Il contributo di sorgenti locali sull'impatto ambientale da Diossine e Furani

Polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are ubiquitous contaminants, mainly released into the environment during combustion processes (point sources), but also from other sources (traffic, waste incinerators, uncontrolled combustion). This Ph.D. thesis is aimed to investigate the contribution of a steel plant in NW Italy (700 000 tons of steel/year) to the air concentrations and the deposition fluxes of PCDDs/PCDFs at local level, through the analysis of measured, modelled and literature data. The investigation on PCDD/F air concentration was carried out in an area of 600 km2, using air quality data measured by the institutional monitoring network, data obtained from AERMOD simulations and literature data. The measured air concentrations were consistent with literature values for similar areas, and both the homologue profiles and PCA analyses showed a clear distinction between the monitoring stations and the source profiles. All the previous results were also confirmed by the air dispersion model (AERMOD), that predicted PCDD/F air concentrations due to the steel plant from four to two orders of magnitude lower than those measured in the monitoring stations, highlighting the presence of other sources. AERMOD is one of the most used models for estimating ambient air pollution concentrations; it is a steady-state, plume dispersion model developed by the US Environmental Protection Agency (EPA). The investigation on PCDD/F deposition fluxes was carried out in an area of a 420 km2 area surrounding the plant. Total measured deposition fluxes of PCDD/Fs were consistent with other studies carried out in Italy in urban and suburban areas and in rural European areas; while these were lower than those measured in other European urban/suburban areas or in sites influenced by industrial sources. Furthermore, the measured deposition fluxes were also compared with the pattern of PCDD/Fs in ambient air sampled at the same sites in the previous part of the study. This comparison showed a similarity between air concentration and deposition patterns and a clear distinction from the source. The study was completed with AERMOD simulations, that calculated deposition fluxes of two or three orders of magnitude lower than those measured in two of the three monitoring points; while the model was not able to calculate the deposition fluxes in the most distant monitoring station, because they were under the limit of sensitivity of the model itself . This results confirmed that the unexposed sampling site was not subject to emissions from the steel plant. In conclusion, this study outlines the limited influence of the source in the local PCDD/F both air concentrations and deposition fluxes and at the same time the usefulness of a joint analysis of measured, literature and calculated data to correctly evaluate the role of a source to the local pollution. The study also highlights the usefulness of AERMOD as a complementary tool to define the correct placement of monitoring stations and to locate those areas expected to have the highest air concentrations deriving from a source.