Ozone layer, a shield against UV rays

Ozone is a protective shield from UV rays. Damaging it means damaging the environment and our health.

Ozone is a gas consisting of three oxygen molecules (O3) instead of two (O2) like the oxygen we breathe.


Generally, ozone is present in the atmosphere in small amounts, in a layer 10 to 60 kilometres above the earth (ozonosphere) and in close proximity to the ground.


The ozone layer serves as protective shield against ultraviolet (UV) rays.


The formation of ozone at low altitudes is mainly due to two factors:

  • Electric discharge (lightning);
  • Reactions with nitrogen oxide molecules coming from the vehicles’ downpipes and thermal power stations.


In the ozonosphere, ozone is formed when a molecule of oxygen (O2) is split by UV rays so that oxygen atoms can combine with another molecule to make a molecule of ozone (O+O+O = O3), which, in turn, is split by UV rays in one molecule of oxygen and one free molecule (O2+O), which, back in circulation, pass through this process forever absorbing UV rays. The layer where these reactions are more likely to happen is 25 km above the earth, in the stratosphere.


When ozone is missing or reduced, the UV light reaches directly the earth surface causing damages to flora (inhibiting the photosynthesis) and fauna, including human beings (skin cancer, eye injuries, weakening of the immune system etc). The explanation is simple: UV rays are harmful to living creatures because with their low wavelength they have high radiant energy.

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