Question

“Good ozone” is found in the
A. Mesosphere
B. Troposphere
C. Stratosphere
D. Ionosphere

Answer 1

This layer is the second major layer of atmosphere and it extends from 10 to 50 km above the Earth’s surface and makes up 21% of the atmosphere. This layer is abundant in ozone, and it absorbs the UV radiation from the sun and uses it to heat this region

Complete answer:
Ozone is a gas made up of three oxygen atoms $(O_3)$ and it protects life on Earth from UV radiations of the Sun. There are two types of UV light: UVB and UVA. UVB causes skin conditions like sun burns and cancers like basal cell carcinoma. UVA is more harmful than UVB as it penetrates more deeply and causes deadly skin cancer and premature aging.

Ozone is found in two different layers of the atmosphere. 90% of ozone is found in the stratosphere, which extends up to about 50 km altitude. Most of the UV radiation from the sun is absorbed by this layer before it reaches the ground. Thus the stratospheric ozone layer acts like a sunscreen on us. In the lower atmosphere- the troposphere, ozone occurs as a result of chemical reactions between various pollutants, including nitrogen oxide, hydrocarbons and other volatile organic compounds. It causes irritation and burning sensation in the throat, lungs and eyes. Hence the tropospheric ozone, which is a harmful pollutant, is called ‘Bad ozone’. On the other hand, the stratospheric ozone is very protective in nature and so is called ‘Good ozone’.

Man Made emissions of CFCs (Chlorofluorocarbons), Carbon tetrachloride and other Ozone depleting substances (ODS) causes significant depletion of the stratospheric ozone layer(ozone Hole ) and more of the UV radiations are allowed to reach the Earth. This leads to more cases of skin cancer, cataracts and immune suppression. UV radiations also affect terrestrial and aquatic ecosystems, destroying the food chains and biochemical cycles. Plant growth is also affected by UV rays, which leads to less agricultural productivity.

Hence the correct answer is option ‘C’ i.e, “Stratosphere”.

Note: Montreal Protocol was proposed in 1987 to unite the World to cut out the production of Ozone depleting substances. Since then the global consumption of Ozone depleting substances has been reduced significantly. As a result the ozone layer is showing the first signs of recovery. But once released these substances stay in the atmosphere for many years and continue to cause damage, so it will take many years for the ozone layer to recover fully.