Using a new inversion matrix for a fast-sizing spectrometer and a photo-acoustic instrument to determine suspended particulate mass over a transient cycle for light-duty vehicles

摘要

Integrated particle size distribution (IPSD) is a promising alternative method for estimating particulate matter (PM) emissions at low levels. However, a recent light-duty vehicle (LDV) emissions study showed that particle mass estimated using IPSD (M-IPSD) with the TSI Engine Exhaust Particle Sizer (EEPS) Default Matrix was 56-75% lower than mass derived using the reference gravimetric method (M-Grav) over the Federal Test Procedure (FTP). In this study, M-IPSD calculated with a new inversion matrix, the Soot Matrix, is compared with M-Grav and also photoacoustic soot mass (M-Soot), to evaluate potential improvement of the IPSD method for estimating PM mass emissions from LDVs. In addition, an aerodynamic particle sizer (APS) was used to estimate mass emission rates attributed to larger particles (0.54-2.5 mu m in aerodynamic diameter) that are not measured by the EEPS. Based on testing of 10 light-duty vehicles over the FTP cycle, the Soot Matrix significantly improved agreement between M-IPSD and M-Grav by increasing slopes of M-IPSD/M-Grav from 0.45-0.57 to 0.76-1.01 for gasoline direct injected (GDI) vehicles; however, for port-fuel injection (PFI) gasoline vehicles, a significant discrepancy still existed between M-IPSD and M-Grav, with M-IPSD accounting for 34 +/- 37% of M-Grav. For all vehicles, strong correlations between M-IPSD and M-Soot were obtained, indicating the (IPSD) method is capable of capturing mass of soot particles. The discrepancy between the M-IPSD and M-Grav for PFI vehicles, which have relatively low PM emissions (0.22 to 1.83 mg/mile), could be partially due to limited size range of the EEPS by not capturing larger particles (0.54-2.5 mu m) that accounts for similar to 0.08 mg/mile of PM emission, uncertainties of particle effective density, and/or gas-phase adsorption onto filters that is not detected by in situ aerosol instrumentation.