World Ozone Day, commemorating the date of the signing, in 1987, of the Montreal Protocol on substances that deplete the ozone layer.
The principal aim of the Montreal Protocol is to protect the ozone layer by taking measures to control total global production and consumption of substances that deplete it, with the ultimate objective of their elimination based on developments in scientific knowledge and technological information.
The Montreal Protocol on substances that deplete the ozone layer regulates production and consumption of nearly 100 chemicals. Since the ban on halocarbons, the ozone layer has slowly been recovering, according to World Meteorological Organisation.
The ozone layer is depleted in two ways. Firstly, the ozone layer in the mid-latitude (e.g., over Australia) is thinned, leading to more Ultraviolet (UV) radiation reaching the earth. Data collected in the upper atmosphere have shown that there has been a general thinning of the ozone layer over most of the globe. This includes a five to nine per cent depletion over Australia since the 1960s, which has increased the risk that Australians already face from over-exposure to UV radiation resulting from our outdoor lifestyle. Secondly, the ozone layer over the Antarctic, and to a lesser extent the Arctic, is dramatically thinned in spring, leading to an 'ozone hole'.
Atmospheric data demonstrates that ozone depleting substances are destroying ozone in the stratosphere and thinning the earth’s ozone layer. Ozone depleting substances are chemicals that include chlorofluorocarbons (CFCs), halons, carbon tetrachloride (CCl4), methyl chloroform (CH3CCl3), hydrobromofluorocarbons (HBFCs), hydrochlorofluorocarbons (HCFCs), methyl bromide (CH3Br) and bromochloromethane (CH2BrCl). They deplete the ozone layer by releasing chlorine and bromine atoms into the stratosphere, which destroy ozone molecules. These and other ozone depleting substances also contribute, to varying extents, to global warming.
Some ozone depleting substances with a high ozone depleting potential are still used in quarantine and safety applications as no suitable alternative exists. Methyl bromide is extremely effective as a quarantine fumigant. The immediate fire suppression qualities of halon are needed in confined spaces such as on airplanes and in submarines. Research is continuing to find suitable replacements.
The theme of World Ozone Day 2021 is “Ozone for Life: 36 Years of Ozone Layer Protection”.
Every four years, the World Meteorological Organisation and the United Nations Environment Programme review the state of the ozone layer. These reviews show that the abundance of ozone depleting chemicals in the atmosphere is now declining, and the ozone layer is expected to recover to pre-1980 levels over the mid-latitudes by 2050 and over the Antarctic by 2065.