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The ozone hole is the depletion of the layer of rarefied ozone (O3) present in the stratosphere between 20 and 30 Km of height in the atmosphere that allows the presence of life on our planet by absorbing 99% of UV radiations of solar light. Without it, in fact, human and animal skin will develop cancer for the rupture of DNA molecules and also vegetable life would be blocked for the damage caused to chlorophyl by UV-rays.

This depletion has been revealed at the beginning of the 1980's and scientists have found the cause in the massive presence of CFC gases (chloro fluoro carbides), widely used for their high chemical inertness as refrigerating gases in spray cans and refrigerating devices until that period. Other responsible molecules are brominated light hydrocarbons, like CH3Br, used as pesticide and to NOx (nitrogen oxides).

This effect is most intense over the Antarctic continent, where it reaches the maximum at the beginning of the spring (September-October), when solar light is more intense and the O3 reduction can reach 70%.

The O3 hole has appeared also on the North Pole, with a reduction up to 30% These gas act as catalysts for the decomposition of O3 and every CFC molecule can destroy, at least, 40,000 O3 molecules. The CFCs reach the stratosphere thanks to atmospheric currents and to diffusion (despite they are heavier than air) within 10-15 years and they can resist without decomposition for 75-100 years.

For this reason, it was particularly important that these molecules and all the others that could cause this effect weren't produced anymore by industry because, already today, their effects will take at least 50 years to decrease.

This is just what happened after the agreements concluded in the Copenhagen Conference, in 1992, among most Countries of the world to ban CFCs production within 1996. The following conference of Vienna (1995) confirmed this ban, so that, today, 180 Countries adhere to this ban; its production dropped down in 2000-2001, from 1,000,000 tons/years to less than 100,000 tons/year, until be nearly equal to zero today.

These compounds have been replaced by much less reactive molecules, like the HFC (hydrogen fluoro carbides), mainly used for cars conditioned air systems, but there are still many suspects on CH3Br, NOx (easy to react with O2 and O3) and also on the greenhouse gases, given their effect on climate, warmer and warmer, as well in the last 20-30 years.

Some scientists are sceptical about the role of CFCs in the O3 hole

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