Ozone%20and%20CFCs

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Ozone and CFCs

• Presented and Compiled by Ashlee Betteridge

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What is Ozone?

• Ozone is an allotrope of oxygen. Its formula is
  O3.
• It is naturally present in the atmosphere.
• It exists both in the troposphere (lower
  atmosphere) and the stratosphere.

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Ozone in the Stratosphere

• 90 of ozone is in the stratosphere
• It absorbs ultraviolet radiation which can be
  harmful to life on earth.
• Stratospheric ozone absorbs 97-99 of the suns
  ultraviolet radiation.
• It is formed in the following way
• O2 (g)? 2O (g)
• O2 (g) O (g) ? O3 (g)

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Ozone in the Troposphere

• Ozone is harmful in the troposphere. It is
  toxic, and harmful to health at low
  concentrations (0.1 ppm)
• It forms photochemical smog by reacting with
  exhaust gases from motor vehicles.
• NO2 (g) sunlight ? NO (g) O (g)
• The oxygen radicals then react with O2, forming
  ozone.
• O2 (g) O (g) ? O3 (g)

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Chlorofluorocarbons (CFCs)

• Synthetic chemicals
• Contain fluorine, chlorine and carbon (no
  hydrogen)
• Have a similar structure to alkanes, with
  hydrogen replaced by fluorine and chlorine.
• E.g. Dichlorodifluoromethane

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Uses of CFCs
Uses of CFCs Prior to the 1987 Montreal Protocol
Source Encyclopedia of the Atmospheric
Environment http//www.doc.mmu.ac.uk/aric/eae/inde
x.html
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CFCs and Ozone 1

• CFCs are chemically inert and are not broken down
  at low altitudes. They are also insoluble in
  water so they are not washed from the atmosphere
  in rain.
• They remain in the troposphere for long periods
  of time, and diffuse into the stratosphere.
• CFCs in the stratosphere cause damage to the
  protective ozone layer.

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CFCs and Ozone 2

• CFCs are broken down by UV radiation in the
  stratosphere releasing halogen atoms, such as
  chlorine, which can react to break up ozone
  molecules.
• CCl3F (g) UV radiation ? CCl2F (g) Cl (g)
• Cl (g) O3 ? ClO (g) O2 (g)
• ClO then reacts with oxygen radicals
• ClO (g) O (g) ? O2 (g) Cl (g)
• Since the chlorine atom is not used up in the
  reaction it can continue breaking up ozone
  molecules indefinitely.
• This removes ozone from the stratosphere, meaning
  it cannot perform its purpose of absorbing
  harmful UV rays as effectively.

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Ozone Depletion
Source Environmental Protection Agency, USA
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The Hole in the Ozone Layer
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Effects of Ozone Depletion

• Global Warming
• Increase in levels of skin cancer, cataracts,
  immune system impairment.
• Impact on crops and agriculture
• Impact on marine food cycle

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CFC Alternatives
Impact of Chlorofluorocarbon Replacements on
Stratospheric Ozone
Source http//www.mp-docker.demon.co.uk/environm
ental_chemistry/topic_2b/page_4.html
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CFCs, HCFCs and HFCs