Ozone Layer Depletion

ozone depletion: Destruction of the stratospheric ozone layer, which shields earth from ultraviolet radiation harmful to life. This destruction of ozone is caused by the breakdown of certain compounds that contain chlorine, bromine, or both (chlorofluorocarbons or halons), which occurs when they reach the stratosphere and then catalytically destroy ozone molecules.

ozone hole: A well-defined, large-scale area of significant thinning of the ozone layer. It occurs over Antarctica each spring.

ozone layer: The protective stratum in the atmosphere, about 15 miles above the ground, that absorbs some of the sun’s ultraviolet rays, thereby reducing the amount of potentially harmful radiation that reaches earth’s surface.

ozone precursors: Chemicals that contribute to the formation of ozone.

Sunlight contains some ultraviolet light, and when we expose ourselves to too much of it, we get a sunburn. Over time, too much exposure to ultraviolet light can lead to cataracts and skin cancer. The earth has a layer in the upper atmosphere, consisting mostly of ozone gas, that filters out most of the ultraviolet in the sun's radiation. Recently there has been scientific evidence that we have been releasing gases that damage this layer. Our country and others have reacted by invoking legislation that should eliminate these contaminants from the atmosphere.

The ozone (O3) layer in the stratosphere protects life on earth from exposure to dangerous levels of ultraviolet light. It does so by filtering out harmful ultraviolet radiation from the sun. When CFCs and other ozone-degrading chemicals are emitted, they mix with the atmosphere and eventually rise to the stratosphere. There, the chlorine and the bromine they contain catalyze the destruction of ozone. This destruction is occurring at a more rapid rate than ozone can be created through natural processes.


The chemicals most responsible for the destruction of the ozone layer are chlorofluorocarbons, carbon tetrachloride, methyl bromide, methyl chloroform, and halons. Chlorofluorocarbons have long been widely used as coolants in refrigerators and air conditioners and as foaming agents, solvents, and aerosol propellants. Carbon tetrachloride and methyl chloroform are solvents used for essential industrial applications. In the United States, carbon tetrachloride is now used almost entirely as a feedstock for the production of chlorofluorocarbons. Hydrogenated CFCs (HCFCs) have many of the same uses as CFCs and are increasingly employed as interim substitutes for CFCs. Halons have been used in fire extinguishers.