Ozone Depletion and CFCs

Madeline Midgett and Anna Lovelace

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

• 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)

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

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

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

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

However….Many countries who have signed this treaty have not

abided by it because of the importance of CFCs to their economies.

CFC Substitutes

• HCFCs: Hydrocarboflourocarbons

• HFCs: Hydroflourocarbons

• Carbon Dioxoide

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

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!

Drawbacks for HFCs

• Lead to enhanced radioactive atmospheric heating

• Some HFC’s decompose to form trifluoroacetic acid (TFA) which has adverse effects on biota.

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!

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

Less Realistic Plan…

• Produce large quantities of ozone

• Release into stratosphere by airplanes

• PROBLEMS:– Very VERY costly– Would require the

collaboration of many countries

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>.

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>.