Turbulence parameterizations for dispersion in sub-kilometer horizontally non-homogeneous flows

Results from numerical simulations of tracer dispersion from a point source (an incinerator plant) over complex terrain are presented. Different modeling chains are used and model output compared with ground concentration measurements from the 2017 Bolzano Tracer EXperiment (BTEX) over the Eastern Italian Alps. In particular, meteorological simulations are run with the Weather Research and Forecasting (WRF) model to reproduce the flow field at sub-kilometer grid resolution (300 m). The simulations apply observational nudging of upper-air and surface meteorological observations, as well as an improved snow cover initialization, which allow to better characterize valley winds in the afternoon. In addition, the simulations are run by substituting the default closure constants of the Planetary Boundary Layer (PBL) scheme with a set of values specific for complex terrain applications. Meteorological results are evaluated comparing wind speed standard deviations with measurements from a SODAR instrumentation deployed during the experiment. The meteorological fields provide the input to two different dispersion models: the CALMET/CALPUFF puff-Gaussian model, representing the reference standard model often used in impact assessments, and the WSI/SPRAY-WEB Lagrangian particle model. Different parameterizations for the calculation of the dispersion coefficients, based either on surface layer scales or on the turbulent kinetic energy from the WRF PBL scheme, are tested. A statistical analysis of the results from all the dispersion models is performed to assess the simulation performance against tracer concentration measurements collected during the BTEX campaign.