Use of Cascade Impactors in the Chemical and Physical Characteristics of Coal-combustion Aerosol Particles

Aerosol particles from combustion of pulverized coal are typically distributed bimodally with respect to size, and contain particles ranging from about 0.01 um to over 100 urn in diameter. Development of control technology, emissions testing, and prediction of health and environmental effects often require characterization of the size distributions of aerosol particulate mass o r the various chemical components. Cascade impaction provides a relatively simple and fundamental measurement of the mass-vs-size distribution and can yield size-segregated material in quantities adequate for determining the distributions of chemical, physical, or biologically active constituents. This paper briefly reviews impactor theory, considers the merits and shortcomings of four cascade impactors, and reviews the principal problems involved in using cascade impactors to measure properties of coal combustion aerosols. These problems include errors in measuring narrow distributions, effects of particle bounce and reentrainment, diffusive deposition of fine particles, and deposition of condensible/adsorbable gases. Ambiguities in data reduction will also be discussed.