This paper investigated the impacts of surface heating on pollutant transport and Air Exchange Rate (AER) in street canyons or different aspect ratios (building height H to street width W) using computational fluid dynamic (CFD) technique. Street canyons of H/W varied from 0.1 to 2 were employed in the study. These street-canyon aspect ratios covered a range of basic flow regimes including skimming flow (H/W = 1 and 2), wake interface flow (H/W=0.5), and isolated roughness flow (H/W=0.1). Different facade/surface heating imposed different influence on the flow field and pollutant transport in street canyons of different H/W. The AER induced by vertical velocity fluctuation $AER_{W^"}$ and mean vertical velocity. $AER_W$ of street canyon with different H/W and different surface heating exhibited their unique characteristics.