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

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 PM2.5 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 similar to 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.