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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
© Author(s) 2017. This work is distributed under
the Creative Commons Attribution 3.0 License.
Model evaluation paper
19 May 2017
Review status
This discussion paper is under review for the journal Geoscientific Model Development (GMD).
Evaluation of high-resolution GRAMM/GRAL NOx simulations over the city of Zurich, Switzerland
Antoine Berchet1, Katrin Zink1, Dietmar Oettl2, Jürg Brunner3, Lukas Emmenegger1, and Dominik Brunner1 1Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
2Air Quality Control, Government of Styria, Landhausgasse 7, 8010 Graz, Styria, Austria
3Office for Environment and Health protection, City of Zürich, Zürich, Switzerland
Abstract. Hourly NOx concentrations were simulated for the city of Zurich, Switzerland, at 10 m resolution for the years 2013–2014. The simulations were generated with the nested mesoscale meteorology and microscale dispersion model system GRAMM/GRAL (versions v15.12/v14.8) by applying a catalogue-based approach. This approach was specifically designed to enable long-term city-wide building-resolving simulations with affordable computation costs. It relies on a discrete set of possible weather situations and corresponding steady-state flow and dispersion patterns that are pre-computed and then matched hourly with actual meteorological observations. The modelling system was comprehensively evaluated using eight sites continuously monitoring NOx concentrations and 65 passive samplers measuring NO2 concentrations on a 2-weekly basis all over the city. The system was demonstrated to fulfil the European Commission standards for air pollution modelling at nearly all sites. The average spatial distribution was very well represented, despite a general tendency to overestimating the observed concentrations, possibly due to a crude representation of traffic-induced turbulence. The temporal variability of concentrations explained by varying emissions and weather situations was accurately reproduced on different time scales. The seasonal cycle of concentrations, mostly driven by stronger vertical dispersion in summer than in winter, was very well captured in the two year simulation period. Short-term events, such as episodes of particularly high and low concentrations, were detected in most cases by the system, although some unrealistic pollution peaks were occasionally generated, pointing at some limitations of the steady-state approximation. The different patterns of the diurnal cycle of concentrations observed in the city were generally well captured as well. The evaluation confirmed the adequacy of the catalogue-based approach in the context of city scale air pollution modelling. The ability to reproduce not only the spatial gradients but also the hourly temporal variability over multiple years makes the model system particularly suitable for investigating individualized air pollution exposure in the city.

Citation: Berchet, A., Zink, K., Oettl, D., Brunner, J., Emmenegger, L., and Brunner, D.: Evaluation of high-resolution GRAMM/GRAL NOx simulations over the city of Zurich, Switzerland, Geosci. Model Dev. Discuss.,, in review, 2017.
Antoine Berchet et al.
Antoine Berchet et al.
Antoine Berchet et al.


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