Abstract: In this study, the traffic characteristics, environmental parameters, and concentration of vehicle exhaust pollutants of the Yingtian avenue in the Yangtze river-crossing tunnel in Nanjing, China, are examined to thoroughly investigate the emission and distribution characteristics of vehicle exhaust pollutants. The traffic characteristics are statistically analyzed using video-recording methods, revealing a distinct diurnal variation pattern, with drastically higher traffic flow in the morning peak than the evening peak, and an inverse relationship between vehicle speed and traffic flow. Night-time testing indicates that pollutant concentrations inside the tunnel initially increase and then decrease along the length of the tunnel, with the PM_2.5 concentration peaking at the bottom of the Vshaped terrain of the tunnel. The CO concentration peak appears slightly later than the PM_2.5 peak because of the influence of the activated fans at the tunnel exit. During daytime testing, when the fans are off, the pollutant concentration peaks at the tunnel exit. In the morning peak, the maximum concentrations of CO and PM_2.5 at the tunnel exit are 31.0 mg/m³ and 145 μg/m³, respectively, which are 3.1 and 2 times the concentration limits, respectively. The Pearson correlation analysis conducted to examine the relationships between various parameters reveals a strong positive correlation between the CO concentration and the number of gasoline vehicles and a strong positive correlation between the PM_2.5 concentration and the number of diesel vehicles. Both pollutants are strongly negatively correlated with wind speed in the tunnel.

Key words: vehicle exhaust pollutant, underwater tunnel, field measurement, CO concentration, PM_2.5 , concentration