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Saving the ozone layer: thirty years ago, scientists fought to stop the destruction of Earth's protective ozone layer. Did their rescue effort work?

Global warming is a hot topic today. But 30 years ago, the idea of pollution causing the planet to heat up was still a small blip on scientists' radar. Instead, their attention was on another pressing environmental issue: Earth's disappearing ozone layer. This layer of gas high in the atmosphere shields us from the sun's harmful rays.

In 1985, scientists at a research station in Antarctica made a startling discovery: a gaping ozone hole over the South Pole. The area of depleted ozone was caused by a group of human-made chemicals called chlorofluorocarbons (CFCs). At the time, CFCs were widely used in spray cans and as coolants in refrigerators and air conditioners. The chemicals are normally inert, or nonreactive. But when CFCs drift up into the atmosphere, they can break down ozone gas (see Nuts & Bolts, p. 20).

Scientists acted quickly to persuade governments around the world to do something about the problem, which they believed would only get worse. That led to the creation of the Montreal Protocol. Countries that signed the 1987 treaty agreed to phase out the use of CFCs and other ozone-destroying substances by 2000.

Did the effort to ban CFCs all those years ago save the ozone layer? "The answer is absolutely yes," says Paul Newman, an atmospheric physicist at NASA's Goddard Space Flight Center in Maryland. At a time when protecting the planet may seem like too big a task to tackle, check out ozone's environmental success story.

SUN BLOCKER

The invisible ozone layer exists high in the stratosphere, or a layer of the atmosphere that is roughly 10 to 50 kilometers (6 to 31 miles) above Earth. This buffer around the planet is made up of ozone gas molecules, which consist of three oxygen atoms (smallest unit of matter) bound together. Ozone molecules are very spread out. "If you could bring all the ozone molecules overhead together down to the Earth's surface, they would form a layer about 3 millimeters [0.1 inches] thick," says Newman. That's only about the thickness of two pennies stacked together.

This thin layer of ozone acts as Earth's natural sunscreen, absorbing the sun's powerful ultraviolet (UV) rays. These invisible energy waves can cause serious damage to living cells.

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A weakened ozone layer allows a larger amount of UV light to reach Earth's surface. Not only does that increase the chances of getting sunburn when you go outside, it could also lead to more skin cancer and eye-clouding cataracts. UV rays also harm the tissues of plants, causing damage to crops. And it's suspected that increased UV radiation could reduce plankton in the world's seas. These tiny marine organisms form the basis of the oceans' entire food web.

GOOD VS. BAD OZONE

Not all ozone is found way up in the sky. Ozone is a key ingredient in the smoggy haze sometimes seen hovering over cities. This "bad" ozone forms when sunlight reacts with pollution from car exhausts and industrial smokestacks.

Ozone at ground level offers very little UV protection. That's because there is much less ozone in smog than what can be found way up in the stratosphere. And because it's a highly reactive gas, breathing in ozone in polluted air can actually damage your lungs. That can be a big problem for people with the breathing disorder asthma.

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It would be great if we could ship "bad" ozone up to the stratosphere to repair the ozone hole. But shuttling ozone to the upper atmosphere to repair a hole the size of North America isn't practical, says Bryan Johnson, who monitors ozone levels for the National Oceanic and Atmospheric Administration. "It would be: like trying to fill an Olympic-size pool using a coffee cup," he says.

MODEL PROBLEM

Although nearly every nation has now signed on to the Montreal Protocol, we continue to see a seasonal ozone hole because of CFCs' long life spans. The chemicals can stick around in the atmosphere for 40 to 100 years before breaking down into less harmful substances.

CFCs still in the air have depleted the ozone layer over areas like the United States by about 6 percent. Over Antarctica, ozone levels plummet each fall by more than 50 percent. The reason? Extreme cold temperatures there produce polar stratospheric clouds. The surface of these clouds provides a place for the chemical reaction between chlorine from CFCs and ozone to take place, accelerating ozone destruction. The result is a yearly ozone hole above Antarctica.

If measures hadn't been taken when the ozone hole was first discovered, scientists like Newman predict there would be an even larger hole over the South Pole today (see "The Future of the Ozone Hole," p. 19). He and other NASA researchers have used computer models to determine what might have happened if the Montreal Protocol had not been enacted. If CFC production had continued even at less than half the rate of the 1970s, by 2045, the ozone hole would have spread across the entire planet--wiping out our protection from the sun's dangerous radiation.

Thanks to the Montreal Protocol, experts say Earth likely avoided a global disaster. Today, CFCs in the atmosphere are on the decline. And the ozone layer is expected to completely recover by 2065. "It's a very positive story. Scientists predicted there would be ozone losses, and politicians paid attention by enacting an agreement that seems to be working," says Newman.

The Future of the OZONE HOLE

Computer models of Earth show how the Montreal Protocol is expected to halt ozone destruction. The blue area over Antarctica represents the ozone hole.

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nuts & bolts

How CFCs Destroy OZONE

Chlorofluorocarbons (CFCs) are human-created molecules made of chlorine (CI), fluorine (F), and carbon (C). When a CFC molecule drifts up into the atmosphere, UV radiation reacts with the molecule, causing it to release a chlorine atom.

The lone chlorine atom breaks apart an atmospheric ozone molecule ([O.sub.3]) by grabbing one of its oxygen atoms.

The result is another [O.sub.2] molecule. Now, the chlorine atom can begin the cycle again, attacking a new ozone molecule.

