Extending the Faraday cup aerosol electrometer based calibration method up to 5 µm

Abstract

A Faraday cup aerosol electrometer based electrical aerosol instrument calibration setup from nanometers up to micrometers has been designed, constructed, and characterized. The set-up utilizes singly charged seed particles, which are grown to the desired size by condensation of diethylhexyl sebacate. The calibration particle size is further selected with a Differential Mobility Analyzer (DMA). For micrometer sizes, a large DMA was designed, constructed, and characterized. The DMA electrical mobility resolution was found to be 7.95 for 20 L/min sheath and 2 L/min sample flows. The calibration is based on comparing the instrument’s response against the concentration measured with a reference Faraday cup aerosol electrometer. The set-up produces relatively high concentrations in the micrometer size range (more than 2500 1/cm³ at 5.3 µm). A low bias flow mixing and splitting between the reference and the instrument was constructed from a modified, large-sized mixer and a four-port flow splitter. It was characterized at different flow rates and as a function of the particle size. Using two of the four outlet ports at equal 1.5 L/min flow rates, the particle concentration bias of the flow splitting was found to be less than ±1% in the size range of 3.6 nm–5.3 µm. The developed calibration set-up was used to define the detection efficiency of a condensation particle counter from 3.6 nm to 5.3 µm with an expanded measurement uncertainty (k = 2) of less than 4% over the entire size range and less than 2% for most of the measurement points.

Copyright © 2018 American Association for Aerosol Research

EDITOR:

• Pramod Kulkarni

Acknowledgments

Authors thank Antti Lepistö, Veli-Pekka Plym and Timo Lindqvist for manufacturing the calibration setup components.

Additional information

Funding

The authors gratefully acknowledge financial support from the MMEA research program of the Cluster for Energy and Environment (CLEEN Ltd., Finland), funded by Tekes – the Finnish Funding Agency for Technology and Innovation.