Emission Factors of Primary Pollutants from a Real-world Tunnel Measurement

With over 1.6 billion vehicles worldwide, the combustion of fossil fuels is a major source of particulate matter (PM) and trace gases, which significantly contribute to air pollution, climate change and cause health burden. Heavy-duty vehicles (HDVs) constitute a small fraction of the global vehicle population but account for a disproportionately large share of total emissions when compared with light-duty vehicles (LDVs). However, uncertainty remains about which vehicle type contribute most to the emission factors (EFs) of various pollutants, particularly in Europe, where diesel technology has historically been favored for LDVs.

Because traditional engine emission tests may not accurately reflect the real-world emissions, there is a need for on-road, real-world emission assessments. In this study, we conducted a three-week measurement campaign in the Fréjus Road Tunnel using MIRO MGA-10, aethalometer and SMPS. We developed a practical method to determine the EFs of primary pollutants, including trace gases (NO_x, CO₂, CO, N₂O, NH₃, CH₄), black carbon (BC), and ultrafine particles (UFP). The calculated EFs will be reported, and selected pollutant species will be compared with previously published data from Asia and America in equivalent units.

Figure 1 shows the results for the species mentioned, where HDV* indicates the proportion of HDVs to the total number of vehicles, taking into account the CO2 emissions from a single HDV and LDV. The results indicated that for most pollutant species, LDVs exhibited higher EFs than HDVs. However, HDVs emitted a higher fraction of N₂O compared to LDVs. The EFs of NO_x, CO, BC, and NH₃ were consistent with previous studies conducted in Europe but lower than data reported from Asia and America. This study’s findings will raise public awareness and provide valuable insights for policymakers to develop strategies to mitigate emissions. 

Figure 1. Emission Factors (g/kg fuel)