Reduction in the Emissions and Toxicity of Polycyclic Aromatic Hydrocarbons from a Heavy-duty Diesel Engine with the Latest Aftertreatment Devices

Abstract

Polycyclic aromatic hydrocarbons (PAHs) bound in particles from automobile emissions may cause adverse human health. In this study, a 3L heavy-duty diesel engine with and without the latest aftertreatment devices were characterized for PAH emissions and toxicity using European Transient Cycle (ETC) and the European Stationary Cycle (ESC). The latest combination of aftertreatment devices including a diesel oxidation catalyst (DOC) and a catalyzed diesel particulate filter (c-DPF) were used to remove diesel exhaust particles (DEP). Particle size distribution and number concentrations were measured using a TSI Engine Exhaust Particle Sizer. Eight PAHs [benz(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, indeno(1,2,3cd)pyrene, dibenz(a,h)anthracene, and benzo(ghi)perylene] within the DEP were analyzed by thermal desorptiongas chromatography/mass spectrometry (TD-GC/MS). Elemental carbon (EC) and organic carbon (OC) were also analyzed with a thermal/optical carbon analyzer. The results indicated that 4-ring PAH emissions are larger than 5 or 6-ring PAH emissions, with and without the aftertreatment devices in place. Number concentrations of particles, PAHs and EC mass emissions in diesel exhaust were dramatically decreased by the aftertreatment devices: > 99%, > 97% and > 99%, respectively. To evaluate the toxicity of PAHs in the DEP, we calculated benzo(a)pyrene equivalent (BaPeq) emissions using a toxic equivalency factor (TEF). Total BaPeq emissions of eight PAHs were also substantially decreased by the aftertreatment devices (> 95%). However, the decrease rate of OC was lower than EC (> 72%). We demonstrated that number concentrations of DEP, PAH emissions, EC and BaPeq emissions were similarly and substantially decreased by the latest aftertreatment devices.