How well can aerosol instruments measure particulate mass and solid particle number in engine exhaust?

Abstract

Aerosol instruments provide more informative engine exhaust particulate matter (PM) data than the gravimetric filter and solid particle number methods prescribed by regulations. Yet their lack of conformity to the regulatory methods can limit their acceptance for vehicle development. This article examines the ability of the Dekati Mass Monitor (DMM), Engine Exhaust Particle Sizer (EEPS), and Micro Soot Sensor (MSS) to measure PM 2.5 mass and solid particle number relative to current motor vehicle PM emissions standards. Simultaneous PM measurements are made by these three instruments and the two regulatory methods for 50 tests of six gasoline direct injection and two port fuel injection vehicles over the U.S. Federal Test Procedure. DMM and EEPS determinations of PM mass correlate well to gravimetric values (regression slopes of 1.06 § 0.04 and 0.98 § 0.08) down to a few mg/mile, below which filter weighing variability becomes problematic. The MSS exhibits a lower slope of 0.79 § 0.03 consistent with it measuring the soot fraction, rather than total PM. At emissions rates above »10 13 particles/mile, solid particle number determined from DMM and EEPS data correlates respectably with, but overestimates the regulatory method (regression slopes are 1.7 § 0.1 and 1.4 § 0.15, respectively). Below this emissions rate, the correlation degrades. EEPS estimates of PM mass are significantly improved with the recent soot optimized inversion algorithm (slope improves from 0.45 to 0.98). While they cannot replace filters and solid particle counting, the present study suggests that these instruments can be used as more informative surrogates during motor vehicle development.

Using partial flow dilution to measure PM mass emissions from light-duty vehicles

“…For GDI vehicles driven over the FTP cycle, PM mass measured by the MSS correlates very well with gravimetric data. The regression slope is approximately 0.8, consistent with a »20% organic component of the total PM (Khalek et al 2010;Maricq et al 2016).…”

Review of Respirable Coal Mine Dust Characterization for Mass Concentration, Size Distribution and Chemical Composition

“…However, knowledge or assumptions of the effective density are required to reconcile differences between mobility diameter-dependent charging efficiency and aerodynamic diameter-dependent impaction separation [83]. ELPIs have been used in engine emission testing with good agreement between the ELPI and gravimetric mass concentrations [84][85][86][87].…”

Investigation of alternative metrics to quantify PM mass emissions from light duty vehicles

“…At lower PM emission rates (< 3 mg/mile), however, the correlations between real-time instruments and gravimetric filter were weaker. The results of some studies may suggest that the variability in the gravimetric method below 3 mg/mi is the cause (Maricq et al, 2016), whereas other studies have shown strong correlations between gravimetric and alternative metrics down to 0.2 mg/mi (Quiros & Zhang, 2015). Other work has specifically shown that suspended PM mass (IPSD) measured by the EEPS and BC mass were highly correlated for several LDVs equipped with different technologies when evaluated over the FTP cycle, where IPSD and BC mass accounted for only one-third of gravimetric PM mass for gasoline PFI vehicles, while a one-to-one relationship was obtained for GDI vehicles (Xue et al, 2016b).…”