Ozone Depletion





The reappearance of the ozone hole over Antarctica has been a hot topic for scientist around the world. A few of these scientists are the atmospheric physicist Richard D. McPeters and several of his colleagues at the NASA Goddard Space Flight Center in Greenbelt. The ozone hole showed up earlier than expected, and it was wider and thinner. It appeared in mid-August, about two weeks ahead of schedule, and on September 19 reached the record size of 10.5 million square miles, more than three and a half times the area of the forty-eight contiguous United States that is a frightening statistic man. The hole actually is a thinning of the ozone layer--was also at a near-record problem. Ozone, a bluish gas whose molecules are made up of three oxygen atoms, occurs naturally in the upper atmosphere, where it acts as a kind of cosmic sun-block, protecting life on earth from the sun\'s harmful ultraviolet rays. The sun\'s rays destroy some ozone, but there was no real loss because ozone regenerates itself from stray oxygen atoms and molecules. At least since 1985, however, that delicate balance has been upset. An Antarctic ozone hole now forms from September to November each year, caused by man-made pollutants that destroy ozone in the atmosphere. The hole has been getting progressively larger. The culprits are chlorofluorocarbons (CFCs), once used as coolants. The chlorine atoms from CFCs react with ozone and destroy it. Sunlight splits off chlorine from CFCs, and the chlorine-ozone reaction takes place most readily on the surface of ice crystals. Thus when the sun returns in the Antarctic spring ice crystals that had formed the winter before are in place to speed the reaction. Investigators are blaming the record size of the most recent ozone hole on unusually cooler temperatures at the South Pole last year. Chemical pollutants combined with unusually low temperatures high in the atmosphere to break a record-breaking hole in Earth\'s protective ozone layer this year, according to measurements made in Antarctica. The stratosphere above both poles has grown colder in recent years for reasons not clear to researchers. The recent Antarctica temperatures, the lowest in 2 decades of measurements, raise concern that the ozone layer will not heal as quickly as scientists had predicted, even though nations are curbing the use of ozone-depleting chemicals. One fear among scientists is that greenhouse gases could be playing a role in lowering all stratospheric temperatures. Carbon dioxide and other forms of pollution trap heat in the lower atmosphere, but they cool off the stratosphere--the layer between 10 and 50 kilometers in altitude. The ozone hole above Antarctica starts forming in September, when springtime sunlight returns to the polar skies. The light energizes chlorine- and bromine-containing chemicals that break down ozone molecules in the stratosphere. A key part of the chemical chain reaction takes place on the surface of frozen cloud particles, so cold temperatures worsen ozone destruction. According to measurements by a NASA satellite, the ozone hole grew to 27.3 million square kilometers on September 19, larger than the North American Continent. The biggest previous ozone hole reached 26 million k in 1996. The satellite also showed that ozone concentration in the worst section of the hole bottomed out. At only one-third of what should normally be there this time of year researchers fear now more than ever. Balloon measurements over the South Pole record a value of 92 Dobson units. The cold temperatures this year helped the ozone hole reach new heights, according to Hofmann. "We saw some ozone loss all the way up to 24 km, which is higher than usual." Normally, temperatures are too warm at that altitude to allow the formation of frozen cloud particles. Scientists trace
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some of the stratospheric cooling in recent years to the loss of ozone molecules, which absorb sunlight and heat up the surrounding air. But this process cannot explain the extremely low temperatures detected in August and September above Antarctica, before much sunlight had returned to the polar skies, says William J. Randel of the National Center for Atmospheric Research in Boulder. One cause could be natural weather conditions in the lower atmosphere, which can sometimes send pressure disturbances rippling up into the stratosphere. These so-called planetary waves warm the polar stratosphere and