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A Level Environmental Science > Ozone Depletion > Flashcards

Ozone Depletion Flashcards

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1
Q

What is the chemical formula for ozone?

A

O3

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2
Q

Where is ozone found naturally?

A

In the ozone layer in the stratosphere

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3
Q

Where else is ozone found?

A

In the troposphere where it acts as a GHG

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4
Q

How is tropospheric ozone formed?

A

It is a secondary pollutant formed through the photochemical reaction of NOx

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5
Q

What function does the ozone layer have?

A

It absorbs harmful UVB and UVC radiation

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6
Q

What impacts could high levels of UV radiation have on Earth?

A
  • Increased risk of skin cancer
  • Increased risk of cataracts
  • Leaf tissue damage to plants leading to reduced rates of photosynthesis
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7
Q

What are the 3 types of UV radiation?

A

UVA (longest wavelength)
UVB
UVC (shortest wavelength)

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8
Q

Which type of UV radiation is the most damaging?

A

UVC

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9
Q

In what state is ozone formation in the stratosphere?

A

Dynamic equilibrium (ozone is continually destroyed and replenished with no significant net change in concentration)

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10
Q

What is dynamic equilibrium?

A

A combination of active processes which cancel out the effects of each other resulting in no overall change

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11
Q

What is the Rowland-Molina hypothesis?

A

A hypothesis in a 1974 paper which suggested that CFCs could deplete the ozone layer due to persistence, dissociation and reaction

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12
Q

How does the persistence of CFCs lead to ozone depletion?

A

CFCs are able to persist until the stratosphere due to chemical stability

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13
Q

How does dissociation lead to ozone depletion?

A

CFCs are broken down by high levels of UV in the stratosphere which they absorb, therefore releasing a Cl free radical

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14
Q

How do reactions lead to ozone depletion?

A

Cl free radicals released by broken down CFCs begin to react with ozone in the stratosphere, hindering dynamic equilibrium

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15
Q

What are CFCs?

A

Anthropogenic-sourced GHG (Chlorofluorocarbons)

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16
Q

What were CFCs originally used for?

A
  • Refrigeration
  • Air conditioning
  • Propellants in aerosols
  • Solvents
17
Q

What other gases can cause ozone depletion?

A
  • Other halogens (iodine, bromine, fluorine)
  • HCFCs (to be phased out by 2030)
18
Q

How is ozone measured?

A

In Dobson Units (DU) - measures the thickness of the ozone layer

19
Q

What can Dobson Units tell us?

A

100 DU = 1mm of ozone
Regular levels of ozone = 300 DU (3mm)
Levels below 220 DU are considered as holes in the ozone layer

20
Q

How is ozone in the stratosphere monitored?

A
  • 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
21
Q

Why is ozone depletion greatest over Antarctica?

A
  • 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
22
Q

What agreement was put in place to restore the ozone layer?

A

The Montreal Protocol (1987)

23
Q

What are the main aspects of The Montreal Protocol?

A
  • 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
24
Q

What alternative processes did The Montreal Protocol outline?

A
  • Pump and trigger-action sprays to replace propellants
  • The use of stick or roll-on deodorants
25
Q

What alternative materials did The Montreal Protocol outline?

A
  • HCFCs (still an ODS)
  • HFCs (more expensive, less functional, GHG)
26
Q

What did The Montreal Protocol outline concerning safe waste disposal of CFCs?

A

Waste CFCs from old fridges are now drained and incinerated before being neutralised

27
Q

Why was The Montreal Protocol successful?

A
  • 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
28
Q

Why has reducing ozone depletion proved much more effective than tackling climate change?

A

It was relatively cheap to phase out CFCs as alternatives already existed, whereas alternatives to reduce climate change are relatively few

A Level Environmental Science (22 decks)

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