Topic 3: Protecting the Ozone Layer
I. A Gas that Can Kill or Save
Why do we need to do to protect
the ozone layer?
A. Meet the Molecule
Isn’t ozone hazardous to human health?
Why is the ozone layer getting smaller?
What can we do (if anything) to
help stop the depletion of our
ozone layer?
I. A Gas that Can Kill or Save
A. Meet the Molecule
-created from oxygen (O2) in atmosphere
-destroyed in atmosphere to give O2
I. A Gas that Can Kill or Save
A. Meet the Molecule
Note: Ozone contains more E than O2.
–
E
More unstable
O3
O2
I. A Gas that Can Kill or Save
B. Location is key.
In troposphere (near earth):
• << 1ppm O3 makes air smell good
• ~1ppm O3 gives sore throats, coughing,
fatigue
• >>1 ppm kills (humans, bacteria,
phytoplankton)
Copyright Angela G. King , 2000
I. A Gas that Can Kill or Save
B. Location is key.
In stratosphere (upper atmosphere):
• ozone layer: 30-35 km from earth, 40 km
thick
• not uniform, thinnest at poles
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Biological Effects of Ultraviolet Radiation
I. A Gas that Can Kill or Save
The consequences depend primarily on:
1. The energy associated with the radiation.
2. The length of time of the exposure.
UV
The most deadly form of skin cancer, melanoma, is
linked with the intensity of UV radiation and the latitude
at which you live.
An Australian product uses
“smart bottle” technology;
bottle color changes from
white to blue when exposed
to UV light.
2.7
II. How Does Ozone Absorb UV Light?
A. Atoms and MoleculesSmall dense nucleus- contains
heavy (+) particles
(protons)
II. How Does Ozone Absorb UV Light?
A. Atoms and MoleculesNeutrons- particle w/ no
charge but same mass as
proton.
.
II. How Does Ozone Absorb UV Light?
A. Atoms and Molecules• Each element is made of many atoms, all of
which contain same # protons and e-, but can
contain different # neutrons…….isotopes.
II. How Does Ozone Absorb UV Light?
A. Atoms and MoleculesIndicate # protons by left subscript, left
superscript = neutrons + protons
Example: Carbon
12
6
C
13
6
C
14
6
Copyright Angela G. King , 2000
C
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II. How Does Ozone Absorb UV Light?
The wavelength and frequency of electromagnetic
radiation are related by:
B. Lighta wavelike form of energy characterized by:
where c = 3 x 108 m/s (the speed of light)
– λ (wavelength) :
– ν (frequency) :
The energy of a photon of electromagnetic radiation
is calculated by:
where h = 6.63 x 10-34 J.s (Plank’s constant)
2.5
What is the energy associated with a photon of light with a wavelength of 240 nm?
E=hν
C = λν
II. How Does Ozone Absorb UV Light?
ν =C
λ
B. Light-
ν=
Light is grouped into types based on wavelength (λ).
2.5
II. How Does Ozone Absorb UV Light?
B. LightWithin the ultraviolet group of wavelengths, there are 3
sub groups:
UVA - lowest E, minimal damage
UVB –
UVC –
Copyright Angela G. King , 2000
*Be able to list these types of light in order of increasing
wavelength, frequency or energy.
II. How Does Ozone Absorb UV Light?
C. Ozone and Light
• Oxygen atoms in O2 are held together by a strong bond.
(imagine a strong spring between two tennis balls)
• Oxygen atoms in ozone are held together by both a strong bond
and a weak bond. (imagine a tennis ball held to one other ball
by a strong spring and to a second ball by a weaker spring)
• Bond strength determines how much E is needed to break apart
molecule.
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II. How Does Ozone Absorb UV Light?
II. How Does Ozone Absorb UV Light?
C. Ozone and Light
C. Ozone and Light
O=O → O + O
• strong bond, requires lots of E
•
O=O-O → O=O + O
III. The Problem
A. Without Man:
Stratospheric ozone, which protects life on
earth by absorbing UV light, is
disappearing. This increases risk of DNA
and eye damage by UV light that isn’t
absorbed.
• Each day 300 million tons O3 made by
lightening
• Each day 300 million tons destroyed by the
Chapman Cycle
Each decade, [O3] in U.S. decreases by 2-3%.
Greater drop at poles.
• No net change
B. With Man: Why Does [O3] Drop?
B. With Man: Why Does [O3] Drop?
1. Nitric oxide (NO) catalyzes conversion of
O3 to O2
2. CFC’s = chlorofluorocarbons
• CClxF4-x (carbon, chlorine, and fluorine
only), very stable, non-flammable, and low
boiling point compounds.
• Developed as refrigerants. Also used as
propellants, solvents, sterilizers, fire
retardants. 1986: 1/2 lb/person
Copyright Angela G. King , 2000
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B. With Man: Why Does [O3] Drop?
B. With Man: Why Does [O3] Drop?
Due to their stability, CFC’s survive the 7-10
year trip to the ozone layer.
Once in ozone layer, CFC’s react with UV
light and generate a chorine atom.
Cl atoms catalyze conversion of O3 to O2 as
they are converted to ClO.
Experimental analyses show that as ClO. concentrations
increase, ozone concentration decreases.
IV. The Future
1978- CFC’s banned as propellants
1987-Countries agree to Montreal Protocol to
end CFC production by 1996
2.9
IV. The Future
Requirements for CFC Replacements:
Toxicity
O3 destruction
flammability
bp
HCFCs are alternatives to CFCs: they decompose more
readily in the troposphere so they will not accumulate
to the same extent in the stratosphere.
2.9
Copyright Angela G. King , 2000
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