Ozone layer

The ozone layer is mainly found in the lower portion of the stratosphere, from approximately 15 to 35 kilometers (9 to 22 mi) above Earth, although its thickness varies seasonally and geographically.

[3] 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.

[4] In 1985, atmospheric research revealed that the ozone layer was being depleted by chemicals released by industry, mainly chlorofluorocarbons (CFCs).

The United Nations General Assembly has designated September 16 as the International Day for the Preservation of the Ozone Layer.

[11] Research has found that the ozone levels in the United States are highest in the spring months of April and May and lowest in October.

While there are natural sources for all of these species, the concentrations of chlorine and bromine increased markedly in recent decades because of the release of large quantities of man-made organohalogen compounds, especially chlorofluorocarbons (CFCs) and bromofluorocarbons.

[14] Atmospheric components are not sorted out by weight in the homosphere because of wind-driven mixing that extends to an altitude of about 90 km, well above the ozone layer.

So despite being heavier than diatomic nitrogen and oxygen, these highly stable compounds rise into the stratosphere, where Cl and Br radicals are liberated by the action of ultraviolet light.

For approximately 5 percent of the Earth's surface, around the north and south poles, much larger seasonal declines have been seen, and are described as "ozone holes".

[16] The discovery of the annual depletion of ozone above the Antarctic was first announced by Joe Farman, Brian Gardiner, and Jonathan Shanklin, in a paper which appeared in Nature on May 16, 1985.

Regulation attempts have included but not have been limited to the Clean Air Act implemented by the United States Environmental Protection Agency.

[17] Effective presentation of information has also proven to be important in order to educate the general population of the existence and regulation of ozone depletion and contaminants.

A scientific paper was written by Sheldon Ungar in which the author explores and studies how information about the depletion of the ozone, climate change, and various related topics.

The ozone case was communicated to lay persons "with easy-to-understand bridging metaphors derived from the popular culture" and related to "immediate risks with everyday relevance".

[22] In 1978, the United States, Canada, and Norway enacted bans on CFC-containing aerosol sprays that damage the ozone layer but the European Community rejected a similar proposal.

After negotiation of an international treaty (the Montreal Protocol), CFC production was capped at 1986 levels with commitments to long-term reductions.

[26] On August 2, 2003, scientists announced that the global depletion of the ozone layer might be slowing because of the international regulation of ozone-depleting substances.

In a study organized by the American Geophysical Union, three satellites and three ground stations confirmed that the upper-atmosphere ozone-depletion rate slowed significantly over the previous decade.

The Galaxy Evolution Explorer, GALEX, is an orbiting ultraviolet space telescope launched on April 28, 2003, which operated until early 2012.

The ozone layer visible from space at Earth's horizon as a blue band of afterglow within the bottom of the large bright blue band that is the stratosphere , with a silhouette of a cumulonimbus in the orange afterglow of the troposphere .
Ozone-oxygen cycle in the ozone layer
UV-B energy levels at several altitudes. Blue line shows DNA sensitivity. Red line shows surface energy level with 10 percent decrease in ozone
Levels of ozone at various altitudes and blocking of different bands of ultraviolet radiation. Essentially all UV-C (100–280 nm) is blocked by dioxygen (from 100–200 nm) or else by ozone (200–280 nm) in the atmosphere. The shorter portion of the UV-C band and the more energetic UV above this band causes the formation of the ozone layer, when single oxygen atoms produced by UV photolysis of dioxygen (below 240 nm) react with more dioxygen. The ozone layer also blocks most, but not quite all, of the sunburn-producing UV-B (280–315 nm) band, which lies in the wavelengths longer than UV-C. The band of UV closest to visible light, UV-A (315–400 nm), is hardly affected by ozone, and most of it reaches the ground. UV-A does not primarily cause skin reddening, but there is evidence that it causes long-term skin damage.
Ozone layer within Earth's atmosphere by altitude
Brewer–Dobson circulation in the ozone layer
NASA projections of stratospheric ozone concentrations if chlorofluorocarbons had not been banned
Levels of atmospheric ozone measured by satellite show clear seasonal variations and appear to verify their decline over time.