Ozone Depletion and CFCs

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Ozone Depletion and CFCs

• Madeline Midgett and Anna Lovelace

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Polar Ozone Holes

• Definition parts in the Antarctic stratosphere
  where ozone concentration is depleted
• Recently ozone levels have
• reached 33 of 1975 levels
• Occurs during Antarctic Spring
• (Sept.-Dec.) with strong westerly
• winds

Largest Antarctic ozone hole ever, Sept, 2006
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• Circulating air creates
• a stream of air, called the polar vortex in
  winter
• Trapped air becomes
• very cold during the
• polar night, forming
• polar stratospheric
• clouds (PSCs)

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These ice particles provide a surface for
reactions
HCl from the earth, and chlorine nitrate produce
chlorine molecules
Spring sunlight breaks chlorine molecules into
atoms
Chlorine atoms destroy ozone
Chlorine monoxide also destroys ozone
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CFCs (chlorofluorocarbons)

• First made in the 1930s, CFCs are colorless,
  odorless, inert, nontoxic, noncombustible,
  readily liquefiable, and volatile
• Used as coolants in
• refrigerators and air
• conditioners, disposable
• foam products, and
• aerosol products

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CFC Ozone Depletion Theory

• CFCs build up, and migrate through atmosphere
• takes 6-8 years to reach the stratosphere, where
  they stay for more than 100 years
• CFCs are broken up by sunlight emitting Cl atoms
• Cl atoms destroys ozone
• Reduced ozone levels causes increased UV-B
• Increased ultraviolet radiation leads to
• skin cancer, cataracts, immune system damage,
  crop/marine life damage

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Whats a World to Do?

• Government Action
• In 1978, the US was one of the first nations to
  ban the use of CFCs in hairsprays and other
  aerosols.
• The Montreal Protocol signed by most industrial
  countries in 1987 in attempt to immediately cut
  back on CFC production and to eradicate use by
  the year 2000

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However.Many countries who have signed this
treaty have not abided by it because of the
importance of CFCs to their economies.
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CFC Substitutes

• HCFCs Hydrocarboflourocarbons
• HFCs Hydroflourocarbons
• Carbon Dioxoide

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Hydrochlorofluorocarbons (HCFC)

• contain hydrogen, chlorine, fluorine, and carbon
• Shorter atmospheric lifetime than CFCs
• Deliver less reactive chlorine to the atmosphere
• In the troposphere, the HCFC molecule is attacked
  by a hydroxyl radical, which releases chlorine.
  This chlorine combines with other molecules and
  dissolves in ice and water which is then removed
  by precipitation
• Some of the HCFC molecules that reach the
  stratosphere, will then undergo photolysis
  (light-initiated decomposition)
• The HCFC molecules undergo two degradations,
  therefore, much less ozone chlorine will reach
  the ozone, resulting in less destruction of
  ozone.
• Drawbacks
• Some chorine reaches the stratosphere, therefore,
  some ozone will still be depleted
• Leads to atmospheric heating
• Because HCFCs allow some chlorine to reach the
  stratosphere, causing some damage, HCFCs are
  being used only as a temporary fix. HCFCs are
  being phased out as well

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Hydroflourocarbons (HFCs)

• Contains hydrogen, fluorine, and carbon
• Long-term potential because it contains no
  chlorine ?
• Presence of hydrogen atoms makes the compound
  more susceptible to oxidation in lower levels of
  the atmosphere (troposphere)
• In the troposphere, the molecule is attacked by a
  hydroxyl radical as shown CH2FCF3 OH ? CHFCF3
  H2O
• The product, CHFCF3 , then reacts with water,
  decomposing further to CO2, H2O, and HF that
  eventually are removed by precipitation
• Because of this reaction, that atmospheric
  lifetime is less than 12 years!

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Drawbacks for HFCs

• Lead to enhanced radioactive atmospheric heating
• Some HFCs decompose to form trifluoroacetic acid
  (TFA) which has adverse effects on biota.

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Underdeveloped Ideas

• Carbon Dioxide
• At extremely high pressures, acts as a
  refrigerant
• Positives? non-toxic, non-flammable, cheap, and
  abundant
• Drawbacks? greenhouse-gas, contributes to
  global warming poses danger to technicians who
  work on system because of the high pressure
• Air
• System that requires no refrigerant, but uses air
  itself as a working medium
• Rovac Corporation
• Circulator expands volume of air and the drop in
  pressure results in a drop in temperature
• Requires 35-40 less energy
• Mitsubishi gave rights to technology and was
  investigating the issue further
• However, this was 20 years ago, and no further
  agenda has been set!

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What can be done about the exsisting CFCs in the
atmosphere?

• ProblemChlorine
• Therefore, by releasing a molecule that reacts
  with chlorine, and that produces products that
  are harmless, ozone depletion can be limited
• Two of these molecules are ethane and propane
• Ethane Reaction
• Cl C2H6 ? HCl C2H5
• Propane Reaction
• Cl C2H8 ? HCl C3H7

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Less Realistic Plan

• Produce large quantities of ozone
• Release into stratosphere by airplanes
• PROBLEMS
• Very VERY costly
• Would require the collaboration of many countries

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References

• Chang, Raymond. Chemistry, ninth edition.
• NewYork McGraw-Hill, 2007.
• Chlorofluorocarbons. Purdue University. May
• 10, 2007. lthttp//www.purdue.edu/dp/enviro
• soft/housewaste/house/chlorofl.htmgt.
• Ozone Depletion and its Impacts. Univeristy of
  Michigan. May
• 10, 2007. ltwww.globalchange.umich.edu/global
• change2/current/lectures/ozone_deplete/ozone_depl
  et e.htmlgt.

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References

• "Clean Air Act." Ozone Depletion.1 U.S
  Enviromental Protection Agency. 9 May 2007
  lthttp//www.epa.gov/ozone/enforce/index.htmlgt.
• "Replacement of CFCs as Refrigerants."1
  Univeristy of Georgia. 9 May 2007
  lthttp//zwhudson.myweb.uga.edu/chem8290/substitute
  s20for20CFCs.htmgt.