Abstract:
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This paper presents a method created to calibrate a condensation particle counter (CPC) used to measure aerosol concentration by comparison to a primary standard aerosol electrometer, traceable to the U.S. Army Primary Standards Laboratory (APSL). The electrometer measures the current produced by an aerosol flow containing particles with a known charge distribution. By measuring the aerosol volumetric flow rate and the number of charges over time, the particle concentration can be calculated through a traceable electronic measurement. This is then compared to the CPC's optical measurement. A charge correction factor is used to correlate the two different measurement methods. An oil-alcohol solution is aerosolized with a constant output atomizer and passed through a krypton-85 neutralizer. This method of atomization requires minimal effort and produces a stable aerosol with a measurable charge distribution and high concentration. The aerosol is introduced into an electrostatic classifier, producing a highly monodisperse aerosol with particles containing mostly single charges and a small percentage carrying multiple charges. For a given solution, the charge distribution is measured using a tandem differential mobility analyzer. This aerosol flow is then split and introduced into the AE and CPC, allowing a comparison of the two measurements. This method is used to calibrate CPC's that verify the performance of gas mask and respirator fit testers, having a direct effect on the health of personnel in both the military and industry.
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