Seasonal variation of PAHs concentration and source attribution through diagnostic ratios analysis

An extensive monitoring campaign was conducted between November 2011 and July 2012 at schools, homes, offices and Regional air quality network stations in Rome, within the LIFE+ EXPAH Project. This study allowed to improve the knowledge of actual concentrations and percent composition of Polycyclic Aromatic Hydrocarbons (PAHs) over the city area. High concentrations of all PAH congeners were observed during winter colder periods, e.g. benzo[a]pyrene weekly average concentration reached 3.0 ng/m3, while much lower values were recorded in summer (<0.1 ng/m3), with seasonal variability (winter-to-summer ratios R) exceeding 10. This latter value was larger than that recorded for other pollutants including PM2.5 (R ~ 2.5). Also the percent composition of PAHs in particulates and the rates of diagnostic concentration ratios between selected congeners changed along the year, allowing to draw insights about the predominant sources and their respective importance. In particular, biomass burning for heating purposes was identified as the prevailing PAH source during winter and vehicle traffic in summer. Discrepancies between PAH profiles estimated from the emission inventory and observations were detected, with possible implication for modelling of PAH congeners.