Mathematical Description of Experimentally Determined Charge Distributions of a Unipolar Diffusion Charger

Abstract

The charge distributions of an improved opposed flow unipolar diffusion charger were measured using a tandem differential mobility analyzer (DMA) set up in a size range of approximately 20-400 nm. The charger is intended to be used in a portable aerosol sizer to measure particle size distributions. The determined charge distributions were represented by lognormal distributions, and a set of equations and coefficients was developed to calculate the charge distributions. These equations can be easily implemented in software for size distribution measurements. The agreement between the mathematically derived and measured charge distributions is very good, with regression coefficients R 2 > 0.96. The investigations showed that approximately 55% of 20-nm particles remain uncharged, while up to 25 elementary charges need to be considered for multiple charge correction of 400-nm particles. Comparison with the Fuchs theory delivered satisfying agreement with the measured average charge levels, but charge distributions cannot be described by the Fuchs theory, likely caused by the charger geometry.

Toward elemental analysis of ambient single particles using electrodynamic balance and laser-induced breakdown spectroscopy

“…As in earlier studies (e.g., J€ arvinen et al 2017; Kaminski et al 2012) the charge distribution was found to closely follow a log-normal distribution. Therefore, the geometric mean was selected as a suitable indicator for the charging efficiency, rather than arithmetic mean.…”

Accuracy of electrical aerosol sensors measuring lung deposited surface area concentrations

“…All of the instruments are based on electrical diffusion charging of the particles and hence follow the same measurement principle. The rationale behind these instruments is that the electrical diffusion charging of submicron particles is approximately proportional to d p 1.13 (Jung & Kittelson, 2005;Asbach et al, 2011;Kaminski et al, 2012) and hence shares the same size dependence with the lung deposited surface area of spherical particles in the size range from approximately 40 to 200 nm and agrees within 730% between 20 and 400 nm (see Fig. 1).…”

Exposure Measurement at Workplaces

“…They all follow the same basic principle as the SMPS (see Section 5.3), i.e., they use a particle charger to obtain a predictable particle charge distribution, a DMA to classify particles based on their electrical mobility and a miniaturized CPC to measure the concentration of the mobility classified particles. Furthermore, the dependence of the electrical mobility on the particle size gets weaker with increasing particle diameter, because in Eqn (2), the number n of elementary charges e is almost proportional to the particle diameter [48,49,51] and hence the dependence of the electrical mobility on particle diameter mainly stems from the Cunningham slip correction factor. To simplify the handling of the instruments, they are equipped with electrical chargers instead of radioactive or X-ray neutralizers.…”