CORRECTING PARTICLE SIZE DISTRIBUTION DATA FOR THE DIFFERENCES BETWEEN SINGLE-STAGE AND MULTI-STAGE COLLECTION OR COUNTING EFFICIENCIES

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Abstract
Cascade impactors, like many other multi-stage particle sizing devices, size particles by sorting them into stages or channels that have certain size intervals associated with them. The collection or detection efficiency as a function of particle size, E(d), is sometimes determined for each stage individually by using particles of known sizes. If there is appreciable overlap in the E(d) curves for adjacent stages or channels, then the efficiencies become E(d)', somewhat different from E(d). Even combining the total counts or masses for adjacent stages or channels cannot completely correct for this effect. An example is given for which the cut diameter corrections were on the order of 10%. It is recommended that multi-stage instruments not be calibrated in a single-stage mode; if they are, the changes in cut sizes should be estimated and corrections considered.