WRF-CFD coupling method to investigate the effect of sea-land breeze on dispersion of time-dependent traffic pollutant at street scales

Wind speed and direction in coastal cities change drastically over time under the effect of the sea-land breeze (SLB). Therefore, the flow field and traffic pollutant dispersion at the street scale are investigated by employing a WRF-CFD coupled model with a high temporal resolution during a typical SLB day. The results show that the sea breeze collides with the land breeze after landfall, causing a drop in wind speeds and the formation of vortex structures in the street network during the SLB collision period. This leads to the accumulation of pollutants in the streets and the peak concentration occurring during non-peak traffic hours. When the sea breeze prevails during the evening peak traffic period, the average wind speed in the street reaches 3 m s^-1, which results in the pollutant concentration during this period being the lowest throughout the day. The order of the pollutant diffusion and dilution capacity from the lowest to the highest for different periods is as follows: SLB collision period, morning peak traffic period, other non-peak traffic period, and evening peak traffic period.