ANSWER: September 16
Explanation:
21st International Day for the Preservation of the Ozone layer was celebrated across the world on September 16, 2015. The theme for this year was 30 Years of Healing the Ozone Together. The 2015 slogan was Ozone: All There is Between You and UV. The year 2015 also marks the 30th anniversary of Vienna Convention for Protection of the Ozone Layer. The Vienna Convention was signed on March 22 1985. The Montreal Protocol on Substances that Deplete the Ozone Layer was signed on September 16, 1987 and since then, this day us celebrated as the international dat for preservation of the ozone layer.