<Table> <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 . (November 2014) (Learn how and when to remove this template message) </Td> </Tr> </Table> <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 . (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>

We are concerned about ozone depletion in what layer of the atmosphere