Ozone Layer and Extinction of Species

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Ozone Layer and Extinction of Species
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Contents

• Ozone layer depletion
• Extinction of species and loss of biodiversity

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Ozone Layer Depletion
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Source of ozone

• Consisted of 3 oxygen atoms, unlike ordinary
  oxygen molecule (which has 2 atoms).
• It has a bluish colour.

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Dual role of Ozone

• At near ground level, ozone is an air pollutant.
  Even at a low concentration (ppm), it is
  irritating to respiratory system.
• It is strongly oxidizing, and is now commonly
  used in sterilization of water.
• Its presence in the stratosphere is vital to life
  on Earth as it can absorb harmful ultra-violet
  radiation (known as UVB, wavelength 270-315nm)
  from sunlight.

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Structure of Atmosphere
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Source NASA
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Formation of Ozone in stratosphere

• O2 (radiation lt 240nm) ? 2 O
• O2 O M ? O3 M
• Molecule M carries the energy of the reaction but
  remain unchanged.

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Destruction of Ozone (I)

• Ozone can be destroyed by a number of free
  radical catalysts, the most important of which
  are the hydroxyl radical (OH), the nitric oxide
  radical (NO) and atomic chlorine (Cl) and
  bromine (Br).
• Human activity has dramatically increased the
  chlorine and bromine. These elements are found in
  certain stable organic compounds, especially
  chlorofluorocarbons (CFCs), which may find their
  way to the stratosphere without being destroyed
  in the troposphere due to low reactivity. Once in
  the stratosphere, the Cl and Br atoms are
  liberated from the parent compounds by the action
  of ultraviolet light, and can destroy ozone
  molecules through a variety of catalytic cycles.

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Destruction of Ozone (II)

• Cl O3 ? ClO O2
• ClO O ? Cl O2
• In sum O3 O ? O2 O2
• gtIncrease rate of recombination of oxygen,
  leading to an overall decrease in the amount of
  ozone.

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Ozone hole in September 2006
Largest hole in the record. Size of North
America
Source NASA
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Concentration Ozone in Antarctic region
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Consequences of Ozone depletion

• Since the ozone layer absorbs UVB ultraviolet
  light from the Sun, ozone layer depletion is
  expected to increase surface UVB levels.
• Possible linked to higher incidence of skin
  cancer.
• Lead to decrease of crop yield.

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Montreal Protocol

• The Montreal Protocol on Substances That Deplete
  the Ozone Layer is an international treaty
  designed to protect the ozone layer by phasing
  out the production of a number of substances
  believed to be responsible for ozone depletion.
  The treaty entered into force on January 1, 1989.
  
• Due to its widespread adoption and implementation
  it has been hailed as an example of exceptional
  international cooperation
• "Perhaps the single most successful international
  agreement to date...".

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Ozone Depleting Substances

• Chlorofluorocarbons (CFCs) were used in air
  conditioning/cooling units, as aerosol spray
  propellants prior to the 1980s, and in the
  cleaning processes of delicate electronic
  equipment.
• It is calculated that a CFC molecule takes an
  average of 15 years to go from the ground level
  up to the upper atmosphere, and it can stay there
  for about a century, destroying up to 100,000
  ozone molecules during that time.

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Current situation

• CFCs have been replaced to some extent by the
  less damaging hydro-chloro-fluoro-carbons
  (HCFCs), although concerns remain regarding HCFCs
  also. In some applications, hydro-fluoro-carbons
  (HFCs) have been used to replace CFCs.
• HFCs, which contain no chlorine or bromine, do
  not contribute at all to ozone depletion although
  they are potent greenhouse gases.

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Recovery of Ozone Layer

• Since the adoption and strengthening of the
  Montreal Protocol has led to reductions in the
  emissions of CFCs, atmospheric concentrations of
  the most significant compounds have been
  declining. These substances are being gradually
  removed from the atmosphere.
• By 2015, the Antarctic ozone hole would have
  reduced by only 1 million km² out of 25
• Complete recovery of the Antarctic ozone layer
  will not occur until the year 2050 or later.
• A detectable recovery will not occur until around
  2024, with ozone levels recovering to 1980 levels
  by around 2068.

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Extinction and Loss of Biodiversity
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Earths Sixth Mass Extinction

• Since 1500 AD, 784 extinctions have been
  documented by the International Union for
  Conservation of Nature and Natural Resources.
• However, since most extinctions are likely to go
  undocumented, scientists estimate that during the
  last century, between 20,000 and two million
  species have become extinct, but the precise
  total cannot be determined more accurately within
  the limits of present knowledge.

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• The World Conservation Unions IUCN Red List
  contains 15,589 species threatened with
  extinction in 2004.
• According to a 1998 survey of 400 biologists
  conducted by New York's American Museum of
  Natural History, nearly 70 percent of biologists
  believe that we are currently in the early stages
  of a human-caused mass extinction
• The same proportion of respondents agreed with
  the prediction that up to 20 percent of all
  living species could become extinct within 30
  years (by 2028).

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Cause of extinction of species

• Deforestation
• Habitat destruction, degradation or fragmentation
• Over-exploitation / hunting
• Human population growth
• Pollution
• Introduction of exotic species
• Climate change

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Some examples of extinct species
Dodo on a flightless bird living on A small
island in Indian Ocean. They Are hunted to
extinction in late 17th Century by sailors and
dogs brought By them as food.
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Baiji, Chinese River Dolphin Declared functionaly
extinct in 2006
Bali Tiger gone extinct in 1937
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Link
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Extinction of Species and Biodiversity

• Extinction of species cause a irreversible loss
  of biodiversity.

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Importance of biodiversity

• Possible new sources of food and drink in unknown
  species
• Possible new medicine
• Possible new industrial materials
• Ecosystem provides important vital resources such
  as oxygen, fresh water and food.
• Leisure, cultural and aesthetic value

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Discussion Question

• What can we do in response of the mass extinction
  of species?

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The End