Researchers have demonstrated that, following the decrease of the atmospheric concentrations of ODS (ozone depleting substances), the antarctic ozone layer has begun to mend.
Compared to its largest area in 2000, the September ozone hole has actually shrunk by 4 million km2. The researchers model, which separates the effect of ODS from those of weather and volcanic emissions, that also influence the ozone layer, confirmed that this decrease was due to the decrease of the stratospheric chlorine loading (figure 2 from the NOAA Ozone Depleting Gas Index ODGI page).
The model also helped to explain the anomalously large October 2015 ozone hole, which was primarily due to the Calbuco (Chile) volcanic eruption in April 2015 that filled the atmosphere with sulfur particles, triggering ozone-destroying reactions.
Contrary to most studies which focus on the October situation, when the ozone hole is at its largest, but also subject to other factors than stratospheric chlorine, the researchers looked at September, when sunlight is back after winter and chemical reactions start to influence the ozone layer. They showed that the rate at which the hole opens up in September has slowed down as the stratospheric chlorine has decreased, which explains why the hole is appearing now around ten days later than in earlier years.
Source: MIT News