Institute for Atmospheric and Climate Science

Stratospheric ozone trends

Johannes Staehelin

Atmospheric ozone mostly resides in the stratosphere and prevents harmful solar UV-B and UV-C radiation from preventing to the Earth’s surface. The anthropogenic release of ozone depleting substances (ODS) caused stratospheric ozone depletion, not only over polar regions (“Antarctic ozone hole” and polar ozone depletion) but also over the more populated mid-latitudes (Fig. c, for more details of the world longest total ozone series see long-term ozone series of Switzerland). The Montreal protocol (1987) and its amendments led to a strong reduction of the emission of ODS (see Fig. a). However, ODS need several years for transport from the Earth’s surface into the stratosphere and some individual ODS have long atmospheric residence times (many decades). Fig. b shows the temporal evolution of chemical ozone depletion over mid-latitudes caused by emission of ODS. The comparison of Fig. c and Fig. b indicates that the increase in total ozone observed over Northern mid-latitudes since the early 1990s can not be directly attributed to the effect of the Montreal protocol (and its subsequent amendments and adjustments), since lowest total ozone values were observed in 1993 while chemical ozone depletion peaked in the second part of the 1990s. Further factors, such as violent volcanic eruptions, long-term climate variability and polar ozone depletion also significantly affect the temporal evolution of the ozone shield. (The strong connection between stratospheric ozone and atmospheric transport make stratospheric ozone measurements also attractive to study climate variability.)

We have analyzed stratospheric ozone changes using both, ground-based measurements such as the total ozone series of Arosa as well as satellite measurements. Ground based measurements started earlier but they don’t provide global coverage of the ozone shield. By data assimilation using meteorological data the ozone series CATO (Candidoz Assimilated Three-dimensional Ozone) was constructed, which provides global coverage and ozone profile information (the data can be down loaded from the web-page Since long-term ozone trends are relatively small the reliability of long-term ozone measurements has high priority. For that purpose we study simultaneous ground based ozone measurements by different instrument types, available at Arosa since the early 1990s (see Swiss long-term ozone series).

Current research topics include:

  • Careful evaluation of ground-based total ozone measurements obtained by Dobson and Brewer instruments operated at Arosa operated by MeteoSwiss.
  • Statistical modeling of the evolution of the stratospheric ozone shield, in particular to study the effect of the Montreal protocol and the effect of climate variability using multiple regression models in order to account for atmospheric processes based on both, ground-based and satellite measurements.

a) World wide production of ozone depleting substances.

b) Chemical stratospheric ozone depletion caused by the release of anthropogenic ozone depleting substances.

c) Total ozone series of Arosa (Switzerland) (for more details see Swiss long-term ozone measurements)




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