Parameters governing the performance of electrical mobility spectrometers for measuring sub-3 nm particles

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http://hdl.handle.net/10138/321496

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Cai , R , Jiang , J , Mirme , S & Kangasluoma , J 2019 , ' Parameters governing the performance of electrical mobility spectrometers for measuring sub-3 nm particles ' , Journal of Aerosol Science , vol. 127 , pp. 102-115 . https://doi.org/10.1016/j.jaerosci.2018.11.002

Title: Parameters governing the performance of electrical mobility spectrometers for measuring sub-3 nm particles
Author: Cai, Runlong; Jiang, Jingkun; Mirme, Sander; Kangasluoma, Juha
Contributor: University of Helsinki, INAR Physics
University of Helsinki, INAR Physics
Date: 2019-01
Language: eng
Number of pages: 14
Belongs to series: Journal of Aerosol Science
ISSN: 0021-8502
URI: http://hdl.handle.net/10138/321496
Abstract: Measuring aerosol size distributions accurately down to similar to 1 nm is a key to nucleation studies, and it requires developments and improvements in instruments such as electrical mobility spectrometers in use today. The key factors characterizing the performance of an electrical mobility spectrometer for sub-3 nm particles are discussed in this study. A parameter named as Pi is proposed as a figure of merit for the performance of an electrical mobility spectrometer in the sub-3 nm size range instead of the overall detection efficiency. Pi includes the overall detection efficiency, the measurement time in each size bin, the aerosol flow rate passing through the detector, and the aerosol-to-sheath flow ratio of the differential mobility analyzer. The particle raw count number recorded by the detector can be estimated using Pi at a given aerosol size distribution function, dN/dlogd(p)( ). The limit of detection for the spectrometer and the statistical uncertainty of the measured aerosol size distribution can also be readily estimated using Pi. In addition to Pi, the size resolution of an electrical mobility analyzer is another factor characterizing the systematic errors originated from particle sizing. Four existing electrical mobility spectrometers designed for measuring sub-3 nm aerosol size distributions, including three scanning/differential mobility particle spectrometers and one differential mobility analyzer train, are examined. Their optimal performance is evaluated using Pi and the size resolution. For example, the Pi value and the size resolution of a diethylene-glycol differential mobility particle spectrometer for 1.5 nm particles are 8.0 x 10(-4) cm(3) and 5.7, respectively. The corresponding relative uncertainty of the measured size distribution is approximately 9.6% during an atmospheric new particle formation event with a dN/dlogd(p) of 5 x 10(5) cm(-3) . Assuming an adjustable sheath flow rate of the differential mobility analyzer, the optimal size resolution is approximately 5-9 when measuring atmospheric new particle formation events.
Subject: Electrical mobility spectrometer
Sub-3 nm particles
Penetration efficiency
Resolution
Uncertainty
Aerosol size distribution
CONDENSATION NUCLEUS COUNTER
AEROSOL-SIZE DISTRIBUTIONS
CHARGE-DISTRIBUTION
HIGH-RESOLUTION
FLOW-RATE
NUCLEATION
ANALYZER
INVERSION
MAGNIFIER
GROWTH
114 Physical sciences
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