In order to account for the meteorological and chemical features of the urban boundary layer at a mesoscale resolution, we have nested several MECO (n) instances into the global EMAC domain to obtain a final resolution of 2 km. (n) hereby stands for the number of instances within the MECO framework.
Human activities lead to an increase of emissions of air pollutants influencing the chemical composition of urban air. Chemical reactions and aerosol formation processes in urban areas in turn are altered due to increased temperature, reduced humidity and modified urban-rural trace substance mixture. Urban-rural circulation patterns driven by the strength of the urban heat island (UHI) further promote the dispersion of pollutants into the rural vicinity, being able to modify local and regional air chemistry and meteorology. For this reason, numerical models describing urban climates need to represent both atmospheric dynamics and air chemistry in order to account for the complex interactions in these areas.
In this range of model resolution, specific features of impervious surfaces on the dynamics of the lower troposphere have to be parametrized. For this purpose we have coupled the urban canopy model TERRA_URB (Wouters 2015, 2016) to the dynamical part of MECO (COSMO).
With this tool, we can analyse a urban heat island effect over Germany (left picture) and the impact of the UHI on NOx mixing ratios near the surface (right picture)