When the inflow wind direction towards the street, The center of the vortex is tilt toward leewind side or higher, the released pollutants from urban street canyons become more diluted.

• 当屋顶来流与街道之间的夹角逐渐增大时，涡旋中心位置由街道中心偏向于背风面及更高层且污染物扩散速度加快。