The formation of polycyclic aromatic hydrocarbons (PAHs) and soot from the pyrolysis of the four butanol isomers: 1-butanol, 2-butanol, iso-butanol and tert-butanol, at three reaction temperatures (1275, 1375 and 1475 K) has been studied. The identification and quantification of the sixteen PAHs, classified by the Environmental Protection Agency (EPA) as priority pollutants, were done using the gas chromatographymass spectrometry (GC-MS) technique. The soot formed was collected at the reactor outlet. Light gases formed were also quantified. The harmful potential of the PAHs through the benzo[a] pyrene equivalent, B [a] P-eq amount, has been evaluated. The main results show that the highest formation of light gases was obtained from the pyrolysis of iso-butanol at 1275 K. The formation of H-2 increases significantly as the temperature increases, following the Hydrogen abstraction carbon addition (HACA) route that leads to form PAHs which subsequently form soot. The tendency to soot formation, under the experimental conditions of the present study, is ranked as follows: tert-butanol, 2-butanol, 1-butanol and iso-butanol. The highest PAHs amount and the highest toxic potential, expressed as B[a] P-eq amount, were found in the pyrolysis of all butanol isomers at 1275 K. (C) 2017 Elsevier Ltd. All rights reserved.