<Tr> <Td> </Td> <Td> This article may be too technical for most readers to understand . Please help improve it to make it understandable to non-experts, without removing the technical details . The talk page may contain suggestions . (November 2014) (Learn how and when to remove this template message) </Td> </Tr> <P> Ozone depletion describes two related phenomena observed since the late 1970s: a steady decline of about four percent in the total amount of ozone in Earth's stratosphere (the ozone layer), and a much larger springtime decrease in stratospheric ozone around Earth's polar regions . The latter phenomenon is referred to as the ozone hole . There are also springtime polar tropospheric ozone depletion events in addition to these stratospheric phenomena . </P> <P> The main cause of ozone depletion and the ozone hole is man - made chemicals, especially man - made halocarbon refrigerants, solvents, propellants, and foam - blowing agents (chlorofluorocarbon (CFCs), HCFCs, halons), referred to as ozone - depleting substances (ODS). These compounds are transported into the stratosphere by the winds after being emitted at the surface . Once in the stratosphere, they release halogen atoms through photodissociation, which catalyze the breakdown of ozone (O) into oxygen (O). Both types of ozone depletion were observed to increase as emissions of halocarbons increased . </P> <P> Ozone depletion and the ozone hole 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 . </P>

Which gas is responsible for depletion of ozone layer around earth