Characterisation of vehicle emissions in a road tunnel in Lisbon

Abstract

In urban areas, road traffic is one of the main sources of air pollutants, mainly as particulate matter (PM). Knowledge about fingerprints of vehicle emissions under real-world driving conditions is scarce for Europe, especially in Portugal. The aim of this study was to characterise and quantify vehicle emissions through road tunnel measurements. The sampling campaign was carried out during one week inside a road tunnel and simultaneously in an urban background site in Lisbon. PM2.5 and PM2.5–10 filters were analysed by PIXE for elemental composition and by a thermal-optical transmittance technique for the determination of organic carbon (OC) and elemental carbon (EC). PM2.5 and PM10 concentrations were, at least, 20 and 10 times higher than those found in the background, respectively. Inside the tunnel, particle organic matter (POM), EC and other anthropogenic compounds accounted for more than 90.0% of the PM2.5 mass. Fe, Ca, Si, S and Cu represented 88.7% of the PM2.5-bound elements, while Fe, Cl, Ca, Si, Cu, Zn, Na, S, Ba mostly contributed to the PM2.5–10 elemental mass fraction (93.8%). Total carbon represented about 58.5% of PM2.5 and 26.5% of PM2.5–10. EC presented a high tunnel/background ratio (T/B = 35.4 for PM2.5 and 48.8 for PM2.5–10). Cu, Fe, Cr, Ba, Mn, Zn and Rb, which are key tracers of tyre and brake wear, showed a T/B > 70 and very good correlations between them. The emission factors (EF) of PM2.5 and PM10 were estimated to be 139 ± 20.7 and 172 ± 23.9 mg veh−1 km−1. The average EF of OC and EC in PM2.5 were 30.9 ± 6.48 and 44.6 ± 7.33 mg veh−1 km−1. This real-world study contributes to define road traffic emission profiles in urban areas, provide data to update European emission inventories, and evaluate the impact of traffic-generated PM on human health and the environment.