The annual formation of the Antarctic Ozone Hole is a dynamic process combining extreme environmental factors with manmade chemicals to destroy the ozone layer in an incredible display of catalytic destruction. While destructive chlorine damages the Ozone Layer globally, the danger is most apparent during the annual formation of the Antarctic Ozone Hole. Before the discovery of the Ozone Hole over Antarctica, there was intense debate over just how dangerous the use of CFC’s (chlorofluorocarbons) could actually be to stratospheric ozone. CFC’s are incredibly useful chemicals that were used in a wide variety of industrial applications, refrigeration, air conditioning, and aerosol delivery because of their safety and non-toxicity. The discovery of the Ozone Hole over Antarctica was a shock to the entire world, even to those who had already been calling for limiting their use.
The stability of CFC’s are actually part of the problem. Though these chemicals do not react with much of anything down at the surface, they are so long-lived, taking decades to break down, that they will eventually find their way high in to the stratosphere. Once above much of the protection of the atmosphere, high energy ultraviolet radiation from the Sun breaks them apart, releasing destructive chlorine directly in to the ozone layer. This free chlorine destroys a small percentage of ozone molecules, but they continually get bound up in semi-stable bonds that mitigate much of their destructive power.
The Polar Vortex
Throughout the long, dark winter in Antarctica, wind currents circling the continent stabilize in to what is known as the “Antarctic Polar Vortex.” Inside the center of the vortex, the South Pole does not see the Sun for six months. Without sunlight to warm the atmosphere, it gets extremely cold. Stratospheric temperatures can plunge to below -90C and strange reactions occur on the surface of ice crystals only seen at these temperatures.
Polar Stratospheric Clouds
These ice crystals form “Polar Stratospheric Clouds” (PSCs) and on their surface the chlorine present in the stratosphere is released while the molecules able to bind them settle out on the relatively heavy ice crystals.
The Return of Sunlight
When the Sun begins to return to the southern hemisphere in August and September, a massive reservoir of free chlorine is prepped and ready to wipe out the Ozone Layer. Weak sunlight is all the chlorine needs to begin a catalytic reaction where a single chlorine molecule will destroy thousands of ozone molecules.
Removing a Single Ingredient
The formation of the Antarctic Ozone Hole is a complex process reliant on both unique environmental conditions and human influence. Without the release of CFC’s, we would not have the large concentrations of chlorine present in the stratosphere ready to destroy ozone. Comparably, without a strong vortex, the supercharged catalytic destruction seen over Antarctica during the past few decades would also not occur to the degree it does now. We do not have control over wind currents and the formation of the Polar Vortex, but we do have control over the creation and use of CFCs. That is why every nation on Earth has ratified the Montreal Protocol on Substances that Deplete the Ozone Layer. This landmark agreement and the quick action of industry and the nations of the World has given us hope to one day see the complete recovery of our protective ozone layer by the middle of the 21st century. Until then and beyond, NOAA and CIRES scientists will continue to monitor the atmosphere and the ozone layer above Antarctica so that we are not surprised again.