Diesel soot

Catalytic removal of diesel soot particulates over LaMnOs perovskite-type oxides... 

Catalytic combustion of diesel soot particulates over LaMnOs perovskite-type oxides prepared by malic acid method has been studied. In the LaMn03 catalyst, the partial substitution of alkali metal ions into A site enhanced the catalytic activity in the combustion of diesel soot particulates and the activity was shown in following order Cs>K>Na. In the LarxCs MnOj catalyst, the catalytic activity increased with an increase of X value and showed constant activity at the substitution of x>0.3... 

Nguyen, T.H., Sabbah, I. Ball, W.P. (2004) Sorption nonlinearity for organic contaminants with diesel soot method development and isotherm interpretation. Environ. Sci. Technol. 38, 3593-3603. 

Table I. Extractable Organic Matter in Diesel Soot...

Analysis of nitroaromatics found by treating diesel fuel with NO2 (column A) compared to nitroaromatics found in extracts of filters of exhaust from a diesel engine (column B) or in extracts of diesel soot deposited in a dilution tunnel of an animal exposure system (13). 

Figure 2. Bioavailability of soot-adsorbed benzo(a)pyrene (BaP). The transfer of l4C-BaP from diesel soot to microsomes was measured. Microsomal protein (0.5 mg) was incubated at 37 C with the [14C]-benzo(a)pyrene-coated diesel particles. ( ) lung microsomes and 0.2 mM NADPH (O) lung microsomes (A) liver microsomes with 0.2 mM NADPH (A) liver microsomes ( ) 0.5 mg albumin ( ) buffer (0.15 M phosphate buffer, pH 7.7, containing 3 mM MgCI2 and 0.1 mM EDTA). The presence of NADPH, a cofactor necessary for BaP metabolism, did not affect the transfer of BaP from the soot. (Reproduced with permission from ref. 15. Copyright 1988 Elsevier.)...

NiS04 and NiCl2 instilled into rat lungs also produced an inflammatory response (17). However, analysis of bronchoalveolar lavage fluid from rodents exposed to diesel exhaust containing 3.5 mg soot/m3, 7 h/day for 2, 12 or 17 days indicated no influx of inflammatory cells (20). Thus, the diesel soot, at lung burdens of 0.5 mg/g lung, does not produce an acute inflammatory response. 

In a study conducted at the Lovelace Inhalation Toxicology Research Institute (ITR1), rats were exposed for up to 30 months, 7 h/day, 5 days/wk, to diesel exhaust containing 0, 0.35, 3.5, or 7.1 mg soot/m3 of air. The diesel engine exhaust was generated as indicated in the section of this paperon "Physical/Chemical Characteristics of Diesel Soot." The lowest exposure concentration, 0.35 mg soot/m3, is directly relevant to some occupational exposures and is 10 to 100 times higher than any current or anticipated environmental exposures. Observations of the animals were made at 6-mo intervals and included measures of dosimetry (mg soot/g lung),... 

Figure 3. Accumulation of diesel soot in lungs exposed to diesel engine exhaust containing 0.35, 3.5, or 7.0 mg soot/m3. Lung burdens at the lower exposure concentration did not exceed 1.0 mg/g lung (Data from ref. 23).

To further investigate the role of genetic vs epigenetic mechanisms in the induction of the tumors, one can compare the response of rats to diesel soot to that elicited by the pure form of soot, carbon black. 

Comparison of Toxicity of Diesel Soot and Carbon Black... 

The inflammatory responses, which were small, and the histo-pathological responses to the two types of particles were identical, indicating that the adsorbed organic compounds do not influence the acute response to the diesel soot. The remaining question is whether long-term exposures to carbon black would induce the same incidence of tumors as did long-term exposures to diesel soot. Those studies are underway at the ITR1 and at the Fraunhofer Institute. 

Figure 8. Accumulation of DNA adducts in rats exposed to carbon black or diesel soot for 12 wk. Quantitation was by the 32P-postlabeling technique (Bond et al. In Assessment of Inhalation Hazards Integration and Extrapolation Using Diverse Data, 1989, pp 315-324).

