chem105 ozone

8/8/2019 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 ?

chem105 ozone

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