Page 13 - Curriculum Visions Dynamic Book

Destruction of ozone in the stratosphere
Ozone mostly occurs in the layer of the upper atmosphere between 20 and 25 km above the Earth’s surface. Here a natural balance between the plentiful oxygen (O2) and ozone (O3) molecules has existed for billions of years.
Ozone is produced by the effect of cosmic rays on oxygen
catalyst: a substance that speeds up a chemical reaction but itself remains unaltered at the end of the reaction.
decompose: to break down a substance (for example by heat or with the aid of
a catalyst) into simpler components.
In such a chemical reaction only one substance is involved.
free radical: a very reactive atom or group with a “spare” electron.
ion: an atom, or group of atoms, that has gained or lost one or more electrons and so developed an electrical charge.
(O ) molecules and by electrical discharges, such as lightning 2
flashes, working on (O2) oxygen molecules. The energy from either source decomposes some oxygen (O2) molecules, leaving the free atoms (O) to link to nearby oxygen molecules to make ozone (O3).
Ozone is also decomposed by ultraviolet sunlight to release oxygen both as molecules (O2) and as atoms (O).
Ozone, however, does not just decompose in ultraviolet light. It can react with other molecules in the upper air, for example, chlorine and chlorine compounds.
The most troublesome of the chlorine-based compounds is a group known as CFCs. They have been widely used in aerosol spray cans, refrigerators, plastic foam and cleaning fluids. Chlorine containing molecules break up the ozone, taking away an oxygen atom and leaving O2. Because this process is in addition to the natural decomposing reactions in the upper air, ozone is decomposing faster than it is forming.
As CFCs cause the ozone concentration to fall, the amount of ultraviolet radiation reaching the Earth rises, and the occurrence of skin cancers increases.
 Ground level ozone cannot be seen, except in the smarting eyes of people walking along the streets.
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 Traffic in Bangkok, Thailand. Along with all the other pollutants such as smoke particles, nitrogen dioxide, sulphur dioxide and carbon monoxide, ozone is also produced by car engines. Ozone has a distinct and pungent odour.
Ground level ozone
Ozone can also be produced as a result of city traffic. The poisonous properties of ozone become apparent here. Even at very low concentrations, ozone can cause eye irritation, and for those people suffering from asthma and other breathing disorders, places with high street-level ozone can cause great discomfort.
Ozone can also be harmful to the growth of plants, contributing to the stress on trees that may make them more liable to suffer the effects of acid rain.