A Fast Method for Estimating the Emission Factors of Air Pollutants from In-Use Vehicles Fleet

Abstract

The real-world emission factors of gaseous and particulate air pollutants emitted from in-use vehicles, can be rapidly estimated using monitoring data of their concentration profiles from inside roadway tunnels using a mobile laboratory equipped with fast monitoring instruments. The concentrations of CO2 and particle-bound polycyclic aromatic hydrocarbons (PM-PAHs) and NOx, were observed to increase linearly with traveling distance inside two successive roadway tunnels: the Hongjimun Tunnel and the Jeongneung Tunnel on the Naebu Express Way in Seoul, Korea, except for a small region of decrease. In the decreasing regions, within a few hundred meters of the entrance and before the exit, outside background air with low concentrations of air pollutants was thought to have intruded. From the slopes of the linear regression between distance and concentrations, a fleet-averaged (light-, medium-, and heavy-duty vehicles with 54%, 36%, and 10%, respectively) emission factor of CO2, PM-PAHs, and NOx at an average speed of similar to 60 km h(-1) could be calculated as 197 +/- 38 g km(-1), 4.2 +/- 0.8 x 10 -4 g km(-1), and 0.530 +/- 0.230 g km(-1), respectively, which are within the ranges of values reported in the literature. For each tunnel, the emission factors of CO2, PM-PAHs, and NOx estimated on days with higher-than-normal fractions of heavy-duty vehicles, were higher than those on other days. From these results, the new fast method proposed in this study is considered useful for estimating real-world emission factors of air pollutants by using a mobile laboratory as a complementary tool to traditional tunnel studies. This method can be used to rapidly make emission maps at roadway tunnels in mega-cities like Seoul, Korea, for urban air-quality management.