Solution:
Good ozone is found in the upper part of the atmosphere called the stratosphere, and it acts as a shield absorbing ultraviolet radiation from the sun. Hence,
Statement 1 is incorrect.
UV rays are highly injurious to living organisms since the DNA and proteins of living organisms preferentially absorb UV rays , and it's high energy breaks the chemical bonds within these molecules .
The thickness of the ozone in a column of air from the ground to the top of the atmosphere is measured in terms of Dobson units( DU ). Hence, Statement 2 is correct.
Ozone gas is continuously formed by the action of UV rays on molecular oxygen and also degraded into molecular oxygen in the stratosphere .
There should be a balance between the production and degradation of ozone in the stratosphere. Of late, the balance has been disrupted due to the enhancement of ozone degradation by chlorofluorocarbons ( CFCs ).
CFCs find wide use as refrigerants . CFCs discharged in the lower part of the atmosphere move upward and reach the stratosphere .
In the stratosphere, UV rays act on them releasing Cl atoms.
Cl degrades ozone releasing molecular oxygen, with these atoms acting merely as catalysts;
Cl atoms are not consumed in the reaction.
Hence, whatever CFCs are added to the stratosphere , they have permanent and continuing effects on Ozone levels.
Although ozone depletion is occurring widely in the stratosphere , the depletion is particularly marked over the Antarctic region.
This has resulted in the formation of a large area of the thinned ozone layer , commonly called the ozone hole .
UV radiation of wavelengths shorter than UV-B is almost completely absorbed by Earth’s atmosphere , given that the ozone layer is intact.
But, UV-B damages DNA and mutation may occur. It causes ageing of the skin, damage to skin cells , and various types of skin cancers. In the human eye, the cornea absorbs UV-B radiation , and a high dose of UV-B causes inflammation of the cornea, called snow-blindness, cataracts , etc. Such exposure may permanently damage the cornea .
Recognizing the deleterious effects of ozone depletion , an international treaty, known as the Montreal Protocol , was signed at Montreal ( Canada ) in 1987 (effective in 1989 ) to control the emission of ozone-depleting substances.
Subsequently, many more efforts have been made and protocols have laid down definite roadmaps , separately for developed and developing countries ,for reducing the emission of CFCs and other ozone-depleting chemicals .
© examsiri.com