What is the ozone layer, and what is its importance to life on Earth?
Between 19 and 23 kilometers above the earth's surface in the stratosphere, a thin coat of gas, the ozone layer surrounding the Earth and protects it from the dangerous rays of the sun.
The ozone layer in the Earth's atmosphere protects us from the harmful ultraviolet rays from the Sun, but it is at risk of depletion.
. The ozone is produced by the effect of sunlight on oxygen and is the only substance in the atmosphere that can absorb the harmful ultraviolet radiation (UV-B) from the sun.
This thin coat known for Ozone ( stratospheric ozone), makes life possible on earth. |
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Since 1974, scientists have warned of a potential global crisis as a result of the progressive destruction of the ozone layer caused by man-made chemicals such as chlorofluorocarbons (CFCs). |
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The ozone layer absorbs 97-99% of the sun's high frequency ultraviolet light , light which is potentially damaging to life on earth. Every 1% decrease in the earths ozone shield is projected to increases the amount of UV light exposure to the lower atmosphere by 2%. Because this would cause more ozone to form in the lower atmosphere, it is uncertain how much of UV light would actually reach the earths surface. Recent UV measurements from around the northern hemisphere indicate small UV increases in rural areas and almost no increase in areas near large cities.
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Units used to measure ozone concentration
When describing the amount or concentration of gas, scientists resort to several different units:
- Dobsin unit (DU)- the principle unit for measuring ozone concentration. One DU is about twenty-seven million molecules per square centimeter ( the palm of your hand covers an area of rougly a hundred square centimeters). The ozone concentration over the US is about 300 DU and the antarctic hole during the late spring can drop to 117 DU.
- Mixing ratios: within a specified volume, it is a fraction of the number of molecules of a particular gas divided by the total number of molecules in that given space. Terms of usually abreviated, like ppmv for parts-per-million or ppbv which is parts-per-billion . For example the concentration of HCl at 3 km is said to be about 0.1 ppbv; this means that if you selected a volume of air that contained 10 billion molecules of air, one of those molecules would be an HCl molecule.
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Ozone layer images & photos
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 viennaconvention.pdf (74kb) viennaconvention.zip (5 |
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The Vienna Convention for the Protection of the Ozone Layer, agreed in Vienna in 1985 finally seems to be unimpaired. The nations agreed to take "appropriate measures ... to protect human health and the environment against adverse effects resulting or likely to result from human activities may alter or modify the ozone layer," but the measures are not specified . No mention is made of substances that could damage the ozone layer and CFCs only appear towards the end of the annex to the treaty, which was mentioned as chemicals that should be monitored. . The main purpose of the Convention was to encourage research, cooperation between the countries and exchanging information. . Still, it took four years developed and agreed. Twenty nations signed it in Vienna, but most did not rush to ratify it. The Convention sets out protocols and determining future amendment procedures and dispute resolution. |
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OZONE LAYER 
