Word: nitrogen
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Dates: during 1990-1999
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...fundamental tenet of atmospheric chemistry is that ozone depletion is controlled by nitrogen oxide radicals and the hydrogen oxide and halogen radicals play a much smaller part," Anderson says. "We have experimentally shown that in the lower ozone layer, the hydrogen oxide radicals are on top and the halogen radicals are dominant. The nitrogen oxide radicals play the smallest role at less than 20 percent...
...engine exhaust deposits nitrogen oxides into the atmosphere, where they can chemically react with and deplete ozone...
Supersonic aircraft, which currently include the Concorde and some military planes, produce these nitrogen radicals in their engines. "Estimates show that a 50 percent increase in nitrogen radicals [in the lower ozone layer] is expected from a fleet of supersonic aircraft," Wennberg says...
...Most of the nitrogen and hydrogen radicals are produced by natural activities," says Salawitch. "But the halogen radicals, primarily bromine and chlorine, are primarily due to industrial activity...
...Anderson acknowledges a weakness in their research. "We only have comprehensive measurements from 13 to 20 kilometers," Anderson says. "The region above is unexplored in hard detail. We know there is a point above 20 kilometers where nitrogen radicals control the depletion of ozone...