Page 206 - Chemistry ICSE Class IX
P. 206

194                                                                                      ICSE Chemistry – 9

                                           Chlorofluorocarbons (CFCs)
                                           Chloro uorocarbons escape into the atmosphere (up to 0.0005 parts per
                                           million) during their use in refrigerators, aerosol sprays, solvent and during
                                           the manufacture of plastic foams. CFCs are 38 million times stronger than
                                           CO  in their global warming capacity.
                                              2

                                           Ozone
                                           Ozone is formed and released at ground level in very small concentration
                                           by automobiles and from certain chemicals. Some other sources of ozone
                                           are high voltage electric equipments.

                                           The Greenhouse Effect


                                           What is meant by the greenhouse effect
                                           Heating up of the earth’s atmosphere due to the trapping of infrared
                                           radiation of longer wavelength by carbon dioxide in the atmosphere is

          KǀĞƌ ƚŚĞ ƉĂƐƚ ŚƵŶĚƌĞĚ LJĞĂƌƐ      called the Greenhouse effect.
          ĂƉƉƌŽdžŝŵĂƚĞůLJ ϯ͕ϲϬ͕ϬϬϬ ŵŝůůŝŽŶ
          ƚŽŶŶĞƐ ŽĨ  K  ŚĂƐ ďĞĞŶ ƌĞůĞĂƐĞĚ
                    Ϯ
          ŝŶƚŽ ƚŚĞ ĂƚŵŽƐƉŚĞƌĞ ĂŶĚ ŝƚ ŝƐ ďĞŝŶŐ   Mechanism of the Greenhouse effect
          ĚŽŶĞ Ăƚ ĂŶ ŝŶĐƌĞĂƐŝŶŐ ƌĂƚĞ͘  Ɛ Ă ƌĞƐƵůƚ   Solar radiations consist of ultraviolet, visible and infrared radiations.
          ŽĨ ƚŚŝƐ͕ ƚŚĞ ƉƌŽƉŽƌƟŽŶ ŽĨ ĐĂƌďŽŶ   Ozone in the upper atmosphere absorbs most of the harmful ultraviolet
          ĚŝŽdžŝĚĞ ; K Ϳ ŝŶ ƚŚĞ ĂƚŵŽƐƉŚĞƌĞ ŚĂƐ
                   Ϯ
          ŝŶĐƌĞĂƐĞĚ ďLJ ĂďŽƵƚ ϭϯй͘  ƵĞ ƚŽ ƚŚĞ   radiation. The visible and infrared radiations pass through this layer and
          ŐƌĞĞŶŚŽƵƐĞ ĞīĞĐƚ͕ ŝƚ ŚĂƐ ĂůƌĞĂĚLJ   reach the earth’s surface. When the earth gets heated up, it starts radiating
          ƌĂŝƐĞĚ ƚŚĞ ƚĞŵƉĞƌĂƚƵƌĞ ŽĨ ƚŚĞ ĞĂƌƚŚ   infrared radiation of longer wavelengths.
          ďLJ ϭΣ& ;Žƌ Ϭ͘ϱΣ Ϳ͘                    Carbon dioxide is heavier than air. So, it stays at the lower heights in
          /ƚ ŚĂƐ ďĞĞŶ ĞƐƟŵĂƚĞĚ ƚŚĂƚ ďLJ ƚŚĞ   the atmosphere. This layer of carbon dioxide does not permit the escape of
          LJĞĂƌ ϮϬϯϬ͕ ƚŚĞ ĞĂƌƚŚ͛Ɛ ĂǀĞƌĂŐĞ   these infrared radiation of longer wavelength through it. As a result, the
          ƚĞŵƉĞƌĂƚƵƌĞ ǁŽƵůĚ ŚĂǀĞ ŝŶĐƌĞĂƐĞ ďLJ   infrared radiation emitted by the warm earth gets trapped in the lower
          ĂďŽƵƚ ϯ͘ϲΣ& ;Žƌ ϮΣ&Ϳ͘
                                           part of the earth’s atmosphere and raises its temperature.



























                                                              ReÀection of the infrared radiation emitted by the
                                                 hot earth by carbon dioxide in the lower atmosphere producing the greenhouse effect
   201   202   203   204   205   206   207   208   209   210   211