Ozone Depletion

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Ozone Depletion

• What is the ozone layer?
• How does it protect us?
• How did it come about?

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Evolution of the Ozone Layer

• Early planet history
• no ozone present
• UV light directly hit planets surface
• Oceans provided only refuge from UV radiation

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Oxygen in the Atmosphere
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(No Transcript)
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Dynamic Equilibrium
creation of ozone
breakdown of ozone
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Anthropogenic Ozone Depletion
creation of ozone
breakdown of ozone
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Modern Impacts to Ozone Layer I

• Chlorofluorocarbons (CFCs)
• What are they?
• How do they impact the ozone layer?

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Development of CFCs

• 1928 DuPont scientists develop CFCs
• ideal compounds for
• refrigerants and propellants
• WHY??

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CFCs as Refrigerants

• vs. CFCs
• Non-flammable
• Non-toxic
• Trap heat (good insulators!)
• Inexpensive
• Light
• Extremely stable, inert

• Traditional Refrigerants
• (ammonia, sulfur dioxide, methyl chloride)
• Highly volatile
• Caustic and toxic
• Remove heat through vaporization of
  liquefied gas (only adequate as
  refrigerants)
• Expensive
• Heavy (transport, storage)

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Key physical characteristics of CFCs

• Light weight
• Extremely stable or inert

• CFCs likely to migrate upwards
• Too light to precipitate out with rainfall
• 5-15 years to migrate to stratosphere

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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

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Original Research

• 1974 Rowland and Molina

Cl- free radical
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Cl- Free Radicals
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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

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Location of Stratosphere
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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

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The science struggles to catch up

• 1982 British science teams in Antarctica
  observe 20 decline in O3 layer using
  weather balloons
• But, US scientists relying on TOMS (Total
  Ozone Mapping Spectrometer) satellite
  measurements observe no change

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Scientific Evidence

• 1983 British scientists observe 30
  reduction in ozone layer.
• US scientists observe NO reduction.
• 1985 British observe 50 reduction.
• US observes NO reduction.
• Late 1985 US re-evaluates and confirms.
• WHY THE SCIENTIFIC SNAFUS??

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

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Lasting impacts of Montreal Protocol

• Follow up meetings result in
• 1992 Industrialized nationstotal ban by 2000
• Developing nationsban 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

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Modern Impacts to Ozone (2)

• Methyl Bromide
• What is it?
• Challenges to Montreal Protocol

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Methyl Bromide
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Uses of Methyl Bromide

• US 60 million lbs /yr
• Agricultural (75)
• Strawberries
• Stored products (11)
• Sterilization
• Pest management (6)
• Termite removal
• Flame retardants (6)
• Chemical production (2)

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Schedule for Elimination

• 1991 Designated Class I ozone depleter in
  Montreal Protocol
• 1997 Agreed to following schedule
• Developed Countrieselimination by 2005
• Developing Countrieselimination by 2015
• Requests for Critical Use Exemptions

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US Strawberry Industry

• Average consumption 4 lb/person/yr
• More importantly
• US supplies 80 of nursery plants and
  strawberries directly to world market

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Benefits of Methyl Bromide

• Worker safety
• Non-toxic
• Reduces need for toxic pesticides
• Economical
• Easy-to-Use
• Highly effective

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Alternatives

• Fumigants applied through drip irrigation
• Harnessing good microbes
• Composting for weed suppression
• Soil solarization
• Crop rotation

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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

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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
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Another potential threat?
Hydrogen Fuel Cells
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Production of Hydrogen

• Currently
• More than 20 of all H manufactured leaks into
  atmosphere
• Future
• Possible to reduce loss of H to 10
• Estimate could see 60 million tons H lost / yr,
  if convert to hydrogen economy (Tromp et al. 2003
  Science 3001740)
• Roughly doubles current input from all sources

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Hydrogen chemistry

• Lightrises rapidly to stratosphere
• Reacts with oxygenforms water

• Atmospheric wetness cools the lower
  stratosphere around Poles
• Water vapor and cool temperatures are catalysts
  for release of free radicals

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Spatial and Temporal Patterns

• Poles have greater ozone loss than other regions
• Colder
• Wetter more vapor formation
• Polar vortex
• Particularly severe in polar spring (October)
• Increased hydrogen would enhance this phenomenon

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Hydrogen Economy

• Atmospheric hydrogen is a catalyst only
• Problematic only if ozone depleting chemicals
  still present in stratosphere
• Depends upon ifand how quicklyhydrogen economy
  introduced

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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

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

• Ozone loss
• Extends beyond Polar regions
• Over US currently 5 below normal rates

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Breakdown of Sources
US Nuclear Regulatory Commission 2003
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Impacts of Ozone Depletion

• Skin cancer
• Melanoma
• Cataracts
• Immune system function
• Increased incidence, severity and duration of
  infectious diseases
• Reduced efficacy of vaccinations

• Pathogens variable locally
• Local biodiversity variable
• Aquatic organisms adversely impacted
• Decreased biomass productivity
• Polar systems especially vulnerable

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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

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Success Story

• What characteristics define ozone depletion
• an environmental success story ?