Organic characterization of PM2.5 in the Emilia-Romagna region (I)

In order to contribute to the understanding of the PM2.5 chemical-physical characteristics in Emilia-Romagna region (Italy), the Project “Supersito” has realized 8 intensive campaigns (November 2011 - May 2014) for measuring different organic and inorganic species in two sites: Bologna-Urban background, residential centre in the Po Valley near Apennines, and San Pietro Capofiume-Rural site, 30 Km north-east from Bologna. In this work organic compounds were analysed, in particular polycyclic aromatic hydrocarbons (PAHs), nitrated polycyclic aromatic hydrocarbons (nitro-PAHs), oxygenated polycyclic aromatic hydrocarbons (Oxy-PAHs), aliphatic hydrocarbons (HCs), carboxilic acids, sugars and phenols. The campaigns were performed in different periods of the year in order to obtain an overview of the diverse weather conditions, multiple emission sources and/or chemical transformation. During the months with high loads of PM in the atmosphere, aerosol samples were collected with a low volume instrument and sampled two times in the day, from 9 am to 6 pm (diurnal sampling) and from 6 pm to 9 am (nocturnal sampling). With this procedure it was possible to evaluate the effect of the planetary boundary layer variations on the PM2.5 concentration and composition. It is important underline that nocturnal samplings were affected by the rush hours of the morning and evening. In the spring months, with minor PM loads, the sampling was performed daily from 9 am to 9 am by using high volume sampler. In order to characterize the possible emission sources, the distribution profiles of different PAHs, nitro-PAHs, Oxy-PAHs and HCs were analyzed. The profiles, that can inform about the finger prints in the different sources, were computed as percentages of any molecular species onto the total class compound in the investigated period. To integrate the information about the sources, the most significative diagnostic ratios were counted and were plotted on five bi-variated graphics. The obtained results seem to represent the largest contribution of petrogenic sources related to the traffic sources, in particular diesel. The average HCs profile during the fall/winter period shows a combination of anthropogenic/biogenic emissions at both sites, with higher contribution of biogenic sources at the rural site, while during the spring/summer season the biogenic source is more evident, also at urban background, as it is confirmed by the carbon preference index. These information were useful for support preliminary source apportionment evaluations. Positive Matrix Factorization was applied to the dataset in order to summarize the obtained results and make the differences and similarities in the organic profile more visible.