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PM2.5 source apportionment in Lombardy (Italy): comparison of receptor and chemistry-transport modelling results

pubblicazioni - Articolo

PM2.5 source apportionment in Lombardy (Italy): comparison of receptor and chemistry-transport modelling results

La presenza di particolato in atmosfera è determinata dal contributo di diverse tipologie di sorgenti, tra le più rilevanti possiamo ricordare il trasporto su strada, il riscaldamento domestico e l’agricoltura. A causa dei complessi processi che portano alla formazione e dispersione del particolato, la ricostruzione del ruolo delle diverse categorie emissive alle concentrazioni totali di PM richiede l’utilizzo di appositi strumenti modellistici. Il lavoro discute e confronta due tipologie di approcci con riferimento all’area padana, una delle zone più critiche a livello italiano ed europeo. L’esatta ricostruzione del contributo delle diverse sorgenti inquinanti alle concentrazioni in atmosfera costituisce un requisito essenziale per la definizione di scenari di riduzione delle emissioni, ivi inclusi quelli determinati da politiche di efficienza energetica.

This work discusses the Source Apportionment results produced by receptor and chemistry-transport modelling for PM2.5 in Northern Italy, selected as case study due to its very critical conditions. Receptor modelling analysis was performed using the Chemical Mass Balance model, while source oriented analysis was performed by means of the CAMx chemistry transport model. Models shared the same source profiles, mostly based on local data. PM2.5 composition data were derived from a field campaign covering 2003-2007 at 9 monitoring sites. CMB showed a better reconstruction of the mass closure, while CAMx systematically underestimated cold season concentrations. Nevertheless both models provided the same source ranking at several receptors. According to CMB results, the most relevant contributions during the cold season, ranging around 10 µg/m3 were yielded by road transport, domestic heating and ammonium nitrate.

CAMx provided similar results for the secondary sources, while systematically underestimated road transport and domestic heating. A similar behaviour was observed during the summer season. The main discrepancies observed between the models were: the questionable results from CMB at some receptors, not identifying the road transport contribution, that, conversely, was clearly pointed out by CAMx/PSAT estimates; the ability of CAMX/PSAT to apportion the contribution of sources sharing similar profiles and strongly correlated such as CI and SI vehicles, altogether recognized as traffic source by CMB; the ability of CAMX/PSAT to identify the contribution of secondary PM deriving either from complex chemical transformation, such as anthropogenic and biogenic SOA, or not characterized by a clear emission pattern, such as mixed anthropogenic activities and long range transport burden.

Finally, the comparison of specific source contribution allowed a deeper investigation of the possible causes of CAMx/PSAT discrepancies. Particularly, the analysis clearly pointed out that CAMx missed the reconstruction of the road transport contribution to the OC fraction during the cold season.

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