## 2 Materials and Methods
### Operational Stage  
During the tunnel's operational stage on 30 June 2021, hazardous gases and tunnel dust were analyzed at four spots: Spot 1 (south portal), Spot 2 (Chainage 1 + 000), Spot 3 (Chainage 4 + 000), and Spot 4 (Chainage 8 + 000). In addition to these spots, dust from the tunnel roadside was also collected at Spot 5 (north portal). Each dust sample (about 1000 g) was collected with a bristle brush in a tightly sealed plastic bag. Through use of the the NOVA AMA instrument (600-2-3-4-5-7-10), hazardous gases such as H\({}_{2}\)S, NO, CO, CO\({}_{2}\), NH\({}_{3}\), and NO\({}_{2}\) were monitored. The gas was pumped into the sample chamber, and the concentration of the gas was detected electro-optically by its absorption of a specific infrared (IR) wavelength. Similarly, O\({}_{2}\) was measured by a Stack gas analyzer (Int-Lancom-III) that uses electrochemical, infrared, and pellistor/catalytic sensors. O\({}_{3}\) was measured with an ozone monitor (C-30 ZX) that has a detection range of 0.02-0.14 ppm. The HAZ Dust Analyzer was used to monitor PM\({}_{10}\), PM\({}_{2.5}\), and PM\({}_{1}\) particulate matter. It works by scattering near-forward light from infrared radiation. The light is scattered as the airborne particles enter the infrared beam. The amount of light received by the photodetector is proportional to the concentration of the aerosol. These instruments were used in compliance with the instrumentation standards of [PERSON] (2011). Each instrument was set up for 1 h of recording at a 1-s frequency, and the average values are reported.  
The morphology and elemental concentration of the tunnel dust was studied by scanning electron microscopy (SEM) and an energy dispersive X-ray system (EDS) using a Jeol SEM vacuum chamber machine (JSM-IT-100). Microphotographs with magnifications of 65 to 250\(\times\) and pixel sizes of 1280 \(\times\) 960 were taken for each sample. The apparatus was run in a high vacuum with a 20 kV acceleration voltage. The EDS microanalysis was carried out with a capture duration of 60 s, a count rate of 2226 to 2315 counts per second, and a dead time of 3-4%. To determine the major elements (Si, Ca, Na, Mg, Fe, and K) and trace elements (Zn, Pd, Ni, Ag, Co, and Cd), atomic absorption spectroscopy (AAS) with Perkin Elmer-700 and UV/VIS spectrometer SP-400 machines was applied. For major elements, a 0.5 g sample was obtained and dissolved in the stock solution using multi-acid (HF, HCIO4, and HCl) digestion. For trace elements, a 1 g sample was dissolved in aqua regia and then diluted in 50 mL of distilled water. The precision was calculated using the reference standards G2, AGVI, and W-2. The analysis achieved a 95% confidence level. Particle size distribution was obtained through an ASTM D792 8-16 hydrometer bulb 152 H standard test. The airflow velocity was measured at Spot 6 (chainage 2 + 200). The velocity data were obtained between 1 September and 30 September 2016, between 1 June and 30 September 2017, as well as between 8 February, and 28 February 2018. Met Set configuration software was applied to a wind speed detector (Met Pak Pro by RationalTechnologies Private Limited, Sonipat, India), with +2% accuracy at 12 m/s and 0.01 m/s resolution. The data were collected every 30 min for 24 h every day.