Ozone Depletion

Topics: Ozone depletion, Oxygen, Ultraviolet Pages: 6 (1702 words) Published: June 27, 2013
Ozone (/ˈoʊzoʊn/; O3), or trioxygen, is a triatomic molecule, consisting of three oxygen atoms. It is an allotrope of oxygen that is much less stable than the diatomic allotrope(O2), breaking down in the lower atmosphere to normal dioxygen. Ozone is formed from dioxygen by the action of ultraviolet light and also atmospheric electrical discharges, and is present in low concentrations throughout the Earth's atmosphere. In total, ozone makes up only 0.6 parts per million of the atmosphere. Gaseous ozone is bluish in color and has a pungent, distinctive smell that condenses at progressively cryogenic temperatures to a dark blue liquid and finally a violet-black solid

The ozone layer is a layer in Earth's atmosphere which absorbs most of the Sun's UV radiation. It contains relatively high concentrations of ozone (O3), although it is still very small with regard to ordinary oxygen, and is less than ten parts per million, the average ozone concentration in Earth's atmosphere being only about 0.6 parts per million. The ozone layer is mainly found in the lower portion of the stratosphere from approximately 20 to 30 kilometers (12 to 19 mi) above Earth, though the thickness varies seasonally and geographically.[1] The ozone layer absorbs 97–99% of the Sun's medium-frequency ultraviolet light (from about 200 nm to 315 nm wavelength), which potentially damages exposed life forms on Earth. Although the concentration of the ozone in the ozone layer is very small, it is vitally important to life because it absorbs biologically harmful ultraviolet (UV) radiation coming from the sun.

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.

The thickness of the ozone layer—that is, the total amount of ozone in a column overhead—varies by a large factor worldwide, being in general smaller near the equator and larger towards the poles. It also varies with season, being in general thicker during the spring and thinner during the autumn in the northern hemisphere. The reasons for this latitude and seasonal dependence are complicated, involving atmospheric circulation patterns as well as solar intensity. The ozone layer is higher in altitude in the tropics, and lower in altitude in the extra tropics, especially in the polar regions.


Scientists have worked to understand the chemistry of the ozone layer since its discovery in the 1920s. In 1930 British geophysicist Sydney Chapman described a process in which strong UV photons photolyze oxygen molecules (O2) into highly reactive oxygen atoms. These atoms rapidly combine with O2 to form ozone (O3) (Fig. 16). This process is still recognized as the only significant source of ozone to the stratosphere. Research and controversy have focused on identifying stratospheric ozone sinks. Ozone is produced by different processes in the stratosphere, where it is beneficial, and near the Earth's surface in the troposphere, where it is harmful. The mechanism for stratospheric ozone formation, photolysis of O2, does not take place in the troposphere because the strong UV photons needed for this photolysis have been totally absorbed by O2 and ozone in the stratosphere. www.learners.org.com


Oxygen absorbs UV-B or more energetic radiation (most commonly from our Sun), and dissociates into two separate oxygen atoms. Some of these...
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