Ozone Depletion Flashcards
What is the chemical formula for ozone?
O3
Where is ozone found naturally?
In the ozone layer in the stratosphere
Where else is ozone found?
In the troposphere where it acts as a GHG
How is tropospheric ozone formed?
It is a secondary pollutant formed through the photochemical reaction of NOx
What function does the ozone layer have?
It absorbs harmful UVB and UVC radiation
What impacts could high levels of UV radiation have on Earth?
- Increased risk of skin cancer
- Increased risk of cataracts
- Leaf tissue damage to plants leading to reduced rates of photosynthesis
What are the 3 types of UV radiation?
UVA (longest wavelength)
UVB
UVC (shortest wavelength)
Which type of UV radiation is the most damaging?
UVC
In what state is ozone formation in the stratosphere?
Dynamic equilibrium (ozone is continually destroyed and replenished with no significant net change in concentration)
What is dynamic equilibrium?
A combination of active processes which cancel out the effects of each other resulting in no overall change
What is the Rowland-Molina hypothesis?
A hypothesis in a 1974 paper which suggested that CFCs could deplete the ozone layer due to persistence, dissociation and reaction
How does the persistence of CFCs lead to ozone depletion?
CFCs are able to persist until the stratosphere due to chemical stability
How does dissociation lead to ozone depletion?
CFCs are broken down by high levels of UV in the stratosphere which they absorb, therefore releasing a Cl free radical
How do reactions lead to ozone depletion?
Cl free radicals released by broken down CFCs begin to react with ozone in the stratosphere, hindering dynamic equilibrium
What are CFCs?
Anthropogenic-sourced GHG (Chlorofluorocarbons)
What were CFCs originally used for?
- Refrigeration
- Air conditioning
- Propellants in aerosols
- Solvents
What other gases can cause ozone depletion?
- Other halogens (iodine, bromine, fluorine)
- HCFCs (to be phased out by 2030)
How is ozone measured?
In Dobson Units (DU) - measures the thickness of the ozone layer
What can Dobson Units tell us?
100 DU = 1mm of ozone
Regular levels of ozone = 300 DU (3mm)
Levels below 220 DU are considered as holes in the ozone layer
How is ozone in the stratosphere monitored?
- Helium balloons / unmanned aircraft collect samples from the atmosphere and analyse them
- Ground-based surveys use specialist equipment to measure the UV reaching Earth’s surface
- Satellites measure the UV that is reflected from Earth’s surface
Why is ozone depletion greatest over Antarctica?
- Extremely cold stratospheric temperatures
- Polar vortex winds which rotate around the poles prevents the mixing of air masses, therefore maintaining a high Cl concentration
- Stratospheric clouds and ice crystals form due to cold temperatures and provide surfaces for reactions to take place which break down CFCs and release Cl free radicals
What agreement was put in place to restore the ozone layer?
The Montreal Protocol (1987)
What are the main aspects of The Montreal Protocol?
- Phased out manufacture and use of CFCs and other ODSs (regulates consumption)
- Phased out use of HCFCs by 2030
- Essential uses of some ODSs are still permitted
- A fund is available to help LEDCs implement the targets set out
What alternative processes did The Montreal Protocol outline?
- Pump and trigger-action sprays to replace propellants
- The use of stick or roll-on deodorants
What alternative materials did The Montreal Protocol outline?
- HCFCs (still an ODS)
- HFCs (more expensive, less functional, GHG)
What did The Montreal Protocol outline concerning safe waste disposal of CFCs?
Waste CFCs from old fridges are now drained and incinerated before being neutralised
Why was The Montreal Protocol successful?
- Signed by all 198 UN member states (international recognition)
- Adaptation fund and longer timeline of change for LEDCs
- Expected recovery to pre-1980 levels by 2050
Why has reducing ozone depletion proved much more effective than tackling climate change?
It was relatively cheap to phase out CFCs as alternatives already existed, whereas alternatives to reduce climate change are relatively few
