Environmental Science
Name: ______________________________
Atmosphere and Climate
Goal: The student will explain how the ozone layer shields the Earth from much of the sun’s harmful radiation,
explain how chlorofluorocarbons damage the ozone layer, explain the process by which the ozone hole forms,
describe the damaging effects of ultraviolet radiation and explain why the threat to the ozone layer is continuing
today.
Vocabulary:
1. ozone layer
2. chlorofluorocarbons (CFCs)
3. ozone hole
4. polar stratospheric clouds
Notes: Chapter 7.4:
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The _______________ Shield is located in the ____________________________; ozone is a form of oxygen
made up of _______oxygen atoms
Ozone ________________________ most of the UV (ultraviolet) rays from the sun
UV rays damage the __________________________material in living cells
The ozone shield acts like a __________________________________ for the Earth and the inhabitants
Chemicals That Cause Ozone Depletion
• During the 1970’s scientists believed Chlorofluorocarbons (___________________) might be damaging the
ozone shield; CFC’s are nonpoisonous, noncorrosive (do not corrode metals) and nonflammable, man-made
______________________________ (thought to be the miracle chemical) used in refrigerators and air
conditioners (coolants)
• Also used as a gassy “fizz” when making ________________________ foams (styrofoam) and as a propellant in
spray cans (deodorants, insecticides and paints)
• CFC’s are chemically _____________________ at the Earth’s surface; __________________ apart high in the
stratosphere where UV ____________________________ is powerful enough to break down CFC molecules
• Over a period of 10 – 20 years, CFC molecules releases at the Earth’s _____________________ make their way
into the stratosphere, each CFC molecule contain between one and four _________________________ atoms;
one single chlorine atom can destroy 10,000 ozone molecules.
The Ozone Hole
• 1985, scientists reported a study about the ozone layer near _________________________________ and how it
had thinned by 50% to 98%; this was the ____________________ news about the ‘ozone hole’ thinning the
________________________________________ ozone over the poles during the spring
• Hole fluctuates depending on the time of year; _________________________________ during the summer
months when the ________________ light is breaking apart the CFC molecules, less during winter when they are
building up
• 1997, ozone over Canadian ______________________ was down to 45% below normal
How Does the Ozone Hole Form?
 During the dark polar _____________________________, strong circulating winds over Antarctica, called the
polar vortex, isolate cold air from surrounding __________________________ air. The air within the vortex
grows extremely cold; when temperatures fall __________________________ about -80 degrees C, high altitude
clouds made of water and nitric acid begin to form (polar stratospheric clouds)
 On the _________________________ of these clouds, the products of CFCs are converted to molecular chlorine;
when sunlight returns to S Pole in spring, molecular chlorine ______________________ into two chlorine atoms
by UV radiation; chlorine atoms __________________________ ozone causing a thin spot, or ozone hole, which
can last several months (up to 70% of ozone layer can be destroyed during spring)
 Ozone is ___________________________ by air pollution so why doesn’t the ozone repair this hole? Because
ozone is very chemically________________________________. Ozone produced by pollution breaks down or
combines with other substances in the _________________________________________ long before it can reach
the stratosphere to replace the ozone that is being destroyed
The Effects of Ozone Thinning on Humans
• As ozone _______________________________ in the stratosphere, more UV light is able to pass through
atmosphere to Earth’s surface causing an _______________________ in skin cancer, cataracts (damages DNA)
Effects of Ozone Thinning on Animals and Plants
 High levels of UV light can _______________________ single-celled organisms called phytoplankton that live
near the surface of the ocean; ________________________ the ocean food chain and reduces fish harvest
 The reduction of phytoplankton would also _________________________ the amount of CO2 in the atmosphere
 Scientists believe the increased UV light will be especially damaging to ____________________________ (toads
and salamanders); lay _________________________ that lack shells in shallow water of ponds and streams
 UV light at _________________________________ levels already kill many eggs of some species by damaging
the unprotected __________________; higher levels might kill more eggs and put amphibian populations at risk
 Ecologists oftentimes use the ______________________________ of amphibian populations as environmental
indicators of environmental changes (sensitive)
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Protecting the Ozone Layer
• In 1987, A group of ______________________ met to take action against ozone depletion (Montreal Protocol);
decided to sharply limit their production of CFC’s
• A second conference was held in Copenhagen, Denmark in 1992; developed countries decided to:
1. Eliminate most CFC’s by 1995; U.S. pledged to ban all substances by 2000
2. Set up a fund to help developing countries switch to substitutes for CFC’s
3. Ban other substances that harm the ozone
 After ____________________________ countries banned most uses of CFCs, chemical companies developed
CFC replacements ( aerosol can no longer use CFCs as propellants and air conditioners are becoming CFC-free)
• Battle to ____________________________the ozone is not over, some countries still make and use CFC’s; CFC
molecules stay active for decades (for 60 -120 years) so it will take ___________________________ for the
ozone to recover
Lesson Reflection:
Assessment:
1. How does the ozone layer shield the Earth from much of the sun’s harmful radiation?
2. Describe some of the damaging effects of UV radiation on humans and on animals.
Active Reading: The Ozone Shield
Lesson Extension (Technology/Application/Connection to Real World):
PBS video: The Thin Green Line