6.2 Stratospheric Ozone Flashcards
What is ozone?
Ozone is a form of oxygen and an effective greenhouse gas. Ozone molecules (O3) are three atoms of oxygen bound together, this is a reactive gas that is colourless and poisonous to breathe.
Would there be life on earth without ozone?
No, as it protects us by forming a shield against harmful radiation from the Sun, known as UV radiation.
What are the three types of UV radiation?
UV-A (This is the UV light responsible for the tanning and ageing processes of the skin.)
UV-B (potentially harmful, but most of it is absorbed by the ozone in the stratosphere)
UV-C (most damaging form of UV radiation as it has the highest energy. Fortunately about 99% of it is absorbed by the ozone and oxygen in the stratosphere)
Where is 90% of ozone contained?
90% of ozone is contained within the lower stratosphere between 19 and 30km
Why is stratospheric ozone important?
Plays an important part in filtering out most of the potentially harmful ultraviolet radiation that reaches the Earth. Ozone in the stratosphere is not a pollutant, and does not contribute to the greenhouse effect.
How is stratospheric ozone formed and broken down?
Ozone constantly breaks down and reforms in a chain reaction. The ozone layer is an example of a dynamic equilibrium
- Ozone is formed when UV radiation is absorbed by oxygen, splitting it into two oxygen atoms.
- Oxygen atoms are extremely reactive and can combine with an oxygen molecule forming ozone.
When is stratospheric ozone depleted?
Ozone depletion occurs when the equilibrium between the processes of stratospheric ozone production and destruction is disturbed, resulting in more ozone being destroyed than is being produced.
What are some causes of stratospheric ozone depletion?
- -> Natural phenomena such as volcanic eruptions can cause temporary ozone loss
- -> chlorine and bromine released from man-made compounds are the main cause of ozone depletion.
What are some examples of compounds that have led to an increase in the amount of chlorine and bromine in the atmosphere?
Chlorofluorocarbons, Hydrochlorofluorocarbons, Hydrofluorocarbons, Methyl Bromide and Halons
What are Chlorofluorocarbons (CFCs) ?
Man-made compounds containing chlorine, fluorine and carbon. They are the main cause of stratospheric ozone depletion (around 80%).
What are CFC’s used for?
- Propellants in aerosol sprays
- Cleaning fluids
- Coolants in refrigerators, freezers and air conditioners
- Blowing agents in the production of plastic foam
- Industrial solvents
How do CFC’s deplete the stratospheric ozone?
- -> CFCs rise slowly into the stratosphere. Once there, they are bombarded by the incoming UV light from the Sun, releasing the chlorine atoms from the parent compound, which can then react with the ozone molecules
- -> One chlorine atom can destroy many molecules of ozone in a chain reaction, which is an example of positive feedback.
What are Hydrochlorofluorocarbons (HCFCs)?
Developed as an alternative to CFCs and are now used in place of them in many products
(made up of hydrogen, chlorine, fluorine and carbon.)
- shorter atmospheric lifetime
- do deplete the ozone layer but they have a shorter atmospheric lifetime than CFCs so they don’t cause as much damage
- HCFCs are powerful greenhouse gases.
How come HCFCs don’t cause as much damage as CFCs?
They still deplete the ozone layer but HCFCs have a shorter atmospheric lifetime than CFCs so they don’t cause as much damage
What are Hydrofluorocarbons (HFCs) ?
another replacement for CFCs. They are made up of hydrogen, fluorine and carbon. HFCs are thought to do very little damage to the ozone layer, but they are powerful greenhouse gases.
What is the ozone ‘hole’?
The ozone layer is being depleted faster in some areas of the world than others. Near the equator, ozone levels have hardly changed. However, the concentration of stratospheric ozone around the south pole drops by 60% every spring due to to Polar Stratospheric Clouds acting as a catalytic surface for chlorine to react with ozone (requires sunlight and thus only begins when sun returns in spring). This is only a temporary thinning of the ozone layer (NOT a destruction), and it repairs itself during the summer.
