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In addition to photolytic destruction by infrared
light (wavelengths of 1140 nanometers or less), stratospheric ozone is destroyed
by interaction with a variety of chemical substances in the stratosphere. Some
of these chemicals, such as the chlorine free radical--liberated by the
photolysis of chlorofluorocarbons, are not normally produced there in nature at
such high concentrations. This leads to the conclusion that human activities,
and not natural chemical cycles, are responsible for the current rate of
stratospheric ozone destruction. Ozone destruction is most noticeable
(alarmingly!) over the South Pole, where seasonal plummeting in stratospheric
ozone concentrations have been measured since the 1970s and are apparently still
increasing (1999). That said, estimates based on declining CFC use (because of
the Montreal Protocol) suggest that the damage to the global ozone layer will
max out soon in the 21st century and that that ozone damage will
decrease within the next 75 to 100 years.
[Nature; v.370; p.429; 1994.]
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