Prediction of dosage-based parameters from the puff dispersion of airborne materials in urban environments using the CFD-RANS methodology

One of the key issues of recent research on the dispersion inside complex urban environments is the ability to predict dosage-based parameters from the puff release of an airborne material from a point source in the atmospheric boundary layer inside the built-up area. The present work addresses the question of whether the computational fluid dynamics (CFD)–Reynolds-averaged Navier–Stokes ( RANS) methodology can be used to predict ensemble-averagedosage-based parameters that are related with the puff dispersion. RANSsimulations with the ADREA-HF code were, therefore, performed, where a single puff was released in each case. The present method is validated against the data sets from two wind-tunnel experiments. In each experiment, more than 200 puffs were released from which ensemble-averageddosage-based parameters were calculated and compared to the model’s predictions. The performance of the model was evaluated using scatter plotsand three validation metrics: fractional bias, normalized mean square error, and factor of two. The model presented a better performance for the temporal parameters (i.e., ensemble-averagetimes of puff arrival, peak, leaving, duration, ascent, and descent) than for the ensemble-averagedosage and peak concentration. The majority of the obtained values of validation metrics were inside established acceptance limits. Based on the obtained model performance indices, the CFD- RANSmethodology as implemented in the code ADREA-HF is able to predict the ensemble-averagetemporal quantities related to transient emissions of airborne material in urban areas within the range of the model performance acceptance criteria established in the literature. The CFD- RANSmethodology as implemented in the code ADREA-HF is also able to predict the ensemble-averagedosage, but the dosage results should be treated with some caution; as in one case, the observed ensemble-averagedosage was under-estimated slightly more than the acceptance criteria. Ensemble-averagepeak concentration was systematically underpredicted by the model to a degree higher than the allowable by the acceptance criteria, in 1 of the 2 wind-tunnel experiments. The model performance depended on the positions of the examined sensors in relation to the emission source and the buildings configuration. The work presented in this paper was carried out (partly) within the scope of COST Action ES1006 “Evaluation, improvement, and guidance for the use of local-scale emergency prediction and response tools for airborne hazards in built environments”.