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Environmental Chemistry - Ozone Depletion (HL)

Basic Understanding of Ozone –
Ozone is a colorless unstable toxic gas with a pungent odor and powerful oxidizing properties, formed from oxygen by electrical discharges or ultraviolet light. It differs from normal oxygen (O2) in having three atoms in its molecule (O3). [1]

Now that you know what is ‘Ozone’
Its time to tell you the importance of it and the destruction of it due to human activities and natural depletion …

~ The Importance ~
The ozone is a layer mainly found in the atmosphere that is close to earth’s surface. Without the filtering action of the ozone layer, more of the sun's UV-B radiation would penetrate the atmosphere and reach the earth's surface. Many experimental studies of plants and animals and clinical studies of humans have shown that excessive exposure to UV-B radiation has harmful effects. Serious long-term effects can include skin cancers and eye damage.

~ The Destruction ~
The depletion of ozone are caused by human activities by and natural causes,
It plays a role of ozone depletion. Natural ozone depletion was and is mainly from methylchloride, which is formed by fungi and algae and explosive volcanic eruptions.
Human activities
Such as Chlorofluorocarbons (CFCs) that contains carbon, chlorine and fluorine, produced as a volatile derivative of methane and ethane. CFCs are being produced by air conditioners, refrigerants, solvents and foam blowing agents. This is the most widely used ozone-depleting substances, accounting for over 80% of total stratospheric ozone depletion which cause the ozone molecules to break down, reducing ozone's ultraviolet (UV) radiation-absorbing capacity.[2]
The other substance would be ‘Halons’ (CBrF3) which are used in some fire extinguishers. One atom of chlorine from a CFC molecule can damage up to 100,000 molecules of O3. The chlorine atom acts as a catalyst in the mechanism for the destruction of ozone, as shown in the reaction mechanism below:
CCl2F2 --> CClF2 + Cl.
Cl. + O3 --> ClO. + O2
ClO. + O3 --> Cl. + O2
Overall Reaction:
O3 + O. --> 2O2
A second ozone-depleting chemical is NOx, and a similar reaction occurs between NOx and ozone. In this reaction mechanism NO acts as a catalyst and NO2 is the reaction intermediate. The overall effect is the destruction of a molecule of ozone by addition of an oxygen radical and the production of two molecules of oxygen. Shown in the reaction mechanism below:
NO + O3 --> NO2 + O2
NO2 + O. --> NO + O2
Overall Reaction:
O3 + O. --> 2O2

Next in position is ‘Methyl Chloroform’ which is mainly used in industry for vapor degreasing, cold cleaning and chemical processing.
Carbon Tetrachloride would also deplete the ozone and could be found in solvents and some fire extinguishers.
Last but not least, Hydrofluorocarbons (HCFCs). They are alternative to CFCs in terms compared to the CFCs; they are much less harmful to stratospheric ozone than CFCs. But HCFCs still cause some ozone destruction and are strong greenhouse gases.
CFCs and HCFCs are usually produced by halogen exchange starting from chlorinated Methane and Ethane. Illustrative is the synthesis of Chlorodifluoromethane from Chloroform:
HCCl3 + 2 HF → HCF2Cl + 2 HCl


Volatile Organic Compounds (VOCs) are organic compounds ground-water contaminants of concern because of the very large environmental releases, human toxicity, and are being released into the atmosphere by anthropogenic and natural emissions.
Many VOCs are human-made chemicals; they are emitted by a wide array of products:
Examples include: paints and lacquers, paint strippers, cleaning supplies, pesticides, building materials and furnishings, office equipment such as copiers and printers, correction fluids and carbonless copy paper, graphics and craft materials including glues and adhesives, permanent markers, and photographic solutions. [6]

Actions to be Taken to Reduce the Amount of Ozone at Ground Level –
Due to the increasing awareness of global warming due to the depletion of ozone, the US government are recommending the use of cleaner fuels and having much efficient vehicles in urban areas. Despite these improvements, ground-level ozone continues to be one of the most difficult pollutants to manage.

The Polar Region at Stake –
The ozone at the two poles on earth tends to have a greater hole in the atmosphere due to ozone depletion. This is because of the Stratospheric ozone is produced from reactions that occur with the energy from the sun (photochemical reactions). Although ozone is created primarily at tropical latitudes, large-scale air circulation patterns in the lower stratosphere move ozone toward the poles, where its concentration builds up.
During the continuously dark polar winter, the air inside the polar vortices becomes extremely cold, a necessary condition for polar stratospheric cloud (PSC) formation. These clouds generally last until the sun comes up in the spring setting up conditions for drastic ozone destruction.
external image ozone_hole_NASA.jpg[4]
Due to such drastic ozone destruction, ozone holes are being form, at the poles CFCs attach to ice particles. When the sun comes out again in the polar spring, the ice particles melt, releasing the ozone-depleting molecules from the ice particle surfaces. Once released, these ozone-destroying molecules do their dirty work, breaking apart the molecular bonds in UV radiation-absorbing ozone.
external image cartoon.gif[5]
The figure above shows a schematic illustrating the life cycle of the CFCs; how they are transported up into the upper stratosphere/lower mesosphere, how sunlight breaks down the compounds and then how their breakdown products descend into the polar vortex.


[1] – "Ozone Facts, information, pictures | articles about ozone."Encyclopedia - Online Dictionary | Get facts, articles, pictures, video. N.p., Updated on 3 May 2011. Retrieved on 2 May 2011. Retrieved from:
[2] – BC Air Quality | The Causes of Ozone Depletion, Province of British Columbia. N.p., n.d. Retrieved on 2 May 2011. Retrieved from:
[3] – Ozone Layer Depletion, ME-Subjects |N.p., Updated on 2010. Retrieved on 2 May 2011. Retrieved from: [4] – "Ozone Hole & Global Warming FAQ | Union of Concerned Scientists." UCS | Union of Concerned Scientists. N.p., Updated on 13 July 2009. Retrieved on 2 May 2011. Retrieved from:
[5] – "The Ozone Hole Tour : Part III. The Science of the Ozone Hole ." Centre for Atmospheric Science. N.p., 1998. Retrieved on 2 May 2011. Retrieved from:
[6] – "Volatile Organic Compounds | Indoor Air Quality | US EPA."US Environmental Protection Agency. N.p., Updated on 22 March 2011. Retrieved on 2 May 2011. Retrieved from:

Other Resources

"Ozone Science: The Facts Behind the Phaseout | Ozone Layer Protection |US EPA." US Environmental Protection Agency. N.p., Updated on 19 August 2010. Retrieved on 2 May 2011.Retrieved from:
Greenhouse Effect | Greenhouse Gases | Information provided by N.p., n.d. Retrieved on 2 May 2011.Retrieved from: