The main cause of ozone depletion and the ozone hole is manufactured chemicals, especially manufactured halocarbonrefrigerants, solvents, propellants and foam-blowing agents (chlorofluorocarbons (CFCs), HCFCs, halons), referred to as ozone-depleting substances (ODS). These compounds are transported into the stratosphere by the winds after being emitted from the surface.Once in the stratosphere, they release halogen atoms through photodissociation, which catalyze the breakdown of ozone (O₃) into oxygen (O₂).Both types of ozone depletion were observed to increase as emissions of halocarbons increased.

Ozone depletion and the ozone hole have generated worldwide concern over increased cancer risks and other negative effects. The ozone layer prevents most harmful UVB wavelengths of ultraviolet light (UV light) from passing through the Earth's atmosphere. These wavelengths cause skin cancer, sunburn and cataracts, which were projected to increase dramatically as a result of thinning ozone, as well as harming plants and animals. These concerns led to the adoption of the Montreal Protocol in 1987, which bans the production of CFCs, halons and other ozone-depleting chemicals.

Through the 1970s and the 1980s, the international community became increasingly concerned that ODS would harm the ozone layer. In 1985, the Vienna Convention for the Protection of the Ozone Layer formalized international cooperation on this issue. This cooperation resulted in the signing of the Montreal Protocol on Substances that Deplete the Ozone Layer in 1987.

The original Montreal Protocol, signed in 1987, was the first step in international efforts to protect stratospheric ozone. Under the original Montreal Protocol agreement (1987), developed countries were required to begin phasing out CFCs in 1993 and achieve a 20% reduction relative to 1986 consumption levels by 1994 and a 50% reduction by 1998. Additionally, developed countries were required to freeze their production and consumption of halons relative to their 1986 levels. After the Montreal Protocol was signed, new data showed worse-than-expected damage to the ozone layer.The Parties to the Montreal Protocol have amended the Protocol to enable, among other things, the control of new chemicals and the creation of a financial mechanism to enable developing countries to comply. The Montreal Protocol also includes a unique adjustment provision that enables the Parties to the Protocol to respond quickly to new scientific information and agree to accelerate the reductions required on chemicals already covered by the Protocol. These adjustments are then automatically applicable to all countries that ratified the Protocol. Since that time, the Montreal Protocol has been repeatedly strengthened by both controlling additional ozone-depleting substances (ODS) as well as by moving up the date by which already controlled substances must be phased out. In addition to adjustments and amendments to the Montreal Protocol, the Parties to the Protocol meet annually and take a variety of decisions aimed at enabling effective implementation of this important legal instrument.several ammendments were made.

U.S. agencies, including EPA, work with the UNEP Ozone Secretariat to implement the Montreal Protocol.

UNEP’s Division of Technology, Industry, and Economics OzonAction Programme provides industry, government, and other stakeholders in developing countries with information exchange services, training, and networking. In addition to these core clearinghouse services, the Programme also provides assistance with Country Programmes and Institutional Strengthening projects.

source:Google.com