Learn about EPA's efforts to address ozone layer depletion through international treaties and initiatives. An international agreement known as the Montreal Protocol on Substances That Deplete the Ozone Layer was reached in 1987.The Montreal Protocol is an international agreement made in 1987. It was designed to stop the production and import of ozone depleting substances. This course on forest and parks issues is the fourth in a series that focuses on environmental and public policy issues in south western Pennsylvania.