3.3.3.3 Ozone depletion

Question 1

Why is ozone important?

Answer 1

It absorbs harmful UV light by nitrogen and oxygen

Question 2

What health hazards does UV light pose?

Answer 2

Skin cancer (damages DNA), cataracts, damage to plant tissue and reduce plankton population in oceans

Question 3

What has caused the recent decrease in levels of ozone in the stratosphere?

Answer 3

Photochemical chain reactions by halogen free-radicals

Question 4

What are chlorofluoroalkanes?

Answer 4

Used as they have low toxicity and non-flammability
Stable in the lower atmosphere, but as they diffuse upwards, they are exposed to UV light

Question 5

In the presence of UV, the following reaction occurs:

Answer 5

F F
| |
R-C-Cl -> R-C* +Cl*
| |
F F

Question 6

The chlorine free radical reacts with ozone:

Answer 6

Cl* +O3 -> ClO* + O2
ClO* + O3 -> Cl* + 2O2

Question 7

The chlorine free radical:

Answer 7

Acts as a catalyst for the decomposition of O3 molecules, so leads to a hole in ozone

Question 8

What is the overall equation for the decomposition of ozone?

Answer 8

2O3 -> 3O2

Question 9

What are the alternatives to CFCS?

Answer 9

Do not contain chlorine, e.g. hydrofluorocarbons. pr trifluoromethane

Question 10

What are the equations for the depletion of ozone?

Answer 10

Cl* +O3 -> ClO* +O2
ClO+O3->Cl+2O2
Overall equation;
2O3 -> 3O2