Polycyclic aromatic hydrocarbons (PAHs) are potentially carcinogenic pollutants emitted by diesel engines, both in the gas phase and adsorbed onto the surface of particulate matter (PM). There remains limited understanding of the complex and dynamic competing mechanisms of PAH formation, growth and oxidation in the gas phase, and their adsorption onto soot and how these processes impact on the abundance and composition of exhaust PAH. Therefore, this paper presents analysis of gas and particulate samples taken from the cylinder and exhaust of a diesel engine during combustion of fossil diesel with the 16 US-EPA priority PAH species identified and quantified. In-cylinder results showed that gas-phase PAHs were more abundant than soot-bound PAHs in the engine cylinder. The in-cylinder PAHs included 2- to 6-ring PAHs; however, 6-ring PAHs were not observed in the soot samples collected from the engine exhaust. Levels of both PM and the total in-cylinder PAHs decreased following a peak at 10 CAD ATDC but subsequently increased significantly during the late combustion phase. The B[a]P equivalence of PM in the engine cylinder increased during the period of early diffusion to late combustion phase, following an initial decrease during the period of premixed to early diffusion combustion.
Keywords: PAH growth mechanisms; US-EPA priority PAH; exhaust sampling; fossil diesel combustion; gas phases PAH; in-cylinder sampling; particulates toxicity; polycyclic aromatic hydrocarbon (PAH); soot-bound PAH.