## 1 Introduction  
During road tunnel construction and operation, pollutants, such as hazardous gases and particulate matter, may represent a substantial health risk [1]. During tunnel construction, these pollutants are produced by blasting, mucking, and concreting [2, 3]. A higher concentration of hazardous gases is reported near the working face of the tunnel that gradually decreases with an increase in distance. During the operating stage, they are mostly generated by traffic flow [4, 5, 6]. The investigation of emissions is vital in preventing tunnel pollution because of their health consequences and source identification [7]. Two sorts of emissions exist: exhaust and non-exhaust. Exhaust emissions come from vehicle tailpipe, whereas non-exhaust emission comes from wear and tear (brakes, tires, and clutches), re-suspension, road surface dust, and abrasion. Exhaust emissions contribute to fine particulate matter, (PM\({}_{2.5}\) and smaller), while non-exhaust emissions contribute to the coarser particulate matter (PM\({}_{2.5}\)-PM\({}_{10}\)) [8]. In general, non-exhaust emissions are defined by trace elements (e.g., Cu, Zn, Ba, Sb, Mn) but organic markers have been used in certain instances [9]. Even in developed countries, current levels of non-exhaust emissions and future forecasts are on the rise. [PERSON] et al. [10] observed that the link between traffic volume and non-exhaust emissions is non-linear. These emissions are affected by vehicles and the road conditions; low traffic volumes in bad conditions cause more pollution than high traffic volumes in good conditions. Reduced traffic paired with poor tunnel road conditions will also increase pollution inside the tunnel. The situation further deteriorateswhen the traffic volume is high and tunnel road conditions are poor. In addition to H\({}_{2}\)S, NO, and SO\({}_{2}\), other gases may trigger explosions in road tunnels [11]. Similarly, H\({}_{2}\)S concentrations exceeding 10 ppm may produce headaches, dizziness, nausea, burning eyes, sore throats, and other respiratory symptoms [12], while concentrations exceeding 500 ppm are deadly [13; 14]. Particulate matter contributes significantly to cardiovascular disease, lung disease, and atherosclerosis [15; 16]. Road traffic is the primary source of PM concentration and the principal contributor of ultrafine and fine nanoparticles of Ba, Zn, and Pb [17], posing a cancer risk to the exposed human population [18; 19]. PM\({}_{2.5}\) reduces tunnel vision, which may result in fatal accidents [20]. In short tunnels (\(\leq\)1 km), natural airflow is usually sufficient to flush out impurities [21]. However, in long tunnels, it is essential to provide fresh air throughout the construction and operational stages to maintain acceptable levels of harmful gases [22; 23; 24; 25; 26; 27; 28]. [PERSON] and [PERSON] [29] demonstrated that rearranging traffic lights along with a ventilation system with a flow rate of 40,000 m\({}^{3}\) per hour substantially reduced pollution levels. In addition, pollution control vehicles and NO\({}_{2}\) absorption technologies may be used to boost airflow and decrease photochemical smog concentrations, which are influenced by traffic volume and vehicle fleet composition [4; 30; 31]. A minimum air velocity of 0.3 m/s is necessary for a clean tunnel environment. Nevertheless, external factors such as rain or snow may interrupt airflow inside the tunnel, thereby increasing the pollutants' concentration [32]. However, [PERSON] and [PERSON] [33] showed that during rainy days, lower particle concentrations can be observed due to reduced particle re-entrainment and re-suspension in the tunnel. The tunnel's airflow is proportional to its cross-section [34]. During the construction stage of a tunnel, a larger-diameter duct is installed to reduce airflow resistance; otherwise, dust levels may exceed 2000 mg/m\({}^{3}\)[35]. In such settings, the health of employees and people passing through the tunnel may be at risk [36].