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A particulate matter (PM) transport model is developed to investigate coarse PM (PM10), fine PM (PM2. 5), and very fine PM (PM1) transport mechanisms in urban street canopies under low-wind conditions. Two common building layouts (ie, the open and staggered street canopies) are considered. Large eddy simulations with the subgrid-scale stress model and the wall function are used to simulate urban streetcanopy flows. The Lagrangian particle tracking approach, considering the effects of the drag force, gravitational force, Brownian motion, and Saffman lift force on particles is adopted to study PM transport behaviors in urban street canopies. The box counting method is used to calculate the canopy-averaged PM10/PM2. 5/PM1 mass concentrations and transport mechanisms at each tracking time. The simulated results show that the removal efficiencies of PM10, PM2. 5, and PM1 in the open street canopies are …