Ozone depletion - PowerPoint Presentation

					Stratospheric Ozone Depletion

ES 110: Introduction to Environmental Science

                3-5 Sep 2008
Ozone Depletion

What is the ―ozone layer?‖
 How does it protect us?
 How did it come about?
  Evolution of the Ozone Layer
Early planet history:
  – no ozone present

  – UV light directly
    hit planet‘s surface

  – Oceans provided
    only refuge from
    UV radiation
Oxygen in the                 Atmosphere
                                      O
                         UV
    O2            +   radiation           +

                                        O



O        +
             O2                   O3 (ozone)
                           O          +
UV       +      O3
              (ozone)                      O2



O    +        O3           O2         +    O2
         (ozone)

                                  +
O    +       O2           O3
                        (ozone)
                                          heat
    Causes of Ozone destruction




Polar stratospheric clouds   Volcanic eruptions
          Dynamic Equilibrium
creation of ozone




                           breakdown of
                               ozone
   Anthropogenic Ozone Depletion
creation of ozone




                          breakdown of
                              ozone
    Modern Impacts to Ozone I

     Chlorofluorocarbons (CFCs)

• What are they?
• How do they impact the ozone layer?
        Development of CFCs
1928:     DuPont scientists develop CFCs
          ―ideal compounds‖ for
          refrigerants and propellants

                 WHY??
                 CFCs as Refrigerants
Traditional Refrigerants                     vs.   CFCs
(ammonia, sulfur dioxide, methyl chloride)

- Highly volatile                            - Non-flammable

- Caustic and toxic                          - Non-toxic

- Remove heat through                        - Trap heat
vaporization of liquefied gas                (good insulators!)
(only adequate as refrigerants)              - Inexpensive
- Expensive                                  - Light
- Heavy (transport, storage)                 -Extremely stable,
                                             inert
Key physical characteristics of CFCs
 • Light weight
 • Extremely stable or ―inert‖


 What are the consequences of these features?


 • CFCs likely to migrate upwards
 • Too light to precipitate out with rainfall
 • 5-15 years to migrate to stratosphere
         Marketing of CFCs
1958: DuPont releases CFCs on the market
      commercially
1971: James Lovelock speculates that CFCs
      put into the atmosphere may still be
      present
1973: Mario Molina and F. Sherry Roland
      start to investigate
                    Original Research
    1974:               Rowland and Molina
                                                         Cl
                                                 C
                                             F
              Cl
                              UV                     F
      C
                         + radiation
F                  Cl                            +
          F                                         Cl-
                                                   ―free
                                                 radical‖
                 Cl-   ―Free Radicals‖…

             +                                      +
     Cl-                 O3
                                       ClO                   O2
―free radical‖       (ozone)



                 +                              +
                     O
      ClO                           Cl-                 O2
                               ―free radical‖
          In the news…
1974:   Molina and Rowland publish their
        hypothesis in Nature.
        New York Times runs front page
        DuPont responds with study
        showing that CFCs in troposphere
        are benign
            Location of Stratosphere


Exosphere       400 km

Thermosphere    300 km



Mesosphere      50 km
Stratosphere    40 km
                10 km
Troposphere
   Based on theory alone…

1979:   The FDA, EPA ban non-essential
        uses of CFCs !

  First time substance EVER banned in
     US without direct proof of harm

1982:   20 other countries join US in ban
How do we know O3 concentrations?
 The challenge of scientific evidence
• British science teams in Antarctica study stratospheric
  ozone using weather balloons and observe:
   – 20% reduction in ozone layer (1982)
   – 30% reduction in ozone layer (1983)
   – 50% reduction in ozone layer (1985)

• US scientists relying on new TOMS satellite
  measurements (Total Ozone Mapping Spectometer)
  observe:
   –   No reduction (1982)
   –   No reduction (1983)
   –   No reduction (1984)
   –   Finally recognize need to recalibrate equipment and validate 50%
       reduction in ozone layer! (1985)

              WHY THE SCIENTIFIC SNAFUS??
                        Total ozone




Total ozone measured above Antarctica, in Dobson Units. From Horel and Geisler, 1996
October Average for
Total Ozone over
Antarctica, 1955-1995




Based on British
measurements from
weather balloons
TOMS Data (corrected)
    Landmark: Montreal Protocol
UN hosts meeting in Montreal in 1988

•    45 Nations sign to reduce CFC use by
     50% by year 2000.
•    Developing countries‘ efforts to reduce
     CFC use would be ‗subsidized‘
Lasting impacts of Montreal Protocol…
 Follow up meetings result in:
 1992: Industrialized nations—total ban by 2000
       Developing nations—ban by 2010, with
       assistance from developed nations
       US agrees to complete phaseout by 1996;
       DuPont to halt production by 1997
 1995: Rowland and Molina receive Nobel Prize
     Ozone loss:
 •     Extends beyond Polar regions
 •     Over US: currently 5% below normal
   Why Protect the Ozone Layer?
                       Or
 Negative consequences of increased UV radiation


Human Health

Ecological Health

Economic Impacts
                        Skin Melanoma Incidence by State, 2004




Source: CDC. 2007. United States Cancer Statistics: 2004 Incidence and Mortality.
     Impacts of Ozone Depletion
    Human Health              Ecological Health

• Skin cancer                • Pathogens variable locally
• Melanoma                   • Local biodiversity variable
• Cataracts                  • Aquatic organisms
• Immune system function       adversely impacted
• Increased incidence,       • Decreased biomass
  severity and duration of     productivity
  infectious diseases        • Polar systems especially
• Reduced efficacy of          vulnerable
  vaccinations
    Impacts of Ozone Depletion
                Economic Concerns
• Plastics
   – designed with stabilizers to withstand UV radiation of
     certain intensity
   – replacement of key medical equipment and supplies,
     decreased lifespan of plastics
• Manufacturing practices
• Agriculture
• Consumer costs and burdens
Breakdown
of Sources




             US Nuclear Regulatory Commission 2003
Current Rate of Ozone Depletion

•   Baseline ozone levels reduced 99% of total UV
•   Decrease in rate of ozone depletion (since 1997)
•   Slowing of buildup of harmful Cl- from CFCs
•   Ozone hole is still growing, but…
       Models anticipate restoration of ―normal‖
       balance of ozone in stratosphere by 2050
Current Ozone Levels




   Sources: WOUDC, GIT, UA Huntville, Hampton U, NASA, NOAA
      Location of Ozone Losses


    Ozone loss:
•     Extends beyond Polar regions
•     Over US: currently 5% below normal
           Success Story


What characteristics define ozone depletion
  “an environmental success story ?”

				
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