On the Performance of an Aerosol Electrometer with Enhanced Detection Limit.

Yixin Yang,Tongzhu Yu,Jiaoshi Zhang,Huaqiao Gui,Jianguo Liu,Jian Wang,Wenyu Wang

doi:10.3390/s18113889

Abstract

An aerosol electrometer with enhanced detection limit was developed for measuring the collected particles electrical current ranging from −50 pA to 50 pA with no range switching necessary. The detection limit was enhanced by suppressing the electric current measurement noise and improving the detection efficiency. A theoretical model for the aerosol electrometer has been established to investigate the noise effect factors and verified experimentally. The model showed that the noise was a function of ambient temperature, and it was affected by the characteristics of feedback resistor and operational amplifier simultaneously. The Faraday cup structure of the aerosol electrometer was optimized by adopting a newly designed cup-shaped metal filter which increased the surface area of the cup; thus the particle interception efficiency was improved. The aerosol electrometer performance-linearity, noise and the particle detection efficiency, were evaluated experimentally. When compared with TSI-3068B, a 99.4% () statistical correlation was achieved. The results also showed that the root mean square noise and the peak-to-peak noise were 0.31 fA and 1.55 fA, respectively. The particle detection efficiency was greater than 99.3% when measuring particle diameter larger than 7.0 nm.

Highlights

Aerosol electrometers (AE), which mainly consist of an electrometer and a Faraday cup-containing filter, is the simplest form of electrical aerosol measurement instrument used in aerosol studies.They have been widely used in characterizing condensation particle counters (CPC) [1,2,3,4], determining the size distribution with a differential mobility analyzer (DMA) [5,6,7,8], and directly measuring net charge on atmospheric ions or charged aerosols [9,10,11,12]
The challenge of AEs being used in different fields is their detection limit, which is mainly affected by electric current measurement noise and the particle detection efficiency
The setup mainly consists of an air supply module, an aerosol particle generator, an unipolar charger, a commercial aerosol electrometer (TSI-3068B), and the designed AE

Summary

Introduction

Aerosol electrometers (AE), which mainly consist of an electrometer and a Faraday cup-containing filter, is the simplest form of electrical aerosol measurement instrument used in aerosol studies They have been widely used in characterizing condensation particle counters (CPC) [1,2,3,4], determining the size distribution with a differential mobility analyzer (DMA) [5,6,7,8], and directly measuring net charge on atmospheric ions or charged aerosols [9,10,11,12]. The challenge of AEs being used in different fields is their detection limit, which is mainly affected by electric current measurement noise and the particle detection efficiency It becomes the general source of uncertainty at low particle number concentration. The CPC counting efficiency curve should be calibrated by taking the concentration ratio of the CPC to the AE for Sensors 2018, 18, 3889; doi:10.3390/s18113889 www.mdpi.com/journal/sensors

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