Comparison of Particle Sizers and Counters with Soot-like, Salt, and Silver Particles

Abstract

Vehicle emission regulations in Europe and many Asian countries include a particle number limit. The number concentration is measured, typically, with condensation particle counters (CPCs). For research purposes, the size distributions provide useful information. Scanning mobility particle sizers (SMPSs) accurately provide the size distribution but are not suitable for transient aerosol. Engine (fast) exhaust particle sizers (EEPSs) cover this gap, but with less accuracy. Fast size distribution instruments are commonly used in the research and development of engines. In the last few years, instrument algorithms have been improved, but studies assessing the improvements are limited, in particular in their lower size range, around 10–20 nm, and for soot-like aerosol. In this paper, we compared the three instruments using salt, silver, diffusion flame soot (CAST), and spark discharge graphite particles. Moreover, vehicle exhaust number concentration measurements with EEPSs over a seven-year period were presented. In terms of particle concentration, EEPS overestimated, on average, 25% compared to CPC, in agreement with previous studies. Its accuracy for mean particle size determination was better than 5 nm compared to SMPS. The agreement between the instruments was satisfactory but the uncertainty increased at low concentrations and larger particle sizes, showing that there is still room for further improvements. Experimental challenges, such as low concentration levels of modern vehicles, losses in the diluters, use of photometric mode by the CPCs, and the material impact, are also discussed.

Assessment of two condensation particle counters (CPCs) in photometric mode for high concentration exhaust emission measurements

“…Differences in the counting efficiencies in the cut-off curve have been reported by many researchers testing in the single counting mode [49][50][51]. These findings justify why there were no differences of the material in the plateau region (25 to 50 nm range) in the photometric mode for graphite, soot, and salt particles in our previous study [14].…”

“…In theory, once calibrated, the photometric mode should remain in acceptable levels of accuracy (±20%) independently of the original type of particles, because all particles grow in similar sizes in the micrometer range before detection and they should have the same refractive index due to the condensed vapor of the working fluid. However, recently we found that small silver particles were underestimated at least 40% compared to soot particles [14]. There are not many studies that have examined the photometric mode range of CPCs, and even less any size dependency [15].…”

“…Corrections for multiply charged particles and diffusion losses were applied by the manufacturer's aerosol instruments manager (AIM) software version 9.0.0. The SMPS was evaluated before the measurement campaign [14]. In parallel to the SMPS, two identical CPCs were measuring; one of them optionally with a diluter (DIL).…”

Exhaust Emissions from Euro 6 Vehicles in WLTC and RDE—Part 2: Verification by Experimental Measurement

“…It allowed for the measurement of particles in the diameter range from 5.6 nm to 560 nm (in this study, particles > 23 nm were counted). Note that EEPS uncertainty is higher than particle counters and that volatiles are also measured [43]. Technical data of the TSI 3090 EEPS analyzer are provided below (Table 3).…”

Euro VI-d Compliant Diesel Engine’s Sub-23 nm Particle Emission

“…In this method, the solid particles of the aerosol are enlarged by dissipating liquid butanol first. Then the particles pass by laser light and light-sensing optics in a detection chamber [ 9 ]. The passing of the enlarged particles causing discontinuity in the laser detection of the optics, allowing the particle count to be determined.…”