## 4 Conclusions  
During the period starting from July 2018 to April 2019, the measurement of exhausts from traveling vehicles was carried out in four seasons for the analysis of the particle number concentration in the exhausts using SMPS in the tunnel located in Seoul, Republic of Korea. The mode of the particle number concentration in the inside and outside of the tunnel appeared in the range 61.5-68.5 nm in summer, fall, and spring, whereas the value was small in winter distributing in the range 21.7-25.9 nm. The mode of particle diameter increased rapidly to 62 nm at a temperature 10-11 \({}^{\circ}\)C, contrary to the slight increase from 20 nm to 28 nm at temperature from 5 \({}^{\circ}\)C to 10 \({}^{\circ}\)C inside the tunnel in winter. The temperature acted as a major cause of determination of final condensation diameter, which is also dependent on diverse environmental effects comprising particle number concentration. The traffic volume of each type of vehicles, obtained from approximately seven million vehicles, were analyzed by using the statistical sampling analysis. The traffic volume of ordinary cars increased by more than twice as much in the period of Asian New Year, the traffic volume of buses/RVs/trucks decreased by more than 25% during weekdays. The particle number concentration discharged from a unit vehicle was 6.96 \(\times\) 10\({}^{12}\) N/veh\(\cdot\)km during weekdays, and the values of weekends and in the period of Asian New Year appeared as 6.08 \(\times\) 10\({}^{12}\) N/veh\(\cdot\)km and 4.43 \(\times\) 10\({}^{12}\) N/veh\(\cdot\)km, respectively. The overall averaged particle number concentration based on the actual seasonal road measurements shows 5.82 \(\times\) 10\({}^{12}\) N/veh\(\cdot\)km. Based on the results of the present study, the actual tunnel flow coefficient can be applied for the further investigation of seasonal chemical components from vehicle emissions. Finally, the quantitative contribution of the particle number concentration from each type of vehicle to atmospheric environment can be investigated on the entire numbers of vehicles of each type in the urban area.  
The following are available online at [[https://www.mdpi.com/2076-3417/11/2/794/s1](https://www.mdpi.com/2076-3417/11/2/794/s1)]([https://www.mdpi.com/2076-3417/11/2/794/s1](https://www.mdpi.com/2076-3417/11/2/794/s1)), Figure S1: Diurnal patterns of (a) temperature, (b) wind speed, and (c) number of vehicles in season inside of the tunnel to determine the seasonal value of tunnel flow coefficient; Figure S2: Diurnal pattern of the mode of number concentration of particle size distribution inside and outside of the tunnel employed for the analysis of effects of temperature on the final condensation diameter; Table S1: Operating conditions of the two employed the Scanning Mobility Particle Sizers (SMPS); Table S2: Hourly number concentration discharged from vehicles (\(\Sigma\)N/veh\(\cdot\)km) by using the TFC (8) (m\({}^{3}\)/veh\(\cdot\)km) and hourly number concentrations of particle size distribution inside and outside of the tunnel; Table S3: Number concentrations of particle size distribution distinguished into values of weekends, weekdays, and period of Asian New Year.  
Data curation, K.K.; Investigation, M.S. and G.P.; Project administration, J.L.; Resources, S.L.; Supervision, M.-S.B.; Validation, T.L.; Writing--original draft, C.P. All authors have read and agreed to the published version of the manuscript.  
This work was supported by a grant from the National Institute of Environment Research (NIER), funded by the Ministry of Environment (MOE) of the Republic of Korea (NIER-2019-04-02-024) and the National Research Foundation of Korea (NRF) (NRF-2020R11A3054851).  
Not applicable.  
We acknowledge the support provided by the Convergence Research Laboratory (established by the MNU Innovation Support Project in 2020) to conduct this research. We thank [PERSON] and [PERSON] for Measurement of Tunnel Flow Coefficient.  
The authors declare no conflict of interest.