National Geographic : 1990 Oct
When a UV ray strikes a CFC molecule, it releases a chlorine atom - Cl--which then attacks ozone molecules in a catalytic reaction (above). The chlorine breaks the ozone - 03- into ordinary oxygen O2 - and combines with the free atom of oxygen to form chlorine monoxide - CIO. This is then stripped of its oxygen atom by anotherfree oxygen atom thatjoins it to become ordinaryoxygen. The chlorine atom is left intactto repeatits destruction. It may do so 100,000 times before it is finally neutralized. Chameleons darken after being injected with a melanin hormone synthe sized by a team led by University ofArizona biologist Mac Hadley. The substance may one day offer fair-skinned people greater protection against skin cancer. PAINTINGBYMARKSEIDLER OZONECONSULTANT: MARKR. SCHOEBERL, NASA/GODDARD SPACEFLIGHTCENTER(GSFC) CHEMISTRYCONSULTANT: MARTINR. FELDMAN,HOWARDUNIVERSITY TOTALOZONEMAPPINGSPECTROMETER IMAGES PROVIDEDBYNASA/GSFC Murray Mitchell and my colleague Charles Stockton see this pulse as a combination of the sunspot cycle and a lunar cycle of 18.6 years and relate it to cyclical droughts in the West, such as the 1930s Dust Bowl. "More than that, varying amounts of a carbon isotope in the tree rings-carbon 14-may be a clue to long-term changes in solar radiation and its effect on the earth's atmosphere," Hughes told me. "The irregularities in the carbon-14 production rate are known as the Suess wiggles, for Hans E. Suess, their discoverer. They are extremely important in calibrating and correcting the carbon-14 calendar used to date ancient events from remnants of organic materials, such as ancient wood or bones." Other theories of sunspot-climate relationships have come and gone, but no true "smoking gun" had been found-until the mid-1980s. Then a German atmospheric physicist, Karin Labitzke of the Free University of Berlin, together with Harry van Loon of NCAR in Boulder, published a remarkable fit between reversing winds in the stratosphere, polar air tempera tures, and the sunspot cycle. If their discovery is confirmed, it will indicate a direct link between sunspots and the atmosphere of earth-a possibly crucial connection. The work has been cited as among the most significant now being pursued at NCAR. One connection may be a better under standing of the ozone hole in the so-called polar vortex over Antarctica each winter, a giant whirlpool of stratospheric winds. SNTHE MID-I980s the world became suddenly aware that the protective ozone shield in the atmosphere was in danger-was, in fact, greatly depleted in a huge "hole" over the frozen wastes of Antarctica. The mysterious stuff called ozone, which until then was known to the public chiefly as an acrid, lung-burning element of smog in over crowded cities, was being destroyed in the stratosphere by chemicals made and released in the 20th century by humans. Ozone is a variant form of oxygen-the most life-sustaining gas of all. Under the intense ultraviolet bombardment from the sun at the upper reaches of the earth's atmosphere, normal two atom molecules of oxygen are split into single atoms-O rather than 02, in chemists' terms. Some of these single oxygen atoms rejoin with 02 molecules to form ozone-O 3 . The amount in the stratosphere is very scant, less than ten parts per million (at sea level the layer would be about as thick as a pane of window glass), but that layer is enough to stop most of the sun's danger ous ultraviolet rays from reaching the earth's surface, 10 to 30 miles below. The possibility of ozone destruction by man-made chemicals had been predicted as early as 1974 by two farsighted research ers, F. Sherwood Rowland and Mario J. Molina, at the Univer sity of California at Irvine.