How the Antarctic Ozone Hole Reached Near-Record Size in October 2023

 Ozone in the stratosphere serves to block potentially damaging ultraviolet (UV) rays from reaching Earth, but is gradually being depleted through chemical reactions with chlorine, bromine, and CFCs created through human activities.

Every winter in Antarctica a powerful whirl of winds forms around the continent and concentrates air rich with halogens, producing special clouds known as Polar Stratospheric Clouds that help break down ozone layer.

Climate Change

Location: high above Earth The ozone layer serves as a layer of sunscreen, blocking out UV radiation. Its dramatic thinning in the stratosphere above Antarctica, commonly referred to as an "ozone hole", typically widens each year until temperatures high up in the atmosphere - called polar vortic - begin rising as winter ends and summer approaches; typically by mid-October it reaches its maximum size before gradually shrinking down towards December's end.

NASA scientists using instruments aboard spacecraft such as Aura, Suomi-NPP and NOAA-20 satellites monitor its growth and evolution each year. NOAA South Pole Station scientists use weather balloons equipped with instruments called ozonesondes to take ground-based measurements as well. All this data feeds into Copernicus Atmosphere Monitoring Service (CAMS), which maintains and updates an assured record of global ozone levels since 2003.

According to CAMS, this year's ozone hole was one of the largest ever seen. At its peak extent, it covered 9.6 million square miles (24.8 million square kilometers), roughly equivalent to North America. This was caused by an unusually large number of chemical reactions occurring when sunlight emerged over Antarctica at the end of winter - only usually occurring under very specific atmospheric conditions, including very cold temperatures present over Antarctica every winter - that destroyed ozone layers.

Volcanoes

In the 1970s and '80s, widespread use of harmful chlorofluorocarbons found in fridges and aerosol cans depleted atmospheric ozone levels by chemical reactions occurring at temperatures below freezing - leading to its depletion by mixing with sunlight to destroy it via photochemistry reactions that opened annually in August with its maximum area covered being reached in October. Each year an "ozone hole" appears which then reached its maximum area coverage.

Temperature and wind patterns in the stratosphere are key elements to whether or not an ozone hole grows or shrinks, along with volcanic eruptions which release water vapor into the atmosphere, contributing to formation of polar stratospheric clouds that further deplete ozone depletion.

Though subject to natural influences, the Antarctic ozone hole has gradually decreased in size since its peak in the 1990s due to reduced production of chemicals that deplete ozone layers. However, it began growing quickly this year compared with past years.

Scientists were taken aback at the rapid expansion of the 2023 ozone hole. One possible cause may have been volcanic eruptions between January and March that released vast amounts of water vapor into the atmosphere - providing chlorine gas clouds with potential to deplete ozone quickly because water vapor acts like a catalyst in this regard.

Solar Activity

The Ozone Layer serves as an invaluable barrier against UV radiation from the Sun, yet remains extremely thin; only 300 Dobson Units thick over Antarctica - equivalent to two pennies stacked atop each other!

Each September, Earth's stratosphere that shields us from ultraviolet rays from the Sun becomes thinner as chemically active chlorine and bromine compounds created by humans attach themselves to high-altitude polar clouds in southern winter and cause reactions that deplete ozone as soon as the Sun rises at the end of Antarctic summer. As a result, an "ozone hole" forms.

NOAA scientists monitor the size of this hole each year through weather balloon releases equipped with ozonesondes (instruments used to measure ozone levels) and measurements made on land with Dobson spectrophotometers, as well as satellite observations which allow them to assess all aspects of ozone layer thickness simultaneously.

This year's ozone hole reached its largest size on October 3 when ozonesondes recorded the lowest total column ozone value measured in their measurements: 101 Dobson units at altitudes between 14-21 kilometers (8-13 miles). This pattern mirrors what happened last year, when nearly no ozone levels existed within this altitude range.

This year's ozone hole was larger than expected due to the eruption of Hunga Tonga-Hunga Ha'apai volcano in January 2022, which released vast quantities of water vapor into the stratosphere and led to increased formation of polar stratospheric clouds that may react with chlorofluorocarbons (CFCs) to deplete ozone layers. Scientists expect it will rebound by around 2050 thanks to Montreal Protocol provisions and reduction in consumption of CFCs ozone depleting substances ozone layers will hopefully return.

Clouds

The Ozone Hole occurs as the result of our planet's protective stratospheric layer being reduced above Antarctica, typically every September when chlorine and bromine from human-made compounds react with air molecules in high-altitude polar clouds, depleting ozone which absorbs solar radiation while protecting our skin from UV rays from sunlight.

The size of the Ozone Hole fluctuates seasonally, typically increasing between late August and mid-October when temperatures in the Southern Hemisphere's stratosphere begin to warm at the end of winter. When an ozone layer depletes, a strong wind band moves across it, effectively blocking air flow between polar and moderate latitudes.

Launched in October 2017, the Copernicus Sentinel-5P satellite employs an innovative multispectral imaging spectrometer called Tropomi to measure total ozone column amounts with increased spatial resolution than ever before. As part of European Union's Copernicus Atmosphere Monitoring Service (CAMS), Sentinel-5P data are being utilized near real time for scientific modeling and forecasting of our atmosphere.

Scientists are still conducting studies into the effects of this year's ozone hole on Antarctic atmosphere. One possibility is that its depletion could have been compounded by January's eruption of Hunga Tonga-Hunga Ha'apai volcano, which released water vapor into the stratosphere and led to faster formation of polar stratospheric clouds, further contributing to depletion by increasing how quickly chlorine compounds produced by humans react with air molecules.