1. 1. Ozone Depletion What is the ozone layer? How does it protect us? How did it come about?
2. 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. 3. Oxygen in the Atmosphere UV radiation+O2 O O + O + O2 O3 (ozone)
4. 4. UV O3 (ozone) O + O2 O + O3 (ozone) O2 O2 + O + O2 O3 (ozone) + heat +
5. 5. Dynamic Equilibrium creation of ozone breakdown of ozone
6. 6. Anthropogenic Ozone Depletion creation of ozone breakdown of ozone
7. 7. Modern Impacts to Ozone Chlorofluorocarbons (CFCs) What are they? How do they impact the ozone layer?
8. 8. Development of CFCs 1928: DuPont scientists develop CFCs ideal compounds for refrigerants and propellants WHY??
9. 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. 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. 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. 12. Original Research 1974: Rowland and Molina UV radiation+Cl Cl F F C C Cl F F + Cl- free radical
13. 13. Cl- Free Radicals Cl- free radical O3 (ozone) + O2ClO + ClO + O Cl- free radical + O2
14. 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. 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. 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. 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. 18. Total ozone Total ozone measured above Antarctica, in Dobson Units. From Horel and Geisler, 1996
19. 19. TOMS Data (corrected)
20. 20. October Average for Total Ozone over Antarctica, 1955-1995 Based on British measurements from weather balloons
21. 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. 22. Location of Stratosphere Thermosphere Exosphere Troposphere Mesosphere Stratosphere 10 km 40 km 50 km 300 km 400 km
23. 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. 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. 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. 26. Modern Impacts to Ozone (2) Methyl Bromide What is it? Challenges to Montreal Protocol
27. 27. Methyl Bromide
28. 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. 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. 30. US Strawberry Industry US supplies 80% of plants from nurseries or strawberries to world market Average consumption: 4 lb/person/yr
31. 31. Benefits of Methyl Bromide Worker safety Non-toxic Reduces need for toxic pesticides Economical Easy-to-Use Effective
32. 32. Alternatives Fumigants applied through drip irrigation Harnessing good microbes Composting for weed suppression Soil solarization Crop rotation
33. 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. 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. 35. Another potential threat? Hydrogen Fuel Cells
36. 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. 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. 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. 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. 40. Current Status of Ozone Hole Extent of ozone depletion: 1981 900,000 sq mi 200117,100,000 sq mi
41. 41. Location of Ozone Losses Ozone loss extends beyond Antarctica and Arctic Polar regions Ozone loss over US currently 5% below normal rates
42. 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. 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. 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. 45. Breakdown of Sources Sterilization 3% Aerosols 5% Refrigeration and Air Conditioning 30% Other Products 12% Solvent Cleaning Products 36%Foam Products 14%
46. 46. Success Story What characteristics define ozone depletion an environmental success story ?