MadSci Network: Environment & Ecology
Query:

Re: Why is the ozone in upper atmosphere important to life on earth?

Date: Tue May 2 22:04:36 2000
Posted By: Ruth Weiner, Faculty, Transportation of Radioactive Materials, Chem and Radiological Risk Assessment, Sandia National Laboratories
Area of science: Environment & Ecology
ID: 954479943.En
Message:

Ozone in the upper atmosphere exists in equilibrium with ordinary molecular 
oxygen and oxygen atoms.  You can wite the equation as

O3 = O2 + O

That, is, all three of these forms are present in the "ozone layer."  Ozone 
(O3) absorbs the far ultraviolet rays of sunlight, and when this absorption 
takes place, the ozone splits into an oxygen molecule and an oxygen atom.  
By absorbing the UV, the ozone layer protects people from the harmful 
effects of the UV -- it appears to cause basal cell skin cancers.

Normally the oxygen molecules and atoms recombine to form ozone, thereby 
maintaining the equilibrium.  However, some jet engine exhaust gases like 
NO, and the photochemical products of Freon aerosols, will combine readily 
with the oxygen atoms so that the oxygen atoms can't recombine with 
molecules to form ozone.  These substances act as oxygen scavengers.  If 
the atomic oxugen is not available to recombine, the ozone layer becomes 
depleted and cannot protect as effectively against UV in sunlight.


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