Why care about ozone?
• The topic of ozone makes headlines on a
regular basis, but why does a single molecule
merit such media coverage?
• How important is the ozone in our
atmosphere and why are scientists so
concerned about its increase near the surface
of the earth and its disappearance higher up
in the atmosphere?
What is ozone?
• Ozone is made of three oxygen atoms
• The oxygen we find in our atmosphere is
made up of two oxygen atoms
• Because of its chemical formulation, a single
atom of oxygen (O) is unstable.
– It wants to combine with something else. That is why
oxygen is almost always found in pairs, in its (diatomic)
form, where it is more stable.
– O3 is less stable than O2 , because it wants to return to the
diatomic state by giving up an oxygen atom.
How is ozone formed?
• Ozone is formed naturally in the upper
stratosphere by short wavelength ultraviolet
radiation.
• Wavelengths less than ~240 nanometers are
absorbed by oxygen molecules (O2), which
dissociate to give O atoms.
• The O atoms combine with other oxygen
molecules to make ozone:
• O2 + hv (light) -> O + O (wavelength < 240 nm)
• O + O2 -> O3
What is the ozone layer?
• The ozone layer is a concentration of ozone
molecules in the stratosphere. About 90% of
the planet's ozone is in the ozone layer.
• The layer of the Earth's atmosphere that
surrounds us is called the troposphere. The
stratosphere, the next higher layer, extends
about 10-50 kilometers above the Earth's
surface.
Aurora
What are the names of the
levels of the atmosphere?
What does the temperature
of the atmosphere look like
as we go up in altitude?
OZONE LAYER
How does ozone interact with UV rays?
What is UV light?
Ozone filters UV
• Stratospheric ozone is a naturally-occurring
gas that filters the sun's ultraviolet (UV)
radiation.
• http://svs.gsfc.nasa.gov/vis/a000000/a000800
/a000834/a000834.mpg
How CFC’s interact with Ozone
http://www.ucar.edu/learn/1_6_1.htm
Click on this link and watch the
animations
• http://www.ucar.edu/learn/1_6_1.htm
How is the ozone layer being
depleted?
• Ozone is produced naturally in the stratosphere. But
this "good" ozone is gradually being destroyed by
man-made chemicals referred to as ozone-depleting
substances (ODS), including chlorofluorocarbons
(CFCs), hydrochlorofluorocarbons (HCFCs), halons,
methyl bromide, carbon tetrachloride, and methyl
chloroform. These substances were formerly used
and sometimes still are used in coolants, foaming
agents, fire extinguishers, solvents, pesticides, and
aerosol propellants.
http://www.epa.gov/oar/oaqps/gooduphigh/
good.html#1
How is the ozone layer being
depleted?
• Once released into the air these ozonedepleting substances degrade very slowly. In
fact, they can remain intact for years as they
move through the troposphere until they
reach the stratosphere. There they are broken
down by the intensity of the sun's UV rays and
release chlorine and bromine molecules,
which destroy the "good" ozone. Scientists
estimate that one chlorine atom can destroy
100,000 "good" ozone molecules.
http://www.epa.gov/oar/oaqps/gooduphigh/good.
How is the ozone layer being
depleted?
• Even though we have reduced or eliminated
the use of many ODSs, their use in the past
can still affect the protective ozone layer.
Research indicates that depletion of the
"good" ozone layer is being reduced
worldwide. Thinning of the protective ozone
layer can be observed using satellite
measurements, particularly over the Polar
Regions.
http://www.epa.gov/oar/oaqps/gooduphigh/
good.html#1
Why care about diminished ozone?
• A diminished ozone layer allows more
radiation to reach the Earth's surface.
• For people, overexposure to UV rays can lead
to skin cancer, cataracts, and weakened
immune systems.
• Increased UV can also lead to reduced crop
yield and disruptions in the marine food chain.
UV also has other harmful effects.
http://www.epa.gov/oar/oaqps/gooduphigh/
good.html#1
What is being done about the
depletion of the ozone layer?
• The United States, along with over 180 other
countries, recognized the threats posed by
ozone depletion and in 1987 adopted a treaty
called the Montreal Protocol to phase out the
production and use of ozone-depleting
substances.
http://www.epa.gov/oar/oaqps/gooduphigh/
good.html#1
What is being done about the
depletion of the ozone layer?
• EPA has established regulations to phase out ozone-depleting
chemicals in the United States. Warning labels must be placed
on all products containing CFCs or similar substances and
nonessential uses of ozone-depleting products are prohibited.
Releases into the air of refrigerants used in car and home air
conditioning units and appliances are also prohibited. Some
substitutes to ozone-depleting products have been produced
and others are being developed. If the United States and
other countries stop producing ozone-depleting substances,
natural ozone production should return the ozone layer to
normal levels by about 2050.
http://www.epa.gov/oar/oaqps/gooduphigh/
good.html#1
Ozone layer animations 1979 and 1992
• Figure 7e-2: Quicktime Animation of Antarctic Ozone Levels
1978-1992.
• The following two animations describe 1979 and 1992 ozone
levels at the South Pole for the period September 15 to
November 15. View these images for comparison:
• Figure 7e-3: Quicktime Animation of Antarctic Ozone Levels
1979; and
• Figure 7e-4: Quicktime Animation of Antarctic Ozone Levels
1992.
http://www.physicalgeography.net/fundament
als/7e.html
Figure 7e-5: Average areal coverage of the ozone hole from 1979 to 2004. In this analysis, the
ozone hole is defined as the area for which ozone is less than 220 Dobson Units. The ozone hole
has grown from a few million square kilometers in 1981 to an area larger than North America
(about 24 million square kilometers) in the year 2000. (Source: NASA, TOMS Multimedia).
Current Ozone Watch
• http://ozonewatch.gsfc.nasa.gov/ozone_maps
/movies/OZONE_D197910%25P1Y_G%5e360X240.LSH.mp4
Tropospheric Ozone and Human
Health Basics
• Ozone is also found in the troposphere, where it can
damage living tissue and human-produced objects. It
is generated both from certain types of pollution and
natural sources.
Ozone on the ground
• In the troposphere, the ground-level or "bad"
ozone is an air pollutant that damages human
health, vegetation, and many common materials.
• It is a key ingredient of urban smog. In the
stratosphere, we find the "good" ozone that
protects life on earth from the harmful effects of
the sun's ultraviolet rays.
• For more info: http://www.epa.gov/oar/oaqps/gooduphigh/
• 1. How is ozone formed?
• From Ozone: Good Up High, Bad Nearby answer the
following questions. 2. Does ozone occur naturally in
the stratosphere? 3. How does stratospheric ozone
become depleted? 4. How does the depletion of
stratospheric ozone affect humans and the
environment? 5. What are the major sources of
ozone precursors in the troposphere? (include
percentages) 6. How does tropospheric ozone affect
humans and the environment?