stratospheric ozone depletion

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Stratospheric Ozone Depletion

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Stratospheric Ozone Depletion. Ozone and LIfe. In the absence of an ozone layer, life could only evolve under water. Formation of O 3 in the Atmosphere. O 2 + UV  O + O O + O 2  O 3 O + O 2  O 3 Overall Reaction: 3O 2 + UV  2O 3. Atmospheric gradient. - PowerPoint PPT Presentation

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Page 1: Stratospheric Ozone Depletion

Stratospheric Ozone Depletion

Page 2: Stratospheric Ozone Depletion

Ozone and LIfe

In the absence of an ozone layer, life could only evolve under water

Page 3: Stratospheric Ozone Depletion

Formation of O3 in the Atmosphere

• O2 + UV O + O

• O + O2 O3

• O + O2 O3

• Overall Reaction: 3O2 + UV 2O3

Page 4: Stratospheric Ozone Depletion

Most of the ozone present in the atmosphere (~90%) is located in the stratosphere. Atmospheric concentrations of ozone average 12 parts per million (ppm).

Atmospheric gradient

Page 5: Stratospheric Ozone Depletion

How Does Stratospheric Ozone Protect Us?

• O3 “absorbs” UV-B radiation and “uses up” its energy, converting it to harmless heat

• UV + O3 O + O2

• Some of the free oxygen atoms combine with other ozone to form oxygen: O + O3 O2 + O2

• Or, they recombine with existing oxygen to re-form ozone: O + O2 O3 + heat

• The ozone layer does not really “shield” us or “reflect” harmful UV-B radiation, but rather “uses up” its energy before it can reach earth

Page 6: Stratospheric Ozone Depletion

Timeline of CFC Development• 1928: DuPont scientists first develop CFCs as a

refrigerant and a propellant.

• CFCs believed ideal: non-flammable, non-toxic, good insulator, inexpensive, stable (inert), light.

• However, because CFCs are inert and light, they do not react in the lower atmosphere, and can be carried by updrafts to the stratosphere where intense UV radiation can break them apart.

• It can take 5-15 years for a CFC molecule to migrate to the stratosphere.

Page 7: Stratospheric Ozone Depletion

Timeline of CFC Development (cont’)• 1951: DuPont begins mass production of CFCs

• 1971: Scientist James Lovelock first speculates that CFCs released to the atmosphere could still be there. (Where is Away??)

• 1973: Atmospheric scientists Mario Molina and F. Sherry Rowland hypothesize that CFCs could be reaching the stratosphere, where they can be broken apart and a single chlorine atom could contribute to the destruction of 100,000 ozone molecules.

• 1974: Molina and Rowland publish their theory in the journal Nature; the story is picked up by a science writer at The New York Times and published on the front page.

• 1974: DuPont responds with their own study claiming that CFCs are safe in the troposphere; calls for more research.

Page 8: Stratospheric Ozone Depletion

Timeline of CFC Development (cont’)

• 1975: 200% increase in CFC use from 1968-1975, annual growth in consumption of 10-20%/year.

• 1979: The FDA and the EPA ban “non-essential” uses of CFCs in aerosol cans. THE FIRST TIME A SUBSTANCE WAS BANNED WITHOUT DEFINITIVE PROOF OF HARM.

• 1982: 20 other nations join U.S. ban on non-essential uses.

Page 9: Stratospheric Ozone Depletion

Early Warnings of Ozone Depletion• 1982: British scientific team in Antarctica using ground-

based instruments announce 20% decline in O3 levels in the stratosphere (in their spring).

• 1982: U.S. team using satellite-based Total Ozone Mapping Spectrometer (TOMS) reports no ozone loss over Antarctica.

• 1983: British team reports a 30% decline in ozone levels, U.S. team contradicts.

• 1985: British team reports a 50% decline in ozone levels. At first, U.S. team contradicts, re-check their instruments and then confirm the British findings.

• Acknowledgement of “ozone hole” in the media creates public and political alarm.

Page 10: Stratospheric Ozone Depletion

Early Warnings (cont’)• 1986: Australian government announces doubling of skin

cancer cases in previous 10 years.• 1986: DuPont scientists speculate that tropospheric (“bad”)

ozone will migrate to stratosphere to “fill” the hole.• 1987: Preliminary research indicates that loss of ozone over

Antarctica due primarily to human emissions of ozone-depleting chemicals.

