The ozone layer is important because it blocks ultraviolet radiation from the sun that causes many detrimental effects to living things. Ultraviolet radiation affects a plant's ability to grow and can cause skin cancer and cataracts in humans. Ultraviolet radiation also affects the fertility rate of some animals.
Ozone is present in the upper and lower layers of the atmosphere. Approximately 90 percent of all ozone is in the upper atmosphere and is responsible for filtering the ultraviolet radiation. This upper level ozone is called the ozone layer. The ozone layer is considered beneficial for life on earth. The lower level ozone is an air pollutant that is highly reactive and is considered toxic to living things. Ozone is a blue gas with a strong odor. It is composed of three oxygen atoms.
Ozone naturally breaks down in the atmosphere, but this generally occurs at a relatively stable rate without the addition of chlorofluorocarbons. The emission of chlorofluorocarbons from refrigerants, fire extinguishers, and aerosol propellants damages the ozone in the atmosphere. This damage results in a thinning of the ozone layer. The Montreal Protocol of 1987 was enacted to limit chlorofluorocarbon production and to allow the ozone layer to repair itself.