The atmosphere is a blanket that covers the world and allows the living creatures of the world to survive. It holds in our oxygen and keeps the harmful UV rays away from the planet. Due to pollution and other causes, this blanket has been torn. Now we are not protected at the same level as before. Ozone depletion is one of the most significant environmental problems, which scientists around the world pays attention to, even in the United States. The ozone layer plays a critical role in filtering the appropriate amount of ultraviolet radiation (UV) penetrates to the surface of the earth. Ozone depletion, the result of over using chemicals such as chlorofluorocarbons and methyl bromide has caused many negative effects on humans, plants, marine ecosystems and materials; however, we can help to reduce further depletion by limiting the use of such chemicals, which has been attempted in some cities in the USA.
             According to the Center for International Earth Science Information Network (2001), the major substance that destroys the ozone layer is the chemical widely known as chlorofluorocarbons (CFCs). This substance was invented in 1920's with the properties of low toxicity, nonflammability and nonreactivity with other chemicals. Because of the beneficial characters of this chemical, it has been widely used, for example, as coolants in refrigeration systems and air conditioners, for cleaning electronic components and as blowing agent in the production of plastic foams. Money (1993) notes that CFCs have been spread over in the air to destroy the ozone layer and have remained in the air for 80 years or more.
             The United States Environmental Protection Agency asserts that Methyl Bromide is also another ozone depleting substance. This element is widely used in agriculture as the pesticide. In the USA, the high percentage of using it is for soil sterilization by injecting into soil before planting, after that 50-95% of methyl bromide gas ...