CFC contributes to Global Warming, Why?

We often heard about global warming. The first time I heard about global warming is when I'm 14 or 15 years old. What about you? Global warming has been a serious worldwide issues. How much you know about global warming? So, What is global warming? Global Warming is defined as the increase of the average temperature on Earth. As the Earth is getting hotter, disasters like hurricanes, droughts and floods are getting more frequent. Most of us has been encourage to decrease the usage of air-conditioners, aerosol sprays and etc. The reason is by using air-conditioner and aerosol spray produces CFC. For your information, CFC actually contributes to global warming. Do you know why? Here's some information about CFC and the answer to the question.

Chloroflourocarbons (CFC’s, freons) are small gaseous molecules containing carbon, fluorine, and chlorine. They were developed in the early 1930s by chemists searching for a new refrigerant to replace the toxic ammonia and sulfur dioxide then in use. Chloroflourocarbons have become widely used as dry-cleaning solvents, as refrigerants for freezers, refrigerators, and air-conditioning units, and as propellants in aerosol cans for dispensing many consumer products, including deodorants, hair sprays, whipped cream, metered-dose inhalants, and window cleaners. Two examples of CFC’s are shown below:

CCl₃F - Freon 11 (bp 24^oC)

CCl₂F₂ - Freon 12 (bp -30^oC)

Because of their stability, chloroflourocarbons are not readily biodegraded or chemically destroyed after use on the earth’s surface. Instead, they slowly diffuse toward the upper atmosphere. In the middle of stratosphere, about 8 to 13 miles above the earth’s surface, is a layer of ozone (O3), a form of elemental oxygen that is approximately 20 miles thick. This ozone absorbs certain levels of ultraviolet radiation and in doing so shields the earth from the harmful effects of ultraviolet rays. As it absorbs the UV light, ozone is converted to molecular oxygen (O2) and oxygen atoms. Recombination of these and other naturally occurring oxygen atoms regenerates ozone.

O₃ ------→O + O₂
uv light

Ultraviolet light also causes chloroflourocarbons to dissociate, a process that produces chlorine atoms, chlorine free radicals. In the stratosphere, there chlorine atoms react with ozone to form chlorine monoxide and molecular oxygen; a molecule of ozone is destroyed. This would not cause a serious ozone depletion if it weren’t for a subsequent reaction in which the chlorine monoxide reacts with naturally radical and molecular oxygen. This new chlorine atom can attack and destroy yet another ozone molecule. A free radical chain reaction is initiated by each CFC molecule that is dissociated, and each chain results in the destruction of thousands of molecules of ozone.

Chain Initiation:

CCl₂F₂ → ·CF₂Cl + Cl·

Chain Propagation:

Cl· + O₃ → ClO· + O₂

ClO· + O₃ → Cl· + 2 O₂

Even small depletions in the ozone layer result in increasing levels of ultraviolet radiation reaching the earth’s surface; this can cause significant increases in sunburn, skin cancer and eye disease. There are also serious implications for plant and aquatic life as well as climatologically changes. Measurable effects of damage to the ozone layer include a decrease in some frog populations because increased UV radiation destroys their eggs, which float near the surface of the water, and regional holes in the ozone shield that appear over the Arctic and Antarctic.

International agreements and accelerated efforts by some nations and industries are in effect to phase out the use of CFC’s and other substances that cause depletion of the ozone layer. Other substances include the agricultural fumigant, methyl bromide; halons, bromide-containing fluorocarbons used in fire protections systems and hydrochloroflourocarbons (HCFC’s), a less threatening replacement of CFC’s (the hydrogen on HCFC’s make them more susceptible to oxidation and destruction in the lower atmosphere). Common aerosol replacements for CFC’s include gaseous hydrocarbons such as propane and butane. Even with those efforts underway, it is uncertain how long it will take the environment to recover from the damage already done.

References:

1. "The Ozone Hole-Chloroflourocarbons". <http://www.theozonehole.com/cfc.htm>
2. "Haloalkane". >
3. "Ozone". >
   
4. "Ozone depletion". <http://en.wikipedia.org/wiki/Ozone_depletion>
5. Bailey, P.S., Bailey, C.A., Organic Chemistry. 6th Ed. Prentice Hall, Upper Saddle River, New Jersey.

© 2009 Lesleygsy