The ozone layer can reform in 43 years


If the hole in the ozone layer remains a major environmental problem, the announcement of its reduction is a great relief to the international community.

In addition to being concrete proof of the possibilities of international cooperation in the field of environmental protection, its reduction also removes the specter of more serious problems.

“Ozone is the only gas in the atmosphere that filters UV B and C,” explains Sophie Godin-Beekmann, CNRS research director and president of the International Ozone Commission. “Their main health threats are skin cancer, skin aging, eye cataracts, [et] weakening of the immune system. »

Like gamma or X-rays, UV rays are high-energy radiation and can have severe effects on the body. In case of excessive exposure, it can cause DNA damage in both humans and all other living things, both animals and plants.

” [Sans la couche d’ozone]UV could do damage […] it could have affected crops and food security,” the scientist adds.

Limited to Antarctica, their damage is limited and clearly decreasing. The health of the local biodiversity, which is also being monitored by scientists, appears fortunately to have escaped the effects of chronic UV exposure.

“The Antarctic continent doesn’t have a lot of biodiversity apart from the peninsula, and the ozone hole happens when the sun is still low on the horizon,” notes Ms Godin-Beekmann. “Studies have been conducted on the effects of the ozone hole on marine organisms and marine phytoplankton, but with no major conclusions. […], because effects on phytoplankton can be multifactorial. »

Ozone regeneration is related to the balance between the different forms of oxygen in the atmosphere. First, oxygen consists of a pair of oxygen atoms and is the most common form at low altitudes. Ozone, on the other hand, is a combination of three oxygen atoms and is found mainly in the stratosphere.

At this level of the atmosphere, the two forms exist in equilibrium and switch from one to the other according to a phenomenon called the Chapman cycle. Formed when molecules are exposed to solar radiation, it allows dioxygen molecules to convert to ozone and vice versa.

It is this cycle that has been present and stable for several billion years and has been disrupted by the presence of CFCs. After being broken down by UV rays, the released chlorine atoms will react with ozone to form other chemical compounds. Oxygen atoms trapped in other molecules could no longer be integrated into the cycle, gradually reducing the reserves of ozone in the atmosphere.

Stopping the introduction of chlorine into the atmosphere thus made it possible to stop this process. Since then, their disappearance has been closely monitored by scientists, particularly the Laboratoire Atmosphères Observations Spatiales (Latmos), where Cathy Clerbaux and Sophie Gobin-Beckman work.

“In our reports, we have been expecting this development for five to ten years and there are no surprises,” explains Ms. Clerbaux. “There is nothing that can prevent a recovery except for countries not following the protocol as well as they did in 2018.”

According to the scientist, the measurements made it possible to detect the growth of CFCs over Japan, for example. In question is the production of CFCs in China, which can be found thanks to the tracking of air currents.

“The system works because we have ground and satellite monitoring systems. However, it can go slower […]the climate is warming [à la surface de la Terre] and cools in the stratosphere with the equilibrium of the system,” the researcher continues. “This means that the polar vortex is also colder and clouds form more. However, the more clouds there are, the more chlorine is trapped and the slower the process. »

Thus, the ozone layer should have recovered by 2060, compared to 2070 now, according to the oldest reports. Another problem to consider is the recovery of CFCs, which are still present in the oldest household appliances.

“For example, it is important to recover and clean the gases in old refrigerators. Above all, they must not enter the atmosphere,” concludes Cathy Clerbaux. “But after there is no more chlorine in the atmosphere, there will be no problem! “.

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