The ozone layer
Ozone (O3) is found in small amounts throughout the atmosphere, but most of it (around 90%) is concentrated in the stratosphere at approximately 15 to 35 kilometres above the Earth's surface. This is commonly referred to as the “ozone layer”.
Ozone in the stratosphere is not the same as the ozone in the troposphere – the layer of the atmosphere that’s closest to the Earth. Whereas stratospheric ozone protects the planet, tropospheric ozone (“ground-level ozone”) is an air pollutant and a major component of photochemical smog, a phenomenon that contributes to poor air quality and can lead to health problems.
Why is it important?
By absorbing most of the sun's harmful UV radiation, the ozone layer plays a vital role in protecting life on Earth.
The ozone layer helps to:
Depletion of the ozone layer
Atmospheric ozone concentrations can fluctuate naturally depending on temperature, weather, latitude and altitude. Natural events, such as volcanic eruptions, can also influence ozone levels in the atmosphere.
However, these natural causes could not explain the annual appearance of an "ozone hole" over the Antarctic region in the 1980s. Rather, scientists discovered that certain human-made chemicals, specifically chlorofluorocarbons (CFCs), were the main cause of this significant depletion in stratospheric ozone levels. These ozone-depleting substances (ODS) started to be used in the late 1950s and found wide application in industrial and consumer goods such as refrigerators, air conditioners, fire extinguishers, and spray cans. Since then, a number of other types of chemicals have been found + to deplete ozone when reaching the stratosphere, ie, the so-called ozone-depleting potential.
To address the issue, the international community agreed on the Vienna Convention (1985), and the Montreal Protocol (1987). The Protocol has been signed by 198 Parties, making it the first universally ratified international treaty and one of the UN’s most successful environmental initiatives.
Given the obligatory requirements of the Protocol, countries have been regulating ODS for decades. The most recent EU legislation on the subject is detailed in Regulation (EU) No 2024/590.
Which human-made substances can damage the ozone layer?
Several groups of chemical compounds containing gaseous chlorine or bromine are known to deplete the ozone layer. These include:
- Chlorofluorocarbons (CFCs)
- Halons (fully halogenated aliphatic carbons)Carbon tetrachloride
- Methylchloroform (1,1,1-Trichloroethane)
- MethylbromideHydrobromofluorocarbons (HBFCs)
- Hydrochlorofluorocarbons (HCFCs)
- Bromochlorometane
These gases are regulated and monitored internationally through the Montreal Protocol. Beyond those covered by the Protocol, Regulation (EU) No 2024/590 also addresses the following substances:
- 1-Bromopropane (n-propyl bromide)
- Bromoethane (ethyl bromide)
- Trifluoroiodomethane (trifluoromethyl iodide)
- Chloromethane (methyl chloride)
- 2-bromo-3,3,3-trifluoro prop-1-en (2-BTP)
- Dichloromethane (DCM)
- Tetrachloroethene (Perchloroethylene (PCE))
How do they cause depletion?
When ultraviolet (UV) radiation breaks down CFCs and other ODS in the stratosphere, the released chlorine and bromine attack and, in turn, break down the ozone molecule. Severe ozone depletion can lead to the creation of “ozone holes” in the stratosphere over the polar regions.
How is the ozone layer monitored?
The EU relies on the Copernicus Atmosphere Monitoring Service (CAMS), which uses satellite observations and ground-based sensors to gather high-quality, real-time data on stratospheric ozone levels globally. This monitoring effort includes tracking seasonal fluctuations, ozone hole formation, and gradual trends in ozone recovery.
Satellite monitoring of the Antarctic ozone hole provides real-time data on its size and severity. The image below, where blue ares indicate severe depletion of ozone, emphasises the need for continued action to reduce global ODS emissions and support the recovery of the Antarctic ozone hole.
For more detailed data and forecasts on the ozone layer, please consult the Copernicus website.
Interaction between ODS and climate change
Most ozone-depleting substances (ODS) are also powerful greenhouse gases (GHG). ODS can have a global warming effect up to 16,000 times stronger than carbon dioxide (CO2), which is the primary greenhouse gas in terms of atmospheric abundance.
The global effort to phase out ODS under the Montreal Protocol, has significantly contributed to tackling climate change and meeting the Paris Agreement’s goal to keep the global temperature rise well below 2 degrees Celsius, while also striving to limit the increase to 1.5 degrees. However, since consumption and production of ODS are already covered by the Protocol, ODS emissions are not specifically included in the Paris Agreement or the EU's climate targets. .
As a result of the phasing out ODS, there has been a significant increase in the use of other types of gases, such as fluorinated greenhouse gases (F-gases). While F-gases do not damage the ozone layer, they still have a considerable global warming effect and as illustrated on our dedicated webpage, measures are being taken at EU and global level to curb F-gas emissions.