The effects of fuel, lubricant, and engine operating parameters on the emission of polycyclic aromatic hydrocarbons (PAHs) associated with particles were studied by means of an automobile engine operated with a number of special fuels under steady-state conditions. More than 90% of the mass of the heavier PAHs (e.g., benzo[a]pyrene) was found on particles with a diameter below 1 gm, while for the light PAHs, a substantial part was in the vapor phase. The aromatic content, the type of aromatic fraction, and the PAH content of the fuel and lubricant had a strong effect on particle-bonded PAH emission; in comparison to this, the lead content of the fuel was of minor importance. The lubricant itself had only slight influence on particle-bonded PAH emission. This varied with the air:fuel ratio in a manner similar to.particulate matter and to unburned hydrocarbons, showing high emissions at very rich as well as very lean mixtures. On increasing the engine load, the particle-bonded PAH emission increased.

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