• 1987: UN holds meetings in Montreal, and 45 nations sign the Montreal Protocol to reduce CFC use by 50% by the year 2000. Protocol is ratified in 1989.

• 1988: DuPont continues to argue that CFCs are safe to use, and initially oppose the Montreal Protocol. However, by year end they announce an impending phase-out of CFC production.

Page 11: Stratospheric Ozone Depletion

1956-1994, for the month of October

Monthly average ozone levels over

Antarctica

Page 12: Stratospheric Ozone Depletion

Newspaper cartoon from 1986

Page 13: Stratospheric Ozone Depletion

OZONE DEPLETING CHEMCIALS• CONTAIN: chlorine or bromine

• CFC’s: Chlorofluorocarbons, (“Freon”) has caused most damage– used in air conditioners, refrigerators, aerosols, foams– no longer used for aerosols, still widely used as refrigerants.

• CCl 4, methyl chloroform: methyl bromide, solvents used in dry cleaning

 • Halons: used in fire extinguishers, refrigerants and foams • Avg Retetion Time of ozone depleting substances = 75 – 150

years. Ozone depletion will continue until the mid 21st century

Page 14: Stratospheric Ozone Depletion

Major ozone-depleting substances developed in

the past centurya type of halogenated halogenated

organic gasesorganic gases

Page 15: Stratospheric Ozone Depletion

UV + CFC releases “chlorine free radical” (Cl)

Cl + O3 ClO (chlorine oxide) + O2

ClO + O Cl (free radical) + O2Cl free radical destroys O3, creating ClO, which reacts with free atomic oxygen (O) to create another Cl free radical and start the process all over again. One CFC molecule can destroy an estimated 100,000 molecules of O3

O3 Chemistry

Page 16: Stratospheric Ozone Depletion

OzoneBalance

Creation

O + O2 O3 + heat

Destruction

UV + O3 O + O2

O3 creation = O3 destruction

Natural balance between ozone creation and ozone destruction

Page 17: Stratospheric Ozone Depletion

Human – made compounds add to natural rates of ozone destruction, resulting in a

net loss of stratospheric ozone

OzoneDestruction

Creation

O + O2 O3 + heat

Destruction

UV + O3 O + O2

Plus human – made compounds

O3 creation < O3 destruction

O3 Destruction

Page 18: Stratospheric Ozone Depletion

uv ProtectionThe ozone layer absorbs and uses up most incoming UV-B radiation before it can strike the surface of the earth. UV-B radiation can cause skin cancer, cataracts, and reduced immune system as well as harming plant life.

Page 19: Stratospheric Ozone Depletion

Ozone shields life on land from damaging UV radiation ( of 0.1 m - 0.4 m)

UVA= .4-.32 m--least energetic, not affected by stratospheric ozoneUVB = .32-.28 m--can cause damage, mostly absorbed by ozone* UVC = .28-.1 m --most energetic, absorbed in stratosphere, doesn't reach Earth's surfaceOzone depletion allows more UVB – this is the problem

Page 20: Stratospheric Ozone Depletion

Daily Dynamic of Ozone Layer

What is a Dobson Unit? The Dobson Unit (DU) is the unit of measure for total ozone. If you were to take all the ozone in a column of air stretching from the surface of the earth to space, and bring all that ozone to standard temperature (0 °Celsius) and pressure (1013.25 millibars, or one atmosphere, or “atm”), the column would be about 0.3 centimeters thick. Thus, the total ozone would be 0.3 atm-cm. To make the units easier to work with, the “Dobson Unit” is defined to be 0.001 atm-cm. Our 0.3 atm-cm would be 300 DU.

Page 21: Stratospheric Ozone Depletion

• http://ozonewatch.gsfc.nasa.gov/

Yearly Dynamic of Ozone Layer

Page 22: Stratospheric Ozone Depletion

Consequences of high uvSkin Cancer

Page 23: Stratospheric Ozone Depletion

Consequences of high uvCataracts

• Cataracts may be a more widespread health effect of ultraviolet-B radiation than skin cancers, because all

populations will be affected.

Cataracts occur when the lens inside your eye becomes increasingly opaque resulting in 'misty' or 'foggy' vision.

