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Ozone layer still declining in key regions, major study reveals

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A study carried out by an international collaboration of researchers has found that global ozone has continued to decline at lower latitudes, despite confidence in the ozone layer recovering in other areas.

Global ozone - the gaseous substance which forms in the stratosphere and surrounds the globe - has been declining since the 1970s, due to man-made chemicals such as solvents, propellants and halocarbon refrigerants. These compounds release halogen atoms through reactions with sunlight, resulting in the breakdown of oxygen and ozone (O3).

There has been a steady decline in the total amount of ozone in the stratosphere and a particularly dramatic decrease in the ozone around the Earth’s poles, where a ‘hole’ appeared. This has led to concern over the increasing risks of skin cancer when there is less ozone to absorb the harmful UVB light before it reaches the surface of earth.

The 1985 Vienna Convention and the 1987 Montreal Protocol - the first universally ratified treaties in UN history - banned the production of numerous ozone-depleting materials. Since then, there has been hope that the ozone would gradually recover over the following decades.

While there are signs of recovery of the Antarctic ozone, an international study using data collected by satellite missions since 1985 has found that the lower part of the ozone layer at lower latitudes and altitudes is not recovering as expected.

While previous individual datasets had indicated ozone degradation, this study appears to confirm the longer-term trend.

The cause for this decline in lower latitudes is not yet known. However, the study’s authors suggest that this could be due to atmospheric circulation being affected by climate change, causing ozone to be swept away from the tropics, or due to short-lived substances destroying ozone in the lower stratosphere.

“The finding of declining low-latitude ozone is surprising, since our current best atmospheric circulation models do not predict this effect,” said Dr William Ball of ETH Zurich. “Very short-lived substances could be the missing factor in these models.”

“The study is an example of the concerted international effort to monitor and understand what is happening with the ozone layer. Many people and organisations prepared the underlying data, without which the analysis would not have been possible.”

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