New Ozone Hole Over Chile, Argentina

Scientists from the Federico Santa Maria Technical University (UTFSM) of the Chilean port of Valparaiso, 120 kilometers west of Santiago, detecting an unusual thinning of the ozone layer in the central and southern zone of Chile in early April.

Luis Da Silva and Christian Stehr, in charge of the UTFSM Ozone Project, told the Chilean daily El Mercurio that reports on April 5 indicated this "hole" had now reached a diameter of more than a thousand square kilometers.

The area affected stretches from Santiago to Puerto Aisen, some 1,500 kilometers south of the capital, reaching from the Pacific to the Atlantic, obviously covering the same latitudes of Argentina.

Ozone is naturally abundant in the stratosphere, at an altitude of 25,000 to 50,000 meters, filtering the sun's harmful ultraviolet rays. The weakening of the ozone layer over the Antarctic as a result of the build-up of ozone-eating chemicals concentrated in the atmosphere has been of growing concern since the 1980s.

On September 16, 1987, the international community accepted the Montreal Protocol, which came into effect on January 1, 1989, with the aim of gradually reducing the use of chlorofluorocarbons (CFCs) and other such gases.

The application of the protocol has meant that CFC emissions, 80 percent of which come from the industrialized countries, have been stabilized, although the biggest reductions in ozone levels will occur between now and the year 2015.

Experts warned the last years of the century would be "the most critical" for the ozone layer, because of the long established accumulation of CFCs in the stratosphere.

Emissions of these compounds move towards the earth's poles where they become active due to a combination of low temperatures and the first solar radiation of the spring.

The ozone "hole" over the Antarctic south pole increases in size between September and October each year, reaching unprecedented dimensions of 8 million square miles during 40 days in 1995.

In September 1996, the NASA Earth Probe and Adeos satellites registered another critical moment, when the ozone measurements reached 204 Dobson Units (DU). Stehr explained that 100 DU means only a millimeter of ozone thickness, and less than 220 units presents risks for human beings due to the ultraviolet radiation.

The ozone hole, an oval weakness in the atmosphere, reached the Magallanes region in the southernmost tip of Chile in September 1996.

The satellite measurements have on several occasions detected extensions of the "hole" towards areas in the far south of Argentina and Chile, including the Falkland Islands.

But the episode of September 1996 was even worse as the volume of ozone over the town of Punta Arenas, capital of the Magallanes region, were only 204 DU, a thickness only normally measured in the most polar areas.

However, the present hole, registered on April 5 this year, is no mere extension or displacement of the same phenomenon as is seen each Antarctic spring.

Da Silva and Stehr told "El Mercurio" the NASA satellites had already detected this new thinning on previous occasions, but that it had never reached the extent of 204 DU before.

The UTFSM scientists said they need to keep the phenomenon under observation because of the risk presented by high levels of ultraviolet radiation over the most heavily populated areas of Chile.