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SAMPLING CHARGED PARTICLES WITH CASCADE IMPACTORS
Citation:
Farthing, W., D. Hussey, W. Smith, R. Wilson, AND Jr. SAMPLING CHARGED PARTICLES WITH CASCADE IMPACTORS. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/7-79/027 (NTIS PB290897), 1979.
Description:
The report discusses three sets of experiments which demonstrate that a cascade impactor sampling a charged aerosol may yield a particle size distribution measurement that deviates from the time distribution. The distributions indicated more large particles and fewer small particles than actually existed, due to the particles' attraction to the grounded impactor plates (stages). Although higher charge levels produced larger deviations from the true size distribution, the magnitude of the deviation and the corresponding correction factor for any given charged aerosol are unpredictable. Also, the error was smaller if glass fiber substrates were used as collection surfaces instead of bare metal. For electrostatic precipitators operating at normal charging conditions (an electric field of 400,000 V/m and a current density of 0.0003 A/sq m/s), the size distribution (measured by the lower stages of an Andersaen cascade impactor with glass fiber substrates) was not significantly different from the true size distribution.