The amount of ozone near the Earth is only a small percent of the amount in the stratosphere, and exchange of molecules between the ozone layer and the air at ground level is thought to be relatively small. Furthermore, the ozone molecule is so unstable that only a tiny fraction of ground-level ozone could survive the long trip to the stratosphere, so the ozone layer will not be replenished to any significant degree by the increasing concentrations of ozone that have been detected in recent years near the earths surface. The long-term averages of ozone both near ground level and in the stratosphere are regulated by continuous processes that are constantly destroying and creating it in each of these places. This is why scientists are so concerned about human beings injection into the stratosphere of chemicals like nitrogen oxides, which are catalysts that facilitate the breakdown of ozone. If the ozone layer is depleted significantly, more ultraviolet radiation would penetrate to the Earths surface and damage many living organisms.
17. The passage suggests that factors contributing to the variation in the amount of ozone above different areas of the Earths surface include which of the following?
I. Some of the ozone found at higher latitudes was produced elsewhere.
II. There is usually a smaller amount of naturally occurring nitrogen oxide over high latitudes.
III. The rate of ozone production over the poles is less than that over the tropics.
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