 | Environmental Education in the Schools (Peace Corps, 1993) |
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Holey ozone!
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OBJECTIVES: AGES: SUBJECTS: MATERIALS: |
Cartoons can make even heavy science easier to understand-and to remember. By looking at a cartoon as they listen to a story, your kids can get a better idea of how CFCs (chlorofluorocarbons) affect the ozone layer.
Start by using the background information in NatureScope: Pollution-Problems and Solutions to tell the kids about the ozone layer and how it absorbs harmful ultraviolet rays from the sun. Also explain that scientists have discovered that CFCs are destroying the ozone layer. Then pass out a copy of page 208 to each person and explain that the cartoon characters represent CFCs (circles) and ozone molecules (triangles). Tell the kids that you'll be reading a story that explains more about what is happening on the page. Encourage the kids to listen carefully because they'll be using the information later on. (In the story, we've simplified some of the information about how CFCs affect ozone. See "More About the Ozone Layer and CFCs" on page 206 for a more detailed explanation.)
After you read "The Ozone Story" (following page), answer any questions the kids may have, using the information on pages 206-207. Make sure they understand that the special conditions over Antarctica worsen the effects that CFCs have on the ozone layer in that region. You can also discuss how people can help protect the ozone layer. Then pass out drawing paper and crayons or markers, and tell the kids that they'll have a chance to create their own cartoon stories that illustrate some aspect of the CFC/ ozone problem- They can either incorporate the ozone and CFC characters from page 208 into their cartoons, or they can make up their own cartoon characters. For example, they could illustrate a CFC molecule's description of how it attacks the ozone layer.
THE OZONE STORY
Hi! I'm an ozone molecule. I spend my time about 15 miles above the earth, soaking up ultraviolet rays from the sun before they zap you people on earth. We ozone molecules take a lot of pride in our work. But something's been happening to us. There aren't as many ozone molecules as there used to be. And I'm here to tell you why. You see, it all started when you people began using chemicals called CFCs. You may not realize it, but you probably use something made with CFCs just about every day. You can see some of these products, such as the plastic foam plates, scattered on the ground. CFCs are used to make the coolants that are in refrigerators and air conditioners. They're used to make computer parts. And CFCs are used to make some plastic foam cups, plates, and other containers.
But CFCs don't stay in those products forever. Look at the old cars in that junkyard-there are loads of CFCs leaking out of the old air conditioners. CFCs also leak out of plastic foam cups and plates as the foam slowly breaks apart. And see that plastic foam factory over there? Lots of CFCs leak into the air as plastic foam is being made. Once they get into the air, CFCs slowly drift higher and higher. In fact, it may take them 10 or 15 years to get way up here where I am. But the longer, the better, as far as I'm concerned. Because once CFCs get near us ozone molecules-well, that's when the trouble begins.
Before CFCs get up here to the ozone layer where we ozone molecules hang out, they're protected from the sun's powerful ultraviolet rays. That's because me and my ozone pals soak up these ultraviolet rays. But when those CFCs drift through us ozone molecules and come out above the ozone layer . . . WHAM! They get zapped by those rays! And a terrible change takes place in the CFCs. They become OZONE EATERS! You can see ultraviolet rays hitting some of the CFCs that just drifted above the ozone layer.
Once CFCs become ozone eaters, they can do a lot of damage. Why, I've heard some of those big-mouthed ozone eaters brag that they've destroyed 100,000 ozone molecules! And as more of us ozone molecules are destroyed, the ozone layer is becoming thinner, and more harmful ultraviolet rays are reaching the earth.
The ozone molecules over Antarctica have really big problems. Down there, the super-cold temperatures make lots of ozone eaters form. I've heard that during some parts of the year, almost half of the Antarctic ozone molecules get eaten. I'm glad I don't live there.
Well, that's the end of my story. Now that you know what's happening up here, I sure hope you'll do something to help us ozone molecules. After all, we've been saving your skin for years!
