scientific Report.

The study found that ozone concentration in the affected area was 220 Dobson Units (du) from December 14 to 17, 2003, with a record low of 190 du ( 100 du equal a one millimetre-thick layer of pure ozone at one standard atmospheric pressure and a temperature of 0C). The normal range for the thickness of the ozone layer is 300-500 du. "The decrease of ozone was caused by airflow exchange... When 'low-ozone' air currents in lower atmosphere enter the upper atmosphere, the overall ozone density is reduced," it says. Experts say ozone depletion over Tibet is caused by variations in air circulation due to global warming .

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Another study, published in the April 11 issue of the Proceedings of the National Academy of Sciences (Vol 103, No 15), suggests that thunderstorms over Tibet provide the main pathway for water vapour and chemicals to disturb the ozone layer over Tibet. But some scientists say the problem is not serious. "It does not yet qualify as a regular ozone hole, like the other two over the poles (Antarctic and the Arctic), as depletion is not that serious," says R P Singh of the Indian Institute of Technology, Kanpur.

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