Attribution of Antarctic ozone recovery to the Montreal protocol requires evidence that (1) Antarctic chlorine levels are declining and (2) there is a reduction in ozone depletion in response to a chlorine decline.
Looking to the future, NASA scientists believe that once the ban of CFCs is maintained, the ozone hole should shrink gradually, but could take decades to recover.
This the first year that measurements of chlorine and ozone during the Antarctic winter were made by NASA's Aura satellite. Measuring has taken place since 2005.
The data obtained during the observation shows a significant reduction in the levels of chlorofluorocarbons (CFCs), which would have allowed the ozone layer to fix itself by about 20 per cent.
The ozone hole forms during Antarctica's winter, which is why researchers measure trace gases over the continent at this time, using an instrument on the Aura satellite known as the Microwave Limb Sounder.
The importance of the ozone layer led the worldwide community to sign in 1987 the Montreal Protocol on Substances that Deplete the Ozone Layer in order to regulate these types of compounds. The protocol, signed in 1987 after the Antarctic ozone hole was discovered, eventually laid down a complete ban on chlorine-containing man-made chemicals known as chlorofluorocarbons, or CFCs, according to the Kenya-based The Ozone Secretariat at the U.N. Environment Programme.
Ozone acts as a key element in the atmosphere, a natural protective layer at high altitudes in the face of ultraviolet radiation harmful to living creatures and plants.
"We see very clearly that chlorine from CFCs is going down in the ozone hole, and that less ozone depletion is occurring because of it", said lead author Susan Strahan.