Since the end of the 20th century, especially during the 1980s and 1990s, one of the most significant environmental concerns in the media has been the gradual and constant destruction of the ozone layer .
holes in the ozone layer
The ozone layer is an area of the Earth’s atmosphere, which extends from 15 to 35 kilometers in altitude, in the lower part of the stratosphere. The so-called ‘holes’ in the ozone layer are not holes, they are actually thinning or reductions in the concentration of this gas, ozone.
Said thinning occurred in some regions of the world in a more worrying way. Sometimes it only lasted for a more or less limited period, but in certain places, such as Antarctica , it was a recurring phenomenon, associated with the seasons, specifically with the southern spring —the hole begins to grow around the month of August and it reaches its maximum size in October.
Although it doesn’t make as many headlines as it did then, the problem of the ozone layer persists. The 2021 hole was the largest in the previous 15 years and recently a new, much larger hole has been detected, which remains throughout the year, forming a tropical belt.
But what is ozone?
Ozone is a colorless gas made up of three oxygen atoms — the oxygen molecule we breathe is made up of two. Its chemical composition makes it a highly oxidizing agent; in fact, ozone is considered the most oxidizing version of oxygen. It is toxic even at low concentrations, which is why it is often used as an antimicrobial agent. It is used in the production of bottled water, in the treatment of meats and other packaged foods, and as a disinfectant agent to purify the air in closed rooms.
Ozone is produced naturally during storms . The electricity present in the storm ionizes the air, breaking the bonds of oxygen molecules and favoring the formation of ozone. That is the origin of the characteristic smell that is perceived when a storm approaches. After rain, this gas mixes with that of some volatile plant compounds and geosmin, produced by soil bacteria, and results in petrichor , the characteristic “wet earth” odor.
How is stratospheric ozone formed?
Ground-level ozone is formed by storms and its concentration is always very low. It does not usually last long, since it is a very reactive gas.
In the stratosphere, ozone only reacts with the pollutants that humans have been pouring into the air and that still accumulate up there. As already indicated, most of the ‘holes’ in the ozone layer disappear during the summer – in Antarctica, starting in December – and reappear at the end of winter – in Antarctica, in August. When the formation of ozone is slower than its destruction, ‘holes’ appear in the ozone layer. However, if the rate of formation is greater than the rate of its degradation, then the ozone layer recovers.
But in the stratosphere there are no storms. There must be some other mechanism that allows ozone to form, which can accumulate. This formation was first described by S. Chapman and published in the Memoirs of the Royal Meteorological Society in 1930. According to his theory, the two-atom atmospheric oxygen molecule, receiving electromagnetic radiation from the sun in the 244-nanometer spectrum — ultraviolet C, the most energetic— breaks. Thanks to a buffer —which is usually some inert gas from the atmosphere—, each of the free atoms then reacts with another molecule of oxygen, thus forming two molecules of ozone.
For this reason, the ozone layer in Antarctica recovers in December or January, when sunlight has enough time to generate new ozone in sufficient quantity to change the balance. The hole reforms in August, after several months of perpetual night.
How do we restore the ozone layer?
Making ozone on the ground and taking it to the stratosphere is an infeasible task. Not only do we have no way of manufacturing enough to replenish the ozone layer, but there would also be no way of transporting it—being highly reactive, it would degrade before it arrived.
As long as there are pollutants in the stratosphere, the ozone will remain in that precarious balance and the holes will continue to appear repeatedly. For the ozone layer to fully regenerate, it will be necessary to remove pollutants . A good first step would be to stop emitting substances that destroy the ozone layer. But until the same atmospheric dynamics does not finish degrading all the accumulated contamination, the ozone layer will continue to fluctuate.
Chapman, S. 1930. A Theory of Upper-atmospheric Ozone. Edward Stanford.
Johnston, HS 1975. Global ozone balance in the natural stratosphere. Reviews of Geophysics, 13(5), 637-649. DOI: 10.1029/RG013i005p00637
National Center for Biotechnology Information. 2022. Ozone (CID 24823; PubChem Compound Summary). PubChem.
Sen, DDJ 2016. Moist earth smelling geosmin as a terpene bicyclic alcohol. World Journal of Pharmaceutical Research, 5(8), 1-8.
Velasco, RM et al. 2008. Stratospheric ozone dynamics according to the Chapman mechanism. Journal of Mathematical Chemistry, 44(2), 529-539. DOI: 10.1007/s10910-007-9326-7