Published: Wed, February 07, 2018
Sci-tech | By Javier West

Protective ozone layer is recovering but not over populated areas

Protective ozone layer is recovering but not over populated areas

A large team of researchers from Europe and North America found that ozone continues to recover in the upper stratosphere but has been unexpectedly declining in the lower layers of the stratosphere, between 60 degrees north and south of the equator.

The researchers from Imperial College London believe the continued decline may be down to climate change causing more ozone to be carried away from the tropics.

Despite these increases, measurements show that the total ozone column in the atmosphere has remained constant, which experts took as a sign that ozone levels in the lower stratosphere must have declined.

CFCs and the other gases were banned under an worldwide agreement, the Montreal Protocol, and since then parts of the layer have been recovering, particularly at the poles.

The study was published on Tuesday in the journal Atmospheric Chemistry and Physics.external link It found that the ozone layer is continuing to decline on a global scale despite decades of worldwide efforts to protect it. Scientists demonstrated this using satellite measurements spanning the past 30 years combined with advanced statistical methods.

"The potential for harm in lower latitudes may actually be worse than at the poles", she said.

But a new study has shown that while it is recovering in Antarctica, where it was worst depleted, the ozone layer is thinning in the lower stratosphere over non-polar areas. It is produced in tropical latitudes and distributed throughout the rest of the world.

In the 1970s it came to know that, CFCs was severely affecting and destroying the ozone layer in the stratosphere. "The impact of the Protocol is undisputed, as evidenced by the trend reversal in the upper stratosphere and at the poles", said Thomas Peter, from ETH Zurich.

The other possibility is that very short-lived substances (VSLSs), which contain chlorine and bromine, could be destroying ozone in the lower stratosphere.

The reason is not known, but it could be to do with chemicals used in paint stripper which were previously believed to be too volatile to affect the stratosphere. One of such chemicals is actually used to create a CFC replacement. Dr. William Ball from ETH Zurich and PMOD/WRC Davos, who led the analysis, said that their team was surprised to find out that the lower latitude ozone is declining since their current best atmospheric circulation models do not predict this effect.

"These short-lived substances could be an insufficiently considered factor in the models", said Ball.

Today's publication combines the datasets of multiple global teams, connecting information from various satellite missions since 1985. New research indicates that the ozone layer, which wraps around the entire Earth, is thinning over non-polar areas.

The researchers say the focus now should be on getting more precise data on the ozone decline, and determining what the cause most likely is, for example by looking for the presence of VSLSs in the stratosphere.

Although individual datasets had previously hinted at a decline, the application of advanced merging techniques and time series analysis has revealed a longer term trend of ozone decrease in the stratosphere at lower altitudes and latitudes.

The study was the work of researchers from Switzerland, the United Kingdom, the U.S., Sweden, Canada and Finland, and included data from satellite missions, including by NASA.

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