Ozone

The Ozone Hole
Ozone (O3) is a gas found in in high levels in the stratosphere, in a region also known as the ozone layer, between 15,000 and 40,000 metres above the surface where it plays an important role screening the sun’s ultraviolet radiations which are harmful for living organisms. In the past years stratospheric ozone levels have declined due to the effect of anthropogenic substances, as chlorofluorocarbons (CFCs), methyl bromide, halon gases and methyl chloroform. Once these gases reach the stratosphere they emit chlorine and bromine, which affect ozone formation.
Since the 1980s slow and gradual depletion of the stratospheric ozone has occurred, especially over Antarctica. Size and rapidity of the ozone hole formation alarmed the scientific community: in 1987 was issued the Montreal Protocol, the first international treaty ratifying the reduction of CFCs use. So far the Montreal Protocol has been adopted by over 190 states (link to sustainability for more information on this subject): nowadays global use of CFCs is lower but many years need to pass before existing CFCs can be eliminated from the atmosphere.
The major direct consequence of the hole in the ozone layer is an increased amount of ultraviolet radiations (UV – frequency from 100 to 400 nm) reaching the Earth’s surface.
These radiations cause:

  • increased risk for skin tumours and eye diseases;
  • decreased immune system functions in men and animals;
  • photosynthesis reduction and DNA damage in plants with a significant negative impact on agriculture;
  • lower levels of marine phytoplankton production causing serious damage to the marine chain in aquatic ecosystems.

Ozone in the Lower Atmosphere
Ozone pollution refers to higher ozone concentration in the troposphere, the only atmospheric layer which can support life, and which shouldn’t be mistaken for the ozone hole.
Tropospheric ozone is formed by the interaction of sun radiations and primary pollutants, especially nitrogen dioxide. Ozone is harmful for men and the environment as it’s a powerful oxidant which can cause negative effects when reaching high concentration in the air, after long-term exposure and high concentration in ambient air breathed by humans.

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