Real-world automotive particulate matter and PAH emission factors and profile concentrations: Results from an urban tunnel experiment in Naples, Italy

On-road particulate matter (PM) mass was measured during a sampling campaign in March of 2015 in the '4 giornate' tunnel in Naples, Italy. Two sets of samples were collected at both sides of the tunnel, each set representing the daily cycle at a 1 hour time resolution. Distance-based - mass per kilometer - and fuel-based - mass per burned fuel - emission factors (EFs) were calculated using mass concentrations, traffic flow rates and wind speed as a function of fleet composition. Also, chemical analyses were performed for polycyclic aromatic hydrocarbons (PAHs) and ionic components.Average particle mass concentrations in the tunnel atmosphere were more than 5 times higher than in the outside background air, revealing their origins almost exclusively from fresh vehicle emissions, but, while the EFs for CO were within the range of expected values, the present study found much higher EFs for particulate matter and PAHs. Average EF for particulate matter was three to four times higher than that expected; also, benzo(a)pyrene, a surely carcinogenic compound, achieved concentrations as high as 70 ng/m (median value of 12 ng/m) at the end of the tunnel and an average EF about three times higher than that expected.Analysis of ionic composition highlighted the increase in calcium concentration, which may derive from non-exhaust sources (road dust, wear of brake pads, clutches, tires) or exhaust emissions (calcium sulfonates, phenates and salicylates added to motor oils). This suggests that an important contribution to PM emissions may derive from resuspended road dust and wear from tires and brakes, which are usually not included in traditional sampling methodologies for assessing vehicular emissions (e.g. dynamometer studies).