Determination of VOC source signature of vehicle exhaust in a traffic tunnel

This study describes the methodology used to obtain the volatile organic compound (VOC) source signature of vehicle exhaust. To accomplish this, C2–C9 VOCs were measured in a traffic tunnel located in Seoul, South Korea. The effect of VOC concentrations from the outside ambient air was considered in the determination of the source signature. To examine the effects of ambient air on VOC concentrations inside the tunnel, the ratio of propane to the total VOC concentrations was compared between the entrance and middle sites in the tunnel. Propane was used as a standard not only because of its insignificant contribution to vehicle exhaust gas, but also the fact that propane is the most abundant VOC in the atmosphere of Seoul. The ratio of propane to the total VOC concentrations was higher at the entrance site than at the middle location by, on average, 60%. This suggests that ambient air affects the inside tunnel air to a greater extent at the entrance site as compared to the middle site. The contribution of ambient air to the air inside the tunnel at the entrance location varied from 30% to 67%, with an average of 55%. This is 1.5 times higher than the value measured at the middle location, which ranged from 20% to 48%, with an average of 36%. This shows that ambient air substantially affects the inside air of the tunnel. Excluding the effects of ambient air on the air inside the tunnel can provide an improved chemical composition for vehicle exhaust using tunnel measurements. We believe that the concentration difference between the two sites within the tunnel provides a more accurate chemical composition of vehicle exhaust as compared to that obtained from a measurement taken at only one point inside the tunnel.