[Air quality assessment and health site guidelines for city squares based on RANS method].

The concentration of pollutants and pathogens in the air directly affects human health. When the pollution source remains unchanged, effective ventilation determines air quality. It is therefore critically needed to establish a quantitative determination index for effective ventilation, which can be used for real-time evaluation of air quality in specific areas, so as to guide residents to choose healthy outdoor activity places. In this study, Reynolds average Navier-Stokes (RANS) method was used to establish urban air pollution simulation system by computational fluid dynamics (CFD) technology. The correlations among wind speed, pollutant concentration, and pollutant diffusion efficiency were analyzed. With real-time meteorological data, wind field simulation and air quality evaluation were carried out for different periods of urban square space. The results showed that the critical wind speed value at pedestrian height (1.5 m) for the effective diffusion of pollutants was 1.0 m·s-1, which could be used as an air quality evaluation standard. With reference to this judgment index and the real-time weather system link, the pedestrian height wind speed distribution could be obtained through simulation. Therefore, the spatial variation of air quality could be visually displayed in real time, which help realize fair, efficient and reasonable use of urban space resources. This work could provide guidelines for choosing healthy outdoor venues, and provide technologies and means for public disease prevention and health promotion.