## 2 Numerical Model and Simulation Setup
### Model Validation
The recommended criteria were NRMSE \(<\sqrt{1.5}\)), VG \(<\) 4, \(|\text{MG}-1|>\) 0.3, \(|\text{FB}|<\) 0.3, R \(>\) 0.8, and FAC2 \(>\) 0.5. Figure 3 shows the time series of the wind directions and wind speeds measured and simulated at the PRNU-SONIC station (the red dot in Figure 1a) located on the building roof (15 m above the ground). The measurement showed that the southwesterly wind persisted in the daytime and that northeasterly-to-northwesterly winds dominated at night (Figure 3a). LDAPS simulated the measured wind directions well, and the wind directions in the T2M case generally followed those of the LDAPS. The measured wind speeds were low (less than 2 m s\({}^{-1}\)) and were stronger in the daytime than at night (Figure 3b). LDAPS overestimated the wind speed overall. The RMSEs for the wind directions and speeds of LDAPS were 56.63\({}^{\circ}\) and 3.20 m s\({}^{-1}\), respectively. The wind speeds of LDAPS did not satisfy the recommended criteria of the statistical indices, except for MG (0.27) (Table 3). The RMSEs for the wind directions and speeds in the T2M case were 63.60\({}^{\circ}\) and 0.73 m s\({}^{-1}\), respectively. The CFD model improved the prediction of wind speed and satisfied the NRMSE, VG, MG, FB, and FAC2 criteria. Figure 2: Daily variation of the PM\({}_{2.5}\) emission rate on the road in the target area. Figure 4 shows the time series of the PM\({}_{2.5}\) concentrations measured and simulated at RF, R1, and R2 (green and yellow dots in Figure 1a). RF was located on the building roof (15 m above the ground), and R1 and R2 were located on lampposts adjacent to the roads (2 m above the ground). The measured PM\({}_{2.5}\) concentrations did not vary much during the measurement period (slightly high in the morning and almost constant otherwise) (Figure 4a). The maximum PM\({}_{2.5}\) concentration at RF was measured at 09 LST when the background concentration was maximal. Meanwhile, the maximum concentrations at R1 and R2, which were thought to be affected by road emissions, were measured at 10 LST. The CFD model underestimated the PM\({}_{2.5}\) concentrations in the early morning (00-08 LST) and late at night (21-23 LST) (Figure 4b-d). This underestimation was caused by the low emission rates at the corresponding times, as well as the low background concentrations, and contributed to relatively high RMSEs in the T2M case (RMSEs at RF, R1, and R2 were 4.25, 4.58, and 5.10 \(\upmu\)g m\({}^{-3}\) per day, respectively). Nevertheless, the PM\({}_{2.5}\) concentrations in the T2M case satisfied the NRMSE, VG, MG, FB, and FAC2 criteria. The CFD model simulated the PM\({}_{2.5}\) concentrations better in the daytime than in the early morning and late at night (Table 4). Figure 4: (**a**) Time series of the measurement, and measured and simulated PM\({}_{2.5}\) concentrations at (**b**) RF, (**c**) R1, and (**d**) R2 (green and yellow dots in Figure 1a). \[\text{RMSE}=\sqrt{\overline{\left(\text{C}_{\text{o}}-\text{C}_{\text{P}} \right)^{2}}} \tag{10}\]0 Time series of the measured and simulated (**a**) wind directions and (**b**) wind speeds at PKNU-SONIC (red dot in Figure 1a). \begin{table}
\begin{tabular}{c c c c c c c} \hline  & **RMSE** & **NRMSE** & **VG** & **MG** & **FB** & **R** & **FAC2** \\ \hline LDAPS & 3.20 & 1.65 & 5.86 & 0.31 & \(-\)1.10 & 0.35 & 0.19 \\ T2M & 0.73 & 0.75 & 2.56 & 1.30 & 0.15 & 0.14 & 0.57 \\ \hline \end{tabular}
\end{table} 
Table 3: The statistical values of the wind speeds (m s\({}^{-1}\)) simulated at PKNU-SONIC (red dot in Figure 1a).