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Chem105 Ozone
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Transcript of Chem105 Ozone
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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 LayerEarly planet history:
no ozone present
UV light directly
hit planets surface
Oceans providedonly refuge from
UV radiation
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Oxygen in the AtmosphereUV
radiation+O2
O
O
+
O +O2 O3 (ozone)
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UV O3(ozone)
O +
O2
O + O3(ozone)
O2 O2+
O + O2O3
(ozone)
+
heat
+
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Dynamic Equilibriumcreation of ozone
breakdown ofozone
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Anthropogenic Ozone Depletioncreation of ozone
breakdown of
ozone
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Modern Impacts to Ozone
Chlorofluorocarbons (CFCs)
What are they?
How do they impact the ozone layer?
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Development of CFCs1928: 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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CFCs as Propellants
Light weight Extremely stable or inert
What are the consequences of these twophysical characteristics?
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 CFCs1958: DuPont releases CFCs on the market
commercially
1971: James Lovelock speculates that CFCsput into the atmosphere may still bepresent
1973: Mario Molina and F. Sherry Rolandstart to investigate
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Original Research1974: Rowland and Molina
UV
radiation+Cl
Cl
F
F
C
C
Cl
F
F
+
Cl-
free
radical
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Cl-
Free Radicals
Cl-
free radicalO3(ozone)
+
O2ClO+
ClO
+O
Cl-
free radical
+
O2
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In the news1974: 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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High Risk and Political Savvy1975:200% increase in CFC use from
1968, only eight years
1979:The FDA, EPA ban non-essentialuses of CFCs !
First time substance EVER banned
without direct proof of harm
1982:20 other countries join US in ban of CFCs
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Scientific Controversies
1982: British science teams in Antarctica
observe 20% decline in O3 layer
US scientists relying on TOMS
(Total Ozone Mapping
Spectrometer) measurements fromspace claim to observe nothing
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Scientific Evidence1983: British scientists obser ve 30%
reduction in ozone layer.
US scientists claims no reduction.
1985: British obser ve 50% reduction.
US claims no reduction.
US re-tests 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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TOMS Data (corrected)
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October Average for
Total Ozone over
Antarctica, 1955-1995
Based on British
measurements from
weather balloons
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Understanding the Science1986: 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?
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Location of Stratosphere
Thermosphere
Exosphere
Troposphere
MesosphereStratosphere
10 km
40 km
50 km
300 km
400 km
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Montreal Protocol Landmark1987: 2 yrs of intensive research reveal
that ozone hole is anthropogenic
1988: UN hold meeting in Montreal
45 Nations sign to reduce CFC useby 50% by year 2000.
Developing countries effortswould be subsidized
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Two steps forward1990- 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
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One step back1995: Congress challenges ozone science:
Junk science gains credibility
despite scientific consensus ofanthropogenic causes of O3 depletion
1996: Ban begins but black market for CFCs appear
WHY?
CFC substitutes (HFC) break down faster, but stillpose problems for ozone depletion
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Modern Impacts to Ozone (2)
Methyl Bromide
What is it?
Challenges toMontreal Protocol
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Methyl Bromide
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Uses ofMethyl Bromide60 million lbs /yr in US
Agricultural (75%)
Strawberries
Stored products (11%)
Flame retardants (6%)
Pest management (6%)
Termite removal
Chemical production (2%)
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Schedule forElimination1991: 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 US supplies 80% of
plants from nurseries
or strawberries toworld market
Average consumption:
4 lb/person/yr
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Benefits ofMethyl Bromide Worker safety
Non-toxic
Reduces need for toxicpesticides
Economical
Easy-to-Use
Effective
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Alternatives Fumigants applied
through drip irrigation
Harnessing goodmicrobes
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 getplant stocks from
nurseries that rely on
methyl bromide
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CFCs vs MEBrWhy 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?ydrogen FuelCells
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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)
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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 watervapor is catalyst for ozone
depletion by freeing Cl free radicals
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Spatial and Temporal Patterns Poles have greater ozone loss than other
regions:
ColderMore vapor formation
Also: polarvortex
Particularly severe in polar spring (October)
Increased hydrogen would enhance thisphenomenon
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Ozone Layer Impacts 7-8% depletion around
Poles anticipated
Depends upon if andhow quickly hydrogeneconomy introduced
If >50 years, may not
be critical issue Possible work to
lessen H leakage
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Current Status of Ozone Hole
Extent of ozone depletion:
1981 900,000 sq mi
200117,100,000 sq mi
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Location of Ozone Losses
Ozone loss extends beyond Antarctica and
Arctic Polar regions
Ozone loss over US currently 5% below
normal rates
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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
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Impacts of Ozone DepletionHumanHealth
Skin cancer
Melanoma
Cataracts
Immune system function
Increased incidence,severity and duration of
infectious diseases Reduced efficacy of
vaccinations
EcologicalHealth
Pathogen locally up &down
Biodiversity locally up &down
Aquatic organismsadversely impacted
Decreased biomassproductivity
Polar systems especiallyvulnerable
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Impacts of Ozone DepletionEconomic
Plastics
designed with stabilizers to withstand UV radiation ofcertain intensity
replacement of key medical equipment and supplies,decreased lifespan of plastics
Manufacturing practices
Agriculture
Consumer costs and burdens
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Breakdown of Sources
Sterilization
3%
Aerosols
5%
Refrigeration
and A ir
Conditioning
30%
Other Pro ducts
12%
Solvent Cleaning
Products
36%Foam Products
14%
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Success Story
What characteristics define ozone depletion
an environmental success story ?