Implementation of a dry deposition module (DEPAC v3.11) in a large eddy simulation code (DALES v4.4)

Abstract. High-resolution data on reactive nitrogen deposition are needed to inform cost-effective policies. Large eddy simulation models coupled to a dry deposition module present a valuable tool for obtaining these high-resolution data. In this paper we describe the implementation of a dry deposition module (DEPAC v3.11) into a large eddy simulation code (DALES v4.4), and its first application in a real-world case study. With this coupled model, we are able to represent the turbulent surface-atmosphere exchange of passive and reactive tracers at the hectometer resolution. A land surface module was implemented to solve the surface energy budget and provide detailed information for the calculation of deposition fluxes per land use (LU) class. Both the land surface model and the dry deposition module are extensively described, as well as the inputs that are needed to run them.

To show the advantages of this new modeling approach, we present a case study for the city of Eindhoven in the Netherlands, focusing on the emission, dispersion and deposition of NO_x and NH₃. We find that DALES is able to reproduce the main features of the boundary layer development and the diurnal cycle of local meteorology well, with the exception of the evening transition. DALES calculates the dispersion and deposition of NO_x and NH₃ in great spatial detail, clearly showing the influence of local LU patterns on small-scale transport, removal efficiencies and mixing characteristics.