Determination of Suspended Exhaust PM Mass for Light-Duty Vehicles

This study provides one of the first evaluations of the integrated particle size distribution (IPSD) method in comparison with the current gravimetric method for measuring particulate matter (PM) emissions from light-duty vehicles. The IPSD method combines particle size distributions with size dependent particle effective density to determine mass concentrations of suspended particles. The method allows for simultaneous determination of particle mass, particle surface area, and particle number concentrations. It will provide a greater understanding of PM mass emissions at low levels, and therefore has the potential to complement the current gravimetric method at low PM emission levels. Six vehicles, including three gasoline direct injected (GDI) vehicles, two port fuel injected (PFI) vehicles, and one diesel vehicle, were tested over the Federal Test Procedure (FTP) driving cycle on a light-duty chassis dynamometer. PM mass emissions were determined by the gravimetric (M_Gravimetric) and IPSD (M_IPSD) methods. The results show a systematic bias between methods, with the M_IPSD underestimating particle mass relative to M_Gravimetric (M_IPSD = 0.63 × M_Gravimetric), although there is a relatively strong correlation (R²=0.79) between the methods. The real-time M_IPSD showed that more than 55% of the PM mass comes from the first 100 seconds of the FTP for GDI vehicles.