Ozone Layer Depletion

Ozone Layer Depletion
The ozone layer is a belt of naturally occurring ozone gas that sits 9.3 to 18.6 miles (15 to 30 kilometers) above Earth and serves as a shield from the harmful ultraviolet B radiation emitted by the sun.
Ozone is a highly reactive molecule that contains three oxygen atoms. It is constantly being formed and broken down in the high atmosphere, 6.2 to 31 miles (10 to 50 kilometers) above Earth, in the region called the stratosphere.
Today, there is widespread concern that the ozone layer is deteriorating due to the release of pollution containing the chemicals chlorine and bromine. Such deterioration allows large amounts of ultraviolet B rays to reach Earth, which can cause skin cancer and cataracts in humans and harm animals as well.
Extra ultraviolet B radiation reaching Earth also inhibits the reproductive cycle of phytoplankton, single-celled organisms such as algae that make up the bottom rung of the food chain. Biologists fear that reductions in phytoplankton populations will in turn lower the populations of other animals. Researchers also have documented changes in the reproductive rates of young fish, shrimp, and crabs as well as frogs and salamanders exposed to excess ultraviolet B.
Chlorofluorocarbons (CFCs), chemicals found mainly in spray aerosols heavily used by industrialized nations for much of the past 50 years, are the primary culprits in ozone layer breakdown. When CFCs reach the upper atmosphere, they are exposed to ultraviolet rays, which causes them to break down into substances that include chlorine. The chlorine reacts with the oxygen atoms in ozone and rips apart the ozone molecule.
One atom of chlorine can destroy more than a hundred thousand ozone molecules, according to the the U.S. Environmental Protection Agency.
The ozone layer above the Antarctic has been particularly impacted by pollution since the mid-1980s. This region’s low temperatures speed up the conversion of CFCs to chlorine. In the southern spring and summer, when the sun shines for long periods of the day, chlorine reacts with ultraviolet rays, destroying ozone on a massive scale, up to 65 percent. This is what some people erroneously refer to as the "ozone hole." In other regions, the ozone layer has deteriorated by about 20 percent.
About 90 percent of CFCs currently in the atmosphere were emitted by industrialized countries in the Northern Hemisphere, including the United States and Europe. These countries banned CFCs by 1996, and the amount of chlorine in the atmosphere is falling now. But scientists estimate it will take another 50 years for chlorine levels to return to their natural levels.

Causes
Only a few factors combine to create the problem of ozone layer depletion.  The production and emission of CFCs, chlorofluorocarbons, is by far the leading cause.
Many countries have called for the end of CFC production because only a few produce the chemical.  However, those industries that do use CFCs do not want to discontinue usage of this highly valuable industrial chemical.
CFCs are used in industry in a variety of ways and have been amazingly useful in many products.  Discovered in the 1930s by American chemist Thomas Midgley, CFCs came to be used in refrigerators, home insulation, plastic foam, and throwaway food containers.
Only later did people realize the disaster CFCs caused in the stratosphere.  There, the chlorine atom is removed from the CFC and attracts one of the three oxygen atoms in the ozone molecule.  The process continues, and a single chlorine atom can destroy over 100,000 molecules of ozone.
In 1974, Sherwood Rowland and Mario Molina followed the path of CFCs.  Their research proved that CFCs were entering the atmosphere, and they concluded that 99% of all CFC molecules would end up in the stratosphere.
Only in 1984, when the ozone layer hole was discovered over Antarctica, was the proof truly conclusive.  At that point, it was hard to question the destructive capabilities of CFCs.
Even if CFCs were banned, problems would remain.  There would still be no way to remove the CFCs that are now present in the environment.  Clearly though, something must be done to limit this international problem in the future.

CFCl₃ + hλ      --------->  CFCl₂ + Cl^-

Cl^- +O_{3    ---------------->}    ClO + O₂

ClO + O_{3   ---------------------->}  Cl^- + 2O₂

So, from one molecule of CFCl3 millions of O3 molecules break down into oxygen, making ozone hole.
                                                                                       
Effects
Even minor problems of ozone depletion can have major effects.  Every time even a small amount of the ozone layer is lost, more ultraviolet light from the sun can reach the Earth.
Every time 1% of the ozone layer is depleted, 2% more UV-B is able to reach the surface of the planet.  UV-B increase is one of the most harmful consequences of ozone depletion because it can cause skin cancer.
The increased cancer levels caused by exposure to this ultraviolet light could be enormous.  The EPA estimates that 60 million Americans born by the year 2075 will get skin cancer because of ozone depletion.  About one million of these people will die.
In addition to cancer, some research shows that a decreased ozone layer will increase rates of malaria and other infectious diseases.  According to the EPA, 17 million more cases of cataracts can also be expected.
The environment will also be negatively affected by ozone depletion.  The life cycles of plants will change, disrupting the food chain.  Effects on animals will also be severe, and are very difficult to foresee.
Oceans will be hit hard as well.  The most basic microscopic organisms such as plankton may not be able to survive.  If that happened, it would mean that all of the other animals that are above plankton in the food chain would also die out.  Other ecosystems such as forests and deserts will also be harmed.
The planet's climate could also be affected by depletion of the ozone layer.  Wind patterns could change, resulting in climatic changes throughout the world.

Is there any solution??
The discovery of the ozone depletion problem came as a great surprise.  Now, action must be taken to ensure that the ozone layer is not destroyed.
Because CFCs are so widespread and used in such a great variety of products, limiting their use is hard.  Also, since many products already contain components that use CFCs, it would be difficult if not impossible to eliminate those CFCs already in existence.
The CFC problem may be hard to solve because there are already great quantities of CFCs in the environment.  CFCs would remain in the stratosphere for another 100 years even if none were ever produced again.
Despite the difficulties, international action has been taken to limit CFCs.  In the Montreal Protocol, 30 nations worldwide agreed to reduce usage of CFCs and encouraged other countries to do so as well.
However, many environmentalists felt the treaty did "too little, too late", as theNatural Resources Defense Council put it.  The treaty asked for CFC makers to only eliminate half of their CFC production, making some people feel it was inadequate.
By the year 2000, the US and twelve nations in Europe have agreed to ban all use and production of CFCs.  This will be highly significant, because these countries produce three quarters of the CFCs in the world.
Many other countries have signed treaties and written laws restricting the use of CFCs.  Companies are finding substitutes for CFCs, and people in general are becoming more aware of the dangers of ozone depletion.

There are two international declaration on protection of ozone layer.
The Vienna Convention for the Protection of the Ozone Layer and The Montreal Protocol on Substances that deplete the Ozone Layer.