ABSTRACT
In the last two decades of the past century, the presence in the atmosphere of ozone-depleting substances (CFCs, HCFCs, halons, carbon tetrachloride, etc.) has been reducing the ozone concentration in the stratosphere over high and mid-latitudes of both hemispheres. Ozone concentration in the atmosphere is very low (about 3 parts in 10 millions), and that of the total ozone column is equivalent to that of 3 mm at standard temperature and pressure. Nevertheless, its optical density is about 45 at the absorption maximum around 255 nm, about 13 at 280 nm, and goes to 0 at 320 nm. Therefore, the stratospheric layer, which contains approximately 90% of the total ozone, has the function of a protective filter for the Earth’s surface, fully cutting off solar radiation under 280 nm and greatly reducing UV-B radiation (280 to 315 nm).
