1. 19-4 How Have We Depleted O3 in the Stratosphere and What Can We Do?

2. 19-4 How Have We Depleted O3 in the Stratosphere and What Can We Do?
Opportunities this weekend:
Free Park Entrance to National Parks
Yosemite Facelift
Turlock Shines

3. Protectant
Pollutant

4. 19-4 How Have We Depleted O3 in the Stratosphere and What Can We Do?

5. 19-4 How Have We Depleted O3 in the Stratosphere and What Can We Do?
Concept 19-4A Widespread use of certain chemicals has reduced ozone levels in the stratosphere, which allows for more harmful ultraviolet radiation to reach the earth’s surface.
Concept 19-4B To reverse ozone depletion, we must stop producing ozone-depleting chemicals and adhere to the international treaties that ban such chemicals.

6. Our Use of Certain Chemicals Threatens the Ozone Layer
Ozone (O3) Layer
Absorbs 95% of UV radiation from the sun.
Absorption results in warming of stratosphere
Ozone Thinning
Seasonal depletion in the stratosphere
Antarctica and Arctic
1930: Midgely
Discovered the first CFC (“Dream” chemical for AC, propellants in cans, etc.)
1984: Rowland and Molina
CFCs were depleting O3

7. Science Focus: Rowland and Moline—A Scientific Story of Courage and Persistence
Research
CFCs are persistent in the atmosphere
Rise into the stratosphere over years
Break down under high-energy UV radiation
Halogens (Cl, F, Br, I) produced accelerate the breakdown of O3 to O2
Each CFC molecule can last years
1988: DuPont stopped producing CFCs
1995: Roland & Moline won Nobel Prize in chemistry

8. Global Average Total Ozone Values in the Stratosphere from 1979–2005

9. Natural Capital Degradation: Massive Ozone Thinning over Antarctica in 2006
Biggest “hole” on record

10. FREE RADICAL Summary of Reactions CFCl3 + UV → Cl + CFCl2
ClO + O → Cl + O2
Repeated many times
Cl + O3 → ClO + O2
Summary of Reactions CFCl3 + UV → Cl + CFCl2
Sun
Ultraviolet light hits a chlorofluorocarbon (CFC) molecule, such as CFCl3, breaking off a chlorine atom and leaving CFCl2.
UV radiation
FREE RADICAL Cl C Cl Cl F C Cl Cl F Cl
Once free, the chlorine atom is off to attack another ozone molecule and begin the cycle again. Cl O O O
The chlorine atom attacks an ozone (O3) molecule,
pulling an oxygen atom off it and leaving an oxygen molecule (O2). O
Ozone O O
A free oxygen atom pulls the oxygen atom off the chlorine monoxide molecule to form O2.
Figure 19.D
Simplified summary of how chlorofluorocarbons (CFCs) and other chlorine-containing compounds can destroy ozone in the stratosphere faster than it is formed. Note that chlorine atoms are continuously regenerated as they react with ozone. Thus, they act as catalysts—chemicals that speed up chemical reactions without being used up by the reactions. Bromine atoms released from bromine-containing compounds that reach the stratosphere also destroy ozone by a similar mechanism. O O O O Cl O O O O
The chlorine atom and the oxygen atom join to form a chlorine monoxide molecule (ClO). Cl O O
Fig. 19-D, p. 525

11. Why Should We Worry about Ozone Depletion?
Damaging UV-A and UV-B radiation
Increase eye cataracts and skin cancer
Impair or destroy phytoplankton
Significance?

12. Figure 19.20
Science: expected effects of decreased levels of ozone in the stratosphere (Concept 19-4A). Question: Which three of these effects do you think are the most threatening? Why?
Stepped Art
Fig , p. 524

13. Science Focus: Skin Cancer
Squamous cell carcinoma
Basal cell carcinoma
Melanoma
Effect of UV-B radiation
How safe are tanning salons?

14. Ultraviolet A Ultraviolet B
Thin layer of dead cells
Squamous cells
Epidermis
Basal layer
Sweat gland
Melanocyte cells
Dermis
Blood vessels
Basal cell
Hair
This long-wavelength (low-energy) form of UV radiation causes aging of the skin, tanning, and sometimes sunburn. It penetrates deeply and may contribute to skin cancer.
This shorter-wavelength (high-energy) form of UV radiation causes sunburn, premature aging, and wrinkling. It is largely responsible for basal and squamous cell carcinomas and plays a role in malignant melanoma.
Ultraviolet A
Ultraviolet B
Figure 19.E
Structure of the human skin and the relationships between ultraviolet (UV-A and UV-B) radiation and the three types of skin cancer. (Data and photos from the Skin Cancer Foundation)
Squamous Cell Carcinoma
Basal Cell Carcinoma
Melanoma
Stepped Art
Fig. 19-E, p. 526

15. Figure 19.E
Structure of the human skin and the relationships between ultraviolet (UV-A and UV-B) radiation and the three types of skin cancer. (Data and photos from the Skin Cancer Foundation)
Fig. 19-E (2), p. 526

16. We Can Reverse Stratospheric Ozone Depletion
Stop producing all ozone-depleting chemicals
60–100 years of recovery of the O3 layer
1987: Montreal Protocol
Worldwide ban on CFC’s
Ozone protocols: prevention is the key

17. We Can Reverse Stratospheric Ozone Depletion
Substitutes for CFCs are available
More are being developed
HCFC-22
Substitute chemical
May still be causing ozone depletion

18. We Can Reverse Stratospheric Ozone Depletion

19. The Bullet we Dodged by Working Together
What Could Have Been w/o CFC Ban

20. The Bullet we Dodged by Working Together
What Could Have Been w/o CFC Ban

21. The Bullet we Dodged by Working Together
What Will Be… CURED!