Besides pollution related ozone hole, what other factor is associated with depletion of Earth’s ozone layer?

Ozone depletion describes two distinct, but related phenomena observed since the late 1970s: a steady decline of about four percent in the total amount of ozone in the Earth’s stratosphere (the ozone layer) and a much larger springtime decrease in stratospheric ozone around the Earth's polar regions. The latter phenomenon is referred to as the ozone hole. In addition to these well-known stratospheric phenomena, there are also springtime polar tropospheric ozone depletion events. Reduction of plankton populations in the ocean's photic zone may result from the increased UV exposure due to ozone depletion.