Ozone Depletion

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Chapter 26

• Ozone Depletion

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OzoneThe Basics

• A form of oxygen in which three atoms of oxygen
  occur together (O3)
• Chemically active and has a short average
  lifetime in the atmosphere
• Forms a natural layer high in the atmosphere that
  protects us from harmful ultraviolet radiation
  from the sun
• A pollutant when present in the lower atmosphere
• Rememberozone is a secondary pollutant.

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Structure of Atmosphere Ozone Concentration
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Ultraviolet Radiation and Ozone

• Ozone Shield Stratospheric ozone layer that
  absorbs ultraviolet radiation
• Ultraviolet A
• Longest length, least energetic
• Can cause some damage to living cells
• Transmitted to earth
• Ultraviolet B
• Intermediate wavelength
• Cause of Ozone Problem because O3 absorbs it
• Ultraviolet C
• Shortest wavelength/ Most energetic

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Part of the EMS showing UV radiation with
wavelengths between 0.01 and 0.4 um.
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Measurement of Stratospheric Ozone

• Dobson Unit
• Commonly used to measure the concentration of
  ozone
• 1 DU is to 1 ppb O3
• Measurements of O3 began in 1970

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Production of ozone in the Stratosphere.
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Ozone Depletion and CFCs

• Ozone depleted due to emission of CFCs
• CFCs are stable and have a long residence time in
  the atmosphere
• In stratosphere, release chlorine and enter into
  catalytic chain reaction that depletes ozone
• More UV radiation reaches lower atmosphere

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Polar Stratospheric Clouds

• Clouds that form in the stratosphere during the
  polar winter
• Polar Vortex
• Artic air masses that in the winter become
  isolated from the rest of the atmosphere and
  circulate about the pole
• Rotates counterclockwise because of the rotation
  of the earth in the Southern Hemisphere

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Hydrochlorid acid and chlorine nitrate are found
on the edges of polar stratospheric clouds
forming HCL ClONO2 ? Cl2 HNO3
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Management Issues

• Key issue is whether ozone depletion is natural
  or human-induced
• Montreal Protocol
• Collection and Reuse of CFCs
• Substitutes for CFCs
• HFCs and HCFCs
• Short-Term Adaptation to Ozone Depletion

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Any Questions?