Q."Ozone is a natural Sun-block" - Discuss.

Ozone in the stratosphere absorbs the sun's harmful UV rays, protecting life like a natural sunscreen; its depletion by CFCs lets more UV through, causing skin cancer, cataract and ecological damage.

Ozone (O3) is a form of oxygen with three atoms per molecule. Although harmful as a pollutant near the ground, in the upper atmosphere (stratosphere, about 15–35 km up) it forms the ozone layer, which is vital for life.

Why ozone is a natural sun-block:

• The sun emits ultraviolet (UV) radiation, of which UV-B and UV-C are especially harmful to living things.
• The stratospheric ozone layer absorbs the bulk of this incoming UV radiation. In doing so it acts exactly like a sunscreen (sun-block), letting visible light through but filtering out the damaging UV before it reaches the earth's surface. This protects humans, animals, plants and microbes from UV damage.

Ozone depletion:

• Human-made chemicals, chiefly chlorofluorocarbons (CFCs) from refrigerants, aerosols and foams, rise to the stratosphere. There UV light frees chlorine atoms, each of which destroys many ozone molecules, thinning the layer — the 'ozone hole', notably over Antarctica.
• With less ozone, more UV-B reaches the ground.

Harmful effects of increased UV (i.e. of losing the sun-block):

• In humans: skin cancer, sunburn, cataract of the eye, ageing of skin and weakening of the immune system.
• In plants: reduced growth and productivity. …