On the basis of chemical reactions involved, explain how do CFCs cause depletion of ozone layer in stratosphere?
Important Points to Remember in Chapter -1 - Environmental Chemistry from Tamil Nadu Board Chemistry Standard 11 Vol II Solutions
1. Environmental and atmospheric pollution::
(i) Environmental Chemistry is the branch of chemistry which deals with the study of various chemical reactions occurring in environment.
(ii) Any undesirable change in the surroundings which has harmful effect on living beings is known as environmental pollution.
(iii) Photochemical Smog: It is formed by photochemical reactions involving solar radiation. The principal constituents are and some photochemical oxidants.
(iv) Air Pollution: Any condition of atmosphere in which the presence of certain substances beyond certain concentration produce harmful effect on man and his environment.
(v) Primary Pollutants: Pollutants which are emitted directly from the sources.
(vi) Secondary Pollutants: Pollutants which are formed in the atmosphere by chemical interactions among primary pollutants.
(vii) Major air pollutants are: and particulates like, dust, smoke, lead salts, fly ash, asbestos dust, acid mist, etc..
(viii) Smog is a mixture of smoke and fog of particulates. Principal constituents of classical smog are , carbon soot. It has reducing nature.
2. Formation and Breakdown of Ozone:
(i) Ozone Layer: Ozone layer is present in stratosphere which protects earth from harmful ultraviolet radiation of sun.
(ii) Ozone hole caused by the depletion of ozone layer, exposes living beings, both plants and animals to the harmful U. V. radiations to leading to many diseases.
3. Global Warming and Greenhouse Effect:
(i) Greenhouse gases are the gases which lead to global warming e.g. carbon dioxide, methane, ozone, chlorofluorocarbons (CFCS) etc.
(ii) Greenhouse Effect. Heating of atmosphere due to absorption of infra-red radiation emitted by carbon dioxide and other gases.
4. Biological oxygen demand (B.O.D.)
It is the amount of oxygen in milligrams dissolved in water needed to break down the organic matter present in one litre of water for five days at .
5. Water pollution:
It is caused by domestic sewage, chemical fertilizers, toxic heavy metals, pesticides, radio-active substances, sediments released during the erosion of soil by agriculture.
6. Soil pollution:
It results by the presence of pesticides, insecticides, herbicides, fungicides, dumping of nuclear wastes from nuclear power plants and also by the release of large number of toxic substances in the manufacturing industry.
7. Green chemistry:
Green chemistry means the production of substances of daily use by chemical reactions which neither employ toxic chemicals nor released the same in atmosphere.
