Ozone hole

The term ‘ozone hole’ refers to the depletion of the protective ozone layer in the upper atmosphere (stratosphere) over Earth's Polar Regions. Humans, plants, and animals living under the ozone hole are harmed by the solar radiation reaching the Earth's surface—where it causes health problems, from eye damage to skin cancer.

Stratospheric ozone is constantly produced by the action of the sun's ultraviolet radiation on oxygen molecules (known as photochemical reactions). Although ozone is created primarily at tropical latitudes, large-scale air circulation patterns in the lower stratosphere move ozone toward the poles, where its concentration builds up.

In addition to this global motion, strong winter polar vortices are also important to concentrating ozone at the poles. During the continuously dark polar winter, the air inside the polar vortices becomes extremely cold, a necessary condition for polar stratospheric cloud formation.

Polar stratospheric clouds create the conditions for drastic ozone destruction, providing a surface for chlorine to change into ozone-destroying form. They generally last until the sun comes up in the spring.

In the 1980s, scientists discovered that the ozone layer was thinning in the lower stratosphere, with particularly dramatic ozone loss—known as the "ozone hole"—in the Antarctic spring (September and October).

Scientists also discovered that the thinning in the ozone layer was caused by increasing concentrations of ozone-depleting chemicals – chlorofluorocarbons or CFCs (compounds with chlorine and/or fluorine attached to carbon) and to a lesser extent halons (similar compounds with bromine or iodine). These chemicals can remain in the atmosphere for decades to over a century.

At the poles, CFCs attach to ice particles in clouds. When the sun comes out again in the polar spring, the ice particles melt, releasing the ozone-depleting molecules from the ice particle surfaces.

Once released, these ozone-destroying molecules do their dirty work, breaking apart the molecular bonds in UV radiation-absorbing ozone.

Most of the ozone-depleting substances emitted by human activities remain in the stratosphere for decades, meaning that ozone layer recovery is a very slow, long process.

The chart below shows the development of the (annual maximum) size of the ozone hole over the Antarctic. The hole grew in the years following ratification of the Montreal Protocol, due to the lag caused by the fact that ozone-depleting substances remain in the stratosphere for a long time. The maximum size of the ozone hole is now decreasing.

 

For the status of the currently ongoing ozone hole, you can visit the Copernicus web site 

https://ozonewatch.gsfc.nasa.gov/  Link to NASA Ozone Watch

Maximum ozone hole extent over the southern hemisphere, from 1979 to 2019.

The images below show analyses of total ozone over the Antarctic by Copernicus. The blue colours indicate the lowest ozone amounts, while yellow and red indicate higher ozone amounts.

Source: European Environment Agency

Actions required globally to continue the recovery of the ozone layer are:

• Ensuring that existing restrictions on ozone-depleting substances are properly implemented and global use of ozone-depleting substances continue to be reduced.
• Ensuring that banks of ozone-depleting substances (both in storage and contained in existing equipment) are dealt with in an environmentally-friendly manner and are replaced with climate-friendly alternatives.
• Ensuring that permitted uses of ozone-depleting substances are not diverted to illegal uses.
• Reducing use of ozone-depleting substances in applications that are not considered as consumption under the Montreal Protocol.
• Ensuring that no new chemicals or technologies emerge that could pose new threats to the ozone layer (e.g. very short-lived substances).