ABSTRACT
In conventional subway cars, the fully mixed ventilation mode leads to airflow cross-contamination. To improve the air quality in subway cars in the post-pandemic period, we analyzed the pollutant concentrations in the subway cars of the Ningbo Rail Transit Line 2. Our results revealed that the CO2 levels in these subway cars exceeded the health standards during peak hours in the morning and evening, with two peaks in the concentration of pollutants along the height of the subway cars. Therefore, we propose a stratum ventilation technology for subway cars to mitigate the stratification of pollutants. Computational fluid dynamics was used to compare the flow field characteristics and pollutant diffusion trajectories in conventional subway cars and those with stratum ventilation. Our observations indicate that subway cars with stratum ventilation enable the formation of an air curtain in the middle of the car, effectively improving air quality within the breathing area of the seated passengers. In addition, the Wells-Riley model for predicting airborne infection was improved by incorporating pollutant concentration as a variable;this enabled the prediction of the probability of pathogenic infection with any pollutant concentration in a confined space. The results of this model revealed that, in a two-passenger mode ¼ subway car, stratum ventilation technology reduces the probability of pathogenic infection among the seated passengers from 25.4% to 3.07%, as compared to conventional subway cars. We believe the present research will help improve the safety performance of ventilation design.