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| ARTICLE |
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| Year : 2011 | Volume
: 34
| Issue : 3 | Page : 164-165 |
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Ozone and Environment
Bhaskar Agarwal1, Srishti Agarwal2, Jeetendra Rao1
1 Department of Prosthodontics, Faculty of Dental Sciences, CSM Medical University, Lucknow, India
2 Dhanvantri Charitable Hospital, Lucknow, India
| Date of Web Publication | 27-Sep-2012 |
Correspondence Address:
Bhaskar Agarwal
Department of Prosthodontics, Faculty of Dental Sciences, CSM Medical University, Lucknow
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0972-0464.101690
Each year for the past few decades during the Southern Hemisphere spring, chemical reactions involving chlorine and bromine cause ozone in the southern polar region to be destroyed rapidly and severely. This depleted region is known as the "ozone hole". Throughout the 20th century, discoveries and observations allow scientists to understand how human-made chemicals like chlorofluorocarbons create a hole in the ozone layer over Antarctica each spring. Keywords: Environment, oxygen, ozone
How to cite this article:
Agarwal B, Agarwal S, Rao J. Ozone and Environment. Radiat Prot Environ 2011;34:164-5 |
| 1. Introduction | |  |
Ozone is a chemical compound consisting of three oxygen atoms (O 3 - triatomic oxygen), a higher energetic form than normal atmospheric oxygen (O 2 ). Thus, the molecules of these two forms are different in structure. It is one of the most important gases in the stratosphere due its ability to filter UV rays which is critical for the maintenance of biological balance in the biosphere. This protective layer can be seen as the blue-colored sky. Ozone is produced naturally from electrical discharges following thunderstorms as well as from ultraviolet rays emitted from the sun which plays the role of electrical discharge over oxygen present in the stratosphere, thus, creating the ozone layer which absorbs most of the ultraviolet radiation emitted by the sun. [1],[2],[3],[4]
1.1 Stratospheric ozone
About 90% of the ozone in the atmosphere is present in the stratosphere, the layer of atmosphere between about 10 and 50 kms altitude. The natural level of ozone in the stratosphere is a result of a balance between sunlight that creates ozone and chemical reactions that destroy it. Ozone is created when the kind of oxygen we breathe (-O 2 -) is split apart by sunlight into single oxygen atoms. Single oxygen atoms can rejoin to make O 2 , or they can join with O 2 molecules to make ozone (O 3 ). Ozone is destroyed when it reacts with molecules containing nitrogen, hydrogen, chlorine or bromine. [3] The total mass of ozone in the atmosphere is about 3 billion metric tons which is only 0.00006% of the atmosphere. The peak concentration of ozone occurs at an altitude of roughly 32 kms (20 miles) above the surface of the earth. At that altitude, ozone concentration can be as high as 15 parts per million (0.0015 percent). Ozone in the stratosphere absorbs most of the ultraviolet radiation from the sun. Ozone screens all of the most energetic, UV-c radiation and most of the UV-b radiation. Ozone only screens about half of the UV-a radiation. Excessive UV-b and UV-a radiation can cause sunburn and can lead to skin cancer and eye damage. Increased levels of human-produced gases such as CFCs (chlorofluorocarbons) have led to increased rates of ozone destruction, upsetting the natural balance of ozone and leading to reduced stratospheric ozone levels. These reduced ozone levels have increased the amount of harmful ultraviolet radiation reaching the Earth's surface. [4],[5]
1.2 Dobson unit
The Dobson Unit is the most common unit for measuring ozone concentration. One Dobson Unit is the number of molecules of ozone that would be required to create a layer of pure ozone 0.01 mm thick at a temperature of 0°C and one atmospheric pressure. Like wise, a column of air with an ozone concentration of 1 Dobson Unit would contain about 2.69×10 16 ozone molecules for every square cm of area at the base of the column. Over the Earth's surface, the ozone layer's average thickness is about 300 Dobson Units or a layer that is 3 mm thick. [3],[4],[5]
1.3 Ozone hole
Ozone hole is not technically a "hole" where no ozone is present, but is actually a region of exceptionally depleted ozone in the stratosphere over the Antarctic that happens at the beginning of Southern Hemisphere spring (August-October). Satellite instruments provide us with daily images of ozone over the Antarctic region. From the historical record we know that total column ozone values of less than 220 Dobson Units were not observed prior to 1979. From an aircraft field mission over Antarctica we also know that a total column ozone level of less than 220 Dobson Units is a result of catalyzed ozone loss from chlorine and bromine compounds. For these reasons, we use 220 Dobson Units as the boundary of the region representing ozone loss. Using the daily snapshots of total column ozone, we can calculate the area on the Earth that is enclosed by a line with values of 220 Dobson Units. [5]
