A physical model consisting of two parallel street canyons with the fire room located in the windward side of the first street canyon was established. Large eddy simulation (LES) was employed to investigate the effects of air pollutant dispersion caused by the fire-induced buoyancy plume on the indoor and outdoor air quality. The effect of thermal buoyancy was firstly taken into account by burning the smoke cakes in wind-tunnel experiments under different Fr (Froude number) cases. Results show that the diffusion characteristics of smoke plume, temperature and velocity distributions by wind-tunnel measurements agreed well with the numerical models. According to the smoke soot's effects on two street canyons, the dispersion of fire pollutants can be divided into three regimes. There exist two critical Fr, Fr-crit,Fr-1= 0.313 and Fr-crit,Fr-2 = 0.389, at which the smoke plume begins to influence the 1st and 2nd street canyons, respec-tively. Moreover, the region areas of w < 0 (vertical velocity) can indirectly represent the concentration distribution of pollutants, and the temperature distribution is closely proportional to the distribution of pollutant (smoke plume, CO2 and CO) concentration, that is, where the plume concentration is high, the temperature is high. The quantitative formulas between U-crit (U-crit,U-1 and U-crit,U-2) and the reference height (Z(ref)) of the fire source at different floors were further confirmed. This study provides a new idea for visualizing the diffusion characteristics of fire pollutants, and is helpful for dealing with the building fire, personnel evacuation and emergency escape. (c) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.