Ozone is a blue gas that is explosive and poisonous .It is denser than oxygen and condenses into a dark blue liquid at – 112° C. This liquid freezes at – 251° C.

Ozone is used in many industries. Factories use it for chemical reactions because it reacts more easily than oxygen does. Ozone also kills germs , which makes it useful for removing bad smells and sterilizing drinking water. Ozone is also used to bleach color out of other substances .

Ozone occurs in our atmosphere in two forms. Near the ground even small amounts of ozone can cause health problems. It irritates your eyes and can lead to coughing and asthma . Ozone is especially dangerous on clear days when exhaust fumes or cars pollute the air. Older people and babies are often told to stay indoors because ozone may weaken your immune system .

About 30 -50 km above the Earth’s surface there is a layer of ozone in the atmosphere that protects us. It absorbs harmful ultraviolet rays from the sun. If too much of this radiation reaches the Earth it may injure your eyes and lead to skin cancer and other diseases .

In the 1970s scientists found out that chemicals released into the atmosphere have been destroying this ozone layer . The first hole in the ozone layer was found over Antarctica. In the last 20 years this hole has been getting bigger and now lies over some parts of Australia, New Zealand and the northern hemisphere as well.

The hole in the ozone layer is caused by CFCs , chemicals often used in spray cans and refrigerators . They escape into the atmosphere and break up the ozone molecules.

Exercises

Before you watch the video make sure you understand these words. After watching, do the exercise below.

• barrier = something that protects you from danger
• expose = to put in a dangerous situation
• trace gas = there is very little of it
• primary culprits = the ones to blame
• aerosol = spray
• rip apart = break away
• misleading = not quite correct
• conversion = to change from one form to another
• emit = to send into the atmosphere
• hemisphere = half of the Earth
• ban = forbid
• ozone-depleting = material that destroys ozone
• shrink = become smaller