A number of environmental applications [3] have been performed in order to size characterize colloids collected in rivers (riverbome particles, SPM, and sediments), clay samples and ground limestone (from soils), coal particles, diesel soot particles (from combustion processes), or airborne particles in urban areas (from waste incinerators, vehicles, household-heating systems, and manufacturing). In many of these cases, not only the size but also the particle size distribution was important and thus, in conjunction with the traditional UV detector, specific detectors such as ETAAS, ICP-MS, ICP-AES were used [40] in order to obtain more detailed, more specific compositional information. 

The physical and chemical complexity of primary combustion-generated POM is illustrated in Fig. 10.1 (Johnson et al., 1994), a schematic diagram of a diesel exhaust particle and associated copollutants. The gas-phase regime contains volatile (2-ring) PAHs and a fraction of the semivolatile (3- and 4-ring) PAHs. The particle-phase contains the remainder of the semivolatile PAHs ( particle-associated ) along with the 5- and 6-ring heavy PAHs adsorbed/absorbed to the surface of the elemental carbon spheres that constitute the backbone of the overall diesel soot particle. Also present is sulfate formed from oxidation of sulfur present in the diesel fuel and gas- and particle-phase PACs. 

We discuss in this section four key aspects of heterogeneous reactions (1) theoretical and experimental structure and reactivity relationships (2) held measurements of relative and absolute PAH decay rates in near-source ambient air and during downwind transport (3) laboratory studies of the photolysis/photo-oxidation and gas-particle interactions with 03 and NOz of key 4- and 6-ring PAHs adsorbed on model substrates or ambient aerosols and (4) environmental chamber studies of the reactions of such PAHs associated with several physically and chemically different kinds of combustion-generated aerosols (e.g., diesel soot, wood smoke, and coal fly ash). Where such data are available, we also briefly consider some toxicological ramifications of these reactions. 

In their thoughtful 1983 review, Nielsen and coworkers noted that particles of diesel soot or wood smoke can absorb significant amounts of water. Thus, they suggested that the most plausible mechanism(s) for nitration (and possibly other electrophilic reactions) of particle-associated PAHs in ambient air may involve reactions both in a liquid film and on solid surfaces and that fundamental laboratory studies of the rates, products, and mechanisms of PAHs in polar solvents would be atmospherically relevant for reactions in the liquid films. Based on this, they proposed a classification scheme for the reactivities of key PAHs in electrophilic reactions, which was subsequently described in detail (Nielsen, 1984). 

McDow, Kamens, and co-workers also conducted laboratory experiments on the effects of common organic constituents (e.g., methoxyphenols) on the rates, mechanisms, and products of the solution-phase photodegradation of PAHs associated with wood smoke and diesel soot (see, for example, Odum et al. (1994a), and McDow et al. (1994, 1995, 1996)). Figure 10.28, for example, shows the degradation of the reactive BaP (Class II reactivity) compared to BeP (Class V reactivity) in two solvents, hexadecane, taken as representative of aliphatics in diesel soot, or a mixture of 11 methoxyphenols found in particulate matter (McDow et al., 1994). As expected, BaP decays much more rapidly than BeP. In addition, the decay in the mixture of methoxyphenols is much faster than that in hexadecane. 

FIGURE 10.28 Rates of photodegradation of benzo[a]pyrene (Class II reactivity see Table 10.30) and benzole]pyrene (Class V) in irradiated solutions of hexadecane or a mixture of methoxyphenols that are representative of important classes of organics present in particles of diesel soot and wood smoke, respectively (adapted from McDow et al., 1994). 

Initially, major attention was focused on emissions of diesel soot from light- and heavy-duty motor vehicles, because the particle extracts contained such direct-acting bacterial mutagens and animal and possible human carcinogens (IARC Group 2B, 1989) as 1-nitropyrene (1-N02-PY) and the 1,6- and 1,8-dinitropyrenes (DNP), as well as a third isomer, 1,3-dinitropyrene, IARC Group III. For example, Paputa-Peck and coworkers (Paputa-Peck et al., 1983 IARC, 1989) reported 100 nitro-PAHs (17 positively identified) in... 

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). 

Weingartner, E., H. Burtscher, and U. Baltensperger, Hygroscopic Properties of Carbon and Diesel Soot Particles, Atmos. Environ, 31, 2311-2327 (1997). 

Klippel N, Nussbaumer T (2007) Health relevance of particles from wood combustion in comparison to Diesel soot. In 15th European biomass conference, Berlin 7-11 May 2007... 

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