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Monday, July 13, 2020

Explained: How the ozone layer hole over Arctic closed

The hole in the North Pole's ozone layer, which was first detected in February, had since reached a maximum extension of around 1 million sq km.

By: Express Explained | New Delhi | Updated: April 28, 2020 8:31:16 am
ozone hole closed, ozone layer above arctic, arctic ozone hole closed, polar vortex, coronavirus lockdown, express explained, indian express, stratosphere, why is ozone important Before this year, the last sizable Arctic ozone hole was reported in 2011. (Photo: Wikimedia Commons)

Last week, the European Union’s Copernicus Atmosphere Monitoring Service (CAMS) announced that a hole in the Arctic ozone layer, believed to be the biggest reported, has closed.

The ozone hole’s closing was because of a phenomenon called the polar vortex, and not because of reduced pollution levels due to Covid-19 lockdowns around the world, reports said.

Read| Largest hole in the ozone layer heals itself: Coronavirus effect?

The hole in the North Pole’s ozone layer, which was first detected in February, had since reached a maximum extension of around 1 million sq km, according to scientists at the German Aerospace Center.

The European agency tweeted on April 23, “The unprecedented 2020 northern hemisphere #OzoneHole has come to an end. The #PolarVortex split, allowing #ozone-rich air into the Arctic, closely matching last week’s forecast from the #CopernicusAtmosphere Monitoring Service.”

The importance of the ozone layer

Ozone (chemically, a molecule of three oxygen atoms) is found mainly in the upper atmosphere, an area called the stratosphere, between 10 and 50 km from the earth’s surface. Though it is talked of as a layer, ozone is present in the atmosphere in rather low concentrations. Even at places where this layer is thickest, there are not more than a few molecules of ozone for every million air molecules.

But they perform a very important function. By absorbing the harmful ultraviolet radiations from the sun, the ozone molecules eliminate a big threat to life forms on earth. UV rays can cause skin cancer and other diseases and deformities in plants and animals.

Ozone holes

The ‘ozone hole’ is not really a hole — it refers to a region in the stratosphere where the concentration of ozone becomes extremely low in certain months.

The ‘ozone holes’ most commonly talked about are the depletions over Antarctica, forming each year in the months of September, October and November, due to a set of special meteorological and chemical conditions that arise at the South Pole, and can reach sizes of around 20 to 25 million sq km.

Such holes are also spotted over the North Pole, but owing to warmer temperatures than the South Pole, the depletions here are much smaller in size. Before this year, the last sizable Arctic ozone hole was reported in 2011.

Why this year’s Arctic ozone hole was massive

This year, the ozone depletion over the Arctic was much larger. Scientists believe that unusual atmospheric conditions, including freezing temperatures in the stratosphere, were responsible.

As per a European Space Agency report, cold temperatures (below -80°C), sunlight, wind fields and substances such as chlorofluorocarbons (CFCs) were responsible for the degradation of the Arctic ozone layer.

Although Arctic temperatures do not usually fall as low as in Antarctica, this year, powerful winds flowing around the North Pole trapped cold air within what is known as the polar vortex— a circling whirlpool of stratospheric winds.

“By the end of the polar winter, the first sunlight over the North Pole initiated this unusually strong ozone depletion—causing the hole to form. However, its size is still small compared to what can usually be observed in the southern hemisphere,” the report said.

Scientists believe that the closing of the hole is because of the same polar vortex and not because of the lower pollution levels during the coronavirus lockdown.

Ozone recovery

As per the Scientific Assessment of Ozone Depletion data of 2018, the ozone layer in parts of the stratosphere has recovered at a rate of 1-3 per cent per decade since 2000. “At these projected rates, the Northern Hemisphere and mid-latitude ozone is predicted to recover by around 2030, followed by the Southern Hemisphere around 2050, and polar regions by 2060,” the report said.

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