These polar clouds, which are composed of frozen nitric acid and sulfuric acid, form when temperatures in the stratosphere fall below minus 108 F (minus 78 C). This is currently the case in vast sections of the Arctic. Chemical processes on the surface of the cloud particles transform the initially harmless chemicals from chlorofluorocarbons (CFCs) into aggressive ozone-depleting substances.
Credit: Markus Rex, Alfred Wegener Institute
Lingering pollutants, called chlorofluorocarbons, and cold temperatures high in the atmosphere have conspired to create record loss of the protective ozone layer above the Arctic, the World Meteorological Organization reports.
At about 12.4 miles (20 kilometers) above the Earth in the stratosphere where the ozone layer is normally concentrated, most of it has been depleted, said Markus Rex, an ozone researcher with the Alfred Wegener Institute for Polar and Marine Research in Germany. [Earth's Atmosphere: Top to Bottom]
In mid-March, Rex and other researchers from Europe, Russia and North America warned that, despite a successful international plan to ban the use of ozone-depleting substances, the Arctic could be facing unprecedented ozone loss this spring.
The ozone layer blocks harmful radiation — which can damage DNA and lead to skin cancer, among other problems — preventing it from reaching the Earth's surface.
In 1987, under the Montreal Protocol, countries agreed to end production of ozone-destroying substances, including CFCs. However, these pollutants are still lingering in the air, and are expected to continue causing ozone losses for decades.
Ozone loss originates inside a polar vortex, which is created by a combination of cold temperatures and the rotation of the Earth. The cold leads to cloud formation and chemical reactions that turn the pollutants into highly reactive molecules that break apart the three oxygen atoms of ozone. The result: loss of the ozone shield.
The similar, but more pronounced, dynamics are responsible for the more infamous ozone hole above Antarctica.
The warmer temperatures of spring will ultimately end the depletion, Rex told LiveScience. "These days temperatures are still cold, but they are predicted to warm up soon so we would think the ozone less period would be over in about 10 days from now."