Cienciaes.com: New actors that delay the recovery of the ozone layer. We speak with Julián Villamayor.

2023-06-12 15:35:46

We need oxygen to breathe, oxygen that in its most common state is made up of molecules containing two atoms. There is another possible association, which contains three oxygen atoms and is known as ozone, a very reactive molecule that if we breathe it in certain concentrations can cause health problems, but released in the upper layers of the atmosphere protects us from harmful ultraviolet rays. .

Ozone is a gas at room temperature, a gas that gives off a peculiar odor that is easy to identify during electrical storms, because it is formed by ionization of the air during the discharge of energy that accompanies lightning. In regions close to the earth’s surface, ozone can be of both natural and artificial origin, because it is generated in many other industrial processes and is widely used as a disinfectant. It is in the stratosphere, at heights above 15 or 20 kilometers where, thanks to the action of the Sun’s ultraviolet rays, ozone is created and destroyed in processes that absorb high-energy ultraviolet radiation (rays UVB y UVC) that are harmful to living beings.

The ozone layer has always existed, but it rose to prominence in the 1980s when it was discovered that the ozone concentration over Antarctica had decreased alarmingly. Certain satellite images, processed to reflect the concentration of Antarctic ozone, showed a wide dark region that was described as the “Ozone Hole”. The cause of this deterioration had been detected ten years earlier by scientists Mario Molina and Sherwood Rowland and was to blame for chlorofluorocarbons or CFCs, products widely used since the 1950s in refrigerating appliances and air conditioning equipment.

Thanks to these investigations, the international community reacted and in 1987 the Montreal Protocol was signed, which regulates the consumption and production of substances that destroy ozone in the stratosphere. The CFCs and other substances that destroy the ozone layer are products that have a long life (between 5 and 100 years), do not react in the troposphere and reach the stratosphere without alterations. Once there, they release chlorine and bromine species that are highly reactive and destroy ozone.

Now, thanks to the reduction of ozone depleting products, the ozone layer is recovering, although more slowly than expected.

An article published in the journal Nature Climate Change and first signed by our guest in Talking to Scientists, Julián Villamayor, postdoctoral researcher in the Department of Atmospheric Chemistry and Climate at the Blas Cabrera Institute of Physical Chemistry, draws attention to other products ozone depleters that could delay recovery. They are the very short-lived halogens (VSLS), which are not included in the Montreal Protocol and therefore there is no limitation to their production.
Los VSLS They are compounds that contain atoms of halogen elements such as Chlorine, Bromine or Iodine, which, once released into the atmosphere, have a useful life of less than 6 months. They are emitted both by natural sources, as a consequence of the photochemical processes that take place in the oceans, and by anthropogenic sources, which have their origin in industrial processes.

The most important products generated by humans are dichloromethane (CH 2 Cl 2 ) and chloroform (CHCl3). Dichloromethane is used as a solvent in aerosols or pesticides and is also used in the coffee industry to obtain decaffeinated coffee. Chloroform was formerly used as an anesthetic and is currently commonly used in dry cleaners as a grease solvent in dry cleaning, or as a fire extinguisher.

Despite their short lifespan, VSLS can rise rapidly through convection in the tropics, these rapid updrafts can cross the troposphere and reach the lower regions of the stratosphere contributing to the destruction of part of the ozone.

The problem is complex, because anthropogenic emissions are added to natural ones and it is the sum of both that, according to the study, contributes to reducing the rate of recovery of the ozone layer.

I invite you to listen to Julián Villamayor, postdoctoral researcher in the Department of Atmospheric Chemistry and Climate of the Blas Cabrera Institute of Physical Chemistry (IQF–CSIC)