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Fire-induced pollutant dispersion under the influence of buoyancy in urban street canyons has attracted wide attention given its adverse impact on human health. This study analyzes the influences of fire source location and crossflowing wind (perpendicular to the canyon centerline) on indoor and outdoor air pollutant dispersion in an idealized urban street canyon by employing large eddy simulation. Three fire scenarios are defined according to the transverse location of the fire source: near the windward building (scenario 1), in the middle of the canyon (scenario 2), and near the leeward building (scenario 3). Results show that a re-entrainment phenomenon appears when the wind velocity reaches a critical value in scenarios 1 and 2, but it doesn't occur in scenario 3. Fire source location significantly influences the critical re-entrainment velocity. The critical velocity in scenario 1 is approximate 1.2–1.5 m/s larger than that in scenario 2. When the heat release rate is large, the critical Fr numbers are less sensitive to changes in HRR, and remain approximately constant with values of 0.47 (scenario 1) and 0.37 (scenario 2). When the wind velocity is large, more compartments are expected to be affected in the upper floors in all of the three scenarios, and smoke is distributed in an inverted triangle within the buildings. The indoor/outdoor temperature and pollutant concentrations are also analyzed. Our findings can provide valuable information for both human and property safety in relation to urban street canyons and their surrounding buildings. [ABSTRACT FROM AUTHOR]