The Ozone Layer and Air Pollution

Question 1

Where is the ozone layer?

Answer 1

At the edge of the stratosphere.

It contains most of the atmosphere’s ozone molecules, O3.

Question 2

When is ozone formed?

Answer 2

When UV radiation from the Sun hits oxygen molecules.

Question 3

If the right amount of UV radiation is absorbed by an oxygen molecule, the oxygen molecule splits into separate atoms or free radicals. The free radicals then combine with other oxygen molecule to form ozone molecules, O3.
Write the equation (s) for this sequence.

Answer 3

O2 + hv -> O. + O.———> O2 + O.-> O3

*hv = a quantum of UV radiation

Question 4

The ozone layer…

Answer 4

protects the Earth.

Question 5

How is the ozone layer constantly being replaced?

Answer 5

UV radiation can reverse the formation of ozone.
The ozone layer is continuously being destroyed and replaced as UV radiation hits the molecules.
An equilibrium is set up, so the concentrations stay fairly constant.

Question 6

The UV radiation from the Sun is made up of different frequencies. These are grouped into what three bands in order increasing frequency and energy?

Answer 6

UVA
UVB
UVC

Question 7

What damage can UV radiation do?

Answer 7

UVB can damage the DNA in cells and cause skin cancer.
It’s the main cause of sunburn too.
UVA can also lead to skin cancer.
Both types of UV break down collagen fibres in the skin fibre, causing it to age faster.

Question 8

Why is UV radiation essential for humans?

Answer 8

We need it to produce vitamin D.

Question 9

What do CFCs do?

Answer 9

CFCs absorb UV radiation and split to form chlorine free radicals.
These free radicals destroy ozone molecules and are then regenerated to destroy more ozone.

Question 10

What do NO. free radicals from nitrogen oxides do?

Answer 10

Destroy ozone.
Nitrogen oxides are produced by car and aircraft engines and thunderstorms.
NO. free radicals affect ozone in the same way as chlorine radicals.

Question 11

What is the equations for how CFCs and Nitrogen Oxides break down ozone where R represents Cl. or NO.?

Answer 11

R + O3 -> RO + O2
RO + O. -> R + O2

The overall reaction is: O3 + O. -> 2O2

Question 12

How can solid heterogenous catalysts provide a surface for a reaction to take place on?

Answer 12

• Reactant molecules arrive at the surface and bond with the solid catalyst. This is called adsorption.
• The bonds between the reactant’s atoms are weakened and break up. This forms radicals. These radicals then get together and make new molecules.
• The new molecules are then detached from the catalyst. This is called desorption.

Question 13

Suggest reasons why there is still concerns about ozone depletion despite CFC’s being restricted.

Answer 13

CFCs take many years to reach the ozone layer
CFCs are still being used
There are other ozone depleting substances