Prof. em. Johannes Stähelin
Prof. em. Johannes Stähelin
Retired Adjunct Professor at the Department of Environmental Systems Science
Additional information
Research area
Stratospheric ozone trend analysis.The Swiss ozone series (total ozone (since 1926) and Umkehr from Arosa and ozone sondes) show the effects of changing emission of ozone depleting substances (ODS) and of dynamics (North Atlantic Oscillation (NAO) and El Nino Southern Oscillation (ENSO)). In CANDIDOZ (Chemical and Dynamical Influences on Decadal Ozone Change) we used satellite ozone measurements to separate the influence of chemical ozone depletion and long-term climate variability. Ball et al. (2018) found evidence for unexpected continuous decline in lower stratospheric ozone offsetting the ozone recovery. Chemistry at tropopause altitude and evaluation of global tropospheric numerical simulations. We measured nitrogen oxides (NO, NO2) and ozone in a B747 of Swissair (NOXAR: Nitrogen OXides and ozone along Air Routes) and in POLINAT-2 (Pollution from Aircraft Emissions in the North Atlantic Flight Corridor). Large horizontal gradients of NOx at tropopause altitude were attributed to production by lightning strokes. Chemistry at the tropopause region was studied in SPURT (SPURenstofftansport in der Tropopausenregion). NOXAR data were used in TRADEOFF (Aircraft emissions: Contributions of various climate compounds to changes in composition and radiative forcing - TRADEOFF to reduce atmospheric impact) for comparison with numerical simulations, in RETRO (REanalysis of TROpospheric chemical composition over the past 40 years) and QUANTIFY (QUANTIFYing the climate impact of global and European transport Systems). Photooxidants, other air pollutants and tropospheric ozone long-term trends. Historical measurements (from Arosa, going back to 1930) and measurements from the 1990s suggest an increase in tropospheric ozone in the rural and alpine air by more than a factor two between World War II and 1990, when anthropogenic emissions dramatically increased. Increases in ozone background concentration in the 1990s in European background air are more difficult to explain when ozone precursor emission significantly decreased in Europe and North America. We studied summer smog in the Swiss project POLLUMET (POLLution and METeorology) and LOOP (Limitation Of Oxidant Production) finding large air pollution originating from the capital of Milan (ozone concentrations approaching 200 ppb). The small decrease in high ozone values in the Swiss polluted planetary boundary layer since the 1990s needs further attention considering the large reduction in ozone precursor emissions. Measurements of trace species performed in Arosa and at the high Alpine site Jungfraujoch (specifically of PAN (Peroxy Acetyl Nitrate) were made to study regional, European, hemispheric contributions and the impact of stratospheric intrusions. Evaluation of emission models. Measurements of Gubrist tunnel (close to Zürich) showed, that the road traffic emission model underestimated nitrogen emissions of heavy-duty (diesel) vehicles by approximately a factor two (confirmed by tunnel studies of the 1990s from Germany and Austria). The time series of Gubrist tunnel of the 1990s showed the successful introduction of catalytic converters in the gasoline driven Swiss fleet. Scavenging of air pollutants by precipitation. Our field experiment “winter precipitation at Rigi” (contribution to WaBoLu (Wasser, Boden, Luft)) and ALPTRAC (High Alpine Aerosol and Snow Chemistry Study) showed the key role of cloud physics (riming) in the transfer of pollutants from the atmosphere into the precipitation. Value and history of long-term Swiss ozone measurements (LKO history project). Pierre Viatte (former coworker of MeteoSwiss) and I reported on the history of the Light Climatic Observatory (LKO) at Arosa (report of MeteoSwiss and IACETH) providing the basis for the book “Licht, Luft, Ozone” written for the public by Martin Läubli (2019) (translated to English).
Johannes Staehelin has been given the title of Professor of ETH in November 2002. He is a lecturer and he leads a research group at the Institute for Atmospheric and Climate Science since 1988.
Johannes Staehelin was born on August 16, 1949 in Basel, Switzerland. He studied chemistry at the University of Zürich. In his dissertation he studied the decomposition of ozone in water at the Swiss Federal Institute for Water Resources and Water Pollution Control (EAWAG) at Dübendorf, Switzerland. This work was awarded by the silver medal of ETH Zurich. Thereafter he was working at the Cooperative Institute for Research in Environmental Sciences (CIRES) in Boulder Co., USA, at the Agricultural Research Institute at Wädenwil (FAW) and at Ciba-Geigy Inc. in Basel. Since 1988 he is the head of a research group at the Laboratory of Atmospheric Physics at ETH Zurich. His research interest include long-term trend analysis of atmospheric ozone and atmospheric gas phase chemistry. The emissions of road traffic, air pollution at urban and remote sites and processes of the upper troposphere and of the lower stratosphere are studied.
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