## 3 Results and Discussion
### Operational Stage
[53],  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \hline  & **Spot** & **Chainage** & **NO** & **CO** & **H\({}_{2}\)S** & **CO\({}_{2}\)** & **O\({}_{3}\)** & **NH\({}_{3}\)** & **NO\({}_{2}\)** & **PM\({}_{10}\)** & **PM\({}_{2.5}\)** & **PM\({}_{1}\)** \\ \cline{3-14}  & & & & & & & & **(ppm)** & & & & \\ \hline \multirow{4}{*}{**Spot**} & 1 & S. Portal & - & 1.94 & - & 459 & 24.0 & - & - & 0.002 & 0.010 & 0.049 & 0.104 \\  & 2 & 1 + 000 & - & - & - & 369 & 24.0 & - & - & 0.002 & 0.515 & 0.076 & 0.094 \\  & 3 & 4 + 000 & - & 5.80 & - & 525 & 23.1 & - & - & 0 who reported the presence of these components in PM\({}_{1-10}\). The dust particles in the tunnel are supplemented by particles eroded from the concrete lining and road abrasion. The suspended and re-suspended dust particles disrupt tunnel vision and pose a health risk to trail users. Figure 5 depicts the particle size distribution of the dust samples obtained at Spots 1-5 in the Lowari Tunnel. The total particle size spans from 0.9 to 4750 \(\upmu\)m, with Spots 1-5 averaging 170, 130, 130, 80, and 90 \(\upmu\)m, respectively. Road dust particle size ranges from 1 to 100 \(\upmu\)m according to the World Health Organization [54] and were identified as 30% of the sample obtained at Spot 1, 45% at Spot 2, 45% at Spot 3, and 56% at Spot 4 and Spot 5. These results are congruent with those obtained from the PM concentration, which demonstrated that the PM concentration within the tunnel is greater than that outside. Road dust is the principal source of particulate matter, which is generated by non-exhaust emissions such as wear and tear (brakes, tires, and clutches), re-suspension, road surface dust and abrasion, and exhaust emissions [9; 55; 56]. Figure 3: \(Cont.\)  
Figure 3: SEM and EDS images of Lowari tunnel dust: (**a**) Spot 1; (**b**) Spot 2; (**c**) Spot 3; (**d**) Spot 4; (**e**) Spot 5. Figure 4: Concentrations of major and trace elements of Lowari Tunnel dust. (**a**) Major elements; (**b**) trace elements. In September 2016, June 2017, and February 2018, the airflow velocity in Lowari Tunnel was measured at Spot 6 (Chainage 2 + 200) during the operational stage. The bars reflect the duration of the airflow, whilst the scatter plot with lines displays the average airflow velocity recorded for 24 h every day, with the standard deviation shown as error bars. The south-to-north airflow velocity is assigned a negative direction, whereas the north-to-south airflow velocity is given a positive direction. For the majority of February 2018 (about 95%), as seen in Figure 6a, the airflow direction was from north to south (ranging from 0.6 m/s to 5.1 m/s). The greater standard deviations in the north-to-south direction show airflow variations, while the smaller standard deviations in the south-to-north direction suggest a stable flow (0 to 3.9 m/s). In June 2017, as seen in Figure 6b, the airflow was mostly north to south (>97%), with a reasonably constant airflow velocity (a range from 1 m/s to 3.7 m/s). In September 2016, as seen in Figure 6c, the direction of the airflow was reversed from south to north throughout the bulk of the month (about 80%), with a constant airflow velocity (a range from 0.8 m/s to 1.5 m/s). The measured statistics indicate that the airflow velocity in Lowari Tunnel fulfills the Safety and Administration [12] minimum airflow velocity for tunnels, bores, shafts, and other subterranean workplaces (0.15 m/s). During the operating phase of the Lowari Tunnel's airflow velocity monitoring period, the amplitude, direction, and fluctuations of airflow were mostly from north to south, with a high airflow velocity in the winter. This is owing to the existence of a high-pressure center in Chitral, north of the Lowari Tunnel, during the majority of the year, particularly in the winter, which causes the airflow direction to change from north to south [57].