Page 24: Stratospheric Ozone Depletion

Consequences of high uvWeakened Immune System

• UV-B irradiation has suppressive effect on immune system

• Skin is an immune organ - certain types of lymphoid cells found predominantly in skin

• Skin-associated lymphoid tissue responds to antigens that enter the

body by way of the skin. – This cutaneous immune surveillance

system is vital to our ability to resist

invasions by infectious agents.

Page 25: Stratospheric Ozone Depletion

Consequences of high uv- Ecosystems

• Ecosystems

– Reduced yield for some crops• (e.g. wheat, oats)

– Decreased forest productivity– Reduced surface phytoplankton

• affects aquatic productivity

Page 26: Stratospheric Ozone Depletion

Consequences of high uvAntarctic Food Chain

uvb

Reduces algal growth

Krill

Page 27: Stratospheric Ozone Depletion

Increased Smog

• Atmospheric Chemistry

– Increased smog (more uv to provide energy for atmospheric chemical reactions)

Page 28: Stratospheric Ozone Depletion

Other greenhouse gases - CFCs

Page 29: Stratospheric Ozone Depletion

Northern Latitudes?

• Southern “hole” now greater than ever• “hole” migrates toward equator• hole now instead over Arctic

– usually less (less land area – need frozen H2O)

– but, more CFCs

– Europe – O3 decline 8% in last 10 yrs.

– winter decline over U.S. – 5%– hole never expected over U.S. – now observed – http://visibleearth.nasa.gov/view_rec.php?id=9556

Page 30: Stratospheric Ozone Depletion

Science and Politics of Ozone Depletion• 1990: Follow-up meeting in London leads to new goal of complete CFC

phase-out in developed countries by 2000 and in developing countries by 2010.

• 1992: Follow up meeting in Copenhagen calls for complete phase-out by 1996, DuPont promises to halt production by 1997.

• 1992: Rush Limbaugh publishes book claiming that the ozone depletion “crisis” is a hoax. (see also http://www.nas.nasa.gov/About/Education/Ozone/controversy.html)

• 1995: Congressional hearings also challenge ozone science.• 1995: Ironically, Rowland and Molina receive Nobel Prize in chemistry

for their early work on ozone depletion.• 1996: Satellite study provides definitive confirmation of human role in

stratospheric ozone depletion. Junk science continues.• 1996: CFC ban begins, but black market appears.

Page 31: Stratospheric Ozone Depletion

TOMS Total Ozone Monthly Averages

Page 32: Stratospheric Ozone Depletion

What’s Happening to the Ozone Layer Today?• Stratospheric ozone concentrations have stabilized, and

concentrations of Cl in the stratosphere are nearing their peak. However, atmospheric concentrations of bromine compounds (another ozone depleter) are still increasing.

• Stratospheric ozone levels over the mid-latitudes of the northern hemisphere are 3-6% below pre-1980 levels, with higher losses in the winter/spring and losses of 1-3% in summer/fall.

• Levels of UV-B radiation reaching the earth’s surface continue to increase, although this trend is expected to reverse itself as the ozone layer is replenished.

• Phase-out of CFC use is almost complete. CFC substitutes like HCFCs and HFCs also deplete the ozone layer, but at only a fraction (1-15%) of the rate of CFCs because they react in the lower atmosphere.

• Recent years have seen record levels of ozone depletion over Antarctica due to atmospheric conditions (polar stratospheric clouds).

Page 33: Stratospheric Ozone Depletion

The Good News

To the extent that CFCs and other ozone-depleting

chemicals are phased out, the ozone layer

should be able to replenish itself by the

middle of this century.

The Bad News

We continue to use other ozone-depleting

chemicals besides CFCs. Recently, the Bush administration

sought to exempt U.S. farmers from a

Montreal Protocol requirement to phase-

out use of the pesticide methyl bromide.

Good News Bad News

Page 34: Stratospheric Ozone Depletion

Cl and Br Sources

Page 35: Stratospheric Ozone Depletion

Remember!

• Difference between good ozone and bad ozone.

•Stratospheric ozone depletion is not the same as global warming. These are two different, albeit related, environmental problems.

Good Ozone v. Bad Ozone

Page 36: Stratospheric Ozone Depletion

Lessons Learned from the Ozone Depletion Story

• There is no away (TINA).• Scientific uncertainty is no excuse for inaction.

Uncertainty will almost always be present.• Not all science is created equal.• Standard media ethics that call for “both sides of

the story” can complicate coverage of some environmental issues.

• The “burden of proof” typically rests with environmentalists.

• Global problems require global solutions.