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Methyl bromide. Control of ozone depleting substances. Reducing ozone depleting substances. Related Topics: Ozone Layer Protection. Contact Us. Additional Information. Qin, M. Manning, Z. Chen, M. Marquis, K. Averyt, M. Tignor and H. Miller eds. Qin, G. Even a small action can make an enormous difference when millions of people do it!
Skip to content. Skip to navigation. If you have forgotten your password, we can send you a new one. Many aerosol propellents contained CFCs before international agreements limited their use. The ozone layer sits in the stratosphere between 15 km and 30 km above the earth. It absorbs most of the sun's ultraviolet radiation UV-B , limiting the amount of this radiation that reaches the surface of the Earth.
Because this radiation causes skin cancer and cataracts, the ozone layer plays an important role in protecting human health. It also prevents radiation damage to plants, animals, and materials. In the s, scientists noticed that the ozone layer was thinning. Researchers found evidence that linked the depletion of the ozone layer to the presence of chlorofluorocarbons CFCs and other halogen-source gases in the stratosphere.
Ozone-depleting substances ODS are synthetic chemicals, which were used around the world in a wide range of industrial and consumer applications. The main uses of these substances were in refrigeration and air conditioning equipment and in fire extinguishers. Other important uses included aerosol propellants, solvents and blowing agents for insulation foams. To halt the depletion of the ozone layer, countries around the world agreed to stop using ozone-depleting substances.
In , the Vienna Convention and the Montreal Protocol became the first treaties in the history of the United Nations to achieve universal ratification. Substances covered by the protocol are referred to as 'controlled substances'. The main substances include chlorofluorocarbons CFCs , hydrochlorofluorocarbons HCFCs , halons, carbon tetrachloride, methyl chloroform and methyl bromide.
The damage to the ozone layer caused by each of these substances is expressed as their ozone depletion potential ODP. These international agreements helped to greatly reduce the worldwide use of ozone-depleting substances in Europe and around the World Figure 1. Scientific monitoring shows signs that the ozone layer is starting to recover. Full recovery is not expected to occur before the middle of the 21st century. The reduction in ozone-depleting substances has also had a beneficial side-effect.
Ozone-depleting substances are also very potent greenhouse gases, contributing to the phenomenon as other substances widely known to have a greenhouse effect like carbon dioxide CO 2 , methane CH 4 and nitrous oxide N 2 O. Therefore, by reducing emissions of ozone-depleting substances, the Montreal Protocol has protected both the ozone layer and the climate at the same time.
The magnitude of this benefit is substantial. The reduction in ODS emissions expected as a result of compliance with the Montreal Protocol has been estimated globally at giga-tonnes of CO 2 -equivalent between and Velders et al. At the time, CFCs were commonly used in aerosol sprays and as coolants in many refrigerators.
As they reach the stratosphere, the sun's UV rays break CFCs down into substances that include chlorine. One atom of chlorine can destroy more than , ozone molecules, according to the U. Environmental Protection Agency, eradicating ozone much more quickly than it can be replaced. The "hole" is actually an area of the stratosphere with extremely low concentrations of ozone that reoccurs every year at the beginning of the Southern Hemisphere spring August to October. Spring brings sunlight, which releases chlorine into the stratospheric clouds.
Recognition of the harmful effects of CFCs and other ozone-depleting substances led to the Montreal Protocol on Substances That Deplete the Ozone Layer in , a landmark agreement to phase out those substances that has been ratified by all UN member countries.
Without the pact, the U. More than 30 years after the Montreal Protocol, NASA scientists documented the first direct proof that Antarctic ozone is recovering because of the CFC phase-down: Ozone depletion in the region has declined 20 percent since And at the end of , the United Nations confirmed in a scientific assessment that the ozone layer is recovering, projecting that it would heal completely in the non-polar Northern Hemisphere by the s, followed by the Southern Hemisphere in the s and polar regions by A study in early found that ozone in the lower stratosphere unexpectedly and inexplicably has dropped since , while another pointed to possible ongoing violations of the Montreal pact.
The world is not yet in the clear when it comes to harmful gases from coolants. Some hydrochlorofluorocarbons HCFCs , transitional substitutes that are less damaging but still harmful to ozone, are still in use. Developing countries need funding from the Montreal Protocol's Multilateral Fund to eliminate the most widely used of these, the refrigerant R The next generation of coolants, hydrofluorocarbons HFCs , do not deplete ozone, but they are powerful greenhouse gases that trap heat, contributing to climate change.
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