This year's hole on Earth, which is bigger than Antarctica, was created by a volcano!

The ozone hole over Antarctica in September this year (Image source: esa)

The ozone hole has returned, and its area is approaching its historical maximum.

Written by | Dong Yuan

Some may remember that at the beginning of this year, the United Nations released a new ozone depletion report, saying that the ozone hole over Antarctica is expected to return to its 1980 level within a few decades.

This makes people start to look forward to it: Is the ozone layer, which has been depleted in large quantities due to human abuse of chlorofluorocarbons (such as Freon used as refrigerant in refrigerators) and eventually had a huge hole, finally recovering?

But the latest monitoring results released by the European Space Agency seem to have poured cold water on this. Satellite monitoring shows that on September 16 this year, the ozone hole above Antarctica reached an area of ​​26 million square kilometers - an area about the size of three Brazils - which is close to the historical record of 29.9 million square kilometers on September 9, 2000 (some measurements show 28.4 million square kilometers).

Changes in the ozone hole from July to September this year (Image source: esa)

Current status of the ozone hole

The ozone layer is located in the stratosphere 15km to 30km above the ground, and plays an important role in preventing Earth's creatures from being harmed by excessive ultraviolet rays. In 1985, scientists discovered a huge and growing ozone hole over Antarctica. In 1987, the Montreal Protocol, in which many countries around the world participated, began to protect the ozone layer by eliminating or restricting nearly 100 "ozone-depleting substances" (ODS) - especially CFCs.

Driven by the Montreal Protocol, the use of "ozone-depleting substances" has been greatly reduced. And since 2000, the ozone hole has been gradually shrinking.

In 2019, the ozone hole area reached its smallest value since 1985 (the annual maximum was 16.4 million square kilometers), but this was more due to the higher air temperature over Antarctica that year, which reduced the efficiency of ozone depletion. In the following years, the ozone hole area returned to a higher level.

The size of the ozone hole over the years (Image source: Copernicus Atmosphere Monitoring Service)

Volcanoes that shook the Earth

In addition to the direct impact of human activities, ozone layer depletion may also be related to some natural events, such as forest fires and volcanic eruptions. Scientists believe that the increase in the ozone hole this year is mainly related to a volcanic eruption.

On January 15, 2022, the Hongahaapai Island submarine volcano (later called Tonga Volcano) in the Kingdom of Tonga in the South Pacific erupted violently. This was the largest volcanic eruption in the past 30 years and the largest volcanic eruption observed by modern equipment.

Tonga volcano eruption (Image source: Wikipedia)

Jim Garvin, a scientist at NASA, said the energy of the volcanic eruption was equivalent to hundreds of times the energy released by the atomic bomb explosion in Hiroshima. The volcanic eruption triggered tsunamis in many parts of the world, and the material erupted from the volcano even reached an altitude of 55 kilometers.

The Tonga volcano eruption has attracted widespread attention from around the world, including scientists. Less than a week after the eruption, a research team launched a weather balloon on an island downwind of the volcano and began observing the meteorological changes caused by the volcano. They found that just one week after the eruption, stratospheric ozone over the tropical southwest Pacific and Indian Oceans decreased by 5%.

Some scientists speculate that the volcanic eruption column will bring low-ozone air from the lower troposphere to the higher stratosphere, resulting in a decrease in stratospheric ozone concentration above the volcano. However, if this is the case, the stratospheric ozone concentration will recover quickly after the eruption ends; in fact, the ozone in the stratosphere continues to decrease for several days after the eruption.

This suggests that, in addition to the effects on tropospheric air, the eruption also caused chemical changes in the stratosphere, leading to a continued rapid depletion of ozone.

The eruption of the Tonga volcano triggered tsunamis in many parts of the world (Image source: Wikipedia)

Volcanoes change the stratosphere

Generally speaking, halogen compounds in the stratosphere are one of the main culprits for ozone depletion, such as hydrogen chloride (HCl), chlorine nitrate (ClNO3) and hydrogen bromide (HBr). Taking hydrogen chloride as an example, they will produce active chlorine radicals or chlorine monoxide radicals under the action of light and hydroxides, and under the action of these free radicals, ozone will be rapidly consumed.

Under normal circumstances, the efficiency of hydrogen chloride decomposing into free radicals under the action of light is very low, but if it is on the surface of clouds or aerosols, the efficiency of this reaction will be very high. This also partially explains why the ozone hole appears over Antarctica - this is mainly because the temperature in Antarctica is very low, which makes it easy for clouds to form in the stratosphere, making more halogen free radicals, which in turn leads to a large depletion of the ozone layer.

The Tonga volcano eruption injected a large amount of halogen compounds into the stratosphere, some of which may have come from evaporated sea salt. But water vapor plays a key role in ozone depletion. The water vapor emitted by this volcanic eruption accounts for 10% of the total global stratospheric load.

Schematic diagram (Image source: Evan et al, 2023)

Large amounts of water vapor make it easier for sulfur dioxide (which exists in the atmosphere and is also released by volcanic eruptions) to form sulfate aerosols, which accelerate the production of halogen free radicals. Measurements by weather balloons show that the peak aerosol surface area density at an altitude of 26.4 kilometers above the volcano is 286.9 square microns per cubic centimeter, which is 600 times higher than the general level in the stratosphere.

In addition, the injection of volcanic water vapor into the stratosphere will increase humidity and enhance radiative cooling, which will also make it easier for halogen radicals to form. In addition, sulfate aerosols will reduce the concentration of nitrogen oxides, thereby accelerating the rate at which halogen radicals consume ozone.

Scientists estimate that the large increase in stratospheric water vapor content caused by this volcanic eruption may last for 4 to 5 years, which may have a very large impact on the ozone layer and will require continued monitoring in the future.

The above study on the impact of the Tonga volcanic eruption on the ozone layer was published in Science on October 20. This may be a reminder that the damage caused by humans to nature may have consequences that can be seen with the naked eye for a long time even after humans have stopped causing harm.

Hopefully, in a few decades, we will see the day when the ozone hole returns to its 1980 level as predicted in the United Nations ozone depletion report.

Changes in the size of the ozone hole over the years (Image source: Copernicus Atmosphere Monitoring Service)

Reference Links:

https://www.science.org/doi/10.1126/science.adg2551

https://www.esa.int/Applications/Observing_the_Earth/Copernicus/Sentinel-5P/Ozone_hole_goes_large_again

https://www.eea.europa.eu/en/topics/in-depth/climate-change-mitigation-reducing-emissions/current-state-of-the-ozone-layer

https://agupubs.onlinelibrary.wiley.com/doi/pdfdirect/10.1029/97JD00912

https://www.science.org/doi/10.1126/science.abo4076

https://earthobservatory.nasa.gov/images/149367/dramatic-changes-at-hunga-tonga-hunga-haapai

https://ozonewatch.gsfc.nasa.gov/statistics/annual_data.html

https://mp.weixin.qq.com/s/EdhcNlMh_uhf2j4hu62w0Q
https://egusphere.copernicus.org/preprints/2023/egusphere-2023-1334/egusphere-2023-1334.pdf

https://en.wikipedia.org/wiki/2022_Hunga_Tonga%E2%80%93Hunga_Ha%CA%BBapai_eruption_and_tsunami

https://mp.weixin.qq.com/s/bEmhhxtMVut5C6Zj4JO2ZA