Determination of heavy-duty vehicle emission factors from highway tunnel measurements in India: Laboratory vs. real-world study

Abstract

This study develops the real-world heavy-duty vehicle (HDV) emission factors (EFs) for regulated and unregulated pollutants from highway tunnel measurements ─ a first in India. Air pollutant and traffic measurements were conducted for two consecutive weeks covering peak and off-peak traffic hours at the entry and exit of a highway tunnel in Mumbai, India. With average traffic of ∼1560 vehicles/hour, this study fleet constitutes 24% of vehicles with poor emission standards. The measured average (±SD) HDV EFs (mg/veh/km) of VOCs, NO2, CO, BC, PM2.5, PM2.5-10 and PM10 were 788 (±354), 1076 (±250), 145 (±55), 318 (±145), 1634 (±412), 175 (±84) and 1792 (±523), whereas for CO2 (g/veh/km) and PNCs ( × 1013/veh/km), it was 495 (±125) and 70 (±19), respectively. The estimated HDV EFs of VOCs, NO2, CO2, BC, PNCs, PM10, PM2.5, and PM2.5-10 in this study were 8.5, 7.2, 3.7, 27.4, 33.3, 15.2, 37.0, and 2.5 folds higher than the LDV EFs, respectively. The developed real-world EFs of regulated pollutants CO, NO2 and PM2.5 in this study were higher than the laboratory EFs by a factor of 1.3, 3.1 and 5.7, respectively. The HDV EFs derived from this study are higher than those reported in American and European countries. These findings highlight the impact of overloaded, dysfunctional, and old vehicles on the measured EFs, and this suggests the need to strengthen the vehicle inspection and maintenance program in India. The measured EFs in this study will be useful in emission inventory, exposure assessment and climate studies as well as in policy making.