Engineering systems such as gas turbines and internal combustion engines utilise gaseous fuels which produce toxic substances when they are burnt. Among these substances are solid soot particles and gas phase polycyclic aromatic hydrocarbons (PAHs). The link between soot and PAHs has long been established. Firstly, PAHs assemble themselves into larger structures which are the soot particles themselves. Secondly, they are mostly found, adsorbed on the surfaces of soot particles and form their toxic components. This paper presents the results of both gas-phase and particle-phase PAHs generated from pyrolysis of ethane, ethylene, acetylene, propane and propylene in a homogenous laminar flow reactor. The PAHs studied were the US EPA 16 priority PAHs, but emphasis was given to those PAHs classified as possible carcinogens to humans (Group B2). Pyrolysis of five gaseous fuel molecules was carried out within the temperature range of 1050-1350 degrees C under oxygen free condition and a fixed fuel concentration of 10,000 ppm on C-1 basis. Soot and gas phase products generated within the reactor were sampled from the exit of the reactor. The PAHs from the samples were then extracted using an accelerated solvent extractor (ASE) and their analysis was carried out using gas chromatography coupled to mass spectrometry (GCMS). The experimental results showed that, depending on the temperature at which a fuel is pyrolysed, its degree of unsaturation plays an important role on the type and concentration of PAHs per unit mass of soot and per unit gas volume. The type of PAH produced and its concentration influenced the overall carcinogenic potential of the gaseous and particulate effluent. It was established that the double bonded C-3 propylene produced the highest amount of soot and particle-phase PAHs per unit mass of soot and per unit volume of gas. Propylene also produced soot particles with the highest carcinogenicity in the temperature range of 1050-1250 degrees C and the carcinogenicity decreased with temperature increase. The triple bonded C-2 acetylene produced the highest amount of gas phase PAHs per unit volume of gas when compared with other C-2 and C-3 fuels. It was concluded that increasing the unsaturation of a fuel increases its gas phase PAHs in the case of the C-2 fuels and particle phase PAHs in the case of the C-3 fuels. The total PAH distribution was therefore dominated by the gas phase PAHs in the C-2 fuels and particle phase PAHs in the C-3 fuels. (C) 2017 Elsevier Ltd. All rights reserved.