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Saturday, 23 February 2008 |
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CFC is short for chlorofluorcarbon, a man-made chemical made up of carbon, chlorine and fluorine atoms. There are many different types of CFCs. They were first developed in the 1930s, and since then have been widely used in refrigerators,  aerosol
cans and fire extinguishers. Man-made CFCs have been the main cause of ozone depletion high up in the atmosphere. One CFC molecule can destroy up to 100,000 ozone molecules. To date, they have accounted for roughly 80% of the total ozone depletion that has been observed. Other man-made chemicals like halons have accounted for the rest. Fortunately, the use of new CFCs has been banned since |
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Last Updated ( Thursday, 03 July 2008 )
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Wednesday, 20 February 2008 |
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Effects of elevated ultraviolet-B (UV-B) on terrestrial plants vary widely among species and even among cultivars of the same species. These effects range from the molecular scale, such as DNA damage, to tissue and whole plant effects, including a decrease in photosynthetic activity and changes in plant structure and biomass. In "The Changing Solar Ultraviolet Climate and the Ecological Consequences for Higher Plants," Caldwell, Teramura, and Tevini (1989) discuss a range of potential consequences from the molecular scale up to ecosystem levels and illustrate these in a flowchart. Large-scale results include a possible shift in competitive balance and species population within communities and ecosystems. The majority of research on elevated UV-B impacts has been carried out in laboratory settings where climatic conditions can be controlled. Notable exceptions to this include field studies of certain agriculturally important species and coniferous trees. Teramura et al. (1991) outline both types of studies in the chapter "Terrestrial Plants" of the United Nations Environment Programme's (UNEP) Effects of Ozone Depletion. |
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Last Updated ( Thursday, 03 July 2008 )
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Saturday, 16 February 2008 |
The problem of ozone depletion is not so much a matter of the rate at which
ozone is produced as the rate at which it is destroyed by anthropogenic
(human-caused) pollutants. Ozone is a reactive, unstable gas. It is
maintained in the stratosphere only because solar radiation continually
supplies the energy needed to produce it.
Ozone is produced in the stratosphere when hard UV light breaks apart O2
molecules into two oxygen atoms; a free oxygen combines with O2 to form
ozone, O3.
O2 + hv -> O + O (wavelength < 240 nm)
O + O2 -> O3
Ozone is naturally destroyed by nitrogen oxides in the stratosphere, which
catalyze the reaction of ozone with an oxygen atom to produce diatomic
oxygen, O2.
O + O3 -> 2 O2
(Note that both the formation and destruction reactions require the
presence of oxygen atoms, which are only produced when the sun shines.) |
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Last Updated ( Thursday, 03 July 2008 )
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Thursday, 14 February 2008 |
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The greenhouse effect is the rise in temperature that the Earth experiences because certain gases in the atmosphere (water vapor, carbon dioxide, nitrous oxide, and methane, for example) trap energy from the sun. Without these gases, heat would escape back into space and Earth’s average temperature would be about 60ºF colder. Because of how they warm our world, these gases are referred to as greenhouse gases. Have you ever seen a greenhouse? Most greenhouses look like a small glass house. Greenhouses are used to grow plants, especially in the winter. Greenhouses work by trapping heat from the sun. The glass panels of the greenhouse let in light but keep heat from escaping. This causes the greenhouse to heat up, much like the inside of a car parked in sunlight, and keeps the plants warm enough to live in the winter.  |
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Last Updated ( Thursday, 03 July 2008 )
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Thursday, 14 February 2008 |
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Ozone is a relatively simple molecule, consisting of three oxygen atoms bound together. Yet it has dramatically different effects depending upon its location. Near Earth's surface, where  comes into direct contact with life forms, it primarily displays a destructive side. Because it reacts strongly with other molecules, large concentrations of ozone near the ground prove toxic to living things. At higher altitudes, where 90 percent of our planet's ozone resides, it does a remarkable job of absorbing ultra violate radiation. In the absence of this gaseous shield in the stratosphere, the harmful radiation has a perfect portal through which to strike  |
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Stratospheric Ozone Depletion 
