Exhaust emissions of polycyclic aromatic hydrocarbons, n-alkanes and phenols from vehicles coming within different European classes

EU emission standards for vehicles do not include many particulate (PM) and gaseous species, despite their considerable impact on air pollution and health. Emission factors (EFs) were measured for unregulated species, i.e. polycyclic aromatic hydrocarbons (PAHs) and n-alkanes (ALKs) in the particle phase, and, for the first time, EFs for phenols in both particle and gas phases. Exhaust samples were collected under controlled operating conditions (chassis dynamometer tests) for in-service vehicles (private cars, PCs and light duty vehicles, LDVs) from different EURO classes. EFs of trace organics were highest for the old EURO 1 vehicles (the tested EURO 1 vehicles were without emission-control devices), and lowest for the more recent EURO 3 and 4 vehicles. ALKs (C20–C32) were the most abundant trace organic compounds found in PM vehicle exhaust, and their EF ranged between 2034 and 101 μg km−1 (Euro 1–4 LDVs). PM-phased phenols EFs were in the range 0.42–2.50 μg km−1, and 4-nitrophenol was the most abundant one. The highest EFs were measured for phenols in the gas phase (dominated by the presence of phenol) for gasoline EURO 1 (43.16 ± 9.99 μg km−1). Emissions of PAHs changed depending on the fuel used. The PAH EFs of diesel-driven PCs were 4–5 times higher than those of gasoline vehicles, with PAHs diesel exhaust being mainly enriched in low 4-ring PAHs (85%), while 5–6 ring PAHs were prevalent (55%) in gasoline vehicles. Results of source profiles from chassis dynamometer tests were compared with ambient data, and the traffic PAH source profile derived from a tunnel study (Milan) agreed with the estimated emissions from a mix of diesel and gasoline vehicles circulating in the same area. Moreover, the impact of EURO regulatory changes on exhaust emissions was calculated, and this made it possible to estimate the downward trend of PAH emissions in the Province of Milan in the period 2005–2020.