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United States Department of Agriculture

Agricultural Research Service

Title: Instrument Limitations in Sizing Airborne Particulate Matter

Authors
item Buser, Michael
item Holt, Gregory

Submitted to: Soil and Water Conservation Society Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: April 20, 2004
Publication Date: July 24, 2004
Citation: Buser, M.D., Holt, G.A. 2004. Instrument limitations in sizing airborne particulate matter [abstract]. Soil and Water Conservation Society.

Technical Abstract: The distribution of particle mass, with respect to particle size, is perhaps the most important physical parameter governing particle behavior. Various methods and/or techniques are currently used to determine particle size distribution characteristics of particulate matter. These methods include: aerodynamic separation (i.e., impactors and cyclones) microscopy, laser diffraction, time of flight, electrical sensing zone, etc. Aerodynamic separation methods are generally less expensive and simpler to use than the other methods. Light microscopy has been used for determining particle size information regarding morphology of microscopic features. Recent advancements in computer technology and pattern recognition algorithms have enhanced the capabilities of scanning microscopy. Laser diffraction techniques pass a jet of aerosol through an optical system where light is scattered from individual particles and detected by a photo-detector array. Discrete signals are counted and sorted by intensity, based on a refractive index. Time of flight methods determine particle velocity by accelerating an aerosol through a nozzle and past two laser beams. Particle velocity is related to particle density and drag force which are used to determine the aerodynamic equivalent particle size. Electrical sensing zone methods pull aerosol samples, dispersed in electrolyte, through an aperture tube and past electrodes, measuring impedance increases as particles pass through the system. These increases are proportional to the volume of electrolyte displaced by the particle. Advantages and disadvantages exist for each of these methods. Unfortunately, there is no single agreed upon method of determining the particle size distribution characteristics of particulate matter.

Last Modified: 12/18/2014
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