A method was developed for assessing the electrical charge levels of aerosols. The technique utilized the filtration differences between charged and charge neutralized particles caused by coulombic and dielectrophoretic interactions between charged particles and bipolar charged filter fibers. Size distributions were measured with an optical particle counter. The method was applied with increasing aerosol concentrations. Test aerosols were sampled through branched sampling trains that allowed nearly instantaneous switching between the filtered line and identical open line. Two sampling rates produced face velocities of 10 and 20 centimeters per second at the filter face. The relationship of filter penetration to charge level was observed on monodisperse particles. The apparatus used to measure how the charge assessment method related filter penetration to both particle charge and size was described. The method was calibrated using monodisperse methylene blue particles charged to a measured level. It was tested using a polydisperse calcium- carbonate (513780) aerosol that was characterized as to size dependent charge levels. The charge level of copy machine toner dust was measured as an example of highly charged workplace aerosol. Results showed that the technique is limited to the size range of 0.1 to 0.7 micrometers depending on characteristics of the electric filter. Electrical mobilities and penetration ratios of particles ranging from 0.01 to 0.07 micrometers in diameter were constant. Another limitation was the requirement of aerosol stability over the sampling period. The authors conclude that the technique has potential for use in the rapid field assessment of aerosol charge levels, but that field studies need to be carried out to validate its utility.
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