On September 16, 1987, 34 years ago, the governments of the world signed the Montreal Protocol to protect the ozone layer and banned the use of ozone-destroying substances like CFCs (chlorofluorocarbons) worldwide. On the initiative of the United Nations, since 1995 September 16 has been declared International Day for the Preservation of the Ozone Layer. That is reason enough to look at the current state of the ozone layer.
The ozone layer protects people and the environment from the sun’s energy-rich ultraviolet radiation. However, in the 1970s it was discovered for the first time that the ozone layer was becoming depleted. Although natural processes like volcanic eruptions can weaken the ozone layer, and its thickness and extent depends on a number of different parameters like temperature, it was soon clear that this depletion was caused by anthropogenic emission of chemical compounds. The phenomenon is referred to as the ozone hole. Its largest expansion is observed annually from mid-September to mid-October. Since the Montreal Protocol came into effect in 1989 the production and use of ozone-destroying substances has been prohibited. But the substances emitted before 1989 remain for many years and decades in the stratosphere. For that reason the recovery of the ozone layers is a slow and drawn-out process. Long term the ozone hole might disappear by the end of the 21st century.
The present ozone hole
However, the ozone hole doesn’t simply become smaller each year. How much ozone breaks down in polar spring over the Antarctic due to CFCs depends on dynamic weather patterns in the atmosphere. After an unusually small ozone hole in 2019 the satellite data for 2020 revealed one of the highest levels of depletion in recent years. The depletion began at the end of August and on October 2 the ozone hole extended over 25 million square kilometres, an area equal to that of the North American continent. A strong and prominent polar vortex ensured very low temperatures over the Antarctic for a long time and kept the ozone hole stable until the end of December.
At present (as of Sept. 20) the ozone hole already covers an area of 23 million square kilometres. Because polar night at the south pole is gradually ending, data over the pole itself is still lacking. It is therefore likely that the hole’s extent will be comparable to that of last year. As to the ozone hole’s further development, how long the polar vortex remains stable and cold is decisive.
Continuous monitoring of the ozone hole will continue to be important also in the future despite its long-term recovery. Nitrous oxide from modern farming and bromine from industrial production are new dangers threatening the ozone hole.
Under satellite observation.
Satellites make a decisive contribution to monitoring the ozone layer. In Europe this effort began in 1995 with the Global Ozone Monitoring Experiment (GOME) on the ERS2 satellite. Ozone measurements continued In the following years, first with SCIAMACHY on ENVISAT and later with OMI on AURA and the GOME-2 instruments on the METOP (A, B, C) satellites. Today, the TROPOMI instrument on the Sentinel 5 Precursor (S5p) Copernicus satellite continues to extend this long European time series. At EOC, TROPOMI instrument data are being assessed as part of the ESA/EU S5P project and the data from the GOME-2 instrument are analyzed for the EUMETSAT ACSAF project.