World ozone day, the (almost) happy ending story of the precious solar filter can teach us a lot about the future of the planet

The September 16 and the World ozone day, which recalls the date of entry into force of Montreal Protocol. Theme of this edition “Ozone for life: 35 years of protection of the ozone layer “.

Strange gas, ozone, unstable molecule composed of three oxygen atoms. In the low-flying air, what we breathe, it is toxic, because it is highly reactive and damages our vital processes, it is also used to disinfect water and air from coronavirus, for its aggressive action on living forms. But in the stratosphere, at about 30 kilometers of altitude, it becomes a precious and irreplaceable protective cloak to defend ourselves from the most energetic part of the ultraviolet radiation emitted by the sun, which could damage life by generating skin cancers and genetic mutations on animals and plants.

In essence, ozone is a natural sunscreen that until the 1930s, when his training had just been understood by the British geophysicist Sydney Chapman, did its work undisturbed over our heads. Then we invented the chlorofluorocarbons or CFC also known as freon. Gas for the operation of refrigerators and air conditioners, and propellants for spray cans. They seemed chemically inert and therefore perfect for these uses. And they were, but only at low altitudes. Dispersed in the atmosphere and migrated to high altitudes, the chlorine contained in them gave rise to an unexpected chemical reaction, which ate the ozone by opening a dangerous hole passable by harmful UV rays. A chlorine atom is able to kill 100,000 ozone molecules on average.

Since the reaction occurs more easily at low temperatures on small ice crystals, the hole opened on the polar zones, especially in Antarctica, but began to extend over important inhabited areas ofSouthern hemisphere: New Zealand, Australia, South Africa and Argentina were gradually forced to issue civil protection warnings prohibiting exposure to the sun of people during the days most at risk.

The first measurements of the vertical column of ozone from the ground began in 1957 under the auspices of the International Geophysical Year and the British meteorologist Gordon Dobson (1889-1975) hence the name la Dobson Unit, unit of measure for the vertical quantity of atmospheric ozone. In 1974 the American chemist Frank Sherwood Rowland of the University of California along with his Mexican student Mario Molina they published on Nature the first evidence that CFCs destroyed ozone, accompanied by the research of the Dutch chemist Paul Crutzen: all three will take the Nobel Prize in Chemistry in 1995 for these pioneering achievements.

Immediately there were protests from the industry which denied the uncomfortable complaint: it is said that the president of the chemical giant Du Pont said that those data were “pure science fiction, a pile of garbage, nonsense”. Also Robert Abplanalp, the inventor of spray can valves sent his protests to the dean of the University of California. All stories that will be repeated later with the climate change, it always happens when science threatens economic interests!

The satellite data, however, will allow to confirm the presence of the huge ozone “hole” on the South Pole in 1985 when British meteorologists Farman, Gardiner and Shanklin published their clear denunciation on Nature. Curiously, the satellite data showed the hole since 1976 but they were ignored thinking they were errors of measurement! Meanwhile, the hole in the South Pole was enlarged to about 30 million km2, a hundred times the size of Italy, and a smaller one appeared even at North Pole.

The global public health alarm will always lead to the adoption of the Vienna Convention, an agreement calling for international cooperation to define binding norms against CFCs. The result will materialize in 1987 with the Montreal Protocol than in 2009 it will achieve universal ratification by all 196 countries. It is the first great success of international environmental jurisprudence, the fruit of science and diplomacy: only a joint effort could have avoided irreversible damage to the planet and to Man.

On this successful example will then be built in 1997 the Kyoto Protocol for the reduction of greenhouse gases and today theParis climate agreement, the application of which is however much more complex since, while for CFCs there were ready technological alternatives at a reasonable price, quickly replace the fossil fuels it is much more difficult as it involves both gigantic economic interests and people’s lifestyles.

The effects of the Montreal Protocol have led to one today slow closing of the Antarctic hole: American chemistry Susan Solomon, one of the leading researchers of stratospheric ozone loss and member of the IPCC, in an article that appeared on Science in 2016, shows that the hole will close perhaps in 2050 if the Montreal Protocol is scrupulously observed, but unfortunately they are making their way evidence of abusive emissions probably coming from China.

It might seem like a story happy ending, certainly full of lessons for the other serious environmental problems that haunt us, but the complexity of the world we have set up leads to new surprises: HFCs, the gases that have replaced CFCs, not harmful to the ozone layer, have in fact revealed very powerful gas serra, with heating potentials per molecule up to 15,000 times those of CO2! For this in the 2016 was also signed the Kigali Agreement, an amendment to the Montreal Protocol in force since 2019, aimed at reducing the production of HFCs that fortunately they are replaceable by hydrofluoroolefins (HFO).

Let’s hope there isn’t another delayed burst side effect here too …

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