Impact of Low- and High-Oxidation Diesel Particulate Filters on Genotoxic Exhaust Constituents

Abstract

Diesel exhaust contains several genotoxic compounds that may or may not penetrate diesel particulate filters (DPFs). Furthermore, the DPF-supported combustion of soot and adsorbed compounds may lead to the formation of additional pollutants. Herein, we compare the impact of 14 different DPFs on emissions of known genotoxic compounds. During a four year period, these DPFs were tested on a heavy duty diesel engine, operated in the ISO 8178/4 C1 cycle. Integral samples, including gas-phase and particle-bound matter were taken. All DPFs were efficient wall-flow filters with solid particulate number filtration efficiencies eta > 98%. On the basis of their CO, NO, and NO(2) emission characteristics, two different filter families were distinguished. DPFs with high oxidation potential (hox, n = 8) converted CO and NO besides hydrocarbons, whereas low oxidation potential DPFs (lox, n = 6) did not support CO and NO oxidation but still converted hydrocarbons. Lox-DPFs reduced NO(2) from 1.0 +/- 0.3 (engine-out) to 0.42 +/- 0.11 g/kWh (eta = 0.59), whereas hox-DPFs induced a NO(2) formation up to 3.3 +/- 0.7 g/kWh (eta = -2.16). Emissions of genotoxic PAHs decreased for both filter families. Conversion efficiencies varied for individual PAHs and were lower for lox- (eta = 0.31-0.87) than for hox-DPFs (eta = 0.75-0.98). Certain nitro-PAHs were formed indicating that nitration is an important step along PAH oxidation. For example, 1-nitronaphthalene emissions increased from 11 to 17 to 21 microg/L without, with lox-, and hox-DPFs respectively, whereas 2-nitronaphthalene emissions decreased from 25 to 19 to 4.7 microg/L. In contrast to our expectations, the nitration potential of lox-DPFs was higher than the one of hox-DPFs, despite the intense NO(2) formation of the latter. The filters converted most genotoxic PAHs and nitro-PAHs and most soot particles, acting as carriers for these compounds. Hox-DPF exhaust remains oxidizing and therefore is expected to support atmospheric oxidation reactions, whereas lox-DPF exhaust is reducing and consuming oxidants such as ozone, when mixed with ambient air.

Emissions of polycyclic aromatic hydrocarbons (PAHs) and nitro-PAHs from heavy-duty diesel vehicles with DPF and SCR

“…With the presence of nitrating species, such as NO 2 , the PAHs can be nitrated to form nitro-PAHs (Heeb et al, 2008(Heeb et al, , 2010. In total, 35 species of nitro-PAHs (Table S.2, Supplemental Materials) in particle phase were analyzed in this study, from 1-nitronaphthalene through 1þ3-nitrobenzo[e] pyrene.…”

“…He stated, "It remains to be shown which of the competing processes dominates in each case." Subsequently, Heeb et al (2010) investigated 14 different DPFs with different oxidation capacity and found that DPFs with low oxidation potential were more pronounced in PAH nitration than the ones with high oxidation potential, suggesting that nitro-PAH degradation dominates in catalyzed after-treatment. The results from the current study do not alter this conclusion: Veh3-DPF3 and the baseline expressed less oxidative capacity, followed by DPF1, DPF2, and DPF4 ).…”

“…Studies have shown that most PAHs derived from diesel fuel are present in the gas phase in the exhaust (Zielinska et al, 2004a). While the particle-associated PAHs have been investigated for decades, the gas-phase PAHs have received increased attention due to their impact on the ambient mutagenic activity (Heeb et al, 2010).…”

“…DOCs were also shown to reduce gaseous PAHs (CONCAWE, 1998;Khalek et al, 2011) as well as the particulate ones, even at a greater extent (McClure et al, 1992;Neeft et al, 1996;Khalek et al, 2011). The gas-phase PAHs are considered the major precursors of nitro-PAHs in the atmosphere (Heeb et al, 2010). Information on gas-phase PAHs from HDDV with after-treatment is rather limited (Khalek et al, 2011).…”

Effects of Retrofitting Emission Control Systems on In-Use Heavy Diesel Vehicles

“…With a passive filter NO 2 emissions are dependent on the NO x flux and exhaust temperature (7). Other approaches and many variations on the above examples exist; emissions vary based on the oxidative capacity of the filter and other factors (8).…”