The team of Scientists from MIT have discovered that the September ozone hole has shrunk by more than 4 million square kilometers. It is about half the area of the contiguous United States. The observation initiated in 2000 the time when ozone depletion was at its peak. The team has also observed that at some point, this recovery has slowed down due to the effects of volcanic eruptions. However, the ozone hole seems to be on its healing path.

The study findings have been published in the journal  Science, where the authors shared that they used fingerprints of the ozone variations with season and altitude to accredit the ozone's recovery to the ongoing decline of atmospheric chlorine from chlorofluorocarbons (CFCs). These chemical compounds has been emitted by old refrigerators, dry cleaning processes, and aerosols. In 1987, the Montreal Protocol was signed virtually by country in the world in an intensive effort to ban the use of CFCs to repair the ozone hole.

Lead author Susan Solomon, the Ellen Swallow Richards Professor of Atmospheric Chemistry and Climate Science at MIT, said that we can now be confident that the things done in the past have put the planet on a path of healing. Solomon's co-authors were Diane Ivy, research scientist in the Department of Earth, Atmospheric and Planetary Sciences, together with researchers from the National Center for Atmospheric Research in Boulder, Colorado and the University of Leeds in the UK.

What is Ozone Hole?

In the 1950s, the time of discovery of the ozone hole, researchers used ground-based data. By the mid-1980s, British Antarctic was surveyed by scientist and noticed that the October total ozone was plummeting. From that time on, scientists worldwide characteristically tracked ozone depletion using October extents of Antarctic ozone.

Ozone is sensitive not only to chlorine, but also to sunlight and temperature. Chlorine grubs away at ozone, but only when light is present or when the atmosphere is sufficiently cold to generate polar stratospheric clouds on which chlorine chemistry occurs. This relationship was first characterize in 1986 by Solomon. Measurements have shown that ozone depletion begins in late August yearly, as Antarctica arises from its dark winter and the hole is completely formed by early October.

Read more about this research at MIT News or through the journal Science. This research was supported by the National Science Foundation and the U.S. Department of Energy.