1-8: Man-made Chemicals, CFCs

Pre-Class Preparation

Objectives

• To understand the special properties of unique manmade chemicals.
• To understand the conditions that make these chemicals reactive.

Procedure

1. Read the learning unit.

   Class images

2. Take the learning unit quiz. Quizzes are available from your portfolio. You may access your portfolio via the list of students participating in this years course, as represented by the icon below.
   
   
3. Additional Required Reading. Although you are not ultimately responsible for content listed in this section, we encourage you to fully explore the links in order to provide a better scope on the upcoming class discussion.

   	Chlorofluorocarbons (CFCs) and Climate Change. (From the United Nations Environment Programme, UNEP)
   	NASA's UARS Confirms CFCs Caused Antarctic Ozone Hole
   	Houghton, J. T., G. J. Jenkins, and J. J. Ephraums, 1990: Climate Change, The IPCC Scientific Assessment. Cambridge University Press. p. 23-25.

Class Discussion

• Problem to ponder...
  If the number mixing ratio of a particular CFC in the stratosphere is uniform with height, will it contribute to stratospheric ozone depletion? Why or why not?

• Class Discussion Summary: by classmates Brad Ross and Eric Richardson.

  The first publicized evidence on ozone depletion came in 1989. In the study, they looked at ozone concentrations over 30 years during the spring months over Antarctica. Ozone is typically found between 20-30 km above the ground. At this level, ozone is produced naturally through photochemical processes. Ozone depletion can be attributed to chlorine, more specifically through CFC´s. Chlorine itself cannot make it up to the stratosphere as it is very reactive. CFC´s enable chlorine to reach the stratosphere due to the fact that it is fairly stable. Once in the stratosphere ultraviolet radiation reacts with the CFC´s, and the chlorine becomes free to destroy ozone. This helps to explain why there is an increase in depletion in ozone over the south pole in the spring time. With the first bit of sun in the spring over Antarctica, chlorine is released in the stratosphere. About a week later, nitrogen is released and starts to collect the chlorine. This is why we saw that Antarctica is back to normal ozone levels at around 300 Dobson units at the present time.

Post-Class Activities

• Participate in the electronic dialog. Use this forum for:
  • continuing class discussion;
  • posing new questions to students or the instructor;
  • responding to issues/questions raised by students in class/electronic dialog.

  Visitor Access (Visitors are welcome to participate in the dialog. Just click on the icon below)	Student Access (Students must post all dialog from their portfolio. Click on the icon below to access the student list.)

• Recommended Reading Materials

  	Atmospheric Ozone Data and Resources. NASA
  	CIESIN Thematic Guide on Ozone Depletion Issues
  	Can the ozone layer be restored?, California Agriculture 48, 4-5.
  	Hoffman, J.S., 1990: Replacing the CFC's: The search for alternatives. Ambio, 19, 329-333.
  	Houghton, J.T., G.J. Jenkins, J.J. Ephraums, eds, 1990: 1990 Intergovernment Panel on Climate Change, Cambridge University Press, 23-24.
  	Houghton, J. T., L. G. Meira Filho, B. A. Callander N. Harris, A. Kattenberg, and K. Maskell, 1996: Climate Change 1995. The Science of Climate Change. Cambridge University Press, 91-97.
  	Shull, R. D., et al., 1993: Nanocomposites for magnetic refrigeration. Mat. Res. Soc. Symp. Proc., 286, 449-453.
  	Williams, Yagi K., et al., 1995: Atmospheric methyl bromide (CH3Br) form agricultural soil fumigations. Science, 267, 1979-1981.

• References

  	Ozone Depletion Glossary
  	Stratospheric Ozone and Human Health