Measurement of Aerosol Concentration as a Function of Size and Charge

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 threedimensional 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 pm in diameter, and as a function of particle charges from -1000 to + 1000 electronic charges.We give illustrations of the sizecharge distributions of diffusion-charged latex aerosols, atomized latex aerosols, and heterodisperse salt and dioctylsebacate aerosols.