Characteristics and major sources of carbonaceous aerosols in PM2.5 in Emilia Romagna Region (Northern Italy) from four-year observations

The concentrations of organic and elemental carbon in PM2.5 aerosol samples were measured in two sites of Emilia Romagna (Po Valley, Northern Italy) in eight campaigns during different seasons from 2011 to 2014. Strong seasonality was observed with the highest OC concentrations during the cold periods (≈5.5 μg m−3) and the lowest in thewarmmonths (≈2.7 μgm−3) as well aswith higher EC levels in fall/winter (≈1.4 μgm−3) incomparison with spring/summer (≈0.6 μgm−3). Concerning spatial variability, therewere no statistically significant difference (p < 0.05) between OC concentrations at the two sampling sites in each campaign, while the EC values were nearly twofold higher levels at the urban site than those at the rural one. Specific molecular markers were investigated to attempt the basic apportionment of OC by discriminating between the main emission sources of primary OC, such as fossil fuels burning – including traffic vehicle emission – residential wood burning, and bio-aerosol released from plants and microorganisms, and the atmospheric photo-oxidation processes generating OCsec. The investigated markers were low-molecular-weight carboxylic acids – to describe the contribution of secondary organic aerosol – anhydrosugars – to quantify primary emissions from biomass burning – bio-sugars – to qualitatively estimate biogenic sources – and Polycyclic Aromatic Hydrocarbons – to differentiate among different combustion emissions. Using the levoglucosan tracer method, contribution of wood smoke to atmospheric OC concentration was computed. Wood burning accounts for 33% of OC in fall/winter and for 3% in spring/summer. A clear seasonal trend is also observed for the impact of secondary processes with higher contribution in the warm seasons (≈63%) in comparison with that in colder months (≈33%), that is consistent with enhanced solar radiation in spring/summer.