The emissions of seventeen 2,3,7,8 substituted Polychlorinated Dibenzo-p-Dioxins, Polychlorinated Dibenzofurans (PCDD/Fs) and sixteen Polycyclic Aromatic Hydrocarbons (PAH) [14] in the exhaust pipes of spark ignition light duty vehicles considered toxic to human health were investigated. The formations of these compounds were evaluated under the influence of variations of fuels and fuel additives. Standard tests in a gasohol (gasohol is pure gasoline plus 20% to 25% of anhydrous ethyl alcohol

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... el (AEAF)) vehicle and in an ethanol vehicle were performed with variations in the quality of fuels. The sampling of the PCDD/Fs followed the recommendations of a modified 23 method and the analysis basically followed the 8290 method. The recommendations of the TO-13 method were followed for the PAH analysis, with the necessary modifications for a vehicular emission laboratory. The emission factors of the total PCDD/Fs varied between undetected and 0.157 pg I-TEQ/km. The emission factors of the total PAH varied from 0.01 µg TEQ/km to 4.61 µg TEQ/km. Significant and positive correlations were observed between the emissions of naphthalene, acenaphthylene, fluorene, phenanthrene, anthracene and fluoranthene and significant and negative correlations were observed between the emissions of CO 2 and fluoranthene in the gasohol vehicle. Significant and positive correlations between carbon monoxide and phenanthrene and between acenaphthylene, fluorene and fluoranthene in the alcohol vehicle were also observed, apart from significant and negative correlations between NOx and phenanthrene. In general way, significant correlations between PAH and PCDD/Fs were not observed, except in the ethanol vehicle considering phenanthrene.