## 4 Summary and Conclusions  
Mostly, tunnel environment research has been undertaken in industrialized countries. To adapt to worldwide environmental standards, building quality, and vehicle conditions, it is necessary to undertake such research in developing nations such as Pakistan. During both the building and operating phases of a tunnel, the monitoring of pollutants such as hazardous gases and particulate matter is essential for maintaining a clean atmosphere. Long tunnels with large slopes, zigzag alignments, water penetration, poor vehicle maintenance, and an insufficient ventilation system pose a high danger of pollutant concentrations exceeding the permitted limits. During the construction stage (about 30 days), the concentration of gases in the Lowari Tunnel was measured between Chainage 4 + 369.8 and 4 + 595. During the monitored period, NO exceeded the high alarming levels for one day, CO for eight days, and CO\({}_{2}\) for three days. SO\({}_{2}\) was not detected, and H\({}_{2}\)S levels were within the permitted range. O\({}_{2}\) levels were determined to be satisfactory (>19.5% minimum) and their concentration did not fluctuate significantly. Maximum amounts of H\({}_{2}\)S, NO, CO, and CO\({}_{2}\) (i.e., 2.8 ppm, 26.3 ppm, 450 ppm, and 14,333 ppm, respectively) were measured in Chainage 4 + 549 at 16:48 on 6 December 2008, when the ventilation system was switched off. Trends in the concentration of gases indicate that, throughout the construction stage, the concentration of measured gases increased significantly after blasting. During the operational stage, the Lowari Tunnel was monitored at four locations for gases and particulate matter. NO, H\({}_{2}\)S, O\({}_{3}\), and NH\({}_{3}\) were not identified at any of the four spots, whereas O\({}_{2}\), CO, and NO\({}_{2}\) concentrations were within acceptable limits. The reduced concentrations are the result of a mix of natural and mechanical ventilation after tunnel breakthrough. Road dust suspensions yielded greater concentrations of PM\({}_{10}\) and PM\({}_{2.5}\) near the portals (0.515 ppm and 0.208 ppm, respectively). PM\({}_{1}\) may move with the vehicle from both sides and concentrate (0.342 ppm) in the middle of the tunnel (Spot 3) owing to the piston effect. At five spots between the north and south portals, angular to sub-angular tunnel dust with a broad range of particle sizes was observed. Overall, the particle sizes were less than 200 \(\upmu\)m, and smaller particles with diameters of less than 1 \(\upmu\)m were attached to the larger particles. The chemical composition of dust included the components Si > Ca > Na > Mg > Fe > K and the trace elements Zn > Pb > Ni > Ag > Co > Cd, indicating the dust's origin as vehicle emissions (both exhaust and non-exhaust). The dust particles in the tunnel are enriched with particles of corroded concrete lining and road abrasion. These suspended and re-suspended dust particles impede tunnel vision and pose health dangers to trail users. The average particle size varied between 80 and 170 \(\upmu\)m in diameter, while the dust percentage varied between 30% and 56%. This is consistent with the PM concentration, suggesting that the PM concentration within the tunnel is greater than that outside the tunnel. At Spot 6, the airflow velocity was tested and determined to be satisfactory. The