Topic 6.2

Question 1

What layers of the atmosphere is the ozone found in?

Answer 1

troposphere and stratosphere

Question 2

Is stratosphere or troposphere considered to be ‘bad’?

Answer 2

stratosphere is good

troposphere is bad

Question 3

What is ozone?

Answer 3

a molecule made up of three oxygen atoms - O3.

Question 4

What does the stratospheric ozone do?

Answer 4

blocks incoming ultraviolet radiation from the sun and protects life from damaging ultraviolet (UV) radiation.

Question 5

How is the ozone an example of dynamic equilibrium?

Answer 5

Through the ozone destruction and reformation.

Question 6

How is the ozone formed?

Answer 6

Oxygen molecules splits into two oxygen atoms to which each combine with another oxygen molecule to form the ozone (O3)

Question 7

How is the ozone destructed?

Answer 7

Ozone absorbs UV radiation which then splits into an oxygen molecule and an oxygen atom. The oxygen atom can react with another ozone molecule, making two oxygen molecules.

Question 8

In both the formation and destruction of the ozone, what is absorbed?

Answer 8

UV radiation

Question 9

Why is the absorption of UV radiation by the ozone layer very important?

Answer 9

Because without it, life on land would be impossible.

Question 10

What are the types of UV radiation?

Answer 10

UV-A
UV-B
UV-C

Question 11

Interpret UV-C radiation

Answer 11

is has the highest energy (shortest wavelength) and is therefore the most harmful type of UV radiation.

Question 12

Interpret UV-A radiation

Answer 12

Relatively harmless because of its longer wavelength (low energy).

Question 13

What percentage of UV-C and B radiation is absorbed by the ozone layer?

Answer 13

more than 99% UV-C

about half UV-B radiation

Question 14

What are the damaging effects of UV radiation?

Answer 14

• Skin cancers
• Cataract formation in eyes - protein of lens denatures and turns cloudy instead of clear, causing blindness if untreated.
• Damage to photosynthetic organisms, especially zooplankton. - causing disruptive effects on food pyramids.

Question 15

What are the beneficial effects of UV radiation?

Answer 15

• In animals, UV radiation stimulated the production of vitamin D in our bodies. Vitamin D deficiency causes rickets when a child’s bones are short of calcium and too soft to support the body.
• Use as a sterilizer as it kills pathogenic bacteria and as an air and water purifier.
• Industrial uses in lasers, viewing old scripts, forensic analysis, lighting.

Question 16

What is the ozone hole?

Answer 16

A break in the ozone layer that is directly above Antarctica in the stratosphere.
The size has been measured since 1950 and has been growing.

Question 17

What time of year does the amount of ozone decrease and increase?

Answer 17

the amount of ozone decreased significantly during the spring (september and October) and increased again in November.

Question 18

What is happening to the thickness of the ozone layer of the ozone hole?

Answer 18

it is decresing

Question 19

What causes ozone depletion?

Answer 19

Air pollution by chemicals that are mostly human-made. (ODS)

Question 20

What is the most important ozone-depleting gases? (ODS)

Answer 20

Halogenated organic gases for example chlorofluorocarbons (CFCs), hydrochlorofluorocarbons (HCFCs), Halons, Methyl bromide and Nitrogen oxides.

Question 21

When were the first ODS developed?

Answer 21

the 1930s

Question 22

Why were ODS the answer to many technical problems?

Answer 22

Previously, used refrigerants were toxic and flammable but ODS are inert (non-reactive) at ground level.

Question 23

How do CFCs deplete the ozone layer?

Answer 23

• Uv radiation in the stratosphere releases the chlorine atoms in CFCs
• The chlorine atoms react with ozone to destroy the ozone.
• The chlorine atoms also react with oxygen atoms to prevent ozone formation
• Both of these processes result in chlorine atoms reforming. 1 chlorine atom can destroy many molecules of ozone (chain reaction with positive feedback).

Question 24

What are the uses/sources for CFCs?

Answer 24

Spray can propellants, plastic foam expanders, refrigerant chemicals, pesticides, flame retardants

Question 25

What are the uses/sources for HCFCs?

Answer 25

Replacement for CFCs

Question 26

What are the uses/sources for Halons?

Answer 26

Industrial fire suppression systems

Question 27

What are the uses/sources for Methyl bromide?

Answer 27

Pesticide

Question 28

What are the uses/sources for Nitrogen oxides?

Answer 28

Bacterial breakdown of nitrates and nitrates in the soil (intensive farming), high flying supersonic aircraft

Question 29

What atoms do CFCs release?

Answer 29

chlorine atoms

Question 30

What atoms do HCFCs release?

Answer 30

chlorine atoms (but have a shorter lifetime in the atmosphere but a stronger greenhouse gas than CFCs)

Question 31

What atoms do Halons release?

Answer 31

bromine atoms

Question 32

What atoms does Methyl bromide release?

Answer 32

bromine atoms

Question 33

What do Nitrogen oxides do?

Answer 33

Nitrogen oxides are converted to NO which reacts with ozone.

Question 34

What did scientists discover in the 1970s about CFCs?

Answer 34

That they were depleting the ozone layer.

Question 35

What cycle did scientists need to understand in order to solve the problems with the CFCs?

Answer 35

The Ozone Cycle.

Question 36

Breakdown the Ozone Cycle.

Answer 36

1. Oxygen molecules are photolyzed (separated by the sun), yielding 2 oxygen atoms (slow)
2. Ozone and oxygen atoms are continuously being interconverted as solar UV breaks ozone and the oxygen atom reacts with another oxygen molecule (Fast). This interconvention process converts UV radiation into thermal energy, heating the stratosphere.
3. Ozone is lost by a reaction of the oxygen atom or the ozone molecule with each other, or some other trace gas such as chlorine. (Slow).

Question 37

What was easy to find in terms of the replacement of ODCs?

Answer 37

It was easy to find effective chemicals to replace CFCs in aerosol cans and blowing agents for plastics.

Question 38

Why was finding effective refrigerants to replace hard?

Answer 38

• Couldn’t go back to previous refrigerants because they are hazardous
• HCFCs were developed
• HCFCs were eventually found to also destroy the ozone layer and contribute to the greenhouse effect.

Question 39

What Protocol focused on reducing ODS?

Answer 39

The Montreal Protocol.

• International agreement to phase out the production of ODS signed in 1987.
• 197 countries ratified this treaty.
• Freeze the consumption and production of ODS to 1986 levels by 1990 and strongly reduce the consumption and production of ODS by 2000.
• Differences between LEDCs and MEDCs: LEDCs got more time to implement treaty due to being less developed i.e having less resources.

Question 40

What was the significance of the Montreal Protocol?

Answer 40

• Example of environmental agreement that is a global agreement. All countries on Earth in 1987 signed the MP.
• Example of experts from many fields coming together to research a problem and find a solution. Decision making was scientifically based.
• First environmental agreement that allowed implementation by economic status.
• Has a clause that allows for monitoring… other global environmental agreements did not include methods to monitor progress.

Question 41

What is the future for CFCs?

Answer 41

• They have a long life in the atmosphere. Chlorine gas in the atmosphere did not reach its highest levels until 2005. Chlorine gas levels will not reach pre-ODS levels before 2050.
• Unfortunately because they are so effective, there is a strong black market for CFCs particularly in the developing world.