MASS DIAMETER VERSUS AERODYNAMIC DIAMETER OF NANOPARTICLES. IMPLICATIONS ON THE CALIBRATION CURVE OF AN INERTIAL IMPACTOR

Calibration of the performance of a hypersonic impactor consists of experimentally finding the relationship between the particle Stokes number of impaction and the dimensionless collector-to-nozzle distance S1/2=f((L/dn)1/2). The Stokes number embraces both the mass and aerodynamic diameter, which differs substantially in the case of nanoparticles (Tammet (1995) J. Aerosol Sci. 126 (3), 459-475). When both diameters are treated as distinct objects, the calibration curve S1/2=f((L/dn)1/2) of an instrument becomes unique for a broad range of operating conditions as expected, pointing out the essential fact that the concept of particle size must be clearly specified. Obviously, the same idea must be applied when obtaining data from inertial impactors.