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Name: Lynne
Status: educator
Age: 40s
Location: N/A
Country: N/A
Date: 1999-2001


Question:
Would not the thinning of the ozone layer increase the rate at which ozone is created, since 1) more radiation will be coming through hitting the 2) increased water in the upper atmosphere due to the "global warming" "greenhouse effect" and therefore take care of itself?

If there is a balance issue, at exactly what rate would ozone have to be destroyed to exceed the natural ability to replace itself? Due to the enormous power of the sun and the unlimited amount of resources for the replenishment, it would have to be a staggering amount like in the neighborhood of 1,000,000,000,000,000,000 times (or greater) the current or recent rate of destruction to be come fatal to the world. And I say fatal because if mankind did find a way to overcome the replenishment rate, there would not be enough time for us to worry about global warming because the radiation coming through the atmosphere at that time would be lethal to all life on the planet.


Replies:
The problem of ozone depletion is not so much a matter of the rate at which ozone is produced as the rate at which it is destroyed by anthropogenic (human-caused) pollutants. Ozone is a reactive, unstable gas. It is maintained in the stratosphere only because solar radiation continually supplies the energy needed to produce it.

Ozone is produced in the stratosphere when hard UV light breaks apart O2 molecules into two oxygen atoms; a free oxygen combines with O2 to form ozone, O3.
  O2 + hv -> O + O  (wavelength < 240 nm)
  O + O2 -> O3

Ozone is naturally destroyed by nitrogen oxides in the stratosphere, which catalyze the reaction of ozone with an oxygen atom to produce diatomic oxygen, O2.
O + O3 -> 2 O2

(Note that both the formation and destruction reactions require the presence of oxygen atoms, which are only produced when the sun shines.)

Chlorine and bromine atoms, which are gradually introduced into the stratosphere by man-made chemicals called freons and halons, are extremely active catalysts for ozone destruction. A pair of representative reactions by which a chlorine atom can remove "odd-oxygen" species (O and O3) from the atmosphere is:
Cl + O3 -> ClO + O2
ClO + O -> Cl + O2

This pair of reactions can remove odd-oxygen species whether or not the sun is shining. (An excellent description of the chemistry of the ozone layer can be found at

http://www.egs.uct.ac.za/csag/faq/ozone-depletion/intro/faq.html.)

But back to your question. As you can see from the chemical equations above, ozone is not produced from water, so water does not play a significant role in the chemistry of the ozone layer. Furthermore, global warming and ozone depletion are seperate and unrelated phenomena. Global warming is something occurring in the troposphere (lower atmosphere), and ozone depletion is a problem in the stratosphere (the second layer of the atmosphere). Very little water from the troposphere reaches the stratosphere, because of the extremely low temperature of the "tropopause," the boundary between the two layers. The tropopause does not act as a barrier to transmission of freons and halons, however. So, ozone depletion is not a self-limiting problem. As more freons and halons migrate to the stratosphere, we can expect the statospheric ozone levels to continue to decline.

Thinning of the ozone layer will and does cause increased levels of ultraviolet light from the sun to reach the earth. I don't know where you got your factor of a quintillion, but if the current rate of ozone destruction were increased by that much, there would be effectively no ozone in the atmosphere at all. As soon as a molecule of ozone were created, it would immediately revert back to O2. However, even total ozone depletion would not become fatal to the world. Some species of plants and animals would probably become extinct, human skin cancer rates would rise, and many species of animals and plants (such as some agricultural crops) would suffer. But it wouldn't be like walking into Chernobyl.

Richard Barrans Jr., Ph.D.



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