ozone depletion and cfcs madeline midgett and anna lovelace
TRANSCRIPT
![Page 1: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/1.jpg)
Ozone Depletion and CFCs
Madeline Midgett and Anna Lovelace
![Page 2: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/2.jpg)
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
![Page 3: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/3.jpg)
• 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)
![Page 4: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/4.jpg)
These ice particles provide a surface for reactions:
C l O C lO O 3 2
HC l C lONO C l HNO 2 2 3
C l hv C l2 2 HCl from the earth, and chlorine nitrate produce chlorine molecules
C lO O C l O 3 22
Spring sunlight breaks chlorine molecules into atoms
Chlorine atoms destroy ozone
Chlorine monoxide also destroys ozone
![Page 5: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/5.jpg)
![Page 6: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/6.jpg)
CFCs (chlorofluorocarbons)
• First made in the 1930’s, 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
![Page 7: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/7.jpg)
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
C l CF hv C lCF C l2 2 2
![Page 8: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/8.jpg)
What’s a World to Do?
• Government Action– In 1978, the US was one of the first nations to
ban the use of CFC’s 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
![Page 9: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/9.jpg)
However….Many countries who have signed this treaty have not
abided by it because of the importance of CFCs to their economies.
![Page 10: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/10.jpg)
CFC Substitutes
• HCFCs: Hydrocarboflourocarbons
• HFCs: Hydroflourocarbons
• Carbon Dioxoide
![Page 11: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/11.jpg)
Hydrochlorofluorocarbons (HCFC)
• contain hydrogen, chlorine, fluorine, and carbon• Shorter atmospheric lifetime than CFC’s• 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 HCFC’s allow some chlorine to reach the stratosphere, causing some damage, HCFC’s are being used only as a temporary fix. HCFC’s are being phased out as well
![Page 12: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/12.jpg)
![Page 13: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/13.jpg)
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!
![Page 14: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/14.jpg)
Drawbacks for HFCs
• Lead to enhanced radioactive atmospheric heating
• Some HFC’s decompose to form trifluoroacetic acid (TFA) which has adverse effects on biota.
![Page 15: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/15.jpg)
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!
![Page 16: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/16.jpg)
What can be done about the exsisting CFC’s in the atmosphere?
• Problem=Chlorine• 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
![Page 17: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/17.jpg)
Less Realistic Plan…
• Produce large quantities of ozone
• Release into stratosphere by airplanes
• PROBLEMS:– Very VERY costly– Would require the
collaboration of many countries
![Page 18: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/18.jpg)
References
Chang, Raymond. Chemistry, ninth edition. NewYork: McGraw-Hill, 2007.
Chlorofluorocarbons. Purdue University. May10, 2007. <http://www.purdue.edu/dp/envirosoft/housewaste/house/chlorofl.htm>.
Ozone Depletion and its Impacts. Univeristy of Michigan. May 10, 2007. <www.globalchange.umich.edu/globalchange2/current/lectures/ozone_deplete/ozone_deplete.html>.
![Page 19: Ozone Depletion and CFCs Madeline Midgett and Anna Lovelace](https://reader035.vdocument.in/reader035/viewer/2022062519/5697c02c1a28abf838cd8d55/html5/thumbnails/19.jpg)
References
• "Clean Air Act." Ozone Depletion.1 U.S Enviromental Protection Agency. 9 May 2007 <http://www.epa.gov/ozone/enforce/index.html>.
• "Replacement of CFCs as Refrigerants."1 Univeristy of Georgia. 9 May 2007 <http://zwhudson.myweb.uga.edu/chem8290/substitutes%20for%20CFCs.htm>.