| Topic | Core indicator | DPSIR | Main topic |
|---|---|---|---|
| Chemicals | State |
Ozone layer above Switzerland
Ozone is a gas that absorbs a portion of the sun's carcinogenic ultraviolet (UV) radiation. It contributes to the so-called ozone layer in the stratosphere, between 10 and 40 km above the Earth's surface. In the 1980s, scientists discovered that this ozone layer was being progressively destroyed as a result of anthropogenic emissions of ozone-depleting substances (e.g. CFCs, HCFCs and halons). The indicator shown here reflects the evolution of the ozone layer above Switzerland. It helps evaluate the effectiveness of existing measures to protect the ozone layer and to assess whether any additional measures are needed. Because emissions of ozone-depleting substances and atmospheric transport processes are global in nature, such measures must be implemented worldwide, as provided for by the Montreal Protocol. The indicator therefore largely reflects global efforts to restore the ozone layer.
medium
unsatisfactory
Since 1995, the annual average ozone concentrations over Switzerland have followed a slightly upward trend, which is not yet statistically significant. In recent years, stronger fluctuations have been observed, partly influenced by global atmospheric transport processes. Due to the longevity of ozone-depleting substances in the atmosphere and their continued emission from existing stocks, in particular insulation foams and refrigeration systems, the middle latitudes of the northern hemisphere are not expected to return to the baseline value (from the reference year 1980) until around 2035. The trend analysis of the Swiss data is uncertain, so it is not yet possible to say whether the ozone layer will actually normalise during this period. Since the baseline will not be reached for several years, but the increase still required is relatively small (less than 5%), the state of the ozone layer over Switzerland is judged to be medium.
For regions outside the middle latitudes of the northern hemisphere, a return to the respective 1980 baseline values is not expected until around 2060, due to different atmospheric processes in the tropics and the polar regions.
The transparency of the atmosphere to solar UV radiation is measured using Dobson and Brewer spectrometers. These measurements are used to calculate the amount of ozone present in the air column above Arosa (until 2020) resp. Davos (from 2021). This total ozone content is given in Dobson Units (DU). A DU is defined as a layer of pure ozone that would be 0.01mm thick if measured at ground level at a temperature of 0 °C and a pressure of 1 atmosphere. Thus, if all the ozone contained in a column of air was brought down to the surface of the Earth, 330 DU would represent an ozone layer 3.3mm thick.
| Targeted trend | Initial value | Final value | Variation in % | Observed trend | Assessment |
|---|---|---|---|---|---|
| Growth | Average 1995-1997 | Average 2020-2022 | 2.85% | Stabilisation | unsatisfactory |
Further information
