The Role of Chemistry in History

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History Effects Ozone

April 23rd, 2008 · 2 Comments ·


Ozone History | Ozone in the Troposphere | Ozone in the Stratosphere | History Effects Ozone | Ozone’s Other Uses

 In the late 1920s, there was a need for a safe refrigerant.  Thomas Midgley, who was working for General Motors at the time, found the answer in chlorofluorocarbons, or CFCs.  This seemed to be the perfect response because CFCs are inert in the troposphere.  So they were used in air conditioning, aerosols and other appliances.  However, in 1974 Mario Molina and Sherry Rowland put forth the hypothesis that the decline in concentration of the ozone layer was due to the CFCs.  This process of man-made destruction of ozone happens because CFCs are long lasting, inert molecules that can accumulate.  Winds carry the CFCs up to the stratosphere, where a UV ray breaks off a chlorine from the CFC, which is highly reactive and takes one of the oxygen atoms in ozone and bonds to that.  Then the oxygen atom bond to another oxygen atom and the chlorine is free to repeat the process.  A single atom of chlorine can kill tens of thousands of ozone molecules before it is removed.  The CFCs travel to Antarctica because of wind patterns and accumulate there, causing the ozone hole.  The hole is also due to chlorine in reservoir species, ClONO2 and HCl, where they get into polar stratospheric clouds and can go reactions which release the chlorine atom.  Because natural ozone formation and destruction needs the Sun’s rays, the destruction of the ozone layer can have an accumulation effect if the levels are never recovered between winters.  In the decade following Molina and Rowland’s findings, industry battled science about the production of CFCs.  In the early 1980s evidence proving their point mounted.  With data going back to 1957, there was a clear decline in ozone concentration and really picked up in the early 1980s.  Also, findings showed that in places with decreased reservoir species had an abundance of active chlorine compounds and a decreased ozone level.  So, in 1987 the Montreal Protocol was held and they decided to cut CFC production in half.  This was a monumental occasion because it was the first international attempt to prevent ozone destruction.  Ozone destroying chemicals dropped ninety-five percent since the late 1980s, and CFCs were eventually banned in the United States. 

            History also effects ozone in the troposphere.  With the mass production of cars in the early twentieth century came pollution.  The combustion of fossil fuels in automobiles creates nitrogen dioxide, which breaks apart because of UV light into a nitrogen oxide radical and oxygen radical.  The oxygen radical then bonds with an oxygen molecule, creating ozone.  


Tags: Ozone