For 10/7/09
From the book:
Chapter 5: 28, 29, 30, 31, 35, 36, 40, 41, 46, 51.
Appendix E of the text has answers to even numbered questions
29. CFC stands for chlorofluorocarbon. The chemical formula of CFC-12 is: CF2Cl2.
Three uses for CFCs are: refrigerants, propellants, solvents for cleaning agents.
31. CFCs do not contain the C-H bond, and are therefore very stable towards chemical
reactions.
35.
185-210nm
CFCl3  h 

 CFCl2  Cl
CF2 Cl 2  h 
 CF2 Cl  Cl
Cl  O 3 
 ClO  O 2
ClO  O 
 Cl  O 2
net : O 3  O 
 O 2  O 2
Br from CH3Br goes through the same catalytic O3 destruction cycle.
41. Chlorine activation occurs when a reservoir species (Cly) is converted to an active
ClOx species. An example of this on the surface of a PSC is the conversion of ClONO2
to Cl2.
51. The ozone ‘hole’ occurs in the Antarctic stratosphere. There are several reasons to
be alarmed. First, when the Antarctic vortex breaks up, ozone depleted air migrates over
populated area of the southern hemisphere, increasing exposure to UV radiation for those
people. It is also alarming that seemingly harmless human activities can have such a
huge impact on a global scale, and that we did not realize the damage that was being done
until the problem was already very bad. Ozone depletion is not as great over the Arctic
because stratospheric temperatures are not as low there. This is due in part to the fact that
there is no substantial Arctic vortex.
Other Problems:
Why is ClONO2 such an important molecule in the stratosphere?
ClONO2 is so important because it is a reservoir species for both NOx and ClOx.
Briefly explain the role that polar stratospheric clouds play in the Antarctic ozone hole.
Without PSCs the ozone hole would not occur. HCl that is absorbed onto the surface of
PSCs allows the conversion of chlorine reservoirs to Cl2, which is easily photolyzed to Cl
radical. Stratospheric nitrogen compounds are also absorbed onto the PSCs during this
process, so that the NOx is not available to sequester the active ClOx in the Antarctic
stratosphere.
Since NOx in the stratosphere leads to catalytic ozone destruction, how can removal of
NOx under present stratospheric conditions lead to increased ozone destruction?
Removing NOx from the stratosphere would remove the major pathway for ClOx to be
converted to Cly, which is:
ClO  NO2 
 ClONO2
Why isn’t there an ozone hole in the Arctic stratosphere?
There is no ozone hole over the Arctic for several reasons. No polar vortex forms around
the Arctic because land masses on the Earth’s surface do not allow the stable winds that
are necessary for it to form. Since there is no vortex, the stratospheric air over the Arctic
is not entirely isolated from the rest of the stratosphere and mixing of NOx and O3 can
occur. The Arctic stratosphere is also not cold enough (also because the vortex does not
form) for a significant number of PSCs to form.
Can the following statement be justified?
Volcanic emissions, not CFCs are what really cause ozone depletion over the
midlatitudes.
Not really; midlatitude O3 depletion is enhanced when volcanic aerosols are injected into
the stratosphere only because chlorine is present. If the chlorine was not present, then O3
levels would not decrease due to the presence of the aerosols.