The measures adopted as a consequence of the Montreal Protocol (1987) have served to stop the production, consumption and emission into the atmosphere of large quantities of chemical compounds (gases manufactured by humans) that cause the disappearance (depletion) of ozone in the high in the Earth's atmosphere. This historic international agreement and its subsequent extensions, such as the Kigali Amendment, are allowing ozone concentrations to recover and, progressively, the so-called hole in the ozone layer to close or disappear.
But the recovery process is slow and is affected not only by human factors but also, as it has always been, by uncontrollable events of natural origin, such as volcanic eruptions. This is precisely what is happening this year with stratospheric ozone measured over Antarctica.
Last September, the Copernicus Atmosphere Monitoring Service (CAMS) announced that the hole in the ozone layer over the South Pole had recorded a slightly earlier than normal appearance of minimum ozone levels during 2023.
Now, the same Copernicus service, using data from the Sentinel-5P satellite, shows that this year's ozone hole over Antarctica is one of the largest ever recorded. "The hole, which scientists call an 'ozone depletion zone', reached a size of 26 million square kilometers on September 16, 2023, approximately three times the size of Brazil," details the European Copernicus program. , world reference in the matter.
The size of the ozone hole fluctuates periodically. From August to October, the ozone hole increases in size, reaching a maximum between mid-September and mid-October. When temperatures high in the stratosphere begin to rise in the Southern Hemisphere, ozone depletion slows, the polar vortex weakens and eventually breaks down, and by the end of December ozone levels return to normal.
Launched in October 2017, Copernicus Sentinel-5P is the first Copernicus satellite dedicated to monitoring our atmosphere. It is part of the fleet of Copernicus Sentinel missions that ESA develops for the European Union's environmental monitoring program.
The satellite carries an advanced multispectral imaging spectrometer called Tropomi. It detects the unique fingerprints of atmospheric gases in different parts of the electromagnetic spectrum to image a wide range of pollutants with greater precision and higher spatial resolution than ever before.
Tropomi total ozone measurements are processed within the Sentinel-5P ground segment at the German Aerospace Center (DLR) using algorithms developed by DLR and the Royal Belgian Institute for Space Aeronomy (BIRA-IASB).
Diego Loyola, senior scientist at DLR, commented: “Sentinel-5P total ozone products are accurate at a percentage level compared to ground-based data and this allows us to closely monitor the ozone layer and its evolution. Tropomi measurements are expanding the record of global ozone data from European satellite sensors that spans almost three decades.”
The Sentinel-5P total ozone column product is provided within three hours of the time of measurement to the Copernicus Atmosphere Monitoring Service (CAMS). CAMS, implemented by the European Center for Medium-Range Weather Forecasts (ECMWF) on behalf of the European Union, includes this Sentinel-5P ozone data in near real-time in its forecasting and data analysis system.
Antje Inness, senior scientist at CAMS, said: “Our operational ozone monitoring and forecasting service shows that the 2023 ozone hole started early and has grown rapidly since mid-August. It reached a size of more than 26 million square kilometers on September 16, making it one of the largest ozone holes ever recorded. “Tropomi ozone data is an important data set for our ozone analysis.”
The variability in the size of the ozone hole is largely determined by the strength of a strong band of wind that flows around the Antarctic zone. This strong wind band is a direct consequence of the Earth's rotation and the strong temperature differences between polar and moderate latitudes.
If the wind band is strong, it acts as a barrier: air masses between polar and temperate latitudes can no longer be exchanged. The air masses are then isolated in the polar latitudes and cool during the winter.
Although it may be too early to discuss the reasons behind current ozone concentrations, some researchers speculate that this year's unusual ozone patterns could be associated with the eruption of Hunga Tonga (Hunga Ha'apai) in January 2022.
Antje explains: “The eruption of the Hunga Tonga volcano in January 2022 injected a large amount of water vapor into the stratosphere, which only reached the south polar regions after the end of the 2022 ozone hole.
“Water vapor could have caused increased formation of polar stratospheric clouds, where chlorofluorocarbons (CFCs) can react and accelerate the depletion of the ozone layer. “The presence of water vapor may also contribute to the cooling of the Antarctic stratosphere, further enhancing the formation of these polar stratospheric clumps and resulting in a more robust polar vortex.”
However, it is important to note that the exact impact of the Hunga Tonga eruption on the Southern Hemisphere ozone hole is still a topic of ongoing research. This is due to the absence of previous cases of such substantial amounts of water vapor being injected into the stratosphere in modern observations.
Claus Zehner, ESA mission manager for Copernicus Sentinel-5P, adds: “Sentinel-5P total ozone plumes provide a precise means of monitoring the occurrence of ozone holes from space. “Ozone hole phenomena cannot simply be used to monitor global changes in ozone, as they are determined by the strength of regional wind fields flowing around polar areas.”
In the 1970s and 1980s, the widespread use of harmful chlorofluorocarbons in products such as refrigerators and aerosol cans damaged the ozone high in our atmosphere, causing a hole in the ozone layer over Antarctica.
In response to this, the Montreal Protocol was created in 1987 to protect the ozone layer by progressively eliminating the production and consumption of these harmful substances, which is leading to a recovery of the ozone layer.
Claus concludes: “Based on the Montreal Protocol and the decline in anthropogenic ozone-depleting substances, scientists currently predict that the global ozone layer will return to normal around 2050.”
