Ozone Depletion

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Ozone Depletion

• A Global Crisis

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What is Ozone?

• Composed of three oxygen atoms
• Unevenly distributed, 90 in Stratosphere

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Atmospheric O3 concentration as a function of
height/altitude
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The concentration of ozone is measured in Dobson
Units the bigger the number, the higher the
concentration of ozone.
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Natural Ozone Process
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UV Facts

• Ozone absorbs 99 of suns UV radiation
• Radiation consists of three bands A, B, C
• Ozone blocks out all C (highest energy)
• Blocks 1/2 of B (2nd highest)
• Blocks small amount of A (lowest)

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17_SBS01-01.JPG
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17_17a.jpg
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Fig. 20-19, p. 487
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Circumpolar VortexDuring the polar winters,
cold winds and chlorine absorbing ice forms over
the poles. During the polar spring the
atmospheric ice melts and large quantities of
ozone destroying chlorine is released
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DU thickness of compressed atmospheric O3 at
0C 100. (e.g., 4mm 400 DU)
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Bar graph of area with Antarctic low O3
concentrations (lt 220 DU) during October and
November (area of North America 24 million km2).
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Fig. 20-20, p. 487
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Monthly average total O3 Northern Hemisphere
spring
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CFCs

• Chlorofluorocarbons- organic compounds made from
  carbon, chlorine, fluorine, and oxygen
• Developed in the 1930s for industrial and
  commercial applications
• React in the atmosphere and release chlorine
• Extremely stable

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CFCs
Oh NO!!!
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17_SBS01-02.JPG
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Stratospheric Ozone Destruction CFCs CFC ? ?
CFC Cl (? lt 215 nm UV-C) O3 ? ? O2 O (?
lt 290 nm UV-B) Cl O3 ? ClO O2 ClO O ? Cl
O2
A single Cl- radical can reside in the
stratosphere for nearly a decade and disrupt the
formation of several hundred thousand O3
molecules. Increased UV-B reached Earths surface
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Depletion

• Begins when CFCs and other ozone depleting
  substances are emitted into the air
• Wind mixes substances through tropophere
• After several years, the substances in the
  troposphere reach the stratosphere, 10 KM above
  Earth
• UV light then begins to break apart the ozone
  depleting substances

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Depletion (cont)

• UV light breaks apart CFCs to release chlorine
• UV light breaks apart halons to release Bromine
• The broken atoms, not intact molecules attack the
  ozone
• 1 chlorine atom can destroy 100,000 ozone
  molecules before being destroyed itself

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Depletion (cont)

• Large increases in chlorine and bromine have
  upset the natural ozone balance
• Depleting the ozone faster than it can be
  naturally produced

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Chemical Process

• Initiated by Polar Night, when high latitudes
  receive no sunlight
• Air above cools and vortex is formed
• Catalytic cycle

Cl O3 gt ClO O2 ClO O gt Cl O2
------------------ net result O3 O gt 2O2
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Besides CFCs the following chemicals can also
deplete the ozone layer methyl bromide, methyl
chloroform, and carbon tetrachloride
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Results of Ozone Depletion

• Increased UV levels reaching Earth
• Causes Skin Cancer and Cataracts
• Impacts phytoplankton activity
• Alters photochemical reaction rates
• Increases smog and surface layer ozone

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Results of UV Radiation

• UV radiation causes 95 of all skin cancers
• 15-40 year lag between high UV exposure and
  cancer
• 900,000 Americans annually get skin cancer
• Melanoma growing 4 a year
• People who get 3 bad burns before age 20 are 5
  time more likely to develop melanoma

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UV results (cont)

• Best way to avoid this while ozone levels are
  low Stay out of sun during peak hours and AVOID
  the tanning salon
• Skin cancer exists in three types Squamous,
  Basal, and Melanoma
• If ozone depletion persists, skin cancer cases
  are expected to rise severely

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Fig. 20-22, p. 489
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Squamous
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Basal
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Melanoma
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Montreal Protocol

• Meeting of 36 nations to cut emissions of CFCs
• Aimed to reduce emissions by 35 between 1989 and
  2000
• Also includes halons, carbon tetrachloride, and
  methyl chloroform
• Landmark international agreement (1987)

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Alternatives to CFCs

• HCFCs
• HFCs
• Helium
• HCs

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HCs

• Pros
• Cheap
• Not patentable
• Easily made in developing countries

• Cons
• Can be flammable and poisonous if released
• Increases ground level pollution

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HCFCs

• Pros
• Break down fast
• 90 less danger to ozone
• Can be used in aerosol, refigeration, air
  conditioning, and cleaning agents

• Cons
• Greenhouse gases
• Expensive
• Health risks unknown
• Low efficiency
• Can be degraded into TFA, which can inhibit plant
  growth

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HFCs

• Pros
• Break down fast
• Do not contain ozone depleting chlorine
• Can be used in aerosol, refigeration, air
  conditioning, and cleaning agents

• Cons
• Greenhouse gas
• Flammable and toxic
• Produces methyl chloroform which can seriously
  deplete the ozone layer

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HFC Emissions
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Helium

• Pros
• Effective coolant

• Cons
• May become scarce if widely used

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HCs

• Pros
• Cheap
• Not patentable
• Easily made in developing countries

• Cons
• Can be flammable and poisonous if released
• Increases ground level pollution