The ozone layer

Question 1

Define troposphere?

Answer 1

The troposphere is the lowest layer of the Earth’s atmosphere, extending from the Earth’s surface up to about 7km (above the poles) and to about 20km (above the tropics).

Question 2

Define stratosphere.

Answer 2

The stratosphere is the second layer of the Earth’s atmosphere, containing the “ozone layer”, about 10km to 50km above the Earth’s surface.

Question 3

What is ozone?

Answer 3

Ozone, O_3,is a molecule consisting of three oxygen atoms.

Question 4

Explain, environmentally where the ozone is bad.

Answer 4

Bad: ozone near to the Earth’s surface in the troposphere is an air pollutant with harmful effects on the respiratory systems of animals.

Question 5

Explain, environmentally where the ozone is good.

Answer 5

Good: ozone in the upper atmosphere in the stratosphere protects living organisms by preventing harmful ultraviolet light from reach the Earth’s surface.

Question 6

Explain how the ozone layer protects living organisms.

Answer 6

The ozone layer is found in the region of the atmosphere called the stratosphere about 10-50km above the Earth’s surface. Ultraviolet radiation from the sun is filtered out by the ozone. The ozone converts this ultraviolet radiation into heat and so the ozone layer is at a higher temperature than other parts of the upper atmosphere.

Question 7

Give the wavelength of the three different UV radiation that hits the ozone and describe the severity of each one and how much the ozone absorbs the radiation.

Answer 7

UV-a (320-400nm) - reaches the Earth’s surface, doesn’t cause much concern because its not that damaging.

UV-b(280-320nm) radiation - can cause sunburn and sometimes genetic damage, which can result in skin cancer. Not much reaches the surface.

UV-c (200-280nm) - is entirely screened out by the ozone.

Question 8

Explain the formation of the ozone(using equations).

Answer 8

1) The first step in the formation of the ozone is the absorbtion of UV radiation with a wavelength less than 240nm by O₂ molecules.

O₂+ (radiation<240nm) ⇒ 2O

2) The O atoms then react with O₂molecules to form ozone molecules. This process generates heat.

O₂ + O ⇒ O₃ + heat

The heat is absorbed by air molecules in the stratosphere, raising its temperature.

Question 9

Explain how the ozone layer works(using equations).

Answer 9

1) The ozone molecules formed in the above reaction then absorb UV with wavelengths between 240nm and 310nm. In this process, O₃ molecules are converted back to O₂ molecules and O atoms.

O₃ +(radiation<310nm)⇒O₂+ O

The atomic oxygen,O, produced immediately reacts with other O₂molecules to reform the ozone:

O₂+ O ⇒ O₃ + heat

and so the cycle continues: In this way, the chemical energy released when O and O₂ combine is converted into kinetic energy of molecular motion(heat).

• The overall effect is to convert penetrating UV radiation into heat, without any net loss of ozone.

This cycle keeps the ozone layer in a stable balance. A natural steady state is reached in which ozone is being formed at the same rate as it is being broken down:

O₂+ O ⇔ O₃

Question 10

Explain the removal of the ozone not using CFC’s(using equations).

Answer 10

When an oxygen atom and an ozone molecule combine, they form two O₂ molecules:

O₃+ O ⇒ 2O₂

Luckily, the removal rate is slow