Learn about EPA's efforts to address ozone layer depletion through international treaties and initiatives. This page summarizes the history of international cooperation on the protection of the ozone layer, including: the Vienna Convention; the Montreal Protocol.Latest events and activities related to the San Antonio area's compliance with the National Ambient Air Quality Standard (NAAQS) for ground-level ozone. Specifically, Bexar County is in exceedance of ground-level ozone standards. An international agreement known as the Montreal Protocol on Substances That Deplete the Ozone Layer was reached in 1987.