The ozone layer refers to the ozone within the stratosphere of the Earth, where over 90 % of the Earth’s ozone resides. This layer absorbs the Sun’s high-energy ultraviolet radiation of wavelengths <290 nm. The concentration of ozone is measured in Dobson units (DU).
The existence of an ozone layer in the upper regions of our atmosphere was detected in 1913 by Charles Fabry and Henri Buisson. In 1924, G.M.B. Dobson built the first spectrograph to measure the seasonal variation of ozone. From 1928 to 1958, Dobson established a worldwide network of ozone monitoring stations that are operating up to date. In his honor the “Dobson unit” was defined as measure of the columnar density of ozone above the Earth surface (see definition below).