Characterization of PM_2.5 and particulate PAHs emitted from vehicles via tunnel sampling in different time frames

The present study investigated the emission characteristics of PM_2.5 and particulate PAHs (25 congeners) emitted from vehicles in real running conditions via air sampling in the longest tunnel in Taiwan. The average PM_2.5 concentrations measured in the tunnel inlet and outlet were 21.9 ± 6.9 µg m^-3 and 46.1 ± 12 µg m^-3, respectively, which are significantly higher than that measured at an ambient station nearby (12.5 ± 6.2 µg m^-3). Total particulate PAHs (P-PAHs) concentration measured at the inlet of the tunnel was 1.68 ± 1.4 ng m^-3, which was significantly lower than that measured at the outlet of the tunnel (6.31 ± 4.8 ng m^-3). Meanwhile, the average concentration of P-PAHs found in ambient air station was only 0.275 ± 0.062 ng m^-3. A higher concentration difference (ΔC = C_out - C_in) of particulate PAHs was found on weekday compared with that observed during the weekend due to the higher number of diesel vehicles passing through the tunnel. The concentration differences of these pollutants were higher in the daytime compared with that in the nighttime because of higher vehicle number. Pyr and PL were the dominant contributors in terms of mass concentration while BcFE was the main contributor to TEQ concentration. The results also indicate that the list of 15 EU-PAHs should be considered for evaluation of the health risk associated with the emission of PAHs from vehicles.