What is Ozone depletion?
[[File:NASA and NOAA Announce Ozone Hole is a Double Record Breaker.png|thumb|Image of the largest [[Antarctica|Antarctic]] ozone hole ever recorded (September 2006).]] [[Ozone]] is a [[Gas]] that is present in the [[ozone layer]] in the [[stratosphere]] of the [[Earth]]. There, it absorbs almost all [[Ultraviolet light|ultraviolet]] light which is harmful to many [[organism]]s. The term '''Ozone depletion''' can refer to a number of distinct, but related phenomena: * Since the 1970s, there has been a decrease in total volume of the Ozone in the ozone layer, of about 4%, per [[decade]]. * There are seasonal variations in the ozone layers; in springtime, there is less ozone in the ozone layer over the polar regions, esp. the south pole. This is generally known as '''ozone hole'''. * In addition to these well-known stratospheric phenomena, there are also springtime polar [[Troposphere|tropospheric]] ozone depletion events. == Causes == The details of polar ozone hole formation differ from that of mid-latitude thinning, but the most important process in both is [[Catalysis|catalytic]] destruction of ozone by atomic [[halogen]]s.<ref>{{cite web | url = http://www.atm.ch.cam.ac.uk/tour/part3.html | title = Part III. The Science of the Ozone Hole | accessdate = 2007-03-05}} </ref> The main source of these halogen atoms in the stratosphere is [[photodissociation]] of man-made [[halocarbon]] refrigerants ([[chlorofluorocarbon|CFCs]], [[freon]]s, halons.) These compounds are transported into the stratosphere after being emitted at the surface.<ref>{{cite web |author=Andino, Jean M. | url = http://www.sciam.com/article.cfm?id=chlorofluorocarbons-cfcs | title = Chlorofluorocarbons (CFCs) are heavier than air, so how do scientists suppose that these chemicals reach the altitude of the ozone layer to adversely affect it? | date=21 October 1999 |publisher=Sci. Am.}} </ref> Both types of ozone depletion were observed to increase as emissions of Halocarbons increased. CFCs and other substances contributing to this effect are