Air

The stratospheric ozone layer

Ozone has been much talked about over the last few years, becoming an increasingly important problem, either because there is too little or too much of it. If there is too much ozone in the troposphere (that is in the part of the atmosphere that is closest to the ground, the one where we live and that we breathe), it represents one of the most harmful substances of photochemical smog (“bad ozone”). In the stratosphere, instead, (i.e. in the part of the atmosphere that is highest and most distant from us), ozone is extremely useful and there must be plenty of it, since it works as a natural screen (good ozone) that filters out the harmful ultraviolet rays emitted by the sun (UV). In the last few years, though, the amount of ozone contained in the stratosphere seems to have decreased due to some substances of anthropogenic origin (the notorious “ozone hole”).  The emissions for industrial, agricultural and private uses of some substances, such as chlorofluorocarbons (CFC), methyl bromide, halons and methyl chloroform, contribute, either directly or indirectly, to destroy the precious molecules of the stratospheric ozone. Even if it affects the whole atmosphere, the stratospheric ozone layer seems to be more depleted at the poles. The most direct consequence of the hole in the ozone layer is an increase in the amount of ultraviolet rays (UV-B) that reach the Earth’s surface. These rays cause: a higher risk of tumours and eye diseases  a decrease in men and animals’ immune defences a reduction in the photosynthesis and damages to the DNA of plants, with a significant impact on farming  a reduction in the production of phytoplankton in the sea, with significant damages in the food chain of water ecosystems.