he ozone layer is a layer in Earth's atmosphere containing relatively high concentrations of ozone (O3). However, "relatively high," in the case of ozone, is still very small with regard to ordinary oxygen, and is less than 10 parts per million, with the average ozone concentration in Earth's atmosphere being only about 0.6 parts per million. The ozone layer is mainly located in the lower portion of the stratosphere from approximately 20 to 30 kilometres (12 to 19 mi) above Earth, though the thickness varies seasonally and geographically.]
The ozone layer was discovered in 1913 by the French physicists Charles Fabry and Henri Buisson. Its properties were explored in detail by the British meteorologist G. M. B. Dobson, who developed a simple spectrophotometer (the Dobsonmeter) that could be used to measure stratospheric ozone from the ground. Between 1928 and 1958 Dobson established a worldwide network of ozone monitoring stations, which continue to operate to this day. The "Dobson unit", a convenient measure of the columnar density of ozone overhead, is named in his honor.