Stratospheric Ozone Depletion

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Stratospheric Ozone Depletion
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Ozone and LIfe
In the absence of an ozone layer, life could only
evolve under water
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Formation of O3 in the Atmosphere

• O2 UV ? O O
• O O2 ? O3
• O O2 ? O3
• Overall Reaction 3O2 UV ? 2O3

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

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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.

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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.

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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.

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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.

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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.

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Monthly average ozone levels over Antarctica
1956-1994, for the month of October
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Newspaper cartoon from 1986
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Major ozone-depleting substances developed in the
past century
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O3 Chemistry
UV CFC ? releases chlorine free radical
(Cl) Cl O3 ? ClO (chlorine oxide) O2 ClO O
? Cl (free radical) O2
Cl 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
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Natural balance between ozone creation and ozone
destruction
Creation O O2 ? O3 heat
Ozone Balance
O3 creation O3 destruction
Destruction UV O3 ? O O2
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O3 Destruction
Human made compounds add to natural rates of
ozone destruction, resulting in a net loss of
stratospheric ozone
Creation O O2 ? O3 heat
Ozone Destruction
O3 creation lt O3 destruction
Destruction UV O3 ? O O2 Plus human made
compounds
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uv Protection
The 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.
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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.
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Yearly Dynamic of Ozone Layer

• http//ozonewatch.gsfc.nasa.gov/

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Consequences of high uvSkin Cancer
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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.
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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.

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Consequences of high uv- Ecosystems

• Ecosystems
• Reduced yield for some crops
• (e.g. wheat, oats)
• Decreased forest productivity
• Reduced surface phytoplankton
• affects aquatic productivity

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Consequences of high uvAntarctic Food Chain
uvb
Reduces algal growth
Krill
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Increased Smog

• Atmospheric Chemistry
• Increased smog (more uv to provide energy for
  atmospheric chemical reactions)

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Other greenhouse gases - CFCs
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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?id9556

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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/cont
  roversy.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.

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TOMS Total Ozone Monthly Averages
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Whats 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 earths
  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).

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Good News Bad News
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.
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.
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Cl and Br Sources
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Good Ozone v. Bad Ozone

• 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.

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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.