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ACTION TIP! CFC CONTROL * Avoid using and buying products that might be made with CFCs. For example, use a reusable cup instead of a plastic foam one. If you're not sure if CFCs are in a product, ask the retailer. Even if they don't know, you'll be informing them that consumers are concerned about CFCs. * When servicing your car, take it to a station that can recycle the air conditioning coolant and keep CFCs from being released into the atmosphere. * Have home and car air conditioners checked for leaks. * Use air conditioners only if needed for health or safety
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MORE ABOUT THE OZONE LAYER AND CFCs OZONE DYNAMICS: Ozone is a form of oxygen. Ozone molecules can be found from 15 to 20 miles above the earth, with the peak concentration (the ozone layer) occurring at about 15 miles. Although ozone absorbs most of the ultraviolet (UV) rays from the sun, it makes up only a very small fraction of the atmosphere. The ozone supply is constantly being recycled. When an ozone molecule absorbs UV light, the molecule splits apart. A new ozone molecule soon forms from the "old parts." If left undisturbed, this cycle maintains a balance of ozone in the atmosphere. CFCs ENTER THE PICTURE: Chlorofluorocarbons, or CFCs, were invented in 1930. Many different kinds of CFCs have been developed since then. Because they are so stable (that is, they won't easily react with other chemicals) and nontoxic, CFC have been used to make a variety of products, such as aerosol propellants, coolants, and plastic foam. (Some plastic foam products are now being made with CFC- substitutes, but there's no way to distinguish these products from those made with CFC-containing foam. And many CFC substitutes, such as HCFCs, also harm the ozone layer.) OZONE WRECKERS: As a CFC molecule drifts above the ozone layer, it's bombarded by the UV rays of the sun. This splits apart the CFC molecules, releasing an atom of chlorine, which in turn "attacks" an ozone molecule. The chlorine atom breaks apart the ozone molecule in such a way that it can't recombine to form a new ozone molecule. This disrupts the ozone cycle, resulting in a net loss of ozone. Scientists have found that a single chlorine atom can destroy up to 100,000 ozone molecules before it becomes inactive or drifts down into the lower atmosphere. This means that introducing just a small quantity of CFCs into the atmosphere can have a big effect on the ozone layer. Scientists have also found that some types of CFCs are more harmful than others, because they last longer in the atmosphere (about 100 years) and release more chlorine molecules. POLAR PERILS: From June to August, the extremely cold winter temperatures over Antarctica help to foster the formation of chlorine molecules, and create a temporary but extreme thinning of the ozone layer. By September, a "hole" the size of the U.S. may form. Ozone levels may drop by as much as 50 percent in the annual Antarctic ozone hole. This hole disappears when temperatures warm up around late November. OZONE AROUND THE WORLD: In contrast to the severe ozone depletion over Antarctica, scientists have found that Arctic ozone levels drop by only 5 to 10 percent during the winter. This less drastic depletion is related to the shorter, warmer Arctic winters Scientists have also detected a 2 to 3 percent drop in average worldwide ozone levels. Some scientists believe that because of this ozone depletion, more of the sun's harmful UV rays are reaching the earth. Many scientists feel this is responsible for a rise in the number of cases of skin cancer. SAVING THE OZONE: Alarmed by warnings from scientists, the U.S. and a few other nations banned the use of CFCs in most aerosols in 1978. Then, in 1985, the announcement of the Antarctic ozone "hole" spurred governments to work together to cut world-wide use of CFCs. Countries eventually agreed to phase out CFCs altogether by the year 2000 and to help less developed countries find alternatives to CFCs. Until CFCs are phased out, consumers should be particularly careful to avoid products made with the following types of CFCs. Although all CFCs can damage the ozone layer to some extent, these CFCs are particularly harmful: * trichlorofluoromethane (CFC- 11 ) Consumers should also be on the lookout for products containing
HCFCs.
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