Stratospheric Ozone

Question 1

Where is ozone found?

Answer 1

Ozone is found it two layers of the atmosphere

• the stratosphere where it is ‘good’
• the troposphere where it is ‘bad’

Question 2

What is ozone?

Answer 2

A molecule made up of 3 oxygen atoms (o3)

A greenhouse gas

Question 3

What is the function of stratospheric ozone?

Answer 3

Stratospheric ozone blocks incoming ultraviolet radiation from the sun + so protects life from damaging UV radiation

Question 4

What is the ozone layer?

Answer 4

• Lower stratosphere
• Dynamic equilibrium as ozone is continuously made from oxygen atoms + is continuously converted back into oxygen
• In both the formation + destruction of ozone, UV radiation is absorbed
• Under influence of UV radiation, oxygen molecules are split into oxygen atoms
• Oxygen atoms = v reactive + combine w an oxygen molecule to form ozone
• Ozone absorbs UV radiation + then splits into an oxygen molecule + an oxygen atom
• Interconversion process converts UV radiation into thermal energy, heating the atmosphere

Question 5

What are the most harmful types of UV radiation and how much of this is absorbed by ozone?

Answer 5

> UV-C radiation has the highest energy (shortest wavelength) + so it most harmful
Ozone layers absorbs 99%+ UV-C
UV-B is second most harmful
Ozone layer absorbs half of UV-B radiation

Question 6

Name 4 damaging effects of UV radiation

Answer 6

• genetic mutation
• cataract formation in eyes
• skin cancers
• damage to photosynthetic organisms, esp. phytoplankton

Question 7

Name 4 beneficial effects of UV radiation

Answer 7

• In animals, UV radiation stimulates production of vit. D in our bodies
• Used to treat psoriasis + vitiligo
• Used as steriliser, air + water purifier as kills pathogens
• Industrial uses in lasers, forensic analysis…

Question 8

What has happened to the ozone hole during the last 40 years?

Answer 8

• minimum thickness of ozone layer has reduced drastically

- recovery has been taking longer

Question 9

What is ozone depletion the result of?

Answer 9

Ozone depletion is the result of:

• air pollution by mostly human-made chemicals
• most important ozone-depleting gases are halogenated organic gases e.g. CFCs

Question 10

When CFCs were developed during 1930s, they seemed to be the answer to many technological problems because they were non-reactive at ground level. What were they used as?

Answer 10

• propellants in aerosols
• expanders of gas-blown plastics
• pesticides
• refrigerants // previously used refrigerants were v toxic + flammable so quickly replaced w non-toxic + non-flammable CFCs

Question 11

How do CFCs deplete the ozone layer?

Answer 11

• UV radiation releases chlorine atoms from CFCs
• Chlorine atoms react w ozone, resulting in ozone destruction
• They can also react w oxygen atoms, so preventing ozone formation
• In both processes, chlorine atoms are formed back + are again able to react w ozone // oxygen atoms
• One chlorine atom can thus destroy many molecules of ozone in a chain reaction w positive feedback

Question 12

Why is it hard to find a replacement refrigerant for CFCs?

Answer 12

• refrigerants used before CFCs not an option due to their dangerous properties
• most suitable CFC replacements are HCFCs
• nearly as good refrigerants as CFCs + also non-toxic and inflammable
• but HCFCs destroy ozone + are greenhouse gases
• only their shorter lifetime in atmosphere makes them less harmful to ozone layer than CFCs

Question 13

Why will measures taken to prevent release of CFCs into the atmosphere take a long time to result in a thicker ozone layer?

Answer 13

CFCs are extremely stable, and will therefore persist in the atmosphere for up to 100 years after their release

Question 14

Reducing ozone-depleting substances // altering human activity

Answer 14

• Replace gas-blown plastics
• Replace CFCs w co2 // propane // air as propellent
• Replace aerosols w pump action sprays
• Replace methyl bromide pesticides

Question 15

Reducing ozone-depleting substances // regulating + reducing pollutants at point of emission

Answer 15

• Recover + recycle CFCs from refrigerators
• Legislate to have fridges returned to manufacturer + coolants removed + stored
• Capture CFCs from scrap car air conditioner units

Question 16

Reducing ozone-depleting substances // clean up and restoration

Answer 16

Add ozone to stratosphere

Remove chlorine from stratosphere

Question 17

What did the general public do in MEDCs before governments + international organisations even took steps on regulating CFC use?

Answer 17

• General public in many MEDCs began boycotting products containing CFCs (mainly spray cans)
• Aerosol industry reacted quickly by changing to ozone-friendly spray cans
• Even before CFCs were forbidden by law, hardly any CFC containing spray cans were produced anymore

Question 18

What was the Montreal Protocol coordinated by UNEP?

Answer 18

• international agreement to phase out production of ozone-depleting substances
• strongly reduce consumption + production of ODS by 2000
• all countries in world ratified agreement
• India + China still using lots of CFCs, as their fast economic growth led to growing use of fridges + air conditioning
• but now also phasing them out

Question 19

What is the significance of the Montreal Protocol?

Answer 19

• Best example of international cooperation on an environmental issue
• First w regulations that were carefully monitored

Question 20

Why are ODS still present in the atmosphere?

Answer 20

• Due to long life of CFCs in atmosphere, chlorine didnt reach peak in stratosphere unit 2005 nor will it return to pre-ODS levels much before 2050
• LEDCs still allowed to make + use some HCFCs until 2030
• There is an illegal market is ODS chemicals