Development of real-world emission factors for on-road vehicles from motorway tunnel measurements

Abstract

Abstract In India, there is uncertainty in vehicular emission estimation due to the lack of reliable emission factors (EFs) that represent the real-world driving conditions. In this study, real-world EFs of particulate (PM2.5, PM10, PM2.5-10, PNCs, and BC) and gaseous (CO, CO2, VOCs, and NO2) pollutants from on-road vehicles were developed from the roadway tunnel measurements. Air pollutants measurement campaign was carried out at the Eastern Freeway tunnel (South-bound) in Greater Mumbai in April 2019. Particulate and gaseous samplers were deployed at the entry and exit of the tunnel to measure the targeted air pollutants covering both peak and off-peak traffic hours. The average traffic in the tunnel was ~2450 h−1, dominated by Light-Duty Vehicles (LDVs) (~98%) with an average (±SD) vehicular speed of 59 (±5) km h−1. Almost ~93% of vehicles plying inside the tunnel were with ≤10 years of age and 87% of the fleet predominantly complied with Bharat Stage-IV (BSIV) emission standards. The measured average (±SD) fleet EFs for PM2.5, PM10, PM2.5-10, BC, NO2 and VOCs were 44.2 (±26.9), 118.1 (±28.5), 69.7 (±20.1), 147.0 (±31.5) and 92.9 (±20.7) mg veh−1 km−1, respectively. For CO and CO2, it was 1.6 (±0.3) and 132.4 (±25.0) g veh−1 km−1, and 2.1 (±0.5) (\xa0×\xa01013 particles veh−1 km−1) for particle number concentrations. The coarse particle EF was 1.6 folds higher than the fine particle EF, signifying the importance of non-exhaust vehicular emission sources. Compared to laboratory-based EFs, the measured real-world EFs were 1.8, 4.8, and 2.2 folds higher for PM2.5, CO, and NO2, respectively. This is likely due to the presence of aged and poorly maintained vehicles in the real-world which were not taken into consideration by the lab-based studies. Capsule We developed hourly EFs of particulate and gaseous pollutants for on-road real-world vehicular fleet (having predominantly LDVs) from air pollution measurements and traffic characterization inside a motorway tunnel in Mumbai, India. Exhaust as well as non-exhaust EFs are developed and compared with the laboratory-based re-constructed EFs (which were 2–5 fold lower than real-world EFs).