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Comparing source apportionment techniques: a preliminary application to the Po valley area

pubblicazioni - Presentazione

Comparing source apportionment techniques: a preliminary application to the Po valley area

La presenza di particolato in atmosfera è determinata dal contributo di diverse tipologie di sorgenti, incluse le biomasse. 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.

This work describes a preliminary comparison of source apportionment results produced by two approaches: source receptor models and chemical transport models. As a case study, the Po valley was selected, being an area subject to very critical conditions with frequent exceedances of the air quality standards. Receptor models analysis was performed using Chemical Mass Balance, Positive Matrix Factorization and UNMIX. Where required, local source profiles were used. Chemistry transport modelling evaluation was performed by applying the CAMx model that implements PSAT, a powerful source apportionment algorithm. CAMx was implemented for the calendar year 2005 over a 5 km resolution domain covering the whole Po valley. A set of 28 source categories was tracked including: transport sector split according to the fuel, residential heating, energy production and agriculture. Results at different receptors located at both urban and rural sites are presented and issues related to the comparison methodology are discussed. Due to the different temporal coverage between the simulation year and the field campaigns used by receptor models, the comparison was performed only on yearly and seasonal basis. As an example, at the Milan receptor site, CAMx results showed that road transport accounts for the 43% of the PM2.5 yearly mean, domestic heating yields 13% (9% is from biomass burning), agriculture and energy production are both responsible of 10%. At the same receptor, preliminary results of receptor modelling identified both primary sources, such as traffic and combustion processes, and secondary sources, mainly ammonium sulphate and nitrate. In the cold season combustion processes and secondary nitrate account for about 33% to the total PM2.5 mass concentration, followed by traffic (22%) and secondary sulphate (10%); in the warm season traffic and secondary sulphate account for about 30%, while secondary nitrate and combustion yield 16% of PM2.5 concentration.

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