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

<p>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 (<i>M</i>_IPSD) with the TSI Engine Exhaust Particle Sizer (EEPS) Default Matrix was 56–75% lower than mass derived using the reference gravimetric method (<i>M</i>_Grav) over the Federal Test Procedure (FTP). In this study, <i>M</i>_IPSD calculated with a new inversion matrix, the Soot Matrix, is compared with <i>M</i>_Grav and also photoacoustic soot mass (<i>M</i>_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 µm 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 <i>M</i>_IPSD and <i>M</i>_Grav by increasing slopes of <i>M</i>_IPSD/<i>M</i>_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 <i>M</i>_IPSD and <i>M</i>_Grav, with <i>M</i>_IPSD accounting for 34 ± 37% of <i>M</i>_Grav. For all vehicles, strong correlations between <i>M</i>_IPSD and <i>M</i>_Soot were obtained, indicating the IPSD method is capable of capturing mass of soot particles. The discrepancy between the <i>M</i>_IPSD and <i>M</i>_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 µm) that accounts for ∼0.08 mg/mile of PM emission, uncertainties of particle effective density, and/or gas-phase adsorption onto filters that is not detected by <i>in situ</i> aerosol instrumentation.</p> <p>Copyright © 2016 American Association for Aerosol Research</p

Measuring Particulate Emissions of Light Duty Passenger Vehicles Using Integrated Particle Size Distribution (IPSD)

The California Air Resources Board (ARB) adopted the low emission vehicle (LEV) III particulate matter (PM) standards in January 2012, which require, among other limits, vehicles to meet 1 mg/mi over the federal test procedure (FTP). One possible alternative measurement approach evaluated to support the implementation of the LEV III standards is integrated particle size distribution (IPSD), which reports real-time PM mass using size distribution and effective density. The IPSD method was evaluated using TSI’s engine exhaust particle sizer (EEPS, 5.6–560 nm) and gravimetric filter data from more than 250 tests and 34 vehicles at ARB’s Haagen-Smit Laboratory (HSL). IPSD mass was persistently lower than gravimetric mass by 56–75% over the FTP tests and by 81–84% over the supplemental FTP (US06) tests. Strong covariance between the methods suggests test-to-test variability originates from actual vehicle emission differences rather than measurement accuracy, where IPSD offered no statistical improvement over gravimetric measurement variability