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Ozone (O 3 ). Good Up High, Bad Nearby!. The Stratospheric Ozone layer. Diffuse layer containing ozone (O 3 ) molecules Reacts with UVB light from the sun Reduces skin cancer where layer is thick. Stratospheric Ozone Formation.

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ozone o 3

Ozone (O3)

Good Up High, Bad Nearby!

the stratospheric ozone layer
The Stratospheric Ozone layer

Diffuse layer containing ozone (O3) molecules

Reacts with UVB light from the sun

Reduces skin cancer where layer is thick

stratospheric ozone formation
Stratospheric Ozone Formation

In the mid-stratosphere over the tropics ozone (O3) is created:

1. Oxygen is split by UV light

  • Ozone formation
  • Ozone absorbs UV light

and is decomposed,

protecting us

the ozone hole
The Ozone Hole
  • “Stratospheric ozone depletion”
  • Sources
    • Anthropogenic (compounds containing Chlorine, such as Chlorofluorocarbons (CFCs)) used in refrigerants, propellant in aerosols, solvents.
    • Natural
natural ozone depletion
Natural Ozone Depletion
  • Ozone photolysis – degradation by sunlight
  • Normally in equilibrium with ozone formation
anthropogenic ozone depletion
Anthropogenic Ozone Depletion
  • Chlorine-containing compounds released into the atmosphere react with ozone
  • Chlorofluorocarbons (CFCs)

ex: freonCl + O3ClO + O2

ClO + O Cl + O2

net: O + O3 2O2

ozone destruction

more on the ozone hole
More on the ozone hole
  • CFCs (like freon) are stable near Earth’s surface at lower atmospheric pressure
  • In the upper atmosphere, CFCs decompose to Cl (chlorine radicals)
  • Since the poles cannot make O3, they are susceptible to O3 depletion in fall and winter when air circulation limits O3 transfer from the tropics
consequences of thinning of the ozone layer
Consequences of thinning of the ozone layer
  • Increased incidence of skin cancer in S. hemisphere
  • Cataracts in humans and animals
  • Disruption of ocean food chains (especially near S. America – phytoplankton in euphotic zone have reduced motility
  • Crop species suffer reduced productivity with increased UVB radiation

Antarctic Ozone hole, Sept, 2006

the montreal protocol 1987
The Montreal Protocol (1987)
  • Rowland and Molina discovered CFCs were destroying our “good” ozone
  • Montreal Protocol was an international treaty which aimed to phase out the use of Ozone depleting substances.
  • This is an environmental success story 
troposheric ground level ozone
Troposheric (ground level) ozone
  • Not usually emitted directly into the air (secondary pollutant)
  • Created by a chemical reaction between oxides of nitrogen (NOx) and volatile organic compounds (VOC) in the presence of sunlight.
  • O3 is unstable. It readily releases an O atom producing O2 and free O atom.
  • Free O can damage living tissues and cause respiratory problems
  • This is the pollutant that most often exceeds EPA NAAQS.
health effects of ground level ozone
Health Effects of Ground level ozone
  • Airway irritation, coughing, and pain when taking a deep breath;
  • Wheezing and breathing difficulties during exercise or outdoor activities;
  • Inflammation, which is much like a sunburn on the skin; 
  • Aggravation of asthma and increased susceptibility to respiratory illnesses like pneumonia and bronchitis
  • Permanent lung damage with repeated exposures.