Neighborhood-scale dispersion of traffic-related PM_2.5: Simulations of nine typical residential cases from Nanjing

Three-dimensional computational fluid dynamics (CFD) simulations based on the discrete phase model were performed to explore the spatial distribution of traffic-related PM_2.5 in summer and winter in nine typical neighborhoods (300 × 300 m) established through investigating realistic samples in Nanjing, China. These cases have different building typologies, building heights, and neighborhood layouts. The focus was on the pollutant dispersion along horizontal and vertical directions and the average near-façade (0.5 m away) concentration of different floors. The harm to residents’ health caused by excessive concentration (>25 μg/m³) was quantified by decrease in life expectancy (DLE). Results show the pollutant dispersion distance along the horizontal direction was limited, up to 100 m; and the concentration decreased, following a nonlinear trend, with increasing height. Façades experiencing excessive concentrations were found to be mainly in the upwind areas for neighborhoods with 3 floor and 6 floor buildings, while in the downwind areas for those with 11 floor and 18 floor buildings. The median DLE was lower than three years, and only a few floor positions experienced a DLE of above 20 years. This study provides insight into pollutant dispersion patterns in typical neighborhoods, which is helpful to improve the early design.