Real-Time Black Carbon Emissions from Light-Duty Passenger Vehicles Using a Portable Emissions Measurement System

•BC emissions of PFI and GDI vehicles are measured using PEMS.•GDI vehicles have higher BC emissions than PFI vehicles.•Cold-start contribute 2–33% of total BC emissions.•A high correlation (R2 = 0.70) is found between BC emissions and vehicle speed. Black carbon (BC) is considered the second largest anthropogenic climate forcer, but the radiative effects of BC are highly correlated with its combustion sources. On-road vehicles are an important source of anthropogenic BC. However, there are major uncertainties in the estimates of the BC emissions from on-road light-duty passenger vehicles (LDPVs), and results obtained with the portable emissions measurement system (PEMS) method are particularly lacking. We developed a PEMS platform and evaluated the on-road BC emissions from ten in-use LDPVs. We demonstrated that the BC emission factors (EFs) of gasoline direction injection (GDI) engine vehicles range from 1.10 to 1.56 mg·km−1, which are higher than the EFs of port fuel injection (PFI) engine vehicles (0.10–0.17 mg·km−1) by a factor of 11. The BC emissions during the cold-start phase contributed 2%–33% to the total emissions. A strong correlation (R2 = 0.70) was observed between the relative BC EFs and average vehicle speed, indicating that traffic congestion alleviation could effectively mitigate BC emissions. Moreover, BC and particle number (PN) emissions were linearly correlated (R2 = 0.90), and compared to PFI engine vehicles, the instantaneous PN-to-BC emission rates of GDI engine vehicles were less sensitive to vehicle specific power-to-velocity (VSPV) increase in all speed ranges.