Stratospheric Ozone Flashcards
Where is ozone found?
Ozone is found it two layers of the atmosphere
- the stratosphere where it is ‘good’
- the troposphere where it is ‘bad’
What is ozone?
A molecule made up of 3 oxygen atoms (o3)
A greenhouse gas
What is the function of stratospheric ozone?
Stratospheric ozone blocks incoming ultraviolet radiation from the sun + so protects life from damaging UV radiation
What is the ozone layer?
- 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
What are the most harmful types of UV radiation and how much of this is absorbed by ozone?
> 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
Name 4 damaging effects of UV radiation
- genetic mutation
- cataract formation in eyes
- skin cancers
- damage to photosynthetic organisms, esp. phytoplankton
Name 4 beneficial effects of UV radiation
- 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…
What has happened to the ozone hole during the last 40 years?
- minimum thickness of ozone layer has reduced drastically
- recovery has been taking longer
What is ozone depletion the result of?
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
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?
- 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
How do CFCs deplete the ozone layer?
- 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
Why is it hard to find a replacement refrigerant for CFCs?
- 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
Why will measures taken to prevent release of CFCs into the atmosphere take a long time to result in a thicker ozone layer?
CFCs are extremely stable, and will therefore persist in the atmosphere for up to 100 years after their release
Reducing ozone-depleting substances // altering human activity
- Replace gas-blown plastics
- Replace CFCs w co2 // propane // air as propellent
- Replace aerosols w pump action sprays
- Replace methyl bromide pesticides
Reducing ozone-depleting substances // regulating + reducing pollutants at point of emission
- Recover + recycle CFCs from refrigerators
- Legislate to have fridges returned to manufacturer + coolants removed + stored
- Capture CFCs from scrap car air conditioner units
