International Day for the Preservation of the Ozone Layer, also known as World Ozone Day, commemorates the date of the signing of the Montreal Protocol on substances that deplete the ozone layer.
It is an international protocol designed to protect the vulnerable ozone layer in the stratosphere from damage by man-made chemicals that were, and still are released into the atmosphere.
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.
South Africa acceded to the Montreal Protocol on substance depletion of the ozone layer in 1990.
Phasing out ozone depleting substances has proven to be a powerful tool for climate action that has helped slow global warming, for example, postponing the first ice-free Arctic summer by up to 15 years.
Ozone facts
Chemically, ozone is very active; it reacts readily with a great many other substances. Near the Earth’s surface, those reactions cause rubber to crack, hurt plant life, and damage people’s lung tissues. But ozone also absorbs harmful components of sunlight, known as “ultraviolet B”, or “UV-B”. High above the surface, above even the weather systems, a tenuous layer of ozone gas absorbs UV-B, protecting living things below.
The Dobson is the unit of measure for total ozone. If you were to take all the ozone in a column of air stretching from the surface of the earth to space and bring all that ozone to standard temperature (0 °Celsius) and pressure (1013.25 millibars, or one atmosphere, or “atm”), the column would be about 0.3 centimeters thick. Thus, the total ozone would be 0.3 atm-cm. To make the units easier to work with, the “Dobson Unit” is defined to be 0.001 atm-cm. Our 0.3 atm-cm would be 300 DU.
What is:
Each year chemical reactions involving chlorine and bromine cause ozone in the southern polar region severely. This depleted region is known as the “ozone hole”. The area of the ozone hole is determined from a map of total column ozone. It is calculated from the area on the Earth that is enclosed by a line with a constant value of 220 Dobson Units. The value of 220 Dobson Units is chosen since total ozone values of less than 220 Dobson Units were not found in the historic observations over Antarctica prior to 1979. Also, from direct measurements over Antarctica, a column ozone level of less than 220 Dobson Units is a result of the ozone loss from chlorine and bromine compounds.
The focus of International Day for the Preservation of the Ozone Layer centers around the theme “Montreal Protocol: Advancing Climate Action,” underscoring the beneficial outcomes of the Montreal Protocol in fostering the recovery of the ozone layer and mitigating climate change.
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