Chemical characterisation of the organic fraction of PM for an urban, rural and remote site of the North of Italy

PM concentrations are measured in three sites of the North of Italy: an urban (Milan-MI; 45°31’19”N, 9°12’46”E), rural (Oasi Bine-OB; 45°13’33’’N, 10°45’00’’E) and high altitude remote site (Alpe San Colombano-ASC, m.2280 asl; 46°46’11’’N 10°30’19’’E). Daily PM2.5 samples are collected by using a low volume gravimetric sampler (38,33 l/min). Samples are chemical characterised for the main inorganic ions (Na+, K+, Ca++, Mg++ NH4+ , F-, Cl-, NO3-, SO42= ,by IC) and carbonaceus fraction (EC and OC, by TOT). Chemical speciation of the organic carbon is focuesed on certain compound classes. Low-molecular weight (C2-C7) carboxylic acids (mono and dicarboxylic acid) are analysed by IC; n-alkanes (C20-C32) and polycyclic aromatic hydrocarbons (PAHs) are analysed by GC-MS;. Carboxylic acids are associated to atmospheric oxidation and they are known to be an important contribution to secondary organic aersol (SOA). The n-alkane pattern is investigated through the carbon precerence index (CPI) and % Cwax to evaluate the contribution of vegetation during different seasons. PAHs concentrations and relative mass contribution to fine PM are a tracer for contribution of combustion source in the three sites. During winter, when high altitude sites are above the mixing boundary layer of the polluted plan, PAHs mass contribution to PM2.5 at ASC site is up to 10 time lower compared with MI site