In 1994, the United Nations proclaimed 16 September the International Day for the Preservation of the Ozone Layer, commemorating the date of the signing, in 1987, of the Montreal Protocol on Substances that Deplete the Ozone Layer.

Ozone, what is it? Where does it come from? Why is the ozone layer important?

Read the text and find out (there are also some exercises and videos about it!). 

PART A

Background information

We are familiar with the most common form of oxygen, the form that we all breathe. It is made up of two oxygen atoms (O2). Ozone is made up of three oxygen atoms (O3) and can be beneficial or harmful, depending on where it is found in the atmosphere.

In the stratosphere, ozone protects us from ultraviolet radiation, so it is beneficial to human health. On the other hand, ground-level ozone is a pollutant and is harmful to human health. Remember, the ozone chemical is the same, but where it is located determines if it is beneficial or a pollutant.

1)      CHOOSE THE CORRECT SYNONYM FOR EACH OF THE FOLLOWING WORDS:

a)      common= usual / habitual

b)      beneficial= worthy/good

c)       harmful= damaging /risky

d)      a pollutant= hazardous substance / infection

PART B 

Stratospheric Ozone

As shown in the picture to the right, the stratosphere is the layer of atmosphere above the troposphere. The stratosphere contains a thin layer of ozone. The stratospheric ozone layer occurs naturally. It protects life on earth by filtering out the sun’s harmful ultraviolet radiation. 

Ozone gas (O3) forms when oxygen molecules interact with ultraviolet rays from the sun. Ozone molecules absorb ultraviolet light and split into molecules of oxygen (O2) and oxygen atoms (O). The ultraviolet light then splits some more of the O2 to form more oxygen atoms. Oxygen atoms (O) combine with O2 to create ozone, which is of course, O3. 

Under normal conditions this ozone layer is continuously being depleted and regenerated. UV light breaks down O2 to single O atoms and then reforms to O3 again and again. This process allows most of the ultraviolet light to be filtered out before it reaches the earth. Ultraviolet light, or UV radiation, can cause skin cancer in humans.2 to form more oxygen atoms. Oxygen atoms (O) combine with O2 to create ozone, which is of course, O3.

2)QUESTIONS

1. Where is the stratosphere?
2. Where is the ozone layer found?
3. Why is the ozone layer important?
4. How often is the ozone layer created?
5. Why is ultraviolet light, or UV radiation threatening to human health?
6. Explain how the ozone layer formation process filters UV radiation.

PART 3

Do you know what CFCs (Chlorofluorocarbons) are? Where are they found?

3) CIRCLE ALL THE ITEMS THAT APPLY:

 Chlorofluorocarbons are found in:

refrigerators /  home and automobile air conditioners / washing powder / batteries/ Styrofoam cups / aerosol cans / plastic packaging / perfumes / plastic foam

Chlorofluorocarbons (CFCs)

Now humans have introduced chlorofluorocarbons (CFCs) to the atmosphere and the chlorine in CFCs reacts with the ozone and changes the whole process. CFCs were first introduced in the 1920s. They were very useful as coolants in air conditioners and refrigerators, propellants for aerosol sprays, and agents used to produce plastic foam. The CFC molecules are very stable close to the earth, but when they reach the stratosphere ultraviolet radiation breaks them up into their more-reactive components. These components then react with the ozone molecules breaking them apart, thus reducing the amount of available oxygen atoms necessary to form ozone. 

Before the chlorine is finally removed from the atmosphere (in one to two years by precipitation), each chlorine atom will have destroyed approximately 100,000 ozone molecules – exposing the earth to more harmful ultraviolet rays.

The amount of ozone has been so depleted in some areas that scientists now refer to “holes” in the ozone. Depletion of the stratospheric ozone layer is of great concern since it protects the earth’s surface by absorbing 99 percent of the ultraviolet light energy coming from the sun.                                                                                                                                                                                                         .                                                                                          

1)      Click here to do a cloze text exercise on part of the above text. 

Throughout the 1980s, several countries–including Canada, Mexico, Australia and several European nations, with the USA having taken action earlier –passed regulations banning CFC use in aerosol containers. Under the Montreal Protocol agreement, CFC propellant production was phased out as of January 1, 1996 in industrialized countries and expected to be phased out by 2010 in developing nations.

 KEY

1)      Correct synonyms

a)      usual

b)      good

c)       damaging

d)      hazardous waste

2) Answers

1. It’s over the troposphere at a height of 10-50 km above the earth.
2. It’s found in the stratosphere.
3. Because it protects life on earth by filtering out the sun’s harmful ultraviolet radiation.
4. Under normal conditions the ozone layer is continuously being regenerated.
5. Ultraviolet light, or UV radiation, can cause skin cancer to humans.
6. Open answer.

3) Answers

    Chlorofluorocarbons are found in:

    refrigerators /  home and automobile air conditioners / Styrofoam cups / aerosol cans / plastic packaging /      plastic foam

TERMS

• Chlorofluorocarbons (CFCs): a group of chemicals used for a wide variety of products such as aerosols and refrigerants

• Ozone: a colorless gas composed of three oxygen atoms.

• Stratosphere: the layer of the atmosphere overlying the troposphere to about 30 miles in altitude.

SOURCES

Environmental Science Institute, The University of Texas at Austin 

http://www.artinaid.com   [picture]

This information is adapted from Environmental Science Institute, The University of Texas at Austin  lessons for Middle School Students and it is created under  (CHECK THIS LICENCE)

RELEVANT VIDEOS:

When CFCs meet Ozone

Information about the Montreal Protocole by scientists. Among them, Dr.F.Sherwook Rowland and Dr Mario Molina the nobel awarded scientists who explained ozone layer depletion back in 1995.