An assessment of the impact of cruise ship emissions while hotelling in the port of Naples has been studied by means of wind tunnel and computational fluid dynamics (CFD) models. An area of about 1.2 km2 was reproduced at a scale of 1:500 for the wind tunnel experiments. The worst but most emission scenario with three cruise ships emitting at the same time was studied. Wind blows from the south-east with a speed of 3 m/s at funnel height in neutral stability conditions of the atmospheric boundary layer. Two different values of the velocity ratio UR = 1 and UR = 4 (funnel gas velocity/wind speed) were considered. In the experiments, Ethane was used as the tracer gas and the concentration was measured at 35 receptor points inside the urban structure and at different heights. Experimental data show good agreement with those estimated by numerically solving steady Reynolds-Averaged Navier-Stokes (RANS) with the k-ω shear-stress transport (SST) turbulence model. The results were used to analyse the accuracy of the predictions of the model CALifornia Puff (CALPUFF), testing two model options: the building downwash module and the parameterisation of the dispersion coefficients. The CALPUFF results are less accurate than the CFD simulations and show a general tendency to underestimate the experimental data. The optimization process improves the performance of CALPUFF. Finally, a more comprehensive analysis of the effect of a varying UR in the range 0.25–16 was undertaken using numerical models. The research provides useful insights to improve the assessment of the impact of ship emissions in port cities.
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