Diesel emissions, PAHs particulate

A wide variety of nitro PAHs have been isolated from different environmental sources including airborne particulates (27-34), coal fly ash (35-37), diesel emission particulates (38-41) and carbon black photocopier toners (42-43). Their presence has also been suggested in the smoke from nitrate-fortified cigarettes (44). The structures of the most commonly detected nitro PAHs are shown in Figure 1 and in each instance it is the kinetically-favored isomer that is found. 

GC-M3) is described for characterization of particulate-bound PAHs in diesel emissions. The term PAH will refer to the parent and alkyl-substituted PAHs. The analytical methodology may also be adaptable to other types of sample matrices. 

Nitro-PAHs are polycyclic aromatic hydrocarbon derivatives that contain one or more nitro groups covalently bound at chemically reactive positions on the aromatic ring. Mixtures of nitrated PAHs are generated either by reactions of PAHs with nitrogen oxides or as byproducts of the incomplete combustion of fossil fuels (65). A wide variety of nitro-PAHs have been isolated from environmental sources, such as coal fly ash, diesel emission particulates, cigarette smoke and carbon black photocopier toners (29, 52, 63, 74, 75, 86, 87, 88). Structures of representative nitro-PAHs isolated from the environment are shown in Figure 1. 

Understanding particulate emissions, their formation and control, is another key issue in meeting the new particulate emission Hmits set by the new EURO emission standards. The particulate emissions formed in diesel engines have a mass median diameter of 0.05-1.0 gm. Particle consists of carbon with various HCs adsorbed on it including polyaromatic hydrocarbon (PAH) as well as nitro-PAH compounds. 

In the mid-1980s, the discovery of significant amounts of 2-nitropyrene in ambient particulate matter collected in a rural region of Denmark by Nielsen and co-workers (1984) and 2-nitrofluoranthene in southern California by Pitts and colleagues (1985b) provided unique initial evidence for the possible formation of nitroarenes by reactions of precursor PAHs in ambient air. Thus, these compounds are not electrophilic nitration products of their parent PAHs and are generally not observed in combustion sources such as diesel soot see, for example, Table 10.34 and the report of Ciccioli and co-workers on the detection of emissions of 2-nitrofluoranthene and 2-nitropyrene solely from a very minor Italian industrial source (see Ciccioli et al., 1993, 1995, 1996, and references therein). 

Road traffic emissions consist of particulate (PM) and gaseous emissions, with active carbonaceous products present in both phases. Particles contain potentially toxic components, such as polycyclic aromatic compounds (PAHs) and trace metallic elements [4-6], which are related to acute and chronic cardiovascular and respiratory diseases [7]. Some studies suggest that especially diesel exhaust emissions are responsible for cardiac hospital admissions [8] and for asthma and chronic bronchitis development in children [9] in densely populated cities. Also fine and coarse particles from non-exhaust sources have been associated with short-term mortality and morbidity [10-13]. 

Nitro-polycyclic aromatic hydrocarbons, referred to as nitro-aromatic compounds hereafter, constitute one of the most troubling classes of environmental pollutants. They are derivatives of polycyclic aromatic hydrocarbons (PAHs) that contain two or more fused aromatic rings made of carbon and hydrogen atoms and at least one nitro group (Fig. 10.1). Concern about these compounds arises partly from their ubiquity nitro-aromatic compounds are released to the environment directly from a variety of incomplete combustion processes [1] and are also formed in situ by atmospheric reactions of PAHs [2]. Nitro-aromatic compounds have been found in grilled food in diesel, gasoline, and wood-smoke emissions and are commonly found in atmospheric particulate matter, natural waters, and sediment [3-8],... 

The composition of PAH emissions varies with the combustion source. For example, emissions from residential wood combustion contain more acenaphthylene than other PAHs (Perwak et al. 1982), whereas auto emissions contain more benzo[g,h,i]perylene and pyrene (Rogge et al. 1993a Santodonato et al. 1981). PAHs in diesel exhaust particulates are dominated by three- and four-ring compounds, primarily fluoranthene, phenanthrene, and pyrene (Kelly et al. 1993 Rogge et al. 

Chemical Composition of the Moderately-Polar Fractions - We have recently reported that the oxy-PAH account for most of the mass contained in the moderately-polar fractions for a light-duty diesel particulate extract(9). We have undertaken a similar analysis for the sample described in this work (figure 1) and found that it is qualltlvely similar but quantitatively different than that previously described for emissions collected from another light duty diesel englne(9). It can be concluded from these results that ... 

The direct mutagenic activity observed in applying the Ames reversion assay to both emission and ambient particulate samples can, at least in part, be explained by the presence of polar PAH-derivatives, e.g. nitroarenes in diesel exhaust. 

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