Chemical speciation of PM emissions from heavy-duty vehicles

Abstract

Particulate matter (PM) is recognised as the deadliest form of air pollution, with vehicle emissions being one of its most important sources. Verification of compliance with the emission standards has been reported in numerous works. However, the detailed chemical speciation of PM is still very poorly understood. In this study, different heavy-duty vehicles (HDV) were tested on a chassis dynamometer under different driving cycles. Particulate matter (PM) emission factors for Euro V and Euro VI vehicles ranged from 24.9 to 51.2 mg kWh−1 and from 8.4 to 14.7 mg kWh−1, respectively. Major and trace elements, in their oxidised form, accounted for PM mass fractions between 6.3 and 58%. The lowest PM values were obtained for the Euro V vehicle fuelled with gas-to-liquids (GTL) under the world harmonised vehicle cycle (WHVC) with cold start, while the highest amounts were observed for the Euro VI vehicle fuelled with diesel over the hot start WHVC cycle. In general, Na and Sr were the most abundant elements, followed by Al and Ca. Several oxygenated organic compounds were detected, as far as we know, for the first time in exhaust particulates. Greater varieties (from C11 to C31 with no preference for odd versus even carbon numbers) and amounts of n-alkanes were detected in the emitted particulate matter (up to 7938 μg per g of PM) for the GTL fuelled vehicle (Euro V) tested by the WHVC driving cycle with cold start. The start-up phase mass fractions of ∑18PAHs were much higher (552 μg g−1) when the diesel-powered Euro V vehicle followed the VTT cycle than in the following tests (28.8–48.1 μg g−1). A homologous series of n-alkanoic acids, from C8 to C22, were found in the exhausts, accounting for particulate mass fractions ranging from 0.50 to 19.4 mg g−1, and peaking at C14, C16 and C18. Benzenedicarboxylic acids were observed at higher concentrations in emissions from Euro VI vehicles compared to Euro V. n-Alkanols from C8 to C30, with a clear dominance of C18 were detected in all PM samples. Ethylene glycol and other glycols were always present.