1.4 Chlorofluorocarbons and ozone
Many people have heard that the ozone hole is caused by chemicals such as chlorofluorocarbons (CFCs). CFCs escape into the atmosphere from refrigeration and propellant devices and processes. In the lower atmosphere, they are so stable that they persist for years, even decades. This long self-life allows some of the CFCs to eventually reach the stratosphere. In the stratosphere, ultraviolet light breaks the bond holding chlorine atoms (Cl) to the CFC molecule. A free chlorine atom participates in a series of chemical reactions that destroy ozone and return the free chlorine atom to the atmosphere unchanged, where it can destroy more and more ozone molecules. [2],[3],[5]
1.5 Ozone hole over Antarctica
Since the annual thinning of the ozone layer over Antarctica was first discovered, measurements have been carried out in all regions. Ozone depletion has been measured everywhere in the world except in the tropics. Depletion is usually worse away from the equator and recently an Ozone hole has been detected above the North Pole in the arctic. There is a lot to learn about the breakdown of ozone in the atmosphere. Warmer region, non polar depletion of ozone in particular is not properly understood. So for the time being the "ozone hole" seems to be Antarctic phenomenon, but a less severe thinning of the ozone layer is pretty much a world-wide thing. How acute and important it will be in the future is not known. [5]
1.6 Ozone hole recovery
The way to stop the formation, growth and spread of ozone thinning is to reduce the production of those chemicals that cause the destruction of ozone, namely CFCs and nitrogen oxides. In 1987, the Montreal Protocol was signed by many nations whereby those nations that signed agreed to reduce their emissions of CFCs to a half (of the 1987 levels) by 2000. Potential problems come from nations that do not see the reduction of CFCs to be a priority, and also from the huge quantity of refrigeration and air conditioning systems in the world that still contain CFCs. If they are not disposed of correctly, then the CFCs will escape into the atmosphere and continue to destroy ozone. [2] The problem is far from settled and is under investigation by research teams all over the world. The latest estimates are that as long as production and release of CFCs is regulated properly, global ozone levels should recover by 2050. [2],[5]
1.7 Latest ozone new
The Environmental Investigation Agency (EIA) reports that the recent decision to accelerate the phase out of hydrochlorofluorocarbons (HCFCs). HCFCs are hydrofluorocarbons (HFCs) - extremely potent greenhouse gases, often more so than the HCFCs they are set to replace. Their use in developed and developing countries is rising quickly and emissions from HFCs are expected to reach at least 1.2 billion tons of carbon dioxide equivalent by 2015, which is about 10 per cent of the total Kyoto Protocol savings between its 1990 baseline and 2012 reduction targets. The decision to bring forward the phase-out of HCFCs, made by the Montreal Protocol in last September, could reduce greenhouse gas (GHG) emissions by up to 16 billion tonnes of carbon dioxide equivalent by 2040, with the majority of savings achieved in developing countries. Many countries are finally beginning to recognise the need to limit the use of these GHGs. [2],[3],[4]
| 2. Conclusions | | |
This is the need of the time to think about to save the environment as well as future of mankind by exploring our knowledge and practice towards minimal use of AC plants, refrigerators, etc., in order to minimize the production of harmful gases affecting the environment.
| References | | |
| 1. | Nogales CG, Ferrari PA, Kantorovich EO, Lage-Marques JL. Ozone Therapy in Medicine and Dentistry. J Contemp Dent Pract 2008;9:75-84. 
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| 2. | Vatis Update: Ozone Layer Protection 2008;4-5. www.eia-international.org
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| 3. | Kirk-Othmer. Encylopedia of Chemical Technology. 4 th ed. J. Kroschwitz, ed. NY: John Wiley; 1996;17:552-64.
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| 4. | ALA 2002. Ozone Generators-What is Ozone Air Pollution? American Lung Association of Washington. http://www.alaw.org/air_quality/information_and_referral/indoor_air_quality/ozone_generatiors.html
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| 5. | Antarctica ozone hole. http://www.coolantarctica.com/Antarctica%20fact%20file/science/ozone_hole.htms
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