Abstract. A multi-model simulation system for street-level
circulation and pollutant tracking (S-TRACK) has been developed by
integrating the Weather Research and Forecasting (WRF), the STAR-CCM+
(computational fluid dynamics model – CFD), and the Flexible Particle
(FLEXPART) models. The winter wind environmental characteristics and the
potential contribution of traffic sources to nearby receptor sites in a city
district of China are analysed with the system for January 2019. It is found
that complex building layouts change the structure of the wind field and
thus have an impact on the transport of pollutants. The wind speed inside
the building block is lower than the background wind speed due to the
dragging effect of dense buildings. Ventilation is better when the dominant
airflow is in the same direction as the building layout. Influenced by the
building layout, the local circulations show that the windward side of the
building is mostly the divergence zone, and the leeward side is mostly the
convergence zone, which is more obvious for high buildings. With the
hypothesis that the traffic sources are uniformly distributed on each road
and with identical traffic intensity, the potential contribution ratios
(PCRs) of four traffic sources to certain specific sites under the influence
of the street-level circulations are estimated with the method of residence
time analysis. It is found that the contribution ratio varies with the
height of the receptor site. As a result of the generally upward motion in
the airflow, the position with the greatest PCR from the four road traffic
sources is located at a certain height which is commonly influenced by the
distance of this location from the traffic source and the background wind
field (about 15 m in this study). The potential contribution of a road to
one of the receptor sites is also investigated under different wind
directions. The established system and the results can be used to understand
the characteristics of urban wind environment and to help the air pollution
control planning in urban areas.