Antarctic ozone hole now larger, thinner & may take longer to recover. Mesosphere has a role to play: Study

Meteorological conditions could have largely driven fluctuations in the size of the Antarctic ozone hole

By Rohini Krishnamurthy
Published: Wednesday 22 November 2023
Photo: iStock

The ozone hole over the Antarctic has not only grown larger but also thinner throughout most of the spring, according to a new study. 

Despite making a recovery in area and depth since the 2000s, the Antarctic ozone hole has been massive in the last four years, the study published in Nature Communications noted. 

There is much less ozone in the centre of the ozone hole compared to 19 years ago. “We find that the concentration of ozone at the center of the ozone hole has reduced, which means the ozone layer has notably thinned,” Hannah Kessenich, lead author from the University of Otago, told Down To Earth.

The ozone hole is a region of exceptionally depleted ozone in the stratosphere over the Antarctic. It happens at the beginning of the Southern Hemisphere spring from August through October.

The ozone layer is on track to recover within four decades, according to the United Nations Environment Programme (UNEP).

But, from 2020-22, the ozone hole has been remarkably large. The extent and duration of the 2022 hole were remarkably similar to the large holes of 2020 and 2021, the paper stated.

Though the analysis included data till 2022, 2023 is also showing the same trend. According to NASA, from September 7 to October 13, the hole averaged 23.1 million square kilometres, approximately the size of North America, making it the 16th largest over this period.

Large ozone hole recorded on 3 October, 2022 Antarctic ozone hole by NASA Ozone Watch.

But that is not the only concern. The ozone layer over the Antarctic is intrinsically linked to the climate and dynamics of the Southern Hemisphere. 

“With the remarkably large Antarctic ozone holes during 2020-2022, we quickly noticed that adding these years onto the observational record impacted previous trends toward ozone recovery. This spurred us to look into the issue further and determine where and when ozone depletion was worsening.” Kessenich explained.

So the group analysed the monthly and daily ozone changes, at different altitudes and latitudes within the Antarctic ozone hole, from 2004 to 2022.

The researchers saw a total reduction of 26 per cent at the core of the ozone hole from 2004 to 2022. 

This reduction is despite the 1987 Montreal Protocol on Substances that Deplete the Ozone Layer, which regulates the production and consumption of human-generated chemicals known to deplete the ozone. 

The Montreal Protocol on Ozone Depleting Substances quadrennial assessment report of 2022 confirmed the phase-out of nearly 99 per cent of banned ozone-depleting substances. 

Meteorological conditions could have largely driven fluctuations in the size of the Antarctic ozone hole, from 2019 to 2021, said the UNEP.

It is known that other factors such as springtime temperature and wind patterns, aerosols from wildfires and volcanic eruptions, as well as changes in the solar cycle ozone hole development could also be responsible.

But other complex factors could also be involved, according to the paper. Kessenich explained that the Antarctic ozone hole sits within the polar vortex, which is a circular pattern of wind in the stratosphere that forms during winter and is maintained until late spring. 

Within this vortex, she added, the Antarctic air from the mesosphere (the atmospheric layer above the stratosphere) falls into the stratosphere.

“This intrusion of air brings natural chemicals (nitrogen dioxide, for example) which impact ozone chemistry in October. This is something that needs to be researched further,” the expert added.

The team plans to unravel the mechanism of descent of air from the mesosphere and also determine how its effects will impact the ozone hole in the future.

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