The Ozone layer has been reducing since the year 1970s.Keeping this in mind government authorities all over the world came together and passed a law named the Montreal protocol, which prohibited using some man-made chemicals.
This comes as a bit of a blow following the good news past year that the hole in the ozone above Antarctica appears to be healing thanks to a ban on chlorofluorocarbons (CFCs).
The stratosphere stretches from 10km above the Earth to 50km and ozone is slowly rising in the upper stratosphere, back towards the levels seen before CFC chemicals caused their damage.
The hole in the protective layer has been closing over Antarctica since ozone-damaging chemicals were banned by the Montreal Protocol, an worldwide treaty, in 1987, but scientists have found that it is thinning in the lower stratosphere above more densely populated parts of the globe. However, a team led by researchers from ETH Zurich and the Physikalisch- Meteorologisches Observatorium Davos in Switzerland have found that despite the ban on CFCs, the concentration of ozone in the lower part of the stratosphere has continued to decline at latitudes between 60 degree South and 60 degree North. The cause is now unknown. The protective layer is situated in the stratosphere region of the atmosphere and a large portion of the ozone layer is present in the lower part of the stratosphere.
It is not yet possible to assess the consequences that this continuing lower stratospheric ozone depletion will have for humans and the ecosystem. "The decreases in ozone are less than we saw at the poles before the Montreal Protocol was enacted, but UV radiation is more intense in these regions and more people live there", informed Haigh.
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The cause of this decline in ozone at lower latitudes is unknown. The reason behind the decline is not certain.
On the one hand, climate change is modifying the pattern of atmospheric circulation, moving air from the tropics faster and further in the polar direction, so that less ozone is formed.
The other possibility is that very short-lived substances (VSLSs), which contain chlorine and bromine, could be destroying ozone in the lower stratosphere. The latter includes chemicals used in solvents, degreasing agents, and paint strippers. "Although the Montreal protocol has done what we wanted it to do in the upper stratosphere, there are other things going on that we don't understand". One is even used in the production of an ozone-friendly replacement for CFCs.
Scientists had thought that VSLSs would not persist long enough in the atmosphere to reach the stratosphere and affect ozone. "Very short-lived substances could be the missing factor in these models". "What matters most for UV at Earth's surface is the total column amount of ozone overhead", says co-author Sean Davis, a research scientist with NOAA's Earth System Research Laboratory in Boulder, Colorado.
To conduct the analysis, the team developed new algorithms to combine the efforts of multiple worldwide teams that have worked to connect data from different satellite missions since 1985 and create a robust, long time series. The researchers will now focus on determining what the most likely cause for the decline of ozone could be, and whether it is connected to the presence of VSLSs in the earth's stratosphere. The study was conducted by 22 scientists at research centres in the United States and Europe.