These data are the results of a large eddy simulation on the dispersion of an inert pollutant in the city of Turku, Finland. The pollutant (passive scalar) is released from a point source located at the top of a stack of a heating plant. The simulations were carried out using PALM 6.0 with three, two-way coupled nests. Results have been presented at the 39th International Technical Meeting On Air Pollution Modeling And Its Application, 22 - 26 May 2023, Chapel Hill, North Carolina, U.S.A. and published in Air Pollution Modeling and Its Application XXIX (Springer).

The PALM 6.0 (B. Maronga et al., 2020, Geosci. Model Dev. 13, Maronga et al., 2015, Geosci. Model Dev. 8) model was used to solve the filtered, incompressible Navier-Stokes equations at a very high Reynolds number together with an equation for a passive scalar. The equations were solved with finite differences on a staggered grid. A fifth order upwind-biased numerical scheme was used for the advective terms together with the third order Runge-Kutta method for the time advancement. Solid obstacles, such as orography and buildings, are resolved using the masking method. Trees and other vegetation are treated as porous objects (momentum sinks). The subgrid-scale (SGS) terms are parametrised using the Deardorff SGS model (J.W. Deardorff, 1980, Bound.-Layer Meteorol. 18).

The simulation were performed using three, two-way coupled domains using the nesting feature of PALM (A. Hellsten et al., 2021, Geosci. Model Dev. 14). The domains have approximate sizes of 12 km × 12 km × 670 m, 6 km × 6 km × 260 m, and 3 km × 3 km × 190 m. The domains have 768 × 768 grid points with grid spacing of 16 metres, 8 metres, and 4 metres. In the largest domain, only the orographical features are accounted for while the other two domains contain buildings and vegetation. The largest domain has cyclic boundaries at the horizontal directions and the slip condition at the upper boundary. The inner domains obtain their lateral and top boundary conditions from the larger domain they are nested in. The flow is driven with a constant pressure gradient that is applied above 350 metres and direction on 15°. The simulation domain represents the city of Turku, Finland. The domains are centred around the Student Village in Turku.

The simulation was started from a laminar flow state with an approximately realistic wind profile in the largest domain. The flow and turbulence was then allowed to develop for eight hours without the smaller domains. After the first spinup simulation, a second eight-hour spinup is performed with two-way coupling enabled. The actual simulations extends for four hours. The scalar was released from a single point source.

The data is arranged in different files. The files are named according to the following conventions: - All files start with "DATA_" - "3D_" indicates three-dimensional data - All files are netCDF format as indicated by "NETCDF_" - The end of the file indicates simulation domain. Empty string indicates root domain (the largest domain), "N02" indicates intermediate domain, and "N03" the smallest domain.