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(1,2,3-cd)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.

Particulate Matter in New Technology Diesel Exhaust (NTDE) is Quantitatively and Qualitatively Very Different from that Found in Traditional Diesel Exhaust (TDE)

“…The high PAH removal efficiencies of the CRT system have been attributed to its ability to both oxidize (DOC component) and filter (DPF component), with the enhanced performance of the SCRT attributed to its ability to break apart heavy hydrocarbons into smaller molecules. 20,25 Other studies have reported similarly high and consistent PAH removal efficiencies for C-DPF-retrofitted engines, 25,37,41,42 whereas other studies have observed more variable removal efficiencies, in particular for the more volatile PAHs. 23,24,28,43 For example, Heeb et al 23 characterized emissions of eight 4-to 6-ring PAHs from a HDDE (6.11 L) operated with two different cordierite-based DPF systems and fuel-borne catalysts (iron-or copper/ironbased).…”

“…39,[41][42][43]62 In contrast, Tobias et al 74 concluded that diesel nanoparticle mass in engines lacking aftertreatment also contains some sulfate, but is dominated by insoluble elemental carbon and branched alkanes and alkyl-substituted cycloalkanes from unburned fuel and/or lubricating oil, some of which is likely to remain in particulate form. Because the sulfate PM found in NTDE nanoparticles is likely to be relatively soluble in the lung, it is not likely to persist there like the insoluble EC making up a large portion of the PM of TDE nanoparticles (see Figure 3).…”

Factors and Trends Affecting the Identification of a Reliable Biomarker for Diesel Exhaust Exposure

“…In some cases, a 3-fold reduction in DPM has been noted in heavy-duty transit vehicles equipped with DPF ( Tzamkiozis et al, 2010 ). Under more controlled conditions, dynamometer testing of a heavy-duty diesel vehicle equipped with a DOC and DPF showed an average reduction of 96% in the emission of eight PAHs ( Shibata et al, 2010 ). Under some operating conditions, use of DPFs can result in the emission of large numbers of nanoparticulates in the nuclei mode of 30 nm or less; but this finding is the subject of considerable debate, with numerous studies showing a decline in nanoparticulate formation ( Kittelson et al, 2006 ; Hesterberg et al, 2011 ).…”