Ozone Depletion by n4qrl4DA

VIEWS: 36 PAGES: 46

									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
          Dynamic Equilibrium
creation of ozone




                           breakdown of
                               ozone
   Anthropogenic Ozone Depletion
creation of ozone




                          breakdown of
                              ozone
     Modern Impacts to Ozone

     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
          CFCs as Propellants
• Light weight
• Extremely stable or ―inert‖

  What are the consequences of these two
        physical characteristics?

• 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
  High Risk and Political Savvy
1975: 200% increase in CFC use from
      1968, only eight years
1979: The FDA, EPA ban non-essential
      uses of CFCs !
     First time substance EVER banned
     without direct proof of harm
1982: 20 other countries join US in ban of CFCs
        Scientific Controversies

1982:      British science teams in Antarctica
           observe 20% decline in O3 layer
           US scientists relying on TOMS
           (Total Ozone Mapping
           Spectrometer) measurements from
           space claim to observe nothing
        Scientific Evidence
1983:   British scientists observe 30%
        reduction in ozone layer.
        US scientists claims no reduction.
1985:   British observe 50% reduction.
        US claims no reduction.
        US re-tests and confirms.
        WHY THE SCIENTIFIC SNAFUS??
                       Total ozone




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




Based on British
measurements from
weather balloons
    Understanding the Science
1986:      DuPont scientists continue to argue
           that tropospheric ozone (smog)
           will migrate up and ―fill the ozone
           hole‖ in the stratosphere

Why doesn‘t this theory fly?
            Location of Stratosphere


Exosphere       400 km

Thermosphere    300 km



Mesosphere      50 km
Stratosphere    40 km
                10 km
Troposphere
  Montreal Protocol Landmark
1987:   2 yrs of intensive research reveal
        that ozone hole is anthropogenic
1988:   UN hold meeting in Montreal
        45 Nations sign to reduce CFC use
        by 50% by year 2000.
        Developing countries‘ efforts
        would be ‗subsidized‘
          Two steps forward…
1990- 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
             One step back…
1995: Congress challenges ozone science:
           Junk science gains credibility
           despite scientific consensus of
           anthropogenic causes of O3 depletion
1996: Ban begins but black market for CFCs appear
                      WHY?
  CFC substitutes (HFC) break down faster, but still
  pose problems for ozone depletion
  Modern Impacts to Ozone (2)


          Methyl Bromide

• What is it?
• Challenges to Montreal Protocol
Methyl Bromide
        Uses of Methyl Bromide
60 million lbs /yr in US

• Agricultural (75%)
   – Strawberries
• Stored products (11%)
• Flame retardants (6%)
• Pest management (6%)
   – Termite removal
• Chemical production (2%)
        Schedule for Elimination
1991:      Designated Class I ozone depleter
           in Montreal Protocol
1997:      Agreed to following schedule
Developed Countries—elimination by 2005
Developing Countries—elimination by 2015
  Requests for ―Critical Use Exemptions‖
       US Strawberry Industry
• US supplies 80% of
  plants from nurseries
  or strawberries to
  world market

• Average consumption:
    4 lb/person/yr
    Benefits of Methyl Bromide
• Worker safety
  – Non-toxic
  – Reduces need for toxic
    pesticides
• Economical
• Easy-to-Use
• Effective
                 Alternatives
• Fumigants applied
  through drip irrigation
• Harnessing ―good
  microbes‖
• Composting for weed
  suppression
• Soil solarization
• Crop rotation
Effectiveness
• Other fumigants do
  not work
• Worker health issue
• Lower yields
• Loss of nurseries
   – Even organic farms get
     plant stocks from
     nurseries that rely on
     methyl bromide
            CFCs vs MEBr
Why did one industry eventually support
ban while another is struggling and begging
for exemptions?


Methyl Bromide                    CFCs
-no viable alternatives   -DuPont developed HFCs
  Another potential threat?
Hydrogen Fuel Cells
      Production of Hydrogen
• Anticipate that 10% of all hydrogen
  manufactured will leak into the atmosphere
  during production, storage and transport.
• Current loss is higher
• Estimate: 60 million tons / year
• Roughly doubles current input (all sources)
         Hydrogen chemistry
• Hydrogen is light—rises rapidly to
  stratosphere
• Reacts with oxygen to form water
• A ―wetter‖ atmosphere would cool the
  lower stratosphere, especially around Poles
• Increase in water vapor is catalyst for ozone
  depletion by freeing Cl free radicals
  Spatial and Temporal Patterns
• Poles have greater ozone loss than other
  regions:
  – Colder
  – More vapor formation
  – Also: polar vortex
• Particularly severe in polar spring (October)
• Increased hydrogen would enhance this
  phenomenon
Ozone Layer Impacts
          • 7-8% depletion around
            Poles anticipated
          • Depends upon if and
            how quickly hydrogen
            economy introduced
          • If >50 years, may not
            be critical issue
          • Possible work to
            lessen H leakage
Current Status of Ozone Hole

    Extent of ozone depletion:
     1981— 900,000 sq mi
     2001—17,100,000 sq mi
   Location of Ozone Losses

Ozone loss extends beyond Antarctica and
Arctic Polar regions
Ozone loss over US currently 5% below
normal rates
Current Rate of Ozone Depletion

• 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
      Impacts of Ozone Depletion
        Human Health                 Ecological Health
•   Skin cancer                •   Pathogen locally up &
•   Melanoma                       down
•   Cataracts                  •   Biodiversity locally up &
•   Immune system function         down
•   Increased incidence,       •   Aquatic organisms
    severity and duration of       adversely impacted
    infectious diseases        •   Decreased biomass
•   Reduced efficacy of            productivity
    vaccinations               •   Polar systems especially
                                   vulnerable
    Impacts of Ozone Depletion
                        Economic
• 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
A ero so ls
    5%                Other P ro ducts
                            12%




                                         So lvent Cleaning
                                             P ro ducts
         Fo am P ro ducts                       36%
               14%




                            Refrigeratio n
                              and A ir
                            Co nditio ning
                                 30%

                                                             Sterilizatio n
                                                                  3%
           Success Story


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

								
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