The depletion would have been lower had it not been for the eruption of the Hunga Tonga-Hunga Ha’apai volcano in January 2022
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The Antarctic ozone hole grew to be 10 million square miles in size at its largest on September 21, 2023. This data comes from an analysis of satellite and balloon-based observations by the United States National Oceanic and Atmospheric Administration (NOAA) and National Aeronautics and Space Administration (NASA).
The annual maximum size of the hole in 2023 was the 12th largest since records began back in 1979, the organisations noted.
The Antarctic ozone hole is defined as the total area where ozone amounts are below the historical threshold of 220 Dobson units.
This year, during the critical period between September 7 and October 13, when ozone depletion is most pronounced, the ozone hole remained on average at 8.9 million square miles. This expansive area mirrors the vast geographical footprint of North America.
In 2022, when the average size of the ozone hole over Antarctica was 8.91 million square miles and in 2021, it was 8.99 million square miles.
Paul Newman, at the helm of NASA’s ozone research team, noted a positive trend in the containment of the Antarctic ozone hole. He attributed this to the decrease in human-caused chlorine compound pollutants, along with favourable weather patterns in the Antarctic stratosphere.
The ozone layer, often described as Earth’s natural sunscreen, plays a vital role in protecting the planet from the sun’s ultraviolet rays, which pose dangers such as skin cancer, cataracts, and other health risks. Each year, as the Southern Hemisphere’s winter gives way to spring, a temporary thinning occurs in this layer, forming what is known as the "ozone hole."
The origins of this depletion, which was first reported in 1985, are rooted in chemical substances, particularly those containing chlorine and bromine, which ascend to the stratosphere and subsequently break down, initiating a chemical onslaught on ozone molecules. Among these are chlorofluorocarbons (CFCs), which were prevalent in numerous consumer products before their phase-out under international agreements.
Bryan Johnson, a NOAA Research Chemist, pointed out that while total ozone never completely vanishes, it approaches near-total depletion at certain stratospheric levels over the South Pole. This year’s measurements indicated a 95 per cent thinning, inching perilously close to a 100 per cent loss within the stratosphere.
The 1987 Montreal Protocol, a critical international treaty, has played a vital role in curbing emissions of CFCs and other harmful chemicals. The decline of these substances in the atmosphere has been linked to signs of recovery in the stratospheric ozone layer.
To monitor these changes, researchers employ an array of satellite instruments aboard platforms such as NASA’s Aura and the joint NOAA-NASA Suomi NPP and NOAA-20 satellites.
Aura’s Microwave Limb Sounder also estimates levels of ozone-destroying chlorine, the organisations shared.
In tandem with these high-altitude observations, ground-based stations such as NOAA’s South Pole Observatory release weather balloons and utilise spectrophotometers to measure the altering concentrations of ozone within the hole over Antarctica.
“NOAA’s measurements showed a low value of 111 Dobson Units over the South Pole on October 3. NASA’s measurements, averaged over a wider area, recorded a low of 99 Dobson Units on the same date,” according to an official statement from NOAA.
The eruption of the Hunga Tonga-Hunga Ha’apai volcano in January 2022 is believed to have had a significant influence on this year’s ozone depletion. The volcano’s eruption sent a large plume of water vapor into the stratosphere, potentially accelerating the chemical reactions that deplete ozone.
Newman surmised that without the eruption, the ozone hole could have been smaller. The full impact of the volcanic event on the ozone hole, however, remains to be fully assessed, he added.
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The ozone hole over Antarctica as measured on September 21, 2023 when it reached its maximum size. Image: NASA Ozone Watch.png)
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