Test: Ozone Depletion (Old NCERT) - NEET MCQ

'Good ozone' is found in the upper part of the atmosphere called the stratosphere and it act as a shield absorbing ultraviolet radiations from the sun. UV rays are, highly injurious to living organisms. 'Bad ozone' is formed in the lower part of atmosphere called troposphere and it harms plants and animals.

Ozone-depleting substances (ODS) are substances that react with ozone present in the stratosphere and destroy the same. The major Ozone-depleting substances are chlorofluorocarbons (14% of total depletion), nitrogen oxides (3.5% depletion), sulphur dioxide, halon, carbon tetrachloride, methyl chloroform, chlorine, etc.

Recognising the deleterious affects 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.

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 production and degradation of ozone in the stratosphere.

Ultraviolet radiations are of three types - UV-C (100 - 280 nm). UV-B (280 - 320nm) and UV-A (320 - 390nm). UV radiation of wavelengths shorter than UV-B, are 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 aging of skin, damage to skin cells and various types of skin cancers.