Diesel vehicles are a major source of fine, atmospheric particulate matter in urban environments. The influences diesel particles exert on solar radiation, on atmospheric chemistry, and on humans depend crucially on the size and chemical character of these particles. In this work, size-resolved diesel particle chemistry has been examined by collecting particles directly from a diesel car exhaust with a low-pressure impactor. The impactor samples have been weighed and analyzed chemically to construct continuous size distributions for selected compounds present in the particulate phase. Submicron diesel-particle mass size distributions displayed three log-normal modes that were centered at 0.09, 0.2, and 0.7−1 μm of particle aerodynamic diameter (EAD) and that had average geometric standard deviations of 1.34, 1.61, and 1.34, respectively. The lowest two modes had approximately the same particulate mass, whereas over 80% of the number of particles were estimated to be found in the mode around 0.1 μm. The third mode contained about 10% of the total particulate mass but less than 0.1% of the particles. The size distributions of elemental (EC) and organic carbon (OC) were quite different:  EC peaked at 0.1 μm, and OC peaked somewhere between 0.1 and 0.3 μm of EAD. The mass ratios of OC to EC were between 0.3 and 0.5 in the bulk of the samples but were considerably lower for most of the particles. The presence of a catalytic converter reduced particulate mass by 10−30%, with the removal being more efficient for OC than EC. The principal mechanism producing the mode around 0.1 μm was shown to be Brownian coagulation between small primary particles formed during the combustion. The two larger size modes in the submicron particle range were hypothesized to be formed by activation and subsequent uptake of condensable organic compounds by some of the mode 1 particles.

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Diesel exhaust particles are the major constituent of urban carbonaceous aerosol being linked to a large range of adverse environmental and health effects. In this work, the effects of fuel reformulation, oxidation catalyst, engine type, and engine operation parameters on diesel particle emission characteristics were investigated. Particle emissions from an indirect injection (IDI) and a direct injection (DI) engine car operating under steady-state conditions with a reformulated low-sulfur, low-aromatic fuel and a standard-grade fuel were analyzed. Organic (OC) and elemental (EC) carbon fractions of the particles were quantified by a thermal-optical transmission analysis method and particle size distributions measured with a scanning mobility particle sizer (SMPS). The particle volatility characteristics were studied with a configuration that consisted of a thermal desorption unit and an SMPS. In addition, the volatility of size-selected particles was determined with a tandem differential mobility analyzer technique. The reformulated fuel was found to produce 10-40% less particulate carbon mass compared to the standard fuel. On the basis of the carbon analysis, the organic carbon contributed 27-61% to the carbon mass of the IDI engine particle emissions, depending on the fuel and engine operation parameters. The fuel reformulation reduced the particulate organic carbon emissions by 10-55%. In the particles of the DI engine, the organic carbon contributed 14-26% to the total carbon emissions, the advanced engine technology, and the oxidation catalyst, thus reducing the OC/EC ratio of particles considerably. A relatively good consistency between the particulate organic fraction quantified with the thermal optical method and the volatile fraction measured with the thermal desorption unit and SMPS was found.

Particulate matter of vehicle exhaust is known to contain carcinogenic compounds such as polycyclic aromatic hydrocarbons (PAH) and is suggested to increase lung cancer risk in humans. This study examines the differences in diesel and gasoline-derived PAH binding to DNA in a human bronchial epithelial cell line (BEAS-2B). Particulate matter (PM) of gasoline exhaust was collected from passenger cars on filters and semi-volatile compounds on polyurethane foam (PUF). The soluble organic fraction (SOF) extracted from the particles was used to expose the cells and to perform PAH analysis. Gasoline extracts, benzo[a]pyrene (B[a]P) and reference materials (SRM 1650 and 1587) were used to study dose-dependent adduct formation in BEAS-2B cells. The levels of DNA adducts were in good accord with the 10 DNA adduct-forming PAH concentrations analyzed in the extracts. Gasoline extracts, SRM 1650, SRM 1587 and B[a]P formed DNA adducts dose-dependently in BEAS-2B cells. The time-dependent DNA adduct formation of 5.0 micro M B[a]P was lower than that of 2.5 micro M B[a]P. The results of this study indicate that reformulated and standard diesel fuels formed about 11- and 31-fold more adducts than gasoline, respectively, when PAH-DNA adduct levels were calculated on an emission basis (adducts/mg PM/km), whereas on a particulate basis (adducts/mg PM) no difference between the diesel and gasoline extracts was observed. We conclude that the genotoxicity of diesel fuel is based on higher particulate emission rates compared to gasoline emission and although the concentration of PAH compounds was higher in diesel particulate extracts, DNA binding by the gasoline particulate-bound PAH compounds was more pronounced than that by the diesel particulate-bound PAH compounds.

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