Ozone Depletion What is the “ozone layer?” How does it protect us? How did it come about?
Transcript
1. Ozone Depletion What is the ozone layer? How does it protect
us? How did it come about?
2. Evolution of the Ozone Layer Early planet history: no ozone
present UV light directly hit planets surface Oceans provided only
refuge from UV radiation
3. Oxygen in the Atmosphere UV radiation+O2 O O + O + O2 O3
(ozone)
4. UV O3 (ozone) O + O2 O + O3 (ozone) O2 O2 + O + O2 O3
(ozone) + heat +
5. Dynamic Equilibrium creation of ozone breakdown of
ozone
6. Anthropogenic Ozone Depletion creation of ozone breakdown of
ozone
7. Modern Impacts to Ozone Chlorofluorocarbons (CFCs) What are
they? How do they impact the ozone layer?
8. Development of CFCs 1928: DuPont scientists develop CFCs
ideal compounds for refrigerants and propellants WHY??
9. 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)
10. 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
11. 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
12. Original Research 1974: Rowland and Molina UV radiation+Cl
Cl F F C C Cl F F + Cl- free radical
14. 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
15. 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
16. 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
17. 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??
18. Total ozone Total ozone measured above Antarctica, in
Dobson Units. From Horel and Geisler, 1996
19. TOMS Data (corrected)
20. October Average for Total Ozone over Antarctica, 1955-1995
Based on British measurements from weather balloons
21. 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 doesnt this theory fly?
22. Location of Stratosphere Thermosphere Exosphere Troposphere
Mesosphere Stratosphere 10 km 40 km 50 km 300 km 400 km
23. 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
24. 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
25. 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
26. Modern Impacts to Ozone (2) Methyl Bromide What is it?
Challenges to Montreal Protocol
27. Methyl Bromide
28. 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%)
29. 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
30. US Strawberry Industry US supplies 80% of plants from
nurseries or strawberries to world market Average consumption: 4
lb/person/yr
31. Benefits of Methyl Bromide Worker safety Non-toxic Reduces
need for toxic pesticides Economical Easy-to-Use Effective
32. Alternatives Fumigants applied through drip irrigation
Harnessing good microbes Composting for weed suppression Soil
solarization Crop rotation
33. 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
34. 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
35. Another potential threat? Hydrogen Fuel Cells
36. 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)
37. Hydrogen chemistry Hydrogen is lightrises 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
38. 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
39. 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
40. Current Status of Ozone Hole Extent of ozone depletion:
1981 900,000 sq mi 200117,100,000 sq mi
41. Location of Ozone Losses Ozone loss extends beyond
Antarctica and Arctic Polar regions Ozone loss over US currently 5%
below normal rates
42. 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
43. Impacts of Ozone Depletion Human Health Skin cancer
Melanoma Cataracts Immune system function Increased incidence,
severity and duration of infectious diseases Reduced efficacy of
vaccinations Ecological Health Pathogen locally up & down
Biodiversity locally up & down Aquatic organisms adversely
impacted Decreased biomass productivity Polar systems especially
vulnerable
44. 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
45. Breakdown of Sources Sterilization 3% Aerosols 5%
Refrigeration and Air Conditioning 30% Other Products 12% Solvent
Cleaning Products 36%Foam Products 14%
46. Success Story What characteristics define ozone depletion
an environmental success story ?