Measurement of Aerosol Concentration as a Function of Size and Charge

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Abstract
We have developed an aerosol diagnostic system that measures the number concentration of aerosols as a function of particle size and charge. This system differs from other methods that measure aerosol concentration as a function of either particle size or particle charge. Previous methods treated only one of the two variables as a parameter. Our system treats both particle size and particle charge as variables in a three-dimensional representation of the aerosol distribution. Size-charge analysis was accomplished by first fractionating the aerosol according to the electrical mobility of the particle, then determining the particle-size distribution of each mobility fraction using either a Climet optical counter or an ASASX-P laser spectrometer. By accumulating a particle-size distribution of each mobility fraction, we could determine by mathematical techniques the aerosol number concentration as a function of both particle charge and size. Use of an LSI-11/23, interfaced to the aerosol instrumentation, allowed us to select the mobility analyzer voltage and acquire data from either of the optical counters. The computer also enabled us to construct three-dimensional contour plots of the aerosol size-charge distributions. We are currently using this system to determine the aerosol number concentration as a function of particle sizes from 0.1 to 3.0 μm in diameter, and as a function of particle charges from −1000 to +1000 electronic charges. We give illustrations of the size-charge distributions of diffusion-charged latex aerosols, atomized latex aerosols, and heterodisperse salt and dioctylsebacate aerosols.