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Ozone

 

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Overview
Ozone is a gas, a form of oxygen, that is found in the layers of the atmosphere, most predominantly in the stratosphere. Here, 90% of the atmosphere's ozone is distributed in a ratio of five ozone molecules to every million molecules of other gases. This minute distribution serves as a shield that helps screen the sun's rays by absorbing some of the ultraviolet(UV-B)radiation. Depletion of the ozone in the atmosphere can have severe consequences on earth. Plants, animals, and humans all suffer when exposed to higher levels of ultraviolet rays. Food crops have stunted growth; marine phytoplankton can die off; and humans are more vulnerable to skin cancer. Atmospheric research in the mid-1980s indicated a serious thinning of the ozone shield, upsetting a natural balance between oxygen and ozone in the stratosphere. This thinning was evident from satellite pictures and showed up as a dark area; thus the term "ozone hole" was coined. It was apparent to scientists studying the ozone depletion that chemicals called chloroflourocarbons (CFCs), used in spray cans, refrigerators and air conditioners, foam, plastics, and cleaning solvents, might be contributing to the problem. After being released, either during the manufacturing process or from consumer use, CFCs reach the stratosphere. There, chemical reactions break apart the CFCs. The chlorine then breaks down the ozone. A single chlorine atom can destroy 100 thousand molecules of ozone. The degree of ozone depletion has followed an annual cycle that corresponds to the amount of sunlight that reaches the Antarctic. The cycle begins every year around June when the vortex winds develop in the Antarctic. Cold temperatures produced by these winds create polar stratospheric clouds that capture the floating CFCs. For the next two months, a reaction occurs on the cloud surface that frees the chlorine in the CFCs but keeps the chlorine contained within the vortex area. In September, sunlight returns to the Antarctic and triggers a chemical reaction, causing chlorine to convert ozone to normal oxygen. Measured ozone levels usually are lowest in October. November brings a breakdown in the vortex that allows the ozone-rich air to combine with the thinning ozone. Wind currents carry this mixture over the southern hemisphere and carry the "hole" over other areas of the earth.

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