19-4 How Have We Depleted O3 in the
Stratosphere and What Can We Do?
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
Protectant
Pollutant
19-4 How Have We Depleted O3 in the
Stratosphere and What Can We Do?
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.
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
Science Focus: Rowland and Moline—A
Scientific Story of Courage and Persistence
 Research
• CFCs are persistent in the atmosphere
• Rise into the stratosphere over 11-20 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 65-385 years
 1988: DuPont stopped producing CFCs
 1995: Roland & Moline won Nobel Prize in
chemistry
Global Average Total Ozone Values in the
Stratosphere from 1979–2005
Natural Capital Degradation: Massive
Ozone Thinning over Antarctica in 2006
Biggest “hole” on record
Sun
UV radiation
Cl
C
F
Summary of Reactions
CFCl3 + UV → Cl + CFCl2
Ultraviolet light hits a
chlorofluorocarbon (CFC)
molecule, such as CFCl3,
breaking off a chlorine
atom and leaving CFCl2.
Cl
Cl + O3 → ClO + O2
ClO + O → Cl + O2
Cl
C
Cl
FREE
RADICAL
Cl
Cl
F
Cl
The chlorine atom attacks
an ozone (O3) molecule,
pulling an oxygen atom
off it and leaving an
oxygen molecule (O2).
O
O
O
Ozone
O
O
O
FREE
RADICAL
Once free, the chlorine
atom is off to attack
another ozone molecule
and begin the cycle again.
O
O
Repeated
many times
O
O
O
A free oxygen atom pulls
the oxygen atom off the
Cl
chlorine monoxide
molecule to form O2.
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
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?
Stepped Art
Fig. 19-20, p. 524
Science Focus: Skin Cancer
 Squamous cell carcinoma
 Basal cell carcinoma
 Melanoma
 Effect of UV-B radiation
 How safe are tanning salons?
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.
Ultraviolet A
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 B
Hair
Thin layer of dead cells
Squamous cells
Epidermis
Basal layer
Sweat gland
Melanocyte cells
Dermis
Blood vessels
Basal cell
Squamous Cell Carcinoma
Basal Cell Carcinoma
Melanoma
Stepped Art
Fig. 19-E, p. 526
Fig. 19-E (2), p. 526
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
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
We Can Reverse Stratospheric
Ozone Depletion
http://www.youtube.com/watch?v=DLHL1Xp9iDo
The Bullet we Dodged by Working Together
What Could Have Been w/o CFC Ban
http://earthobservatory.nasa.gov/Features/WorldWithoutOzone/page2.php
The Bullet we Dodged by Working Together
What Could Have Been w/o CFC Ban
http://earthobservatory.nasa.gov/Features/WorldWithoutOzone/page2.php
The Bullet we Dodged by Working Together
What Will Be… CURED!
http://earthobservatory.nasa.gov/Features/WorldWithoutOzone/page2.php