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Lecture 23 Env Issues.pptx

Lecture 23 Env Issues.pptx - LECTURE 23 Current...

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LECTURE 23: Current Environmental Issues Course Instructor: Md Asif Rahman (ASR) Lecturer, Department of Mathematics and Natural Sciences (MNS) University Building 2 (15 th Floor) E-mail: [email protected]
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Ozone Layer Depletion The atmosphere of the Earth plays a crucial role in making it the only planet with life. Basically, the Earth's atmosphere is divided into several layers - stratosphere being one of them. Within the stratosphere, there lies a layer, made of a specialized form of oxygen , known as the ozone layer . The ozone layer is found between 10 to 20 miles above the surface of the Earth. This layer traps the harmful ultraviolet-B (UV-B) radiation emitted by the Sun, and hence plays a crucial role in supporting life on the Earth.
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Causes of Ozone Depletion The cause of ozone depletion is the increase in the level of free radicals such as hydroxyl radicals, nitric oxide radicals and atomic chlorine and bromine. The most important compound, which accounts for almost 80% of the total depletion of ozone in the stratosphere are chlorofluorocarbons (CFC). These compounds are very stable in the lower atmosphere of the Earth, but in the stratosphere , they break down to release a free chlorine atom due to ultraviolet radiation . A free chlorine atom reacts with an ozone molecule (O 3 ) and forms chlorine monoxide (ClO) and a molecule of oxygen. Now chlorine monoxide reacts with an ozone molecule to form a chlorine atom and two molecules of oxygen. The free chlorine molecule again reacts with ozone to form chlorine monoxide. The process continues and the result is the reduction or depletion of ozone in the stratosphere.
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Effects of ozone depletion The ozone layer is responsible for absorbing the ultraviolet rays and thereby preventing them from passing through the atmosphere of Earth. Ultraviolet rays of the Sun are associated with a number of health related and environmental issues.
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