The ozone depletion phenomenon
Ozone depletion occurs when chlorofluorocarbons CFCs and halons—gases formerly found in aerosol spray cans and refrigerants—are released into the atmosphere see details below.
We publish prepublications to facilitate timely access to the committee's findings. A case in point: the group of chemicals known as CFCs. It is important to precise that HFCs do not act as ozone depleting substance.
Ozone layer depletion facts
Hartley discovered that a broad band of ultraviolet light reaches Earth almost unimpeded. However, more recent analysis in by David W. As this layer prevents the Ultra Violet OV rays of the sunlight coming to the Earth, it protects animals and vegetation from the dangerous effect of UV rays. With less ozone in the atmosphere, more ultraviolet radiation strikes Earth, causing more skin cancer, eye damage, and possible harm to crops. Chemical reactions that take place on PSC particles convert less-reactive chlorine-containing molecules to more-reactive forms such as molecular chlorine Cl2 that accumulate during the polar night. One Dobson unit represents 0. The rate of stratospheric ozone depletion slowed considerably after the implementation of the Montreal Protocol adopted in , see below , banning the use of CFCs and replacement substances also recognised as ozone-depleting pollutants. Gardiner, and Jonathan D. By the late s, atmospheric scientists had isolated carbon monoxide and inferred the existence of a second combustible gas in the air, which they tentatively identified as methane, the simplest hydrocarbon. They identify key chemical reactions and transport processes that bring CFC photolysis products into contact with ozone.
Some stratospheric cooling is also predicted from increases in greenhouse gases such as CO 2 and CFCs themselves; however, the ozone-induced cooling appears to be dominant. After eight weeks, the hole leaves Antarctica, only to pass over more populated areas, including New Zealand and Australia.
They prohibit production of CFCs.
Ground-level ozone is generally recognized to be a health risk, as ozone is toxic due to its strong oxidant properties.
The Montreal and Vienna conventions were installed long before a scientific consensus was established or important uncertainties in the science field were being resolved.
Article on ozone layer
The latter phenomenon is referred to as the ozone hole. In the simplest example of such a cycle, a chlorine atom reacts with an ozone molecule, taking an oxygen atom forming ClO, chlorine monoxide and leaving a normal oxygen molecule O2. However, more recent analysis in by David W. Together, they form the ozone layer, which covers the entire globe in varying thicknesses. A satellite image of the ozone hole pink area over Antarctica taken on September 25, In , the Protocol had been ratified by Parties to the Convention. By , when better evidence on the speed of critical reactions was available, this estimate was changed to 5 to 9 percent steady-state depletion. Key Points Photochemical reactions in the stratosphere lead to the conversion of oxygen gas O2 into atomic oxygen O and ozone O3 ; these forward and reverse reactions are in very delicate balance. However, scientific completeness required that the researchers explore not only the fate of the CFCs, but also of the highly reactive atomic and molecular fragments generated by the ultraviolet radiation. The most prominent decrease in ozone has been in the lower stratosphere.
Atmospheric gases are not sorted by weight, however; wind forces can fully mix the gases in the atmosphere, which readily diffuse into the stratosphere. The participants agreed to phase out CFCs and halons entirely aside from a very small amount marked for certain "essential" uses, such as asthma inhalers by in non-Article 5 countries and by in Article 5 less developed signatories.
based on 117 review