October 5, 1995. Copyright, 1995, Graphic News. All rights reserved

LARGEST EVER OZONE HOLE EXPECTED
By Nicholas Booth, Science Editor.

LONDON, October 5, Graphic News Ñ Later today (Thursday), scientists expect to record the lowest ever ozone readings over the South Pole. Already, this year's hole in the ozone layer has covered the largest area ever seen by this date, when ozone levels reach their minimum each southern spring. 'This week the hole has been covering the whole of the Antarctic continent,' reports Jonathan Shanklin of the British Antarctic Survey. 'A year ago it was about 80% coverage at this time.' Shanklin was one of the discoverers of the ozone hole ten years ago, from measurements made at the Survey's scientific base in Halley Bay. 

The ozone hole is a seasonal phenomenon resulting from the unique geography of the South Pole. During the wintertime, air around Antarctica is effectively cut off from the rest of the atmosphere and it is in this vortex where chlorine from manmade chlorofluorocarbons Ð CFCs Ð acts to strip away the ozone layer. In the freezing cold of the Antarctic stratosphere, the return of sunlight during the springtime serves to fire chemical reactions which can remove up to 60% of the ozone above the pole. In recent years, the pace of ozone destruction worldwide has accelerated with marked depletions in the northern spring and palpable destruction also seen around the world.

Ozone is created high above the equator by the action of ultraviolet light upon the oxygen which we breathe. It is transported around the world by winds in the upper atmosphere whose strength may change and therefore alter ozone levels measured from the ground. They are normally recorded in Dobson units, after the Oxford professor who invented the instrument used to measure its presence. An average value is 300 Dobson Units, but this time last year, the lowest ever recorded value was established with 96 Dobson Units.

Scientists had thought the recent trend for very low ozone levels may have been aided by chemical reactions taking place on dust particles thrown into the atmosphere from the explosion of Mount Pinatubo, a Philippine volcano in 1991. But the dust particles have now dispersed and this week's ozone levels were reaching very low limits. Dr. Shanklin suggested that changes in atmospheric circulation may stop the ozone from reaching last year's lowest ever value. But unlike last year, the hole seems offset from the centre of the southern continent and is now encroaching upon South America and the Falklands.

Though the hole is appreciably larger, there has not been any discernible increase in ultraviolet radiation reaching the surface around the edges of the hole. But there is no room for complacency, the scientists warn, for although CFCs are being phased out at the end of this year, they remain in the upper atmosphere for many years. The depletion being seen now results from CFCs released in the 1960s and it will be the end of the next century before ozone levels return back to normal each spring in Antarctica.


SOURCES: British Antarctic Survey, NASA, US National Oceanic & Atmospheric Administration & World Meteorological Organisation.