Fine particulate-bound polycyclic aromatic hydrocarbons in vehicles in Rome, Italy

Urban commuters are exposed to elevated levels of air pollutants, especially in heavily polluted areas and traffic congested roads. In order to assess the contribution of commuting to citizens' exposure, measurements of fine particulate (PM_2.5) and polycyclic aromatic hydrocarbons (PAHs) were carried out in cars, busses, and metro trains, within the LIFE+ EXPAH Project. Monitoring campaigns were performed in Rome, Italy, from April 2011 to August 2012. Inside the busses, the concentration of total PAHs ranged from 2.7 to 6.6 ng/m³ during the winter and from 0.34 to 1.51 ng/m³ in the summer. In cars, internal concentrations were in the range 2.2-7.3 and 0.46-0.82 ng/m³, respectively, in the 2-year time. Analogous differences between seasons were observed examining the benzo[a]pyrene-equivalent carcinogenicity. In the metro trains, total PAHs ranged from 1.19 to 2.35 ng/m³ and PM_2.5 ranged from 17 to 31 μg/m³. The PM_2.5 concentration in all transport modes ranged from 10 to 160 μg/m³ during the cold season and 15-48 μg/m³ during the warm time. The average inside-to-outside ratio (R _I/O) was found to exceed 1.0 for PM_2.5 only in busses, probably due to dust re-suspension caused by crowding and passenger activity. The molecular PAH signature suggests that vehicle emissions and biomass combustion were the major sources of commuters' exposure to these toxicants in Rome. According to linear regression analysis, the PAH concentrations inside the vehicles were linked to those detected outside. Statistically significant differences (p < 0.05) were found between the in-vehicle locations and the urban pollution network stations, with higher PAH values detected, on the average, in these latter.