That leaves a chlorine monoxide molecule (CIO) and an oxygen molecule ([O.sub.2]). The chlorine monoxide molecule transfers the oxygen atom it holds to a free oxygen atom in the air.

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web extra

September 16 is International Ozone Day. The date marks the anniversary of the signing of the Montreal Protocol. Find out more at: www.scholastic.com/scienceworld

HANDS-ON SCIENCE (No Lab Required)

After reading "saving the ozone layer" (p. 18), try this activity to learn more about how CFCs break down ozone in the upper atmosphere.

PREDICT

What happens to ozone in the upper atmosphere when CFCs are added?*

*Teachers: See teacher's edition (TE3) for background Information.

MATERIALS

* marker * paper * tape

DIRECTIONS

1) In this activity, you will play a game. Your teacher will assign 2/3 of the class to play an oxygen (O) atom, 1/6 to play a UV ray, and 1/6 to play a CFC molecule.

2) Depending on your assigned role, create a name tag labeled O; UV; or CFC. If you have a CFC name tag, also write chlorine, or CI, on the back of it.

3) Hold up your name tag, or tape it to your shirt. You are ready to begin the game.

4) Students with oxygen (O) tags should go to the center of the room and form as many groups of three oxygen atoms as possible. These groups represent one ozone molecule. Any remaining oxygens should try to form a group of two to represent a more stable oxygen molecule. Any leftover oxygens should remain alone to represent an oxy

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5) The CFCs should walk among the ozone molecules, oxygen molecules, and oxygen atoms.

6) The UV rays should find a CFC and gently tap one of them. Once tapped, CFCs should "release a chlorine atom" by flipping over their tag. They now play the role of a chlorine atom. UV rays sit down now because they used up their energy.

7) Your teacher now will tally the numbers of ozone molecules ([O.sub.3]), oxygen molecules ([O.sub.2]), oxygen atoms (0), and chlorine atoms (CI), and write the numbers on the board.

8) Next, your teacher will have each chlorine atom find a pair or trio of oxygen atoms and tag one of the members. Once tagged, this oxygen atom must leave its group. This represents chlorine breaking down ozone and oxygen molecules.

9) After all of the chlorines tag an oxygen, your teacher will tally the number of each molecule and atom again.

10) Repeat Steps 8 and 9 a second time.

CONCLUSIONS

1) How many ozone molecules were left after step 9? After step 10?

2) During the game, how did the chlorine atoms released from the CFCs affect the ozone molecules?

3) If countries had not agreed to ban CFCs in 1987, what would have happened to the ozone layer?

Note to Teachers: In "Hands-On Science" on p. 21, students will act out the key steps in the breakdown of ozone by CFCs. This is only part of the complex interaction among UV light, chlorine, and ozone taking place in the upper atmosphere. While chlorine atoms further break apart oxygen molecules, ozone is also constantly being created and destroyed as UV light strikes pairs and trios of oxygen atoms.

PRE-READING PROMPTS:

* What is ozone? Why is it important?

* A major hole in the ozone layer has formed over one continent. Which continent do you think that is?

* What human activities do you think contributed to the hole in the ozone layer?

DID YOU KNOW?

* Just as the ozone hole expands over Antarctica in the fall, an ozone hole forms over the Arctic Ocean each spring.

* French physicists Charles Fabry and Henri Buisson first discovered the ozone layer in 1913.

* Ozone molecules are constantly being broken apart by ultraviolet light and recombining to form new ozone in the upper atmosphere.

CRITICAL THINKING:

* How is the issue of ozone depletion similar to today's topic of global warming? Do you think the Montreal Protocol could be used as a prototype to tackle climate change? Why or why not?

CROSS-CURRICULAR CONNECTIONS:

SOCIAL STUDIES: CFCs aren't the only chemicals to be banned after they were discovered to damage the environment. Last summer, Spokane, Washington, banned the use of phosphates in dishwashing detergents, due to concerns about the chemicals' effect on the local waterbodies. Should this ban be made national? Split into two groups: those in favor of a national ban, and those against it. For more information on phosphates, check out this site on reducing phosphorus from Washington State's Department of Ecology: www.ecy.wa.gov/programs/wq /nonpoint/phosphorus/PhosphorusBan.html.

RESOURCES

You can access these Web links at www, scholastic.com/scienceworld.

* For lesson ideas using atmospheric data from NASA, go to http://mynasadata.larc.nasa.gov/L9_Murphy.html.

* Learn more about what you can do to protect yourself from harmful UV rays, at the EPA's SunWise Kids Web site: www.epa.gov/sunwise/kids/kids_ozone.html.

* NASA's Ozone Hole Watch Web site has a multimedia gallery full of ozone-related videos and animations: http://ozonewatch.gsfc.nasa.gov/multimedia/index.html.

CHECK FOR UNDERSTANDING

DIRECTIONS: Below are five major events related to the creation of the ozone hole and efforts made to save the ozone layer. Read each sentence, then place the letters of the sentences in the order in which they occur, from first to last.

a. The ozone layer repairs itself over time.

b. Manufacturers use CFCs as coolants in products such as air conditioners.

c. The first countries sign the Montreal Protocol, agreeing to phase out the use of CFCs and other ozone-destroying substances.

d. A hole in the ozone layer over the South Pole is discovered.

e. The amount of CFCs in the atmosphere starts to decline.

First --, --, --, --, Last

ANSWERS

b, d, c, e, a
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Title Annotation:PHYSICAL: ATOMS
Author:Crane, Cody
Publication:Science World
Geographic Code:1USA
Date:Sep 7, 2009
Words:1998
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