- Books Name
- Science Made Easy Science Book
- Science Made Easy
- CBSE Class 9
Green House Effect
→ Carbon dioxide keeps the earth warm much like glass which keeps the green house warm.
• Effect of Increase in carbon dioxide (CO2):
(i) intensifies green house effect.
(ii) leads to global warming.
(iii) increase in average temperature of earth.
(iv) may lead to melting of polar caps.
(v) sub-merging number of coastal cities.
→ Changes in environment affects us and our acitivities change the environment around us.
Environmental Problems Caused by Humans
Depletion of Ozone Layer
→ Ozone layer is a protective blanket around the earth which absorbs most of the harmful UV
(ultraviolet) radiations of the sunlight, thus protecting living beings from many health hazards such
as skin cancer, cataract, destruction of plants etc.
→ Ozone (O3) layer is present at higher levels of atmosphere (i.e. stratosphere). It is a deadly poisonous at ground level.
→ Ozone layer is present in the stratosphere which is a part of our atmosphere from 16 km to 60 km
above sea level.
→ Ozone is an allotrope of oxygen. Its molecule is made up of three oxygen atoms. Molecular
formula is O3.
→ Ozone layer absorbs the ultra-violet rays coming from the sun and protects living being from
their harmful effects like skin cancer, cataract in eyes, weaken immune system.
→ The decline of ozone layer thickness in Antartica was first observed in 1985 and was termed as
Reason of Ozone Depletion
→ Excessive use of CFCs (Chloro Fluoro Carbon) in refrigeratos, jet planes, spray cans, fire
→ Nuclear explosion
→ Smog is a type of air pollution.
→ The word ‘smog’ comes from the blend of two words: Smoke and fog.
→ Smog can form in any climate where there is a lot of air pollution especially in cities.
Formation of ozone molecule
(i) The high energy UV radiations break down the O2 molecules into free oxygen (O) atoms.
O2 +uv → O + O (atoms)
(ii) These oxygen atoms then combine with oxygen (O2) molecule to form the ozone molecule.
O2 + O → O3 (ozone)
Depletion of ozone layer
→ The decrease in the thickness of ozone layer over Antarctica was first observed in 1985 and was
termed as ozone hole.
→ This decrease was linked to excessive use of synthetic chemicals like chlorofluorocarbons (CFC
which are used in refrigerators, ACs, fire-extinguishers, aerosols sprays etc.
→ United Nations Environment Programme (UNEP) succeeded in forging an agreement to stop CFC
production at 1986 levels (KYOTO PROTOCOL) by all countries.