Stratospheric Ozone Depletion

1
Stratospheric Ozone Depletion

• ES 110 Introduction to Environmental Science
• 3-5 Sep 2008

2
Ozone Depletion

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

3
Evolution of the Ozone Layer

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

4
Oxygen in the Atmosphere
5
(No Transcript)
6
Causes of Ozone destruction
Polar stratospheric clouds
Volcanic eruptions
7
Dynamic Equilibrium
creation of ozone
breakdown of ozone
8
Anthropogenic Ozone Depletion
creation of ozone
breakdown of ozone
9
Modern Impacts to Ozone I

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

10
Development of CFCs

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

11
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)

12
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

13
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

14
Original Research

• 1974 Rowland and Molina

Cl- free radical
15
Cl- Free Radicals
16
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

17
Location of Stratosphere
18
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

19
How do we know O3 concentrations?
20
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??

21
Total ozone
Total ozone measured above Antarctica, in Dobson
Units. From Horel and Geisler, 1996
22
October Average for Total Ozone over Antarctica,
1955-1995 Based on British measurements from
weather balloons
23
TOMS Data (corrected)
24
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

25
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
• Ozone loss
• Extends beyond Polar regions
• Over US currently 5 below normal

26
Why Protect the Ozone Layer?Or Negative
consequences of increased UV radiation

• Human Health
• Ecological Health
• Economic Impacts

27
(No Transcript)
28
(No Transcript)
29
Skin Melanoma Incidence by State, 2004
Source CDC. 2007. United States Cancer
Statistics 2004 Incidence and Mortality.
30
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

31
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

32
Breakdown of Sources
US Nuclear Regulatory Commission 2003
33
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

34
Current Ozone Levels
Sources WOUDC, GIT, UA Huntville, Hampton U,
NASA, NOAA
35
Location of Ozone Losses

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

36
Success Story

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