1. OZONE DEPLETION IN THE STRATOSPHERE
Less ozone in the stratosphere allows for more harmful UV radiation to reach the earth’s surface.
The ozone layer keeps about 95% of the sun’s harmful UV radiation from reaching the earth’s surface.
Chlorofluorocarbon (CFCs) have lowered the average concentrations of ozone in the stratosphere.

2. Ultraviolet light hits a chlorofluorocarbon
(CFC) molecule, such as CFCl3, breaking
off a chlorine atom and
leaving CFCl2.
Sun Cl
Once free, the chlorine atom is off
to attack another ozone molecule
and begin the cycle again.
UV radiation
A free oxygen atom pulls
the oxygen atom off
the chlorine monoxide
molecule to form O2.
The chlorine atom attacks
an ozone (O3) molecule,
pulling an oxygen atom off
it and leaving an oxygen
molecule (O2).
Figure 20.18
Natural capital degradation: 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 reaction. Bromine atoms released from bromine-containing compounds that reach the stratosphere also destroy ozone by a similar mechanism.
The chlorine atom
and the oxygen atom
join to form a chlorine monoxide molecule (ClO).
Summary of Reactions
CCl3F + UV Cl + CCl2F
Cl + O3 ClO + O2
Cl + O Cl + O2
Repeated
many times
Fig , p. 486

3. OZONE DEPLETION IN THE STRATOSPHERE
Ozone thinning: caused by CFCs and other ozone depleting chemicals (ODCs).
Increased UV radiation reaching the earth’s surface from ozone depletion in the stratosphere is harmful to human health, crops, forests, animals, and materials such as plastic and paints.

4. • Immune system suppression
Natural Capital Degradation
Effects of Ozone Depletion
Human Health
• Worse sunburn
• More eye cataracts
• More skin cancers
• Immune system suppression
Food and Forests
• Reduced yields for some crops
• Reduced seafood supplies from reduced phytoplankton
• Decreased forest productivity for UV-sensitive tree species
Wildlife
• Increased eye cataracts in some species
• Decreased population of aquatic species sensitive to UV radiation
• Reduced population of surface phytoplankton
Figure 20.21
Natural capital degradation: expected effects of decreased levels of ozone in the stratosphere. QUESTION: Which five of these effects do you think are the most important?
• Disrupted aquatic food webs from reduced phytoplankton
Air Pollution and Materials
• Increased acid deposition
• Increased photochemical smog
• Degradation of outdoor paints and plastics
Fig , p. 488
Global Warming
• Accelerated warming because of decreased ocean uptake of CO2 from atmosphere by phytoplankton and CFCs acting as greenhouse gases

5. Squamous Cell Carcinoma
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
Thin layer of
dead cells
Hair
Squamous cells
Epidermis
Basal layer
Sweat
gland
Melanocyte cells
Dermis
Basalcell
Blood
vessels
Figure 20.22
Science: 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
Fig , p. 489

6. Montreal Protocol on Substances That Deplete the Ozone Layer
Proposed in 1987 and put into action in 1989.
Considered to be the most successful international agreement on behalf of the environment
Stopped production of all CFC’s except in a few cases where there aren’t substitutes (ie. some types of medical inhalers)
Use of some substitutes is problematic however as they don’t damage ozone but are Greenhouse gases (HFC’s, etc)

7. As of 2014, stratospheric ozone has held steady and/or improved.
Levels of CFC’s remaining in atmosphere have continued to drop.
Appears to be a success story in the making!!