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 http://iac.ethz.ethz.ch/cato/). 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:
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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