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Geoscientific Model Development An interactive open-access journal of the European Geosciences Union
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Discussion papers
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Model description paper 11 Jan 2019

Model description paper | 11 Jan 2019

Review status
This discussion paper is a preprint. A revision of the manuscript is under review for the journal Geoscientific Model Development (GMD).

The Eulerian urban dispersion model EPISODE. Part II: Extensions to the source dispersion and photochemistry for EPISODE-CityChem v1.2 and its application to the city of Hamburg

Matthias Karl1, Sam-Erik Walker2, Sverre Solberg2, and Martin O. P. Ramacher1 Matthias Karl et al.
  • 1Chemistry Transport Modelling, Helmholtz-Zentrum Geesthacht, Geesthacht, Germany
  • 2Norwegian Institute for Air Research (NILU), Kjeller, Norway

Abstract. This paper describes the CityChem extension of the Eulerian urban dispersion model EPISODE. The development of the CityChem extension was driven by the need to apply the model in lower latitude cities with higher insolation than in northern European cities. The CityChem extension offers a more advanced treatment of the photochemistry in urban areas and entails specific developments within the sub-grid components for a more accurate representation of the dispersion in the proximity of urban emission sources. The WMPP (WORM Meteorological Pre-Processor) is used in the point source sub-grid model to calculate the wind speed at plume height. The simplified street canyon model (SSCM) is used in the line source sub-grid model to calculate pollutant dispersion in street canyons. The EPISODE-CityChem model integrates the CityChem extension in EPISODE, with the capability of simulating photochemistry and dispersion of multiple reactive pollutants within urban areas. The main focus of the model is the simulation of the complex atmospheric chemistry involved in the photochemical production of ozone in urban areas. EPISODE-CityChem was evaluated with a series of tests and with a first application to the air quality situation in the city of Hamburg, Germany. A performance analysis with the FAIRMODE DELTA Tool for the air quality in Hamburg showed that the model fulfils the model performance objectives for NO2 (hourly), O3 (daily max. of the 8-h running mean) and PM10 (daily mean) set forth in the Air Quality Directive, qualifying the model for use in policy applications. Observed levels of annual mean ozone at the five urban background stations in Hamburg are captured by the model within 15 %. Envisaged applications of the EPISODE-CityChem model are urban air quality studies, emission control scenarios in relation to traffic restrictions and the source attribution of sector-specific emissions to observed levels of air pollutants at urban monitoring stations.

Matthias Karl et al.
Interactive discussion
Status: final response (author comments only)
Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Matthias Karl et al.
Model code and software

City-scale Chemistry Transport Model EPISODE-CityChem (Release version 1.2) M. Karl and M. O. P. Ramacher

Matthias Karl et al.
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Short summary
A large part of the population living in cities is exposed to ozone levels above the EU air quality target value. The CityChem extension of the urban air quality model EPISODE enables a detailed treatment of the atmospheric chemistry in urban areas and the near-field dispersion close to industrial stacks and in street canyons. The application of the model in the city of Hamburg (Germany) shows good performance for ozone, nitrogen dioxide and particulate matter at air quality monitoring stations.
A large part of the population living in cities is exposed to ozone levels above the EU air...