In last years, atmospheric dispersion models have reached considerable popularity in environmental research field. In this regard, given the difficulties associated to the estimation of emission rate for some kind of sources, and due to the importance of this parameter for the reliability of the results, Backward dispersion models may represent promising tools. In particular, by knowing a measured downwind concentration in ambient air, they provide a numerical value for the emission rate. This paper discusses a critical validation of the WindTrax Backward model: the investigation does not only deal with the strict reliability of the model but also assesses under which conditions (i.e. stability class, number, and location of the sensors) the model shows the greatest accuracy. For this purpose, WindTrax results have been compared to observed values obtained from available experimental datasets. In addition, a sensitivity study regarding model-specific parameters required by WindTrax to replicate the physics and the random nature of atmospheric dispersion processes is discussed. This is a crucial point, since, for these settings, indications on the numerical values to be adopted are not available. From this study, it turns out that the investigated model specific settings do not lead to a significant output variation. Concerning the validation study, a general tendency of the model to predict the observed values with a good level of accuracy has been observed, especially under neutral atmospheric conditions. In addition, it seems that WindTrax underestimates the emission rate during unstable stratification and overestimates during stable conditions. Finally, by the definition of alternative scenarios, in which only a portion of the concentration sensors was considered, WindTrax performance appears better than acceptable even with a small number of concentration sensors, as long as the positioning is in the middle of the plume and not in the strict vicinity of the source.

Dispersion modeling is a useful tool for reproducing the spatial–temporal distribution of pollutants emitted by industrial sites, particularly in the environmental odor field. One widely used tool, accepted by regulatory agencies for environmental impact assessments, is the CALPUFF model, which requires a large number of input variables, including meteorological and orographical variables. The reliability of model results depends on the accuracy of these input variables. The present research aims to discuss a comparative study of odor dispersion modeling by initializing the CALMET meteorological processor with different input data: surface and upper air observational meteorological data, 3D prognostic data, and a blend of prognostic and measured data. Two distinct sources (a point and an area source) and two different simulation domains in Cuba and Italy are considered. The analysis of results is based on odor impact criteria enforced in some Italian regions by computing the 98th percentile of odor peak concentrations on an annual basis. For the area source, simulation results reveal that the ‘OBS’ and ‘HYBRID’ modes are largely comparable, whereas prognostic data tend to underestimate the odor concentrations, likely due to a reduced percentage of wind calms. For point sources, different input meteorological settings provide comparable results, with no significant differences.

One of the most complex challenges in the field of industrial odour emissions is the characterization of passive area sources, which emit contaminants even if not endowed with their own gas flow. Two primary sampling devices have been developed for this scope: Wind Tunnel (WT), with a unidirectional airflow without vertical mixing, and Flux Chamber (FC), with a turbulent well-mixed flow. Essentially, two are the debated issues about the sampling instrumentation. The first concerns which device is more suitable for accurately describing the real fluid dynamic behaviour at the liquid-gas interface. The second issue involves the extent to which the emission rates, estimated by the two sampling systems, differ. This study addresses these debates providing experimental data on the real atmospheric motion near liquid surfaces, aiding the choice between WT and FC. Field tests reveal that atmospheric conditions can make the fluid dynamics similar to either WT or FC, with the general scenario showing an intermediate wind behavior. Thus, it is not possible to a priori determine the most suitable device. Concerning the second issue, this research presents an experimental comparison of VOCs (Volatile Organic Compounds) emission rates between a recently developed WT and a US-EPA design FC. These trials indicate that for soluble compounds, WT and FC yield comparable results. However, for gas-phase controlled species (low-solubility VOCs), WT tends to overestimate emissions compared to FC, with the ratio of specific emission rates ranging from 2 to 4.5. The developed theoretical mass transfer model aligns well with observed values, except for toluene due to its non-ideal mixture with water.