Editing Ozone (section)

====Importance to surface-dwelling life on Earth====
[[File:Ozone altitude UV graph.svg|thumb|upright=1.25|Levels of ozone at various altitudes and blocking of different bands of ultraviolet radiation. Essentially all UVC (100–280&nbsp;nm) is blocked by dioxygen (at 100–200&nbsp;nm) or by ozone (at 200–280&nbsp;nm) in the atmosphere. The shorter portion of this band and even more energetic UV causes the formation of the ozone layer, when single oxygen atoms produced by UV [[photolysis]] of dioxygen (below 240&nbsp;nm) react with more dioxygen. The ozone layer itself then blocks most, but not quite all, sunburn-producing UVB (280–315&nbsp;nm). The band of UV closest to visible light, UVA (315–400&nbsp;nm), is hardly affected by ozone, and most of it reaches the ground.]]

Ozone in the ozone layer filters out sunlight wavelengths from about 200&nbsp;nm UV rays to 315&nbsp;nm, with ozone peak absorption at about 250&nbsp;nm.<ref>{{cite journal |title=Photolysis of Atmospheric Ozone in the Ultraviolet Region |year=2003 |last1=Matsumi |first1=Yutaka |last2=Kawasaki |first2=Masahiro |journal=Chemical Reviews |volume=103 |issue=12 |pages=4767–82 |pmid=14664632 |doi=10.1021/cr0205255}} See the graphical absorption of ozone in two of its absorption bands, as a function of wavelength.</ref> This ozone UV absorption is important to life, since it extends the absorption of UV by ordinary oxygen and nitrogen in air (which absorb all wavelengths < 200&nbsp;nm) through the lower UV-C (200–280&nbsp;nm) and the entire UV-B band (280–315&nbsp;nm). The small unabsorbed part that remains of UV-B after passage through ozone causes sunburn in humans, and direct DNA damage in living tissues in both plants and animals. Ozone's effect on mid-range UV-B rays is illustrated by its effect on UV-B at 290&nbsp;nm, which has a radiation intensity 350 million times as powerful at the top of the atmosphere as at the surface. Nevertheless, enough of UV-B radiation at similar frequency reaches the ground to cause some sunburn, and these same wavelengths are also among those responsible for the production of [[vitamin D]] in humans.

The ozone layer has little effect on the longer UV wavelengths called UV-A (315–400&nbsp;nm), but this radiation does not cause sunburn or direct DNA damage. While UV-A probably does cause long-term skin damage in certain humans, it is not as dangerous to plants and to the health of surface-dwelling organisms on Earth in general (see [[ultraviolet]] for more information on near ultraviolet).