On-road particulate matter (PM 2.5) and gaseous emissions in the Shing Mun Tunnel, Hong Kong

Abstract

Real-world emission factors of PM 2.5 (particle's aerodynamic diameter of less than 2.5 μm), NO x (the sum of NO 2 and NO), and CO from mixed vehicles in the Shing Mun Tunnel in Hong Kong have been determined. A total of 16 runs were made during varying times that encompassed different traffic fractions of diesel-fueled vehicles. During the study, a total of 27,310 vehicles traversed the tunnel, comprising approximately 50% diesel-fueled vehicles, 41% gasoline-fueled vehicles, and 9% LPG-vehicles. The PM 2.5 emission factors, derived from the DRI (Desert Research Institute, USA) particulate sampler, ranged from 0.066 to 0.190 g veh −1 km −1. Result from a t-test showed no statistical significance for PM 2.5 difference in summer and winter. The PM 2.5 emission factors were found to correlate well with NO x ( R 2=0.65) and both had a positive relationship with the proportion of diesel-fueled vehicles. Two DustTrak air monitors were also used to monitor PM 2.5 masses in the tunnel. The mean emission factor derived from DustTrak, 0.150±0.045 g veh −1 km −1, had reasonable agreement with the filter method, 0.131±0.037 g veh −1 km −1, demonstrating that the DustTrak air monitor can be used in tunnel studies, but needs careful calibrations with the filter method. The emission factors for PM 2.5 mass and NO x were obtained for on-road diesel-fueled vehicles based on the linear regression analysis and they were 0.257±0.031 and 1.931±0.309 g veh −1 km −1, respectively.