FunNature & AnimalThe ozone layer begins to recover

The ozone layer begins to recover

About 460 million years ago, something strange began to pass 50 kilometers above the surface of the Earth. The oxygen in the atmosphere, thanks to solar radiation, began to give rise to a gas called ozone, which began to form a layer around planet Earth. Some 120 million years later, this layer was thick enough to absorb harmful radiation from the Sun and allow living things to begin to colonize the terrain, which until now had been limited to living in the safe environment of the ocean.

Many millions of years later, the industrial and technological activity of a certain species, the human being, began to seriously degrade the planetary ecosystems. At the same time, the emission of greenhouse gases that causes the global increase in temperatures (climate change) together with the destruction of the ozone layer began to worry scientists and governments around the world.

However, now, for the first time, scientists have shown, through direct satellite observations of the ozone hole, that levels of ozone-depleting gases are decreasing.

It seems that the international ban on chemicals containing chlorofluorocarbons, known by their acronym CFCs, has borne fruit: the deterioration of the ozone layer has been reduced by 20% during the Antarctic winter than in 2005, the first year that the Chlorine and ozone measurements were made by NASA’s Aura satellite. At least that is what scientists have confirmed in a study published by the journal Geophysical Research Letters .

“We see very clearly that the amount of chlorine in CFCs is decreasing in the ozone hole and that ozone depletion is decreasing as a result,” according to lead author Susan Strahan, atmospheric scientist at the Space Flight Center. Goddard of NASA in Greenbelt, Maryland.

Previous studies have used statistical analyzes of changes in the size of the ozone hole to confirm that ozone depletion is slowing down. But this study is the first to use measurements of the chemical composition within the ozone hole to confirm that not only is ozone depletion decreasing, but that the decline is caused by decreasing CFCs.

The change in ozone levels over Antarctica from the beginning to the end of the southern winter, from early July to mid-September, was calculated on a daily basis each year between 2005 and 2016. “During this period, Antarctic temperatures are always very low. The rate of ozone destruction depends mainly on the amount of chlorine there is, “the researchers indicate in the study.

Thus, the scientists observed how less ozone is being lost, but they needed to know if the decrease in CFCs was responsible.

When ozone destruction occurs, chlorine is in many molecular forms, most of which are not measured. But after chlorine has destroyed most of the available ozone, it reacts with methane to form hydrochloric acid, a gas that can be measured.

Nitrous oxide is a long-lived gas that behaves like CFCs in much of the stratosphere. CFCs are decreasing at the surface, but nitrous oxide is not. If CFCs in the stratosphere are decreasing, over time, less chlorine should be measured for a given value of nitrous oxide. By comparing measurements of hydrochloric acid and nitrous oxide each year, it was determined that total chlorine levels decreased on average by about 0.8 percent per year.

“But we still do not see a clear decrease in the size of the ozone hole because that is controlled mainly by temperature, which varies a lot from one year to another,” the researchers warn.

Far from full recovery

Despite the encouraging news, the damage done to the ozone layer is not so easy to repair.

Looking ahead, the Antarctic ozone hole should continue to gradually recover as CFCs leave the atmosphere , but full recovery will take decades.

“CFCs have a useful life of 50 to 100 years, so they remain in the atmosphere for a long time,” according to Anne Douglass, an atmospheric scientist and co-author of the study. “As far as the ozone hole is concerned, we are calculating for the 2060s or 2080s. And even then, there could be a small hole.”

What are CFCs?

CFCs are long-lived chemical compounds that eventually rise to the stratosphere, where they are separated by ultraviolet radiation from the Sun, releasing chlorine atoms that destroy ozone molecules. Stratospheric ozone protects life on the planet by absorbing potentially harmful ultraviolet radiation that can cause skin cancer and cataracts, suppress the immune system, and damage plant life.

Finally, if the ozone layer is damaged enough, life on Earth simply would not be possible.

Two years after the discovery of the ozone hole in Antarctica in 1985, the nations of the world signed the Montreal Protocol on Substances that Deplete the Ozone Layer, which regulated compounds that deplete the ozone layer. Post-Montreal Protocol reforms completely eliminated CFC production.

Reference:

Susan E. Strahan, Anne R. Douglas. ‘Decline in Antarctic Ozone Depletion and Lower Stratospheric Chlorine Determined From Aura Microwave Limb Sounder Observations’. DOI: 10.1002 / 2017GL074830

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