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Since the 80’s of the last century, a hitherto unknown environmental threat began to alarm society. Starting in 1985, and especially over the next two decades, it made headlines in the press: a huge hole in the ozone layer had been detected in Antarctica .
Quickly, a series of terms related to this event became popular: ‘chlorofluorocarbons’ , ‘ global warming ‘ or ‘climate change ‘, although not everyone understood exactly what they meant or how these terms were interrelated.
the ozone layer
The ozone layer or ozonesphere is an area of the Earth’s atmosphere that extends between 15 and 35 kilometers in altitude. Unlike other defined layers of the atmosphere —such as the troposphere, the stratosphere, the mesosphere, the thermosphere or the exosphere, which are defined based on various variables, and between which more or less clear limits can be found: tropopause, stratopause, etc.—, the ozone layer is a more or less diffuse area located in the lower region of the stratosphere.
What characterizes this area, as its name suggests, is its high concentration of ozone gas, a molecule made up of three oxygen atoms, with the ability to absorb ultraviolet radiation . In fact, it absorbs between 97 and 99% of the high-frequency ultraviolet radiation coming from the sun.
In the lower regions, ozone is produced by thunderstorms, and when its concentration is too high it can be a pollutant—although much less so than in the lower stratosphere. This is because it is a highly reactive and very oxidizing substance. So much so that it is used to sterilize rooms and tools.
holes in the ozone layer
When speaking of holes in the ozone layer, reference is not made to a physical hole itself, but to a significant thinning of the thickness of said layer, and to a lower concentration of ozone gas. Also, this thinning and loss of density is not usually permanent, but generally fluctuates with the seasons.
This hole in the ozone layer is produced mainly by the presence of pollutants that react with ozone , breaking it down. Among them, the stratospheric aerosols derived from sulfur produced by volcanoes, which have a punctual influence, stand out. However, there are other compounds that cause sustained drops in ozone concentration over time, halocarbons and gases derived from chlorine, particularly chlorofluorocarbons (CFCs). These molecules, used as propellants and refrigerants, remain stable in the atmosphere for up to 200 years; when they reach the stratosphere, ultraviolet radiation, which is stronger up there, dissociates the molecule, releasing chlorine, which, by reacting with ozone, decomposes it.
The reduction in the amount of ozone in the stratosphere allows the passage of ultraviolet light with greater intensity, which causes greater release of chlorine from CFCs. This ends in a feedback loop, a diabolical spiral in which the depletion of the ozone layer causes further depletion of the ozone layer.
To prevent this from happening in aeternum , in recent decades CFCs have been replaced by other less dangerous compounds, such as hydrofluorocarbons (HFCs) for refrigeration or isobutane as a propellant. But all those that have been released for more than half a century remain in the atmosphere, causing this degradation.
The hole in Antarctica
In 1985, a revolutionary scientific publication in the prestigious journal Nature revealed that ozone levels in the stratosphere over Antarctica, especially during the southern spring —from September—, fell alarmingly. Since the atmospheric dynamics had not changed significantly, they concluded that the effect had a chemical cause.
In the hole in Antarctica , during the southern summer and autumn, ozone levels partially recover, but the cold of winter favors a higher concentration of chlorine compounds, and every year, in spring, the hole forms again .
Although this was the first hole in the ozone layer detected, it was not the only one . There is another smaller hole over the North Pole, and one more hole over Tibet, observed in 2006 and 2011.
A new hole, a new threat
A very recent scientific publication in AIP Advances reveals a hole in the ozone layer that until now had gone unnoticed, although it has been there for more than 20 years.
Unlike the hole in Antarctica, which appears only in spring, this one remains throughout the year, forming a band between the tropics . The magnitude of the hole is similar to that of Antarctica, but its size is seven times larger.
This great tropical and permanent ozone hole is very worrying; Its effects cover up to 50% of the inhabited surface of the planet , and approximately half of humanity could be affected.
The depletion of the ozone layer, after all, implies a weaker filter of ultraviolet radiation that reaches the surface more easily and in greater quantity. It is more than proven that ultraviolet radiation has pernicious effects on the health of people and other living beings; effects that of course have an impact on terrestrial and aquatic ecosystems, and become the engine of biodiversity loss.
References:
Dunbar, J. 2001. The Ozone Layer. POT.
Farman, JC et al. 1985. Large losses of total ozone in Antarctica reveal seasonal ClOx/NOx interaction. Nature, 315(6016), 207-210. DOI: 10.1038/315207a0
Lu, Q.-B. 2022. Observation of large and all-season ozone losses over the tropics. AIP Advances, 12(7), 075006. DOI: 10.1063/5.0094629
