Comparison of Vehicle Exhaust Particle Size Distributions Measured by SMPS and EEPS During Steady-State Conditions

Abstract

Fast-sizing spectrometers, such as the TSI Engine Exhaust Particle Sizer (EEPS), have been widely used to measure transient particle size distributions of vehicle exhaust. Recently, size distributions measured during different test cycles have begun to be used for calculating suspended particulate mass; however, several recent evaluations have shown some deficiencies in this approach and discrepancies relative to the gravimetric reference method. The EEPS converts electrical charge carried by particles into size distributions based on mobility classification and a specific calibration, and TSI recently released a matrix optimized for vehicle emissions as described by Wang et al. (Submitteda). This study evaluates the performance of the new matrix (soot matrix) relative to the original matrix (default matrix) and reference size distributions measured by a scanning mobility particle sizer (SMPS). Steady-state particle size distributions were generated from the following five sources to evaluate exhaust particulates with various morphologies estimated by mass-mobility scaling exponent: (1) A diesel generator operating on ultralow sulfur diesel, (2) a diesel generator operating on biodiesel, (3) a gasoline direct-injection vehicle operating at two speeds, (4) a conventional port-fuel injection gasoline vehicle, and (4) a light-duty diesel (LDD) vehicle equipped with a diesel particulate filter. Generally, the new soot matrix achieved much better agreement with the SMPS reference for particles smaller than 30 nm and larger than 100 nm, and also broadened the accumulation mode distribution that was previously too narrow using the default matrix. However, EEPS distributions still did not agree with SMPS reference measurements when challenged by a strong nucleation mode during high-load operation of the LDD vehicle. This work quantifies the range of accuracy that can be expected when measuring particle size distribution, number concentration, and integrated particle mass of vehicle emissions when using the new static calibration derived based on the properties of classical diesel soot.

Investigation of vehicle exhaust sub-23 nm particle emissions

“…The recently-introduced inversion 'soot' algorithm that was designed for fractal particles was used (Wang et al 2016). We should also add that the nucleation mode measured by the EEPS is sometimes underestimated (Xue et al 2015).…”

Integrating Cloud Condensation Nuclei Predictions with Fast Time Resolved Aerosol Instrumentation to Determine the Hygroscopic Properties of Emissions Over Transient Drive Cycles

“…With low SS, and thus, low CCN concentrations, only the most hygroscopic of the sample aerosol (the upper end of the size distribution) are captured. The EEPS approximates a lognormal fit (Johnson et al 2004;Xue et al 2015); the CCN concentrations are derived from few size bins, resulting in fewer approximated counts. Previous work has shown the EEPS reporting lower particle concentrations than those reported by the SMPS in the high accumulation mode range due to more fractal like particles (Zimmerman et al 2014;Xue et al 2015).…”

Evaluating Nitrogen Oxides and Ultrafine Particulate Matter Emission Features of Urban Bus Based on Real-World Driving Conditions in the Yangtze River Delta Area, China

“…In addition, an exhaust flow meter (Pitot tube flowmeter) (0-30 m 3 •min −1 ) was installed behind the exhaust port measuring the exhaust flow rate and exhaust temperature. Particle testing equipment was TSI company's EEPS-3090 exhaust particle number and particle size analyzer [6,11,16,19,20]. This analyzer can be used to quickly measure the particle number concentration and particle size distribution of motor vehicle exhaust.…”