10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Performance Study of the HR-ELPI+ Instrument
Sampo Saari, ANSSI ARFFMAN, Juha Harra, Topi Rönkkö, Jorma Keskinen, Tampere University of Technology
Abstract Number: 1140 Working Group: Instrumentation
Abstract Data inverting methods in aerosol measurement instruments have significant influence on the resolution and quality of the result. A new ELPI instrument, High Resolution ELPI+ (HR-ELPI+, Dekati Ltd.) uses a modern iterative inversion calculation method to improve particle size resolution and data analysis. In this study (Saari et al., 2018), the performance of the HR-ELPI+ is critically analyzed by simulations and experiments in the laboratory and field conditions, and the results are compared to the conventional inversion data analysis method (cut-point diameter concept) and common reference instruments (e.g. SMPS, EEPS).
Operating principle of the HR-ELPI+ is the same as ELPI+ operation added with the data inversion software. The data inversion calculation method is based on the kernel functions (Järvinen et al., 2014) and iterative calculation routine resulting in determination of particle size distribution with enhanced resolution. The inversion calculation runs in real-time and is simple to use and do not require any adjustments nor optimizations from the user of the instrument.
The simulation studies included the effects of two different sources of noise: 1) signal dependent noise by variation of concentration, 2) constant electric noise by electrometer. To find out the effect of the particle size, GMD of the simulated aerosol varied from 5 nm up to 9000 nm (GSD was fixed to 1.5). To study the effect of the GSD of the simulated aerosol, GSD values were tested between 1.01 and 2 (GMD was fixed to 100 nm). To investigate responses against multimode particle size distributions, a typical bi-modal (nucleation and soot modes) particle size distribution from a heavy-duty diesel truck engine and typical atmospheric aerosol modes (nucleation, soot, accumulation and coarse mode) were simulated and tested.
In the laboratory experiments, performance of the HR-ELPI+ was tested against dioctyl sebacate (DEHS) and NaCl aerosol generated using a nebulizer. Typical diesel exhaust aerosol from a passenger car on a dynamometer was tested in the field experiments. Experimental set-up consisted of parallel test aerosol measurements with the HR-ELPI+ and other reference instruments. The reference instruments were Engine Exhaust Particle Sizer 3090 (EEPS, TSI Inc.), two Scanning Mobility Particle Sizer Spectrometer: nanoSMPS (TSI Inc.) and longSMPS (TSI Inc.) and high-resolution low-pressure cascade impactor (HRLPI, Arffman et al., 2014).
Simulations showed that the HR-ELPI+ inversion performs accurately for lognormal unimodal and multimodal size distributions in the size range of 10 nm – 9 µm. Experimental results confirmed the simulated performance with laboratory test aerosols and field measurements. The results also indicated that the performance of the HR-ELPI+ may suffer if the raw currents have electrical noise more than 1%. However, the HR-ELPI+ clearly produces better resolution and quality with a low oscillation risk compared to the conventional cut-point diameter concept of ELPI. The HR-ELPI+ also generally showed very similar size distributions and concentrations compared to the EEPS and SMPS reference devices.
[1] Arffman et al. (2014), High-resolution low-pressure cascade impactor. Journal of Aerosol Science 78:97-109. [2] Järvinen et al. (2014), Calibration of the new electrical low pressure impactor (ELPI+). Journal of Aerosol Science 69:150-159. [3] Saari et al. (2018), Performance evaluation of the HR-ELPI+ inversion. Submitted to Aerosol Science and Technology.