DENA ozone

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Slide1: 

About 20 kilometers (12½ miles) thick, this giant umbrella is made up of a layer of ozone gas (O3). This gas is found some 15 to 35 kilometers above the Earth's surface in the upper atmosphere or "stratosphere". The Ozone Layer

Slide2: 

Like a good pair of sunglasses, the ozone layer acts like a natural filter, blocking out most of the sun's harmful UV (ultraviolet) rays.

Slide3: 

Ozone...

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The ozone layer is our natural shield against UV rays. But, there isn't a lot of ozone up there. Ozone is continually created and destroyed. It's a natural cycle of events that continually creates our shield against UV rays.

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UV plays a key role in creating and destroying ozone. Step 1: UV-C rays strike oxygen molecules (O2), splitting them into separate oxygen atoms. Step 2: Each oxygen atom is free to bond. Those that bond with O2 produce ozone, or O3. And… conversely UV-B rays destroy ozone by breaking one of its bonds and releasing an oxygen molecule and an oxygen atom. This is the natural cycle of our shield.

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The problem is that our actions have tipped the balance toward too much destruction. The result is that more harmful UV-B rays are reaching the surface of the Earth. Unfortunately, ground level ozone is increasing while stratospheric ozone decreases. We cannot move the lower ozone gas up to help the ozone layer. The best solution is to continue to reduce all sources of pollution affecting our atmosphere.

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Certain human-made chemicals are the cause...

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The main cause of ozone loss is chlorofluorocarbons (CFCs). We've used CFCs and the other ozone-depleting chemicals for many purposes: CFCs - coolants in refrigerators and air conditioners, solvents, foams. Halons - fire extinguishers. Carbon tetrachloride - toxic chemical used as a dry cleaning agent, pesticide and solvent. Methyl chloroform - solvent in cleaners, degreasers and adhesives. HCFCs (hydrochlorofluorocarbons) - a temporary replacement chemical for the more dangerous CFCs. Methyl Bromide - pesticide.

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As they drift upward, CFCs eventually go through the ozone layer. There, the sun's UV-C rays break them apart into chlorine or bromine atoms. Then chlorine or bromine atoms fall onto the ozone layer. They attack ozone by stealing an oxygen atom away and freeing it to build an O2 molecule. CFCs

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There is now a huge stockpile of CFCs and other chemicals in the atmosphere, with lifespans of 100 years or more. Almost all CFCs released in the past century are still in the atmosphere

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The Right Choices at the Right Time… Vienna Convention for the Protection of the Ozone Layer The Montreal Protocol on Substances that Deplete the Ozone Layer By studying the ozone layer, we have a much better understanding of the impact we've had on this fragile part of nature.

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Recent volcanic eruptions (Mexico's El Chichon in 1982 and the Philippines' Mt. Pinatubo in 1991) have led to a decrease in the ozone layer. Volcanic debris can remain in the upper atmosphere for two to three years. Scientists also believe that volcanic debris speeds up the destruction caused by CFCs. Natural events leading to ozone depletion….

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Can the ozone layer heal itself? Yes. But we must stop releasing CFCs and other chemicals into the atmosphere. It will take decades for the atmosphere to cleanse itself of these human-made chemicals. The ozone layer can heal itself, but only if we allow it to return to its natural balance.

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The ozone layer in the Earth's upper atmosphere screens out... Space Dust. UV-Rays. Smog. None of the above.

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UV-Rays

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The ozone layer is created in nature by a reaction between oxygen and... UV-A rays. UV-B rays. UV-C rays. None of the above.

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UV-C rays

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The ozone layer is naturally destroyed by a reaction with... UV-A rays. UV-B rays. UV-C rays. None of the above.

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UV-B rays