Depletion Of The Ozone Layer

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Term Paper Title	Depletion Of The Ozone Layer
# of Words	1140
# of Pages (250 words per page double spaced)	4.56

Depletion Of The Ozone Layer

     The ozone layer diminishes more each year. As the area of
polar ozone depletion (commonly called the ozone hole) gets
larger, additional ultraviolet rays are allowed to pass through.
These rays cause cancer, cataracts, and lowered immunity to
diseases.1 What causes the depletion of the ozone layer?

     In 1970, Crutzen first showed that nitrogen oxides produced
by decaying nitrous oxide from soil-borne microbes react
catalytically with ozone hastening its depletion. His findings
started research on "global biogeochemical cycles" as well as the
effects of supersonic transport aircraft that release nitrogen
oxide into the stratosphere.2

     In 1974, Molina and Rowland found that human-made
chlorofluorocarbons used for making foam, cleaning fluids,
refrigerants, and repellents transform into ozone-depleting
agents.3

     Chlorofluorocarbons stay in the atmosphere for several
decades due to their long tropospheric lifetimes. These compounds
are carried into the stratosphere where they undergo hundreds of
catalytic cycles with ozone.4 They are broken down into chlorine
atoms by ultraviolet radiation.5 Chlorine acts as the catalyst
for breaking down atomic oxygen and molecular ozone into two
molecules of molecular oxygen. The basic set of reactions that
involve this process are:
                    Cl + O3 -->ClO + O2 and
                    ClO + O -->Cl + O2
     The net result:
                    O3 + O -->2O2

     Chlorine is initially removed in the first equation by the
reaction with ozone to form chlorine monoxide. Then it is
regenerated through the reaction with monatomic oxygen in the
second equation. The net result of the two reactions is the
depletion of ozone and atomic oxygen.6

     Chlorofluorocarbons (CFCs), halons, and methyl bromide are a
few of the ozone depletion substances (ODS) that break down ozone
under intense ultraviolet light. The bromine and fluorine in
these chemicals act as catalysts, reforming ozone (O3) molecules
and monatomic oxygen into molecular oxygen (O2).

     In volcanic eruptions, the sulfate aerosols released are a
natural cause of ozone depletion. The hydrolysis of N2O5 on
sulfate aerosols, coupled with the reaction with chlorine in HCl,
ClO, ClONO2 and bromine compounds, causes the breakdown of ozone.
The sulfate aerosols cause chemical reactions in addition to
chlorine and bromine reactions on stratospheric clouds that
destroy the ozone.8

     Some ozone depletion is due to volcanic...

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