September 16th every year is marked as the International Day for the Preservation of the Ozone Layer. On this day 32 years ago, 45 countries signed a treaty to phase out the use of the substances that harm or deplete the ozone layer, however all 197 countries of the world ratified the agreement later. The ozone layer is a part of the atmosphere that has high concentrations of ozone, compared to oxygen molecules that exist in nature as a pair of oxygen atoms. It exists 10-40 kms above the surface of the earth in a region called the stratosphere and contains 90% of all the ozone in the atmosphere.