Measurements show that the decline in chlorine, resulting from an international ban on chlorine-containing manmade chemicals called chlorofluorocarbons (CFCs), has resulted in about 20 percent less ozone depletion during the Antarctic winter than there was in 2005—the first year that measurements of chlorine and ozone during the Antarctic winter were made by NASA's Aura satellite. "We see very clearly that chlorine from [chlorofluorocarbons] is going down in the ozone hole, and that less ozone depletion is occurring because of it," Susan Strahan, lead author and atmospheric scientist from NASA's Goddard Space Flight Center, said in a statement. The study published in the journal Geophysical Research Letters says that CFCs are long-lived chemical compounds which rise to the stratosphere and get broken apart into its constituent elements on exposure to sun's ultraviolet radiation. The ozone layer acts as a protective shield around the Earth, absorbing the Sun’s harmful ultraviolet radiation which can cause cancers, suppress the immune system in humans and damage plant life. That’s what happened to the hole on the Earth’s ozone layer, which has been found to be shrinking since the 1980s after nations agreed to ban the use of chlorofluorocarbons (CFCs), or chemicals that deplete the ozone layer. To determine how ozone and other chemicals have changed year to year, scientists used data from the Microwave Limb Sounder (MLS) aboard the Aura satellite, which has been making measurements continuously around the globe since mid-2004. While many satellite instruments require sunlight to measure atmospheric trace gases, MLS measures microwave emissions and, as a result, can measure trace gases over Antarctica during the key time of year: the dark southern winter, when the stratospheric weather is quiet and temperatures are low and stable. But after chlorine has destroyed nearly all the available ozone, it reacts instead with methane to form hydrochloric acid — a gas measured by MLS. By comparing the Microwave Limb Sounder (MLS) measurements of hydrochloric acid and nitrous oxide each year, the scientists determined that the total chlorine levels were declining on average by about 0.8 per cent annually. “CFCs have lifetimes from 50 to 100 years, so they linger in the atmosphere for a very long time,” said Anne Douglass, a fellow atmospheric scientist at the Goddard Centre.”As far as the ozone hole being gone, we’re looking at 2060 or 2080.
NASA research, published in Geophysical Research Letters, implies that the ozone layer is starting to recover due to man's actions. The decline in ozone-depleting chemicals, specifically chlorine from chlorofluorocarbon (an effect from the 1980's CFC ban, say the scientists), has resulted in 20 percent less depletion since 2005.