A comparison of cascade impactor data reduction methods

Abstract

The mass median aerodynamic diameter, dg, and geometric standard deviation, σg, of an aerosol is typically determined from a reduction of data obtained with a cascade impactor under the simplifying assumption that each stage of the impactor has an ideal collection efficiency. Two such reduction techniques are described and compared to an "inversion" method that incorporates the actual collection efficiencies of an impactor. Theoretical comparisons were made to demonstrate the difference in the estimate of dg and σo between the 2 ideal reduction methods and the inversion technique. Results indicated that, in general, both dg and σg are overestimated when the collection efficiencies are assumed to be ideal. A spreadsheet application of the inversion method is described.