Ozone Cycle

     Chemical engineers will play a valuable role in saving the Earth's ozone layer.  The ozone is responsible for absorbing ultraviolet (UV) radiation from the sun.  In the absence of the ozone, more UV radiation is allowed to reach the Earth.  This UV radiation is very damaging to the skin.  So what is ozone?  Ozone is simply three oxygen atoms bonded together (O₃).   Ozone in the stratosphere is produced in a cycle.

     The O* atom in the cycle refers to an oxygen atom that is said to be "electronically excited".  Usually in nature, oxygen has 6 electrons on its outer shell:

In the ozone cycle, one of the electrons in the outershell, "jumps" to a higher level shell as seen in Figure 3.  As you can see from the ozone cycle, any substances other than oxygen that combine with O* will remove the O* from the ozone cycle and decrease the volume of ozone being produced.  When this happens, more UV radiation passes through the ozone and is allowed to reach the Earth's surface.  With the use of chlorinated refrigerants, chlorine atoms can reach the ozone layer and react with ozone.  This is especially dangerous because not only does the chlorine atom destroy the ozone molecule, it too starts its own cycle.

It's easy to see why it is so important to minimize the amount of chlorine that reaches our ozone layer.  The approach to this problem must be handled carefully.  It's not necessary to use chlorine in refrigerants (see "Toward a Safer Refrigerant") so that is a fairly easy decision.  However, chlorine is a very important chemical (see "Chlorine's Bad Reputation").  The problem is very real and many regulations and much new research should help preserve our ozone layer.