1. Atmosphere and Climate Change
Section 2: The Ozone Shield
Day one

2. The Ozone Shield Ozone layer = altitude of 15 to 40 km high
ozone absorbs UV radiation.
Ozone is a molecule made of three oxygen atoms.
UV light is harmful to organisms
can damage genetic material in living cells.

3. Anthropogenic Ozone Depletion
Chlorofluorocarbons (CFCs) = hydrocarbons where hydrogen atoms replaced by chlorine and fluorine.
Used in:
coolants for refrigerators and air conditioners
cleaning solvents.
propellant in spray cans of everyday products
deodorants, insecticides, and paint.
Use of CFC’s now illegal or restricted

4. When CFC’s meet the ozone layer?

5. Chemicals That Cause Ozone Depletion
At Earth’s surface, CFCs are chemically stable.
CFC molecules break apart in the stratosphere where UV radiation is absorbed.
Once CFC molecules split, parts of the CFC molecules destroy ozone.

6. Chemicals That Cause Ozone Depletion
Each CFC molecule contains from one to four chlorine atoms,
Scientists estimate a single chlorine atom in the CFC structure can destroy 100,000 ozone molecule.

7. The Ozone Hole
In 1985, scientists in Antarctica discovered the ozone layer above the South Pole had thinned by 50 to 98 percent.
Ozone hole = thinning of stratospheric ozone that occurs over the poles during spring.
Able to see the first signs of ozone thinning around 1979.
Ozone levels decreased over Canada and other Arctic regions
By March 1997, areas were 45% below normal

8. 2005 Ozone Layer Hole https://www.youtube.com/watch?v=0ZfBgjUnXIs
The Ozone Hole
(credit: NASA)
2005 Ozone Layer Hole

9. How Does the Ozone Hole Form?
On the surfaces of polar stratospheric clouds, CFCs are converted to molecular chlorine.
Sunlight splits CFC molecule into two chlorine atoms by UV radiation.
The chlorine atoms rapidly destroy ozone.
Strips 1 oxygen atom from O3, creating O2 and ClO
ClO breaks down into Cl- and O2
The Cl- ion seeks more ozone to destroy

10. Effects of Ozone Thinning of Animals and Plants

11. Protecting the Ozone Layer
In 1987, a group of nations made an agreement, called the Montreal Protocol, to sharply limit their production of CFCs.
At a second conference in Copenhagen, Denmark in 1992, developed countries agreed to eliminate most CFCs by 1995.
The United States pledged to ban all substances that pose a significant danger to the ozone layer by the year 2000.

12. Protecting the Ozone
After developed countries banned most uses of CFCs, chemical companies developed CFC replacements.
Aerosol cans no longer uses CFCs as propellants, and air conditioners are becoming CFC free.
Because many countries were involved and decided to control CFCs, many people consider ozone protection an international environmental success story.

13. Protecting the Ozone Layer

14. Protecting the Ozone Layer
CFC molecules remain active in the stratosphere for 60 to 120 years.
CFCs released 30 years ago are still destroying ozone today, so it will be many years before the ozone layer completely recovers.

15. Question:
Answer the following question at the end of your section 2 notes:
Why is ozone an important component in the proper balance of the greenhouse effect?