International Day for the Preservation of the Ozone Layer is observed on September 16, 2017. The day was designated by the United Nations General Assembly. This designation was made on December 19, 1994, in commemoration of the date, in 1987, on which nations signed the Montreal Protocol on Substances that Deplete the Ozone Layer.
The ozone layer is a layer in Earth's atmosphere which absorbs most of the Sun's UV radiation. The ozone layer absorbs 97–99% of the Sun's medium-frequency ultraviolet light, which otherwise would potentially damage exposed life forms on Earth. Ozone depletion describes two distinct but related phenomena observed since the late 1970s: a steady decline of about 4% per decade in the total volume of ozone in Earth's stratosphere, and a much larger springtime decrease in stratospheric ozone over Earth's polar regions. The latter phenomenon is referred to as the ozone hole.
CFCs and other contributory substances are referred to as ozone-depleting substances. Since the ozone layer prevents most harmful UVB wavelengths of UV light from passing through the Earth's atmosphere, observed and projected decreases in ozone have generated worldwide concern leading to adoption of the Montreal Protocol that bans the production of CFCs, halons, and other ozone-depleting chemicals such as carbon tetrachloride and trichloroethane.
It is suspected that a variety of biological consequences such as increases in skin cancer, cataracts, damage to plants, and reduction of plankton populations in the ocean's photic zone may result from the increased UV exposure due to ozone depletion.
(With material from: Wikipedia)