Aerosol Sprays and the Ozone Layer.

Ozone is the main component of the upper atmosphere, located between 20 and 50 km above sea level. Ozone at this altitude is essential for life on earth, as it absorbs a large proportion of the sun's ultraviolet (UV) rays, thereby limiting their mutagenic and carcinogenic effects.

The decline in stratospheric ozone observed since the 1970s is due to the transformation of primary pollutants such as chlorofluorocarbons (CFCs) and methylene chloride into chloride radicals (ClO and Cl) under the effect of UV radiation. These free radicals react rapidly with ozone, contributing to its depletion in the upper atmosphere. The effects are both climatic and biological. The direct consequence of this pollution is the ozone hole. This appears in spring and winter every year, mainly over Antarctica. Today, the ozone hole is much smaller than it was thirty years ago.

In the early 1970s, it was British Antarctic Survey meteorologist Jonathan Shanklin who sounded the alarm on the considerable deterioration of the ozone layer. This was a dangerous and important phenomenon, since the drop in ozone concentration led to an increase in average worldwide ultraviolet radiation (UV-B) on the earth's surface. This overexposure was particularly harmful to health, as it could lead to a number of unpleasant side effects.

• A tendency to “sunburn”, characterized by skin dryness and even burns;

• Increased risk of skin cancer;

• Low immune system resistance to disease;

• Ocular disorders, resulting in inflammation of the cornea.

The thinning of the ozone layer could also have deleterious consequences on the environment, such as a slowdown in plant development or a reduction in immunity to infectious diseases, leading to a drop in forestry and agricultural production.

In 1985, studies showed that several types of aerosol emitted volatile organic compounds (VOCs), including chlorofluorocarbons (CFCs), which were responsible for thinning the ozone layer. CFCs were in fact propellants used since the Second World War because of their interesting properties: non-flammable, odorless and stable. In cosmetics, they were found particularly in deodorants and hairsprays. However, these gases release chlorine and bromine atoms which rise into the stratosphere to react with ozone, destroying it.

The solution was radical and swift: in 1987, with the Montreal Protocol, world leaders agreed to phase out CFCs. Manufacturers then proposed replacement solutions to be incorporated into aerosol cans.

Thanks to this global action, the hole in the ozone layer began to close up considerably in the 2000s. According to specialists' predictions, the upper ozone layer over the Northern Hemisphere could be fully restored by 2030, while the gaping hole over Antarctica should disappear by the 2060s!

• Farman, J. C., B. G. Gardiner and J. D. Shanklin (1985), Large losses of total ozone in Antarctica reveal seasonal ClOx/ NOx interaction, Nature, 315, 207-210.

• Marie-Lise Chanin, Livret sur l’environnement, L’ozone stratosphérique, (2020).