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

Abstract

In total, 24 polycyclic aromatic hydrocarbons (PAHs) in both gas and particle phases and 35 nitro-PAHs in particle phase were analyzed in the exhaust from heavy-duty diesel vehicles equipped with after-treatment for particulate matter (PM) and NO X control. The test vehicles were carried out using a chassis dynamometer under highway cruise, transient Urban Dynamometer Driving Schedule (UDDS), and idle operation. The after-treatment efficiently abated more than 90% of the total PAHs. Indeed, the particlebound PAHs were reduced by >99%, and the gaseous PAHs were removed at various extents depending on the type of after-treatment and the test cycles. The PAHs in gas phase dominated the total PAH (gas þ particle phases) emissions for all the test vehicles and for all cycles; that is, 99% of the two-ring and 98% of the three-ring and 97% of the four-ring and 95% of the carcinogenic PAHs were in the gas-phase after a diesel particle filter (DPF) and not bound to the very small amount of particulate matter left after a DPF. Consequently, an evaluation of the toxicity of DPF exhaust must include this volatile fraction and cannot be based on the particle fraction only. The selective catalytic reduction (SCR) did not appear to promote nitration of the PAHs in general, although there might be some selective nitration of phenanthrene. Importantly the after-treatmtent reduced the equivalent B[a]P (B[a]Peq) emissions by >95%, suggesting a substantial health benefit.Implications: This study demonstrated that after-treatments, including diesel particulate filters (DPF), diesel oxidation catalysts (DOC), and selective catalytic reduction (SCR), significantly reduce the emissions of PAHs from heavy-duty diesel engines. The gasphase PAHs dominate the total PAH (gas þ particle phases) emissions from heavy-duty diesel vehicles retrofitted with various DPFs and not bound to the very small amount of particulate matter left after a DPF. Consequently, an evaluation of the toxicity of DPF exhaust must also include this volatile fraction and cannot be based on the particle fraction only.

Chemical Characteristics of Particulate Matter Emission from a Heavy-Duty Diesel Engine Using ETC Cycle Dynamometer Test

“…Proportions of two-ring, three-ring and four-ring p-PAHs in this study were similar to those in Jin et al (2014) and Lu et al (2012), studies in China. However, the two-ring percentage was higher than that in Hu et al (2013), but lower than that in Shah et al (2005). For three-ring p-PAHs, result in this study was higher than that in Hu et al (2013) and Shah et al (2005).…”

“…However, the two-ring percentage was higher than that in Hu et al (2013), but lower than that in Shah et al (2005). For three-ring p-PAHs, result in this study was higher than that in Hu et al (2013) and Shah et al (2005). Proportion of four-ring p-PAHs was lower than that in Hu et al (2013), but higher than that in Shah et al (2005).…”

“…Compared with their newer counterparts (model year 1992-1999), relative abundances of PAHs in DPM emitted from older vehicle (model year 1985) were significantly higher (Riddle et al, 2007). With advanced emission control technology, DPM PAHs and inorganic elements emissions have been reduced significantly (Pakbin et al, 2009;Khalek et al, 2011;Hu et al, 2013). Positive relations between diesel sulfur content and inorganic elements emissions, as well as between diesel sulfur content and particle-phase PAHs emissions have been found (Lim et al, 2007;Lu et al, 2012).…”

“…Volatility of PAHs increases with the decrease their molecular weight or number of rings and lighter PAHs are found mostly in gas phase (Ravindra et al, 2008a;Hu et al, 2013). However, the proportions of p-PAHs with different rings vary significantly among studies as shown in Fig.…”

Effects of Selective Catalytic Reduction on the Emissions of Persistent Organic Pollutants from a Heavy-Duty Diesel Engine

“…For example, exhaust gas recirculation (EGR), selective catalytic reduction (SCR) and retarding of the fuel injection time have been employed extensively in controlling NO x formation while diesel particulate filters (DPFs) with diesel oxidation catalysts (DOCs) have been used to reduce PM in heavy duty diesel engines (HDDEs) (Koebel et al, 2000;Zheng et al, 2004). DPFs can reduce PM mass by over 95% and will also reduce CO, HC and PAHs (Biswas et al, 2009;Hu et al, 2013). However, they can also be sources for persistent organic pollutants (POPs) emissions, especially when they have an accumulation of organic particulates, which could provide the necessary precursors or carbon matrix for their formation (Heeb et al, 2013;Chen et al, 2017).…”