Page 206 - Chemistry ICSE Class IX
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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