Lecture 8

October 24

Atmospheric Photochemistry and Ozone Depletion

1. Photodissociation and Photoionization. High energy UV light can break the chemical bond in molecules and produce individual atoms, such as O and N (photodissociation). It can also strip a molecule of an electron (photoionization) to give a molecular ion. These processes and the subsequent reactions, for example, produce the ozone of the upper atmosphere, as well as numerous other molecules and ions.
2. The importance of these processes is that they prevent much of the UV intensity from reaching the earth's surface. But there is a window at about 240nm that would get through, were it not for the presence of ozone that absorbs at this wavelength.
3. Catalysis of ozone decomposition by nitrogen oxides and chlorine
4. The CFC story. What are they? Why are they manufactured on a massive scale? What happens to them in the troposphere and stratosphere? How do they deplete the ozone layer?
5. The antarctic ozone hole, and why it is formed. It's still getting bigger! I hope to show a brief video of the progress of the hole.
6. Global action to reduce and eliminate CFCs. The Montreal protocol. What are the alternatives?

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