Non-ideal collection characteristics of inertial impactors—II. Cascade impactors

Abstract

Calibration of the four-stage Lundgren impactor and the six-stage Andersen sampler with oil particles, and particle bounce in the Andersen sampler with solid particles are described. Collection characteristics of oil-coated steel plates, uncoated steel plates, glass fiber filters and Whatman filters in the Andersen sampler were determined using monodisperse polystyrene latex and methylene blue aerosols. For the Lundgren impactor, whose design and operation satisfy the assumptions of impactor theory, the calibration curves are in good agreement with the theoretical curves. However, the calibration curves of the Andersen sampler are less steep and are shifted towards higher aerodynamic dia. With oil-coated steel plates, the collection efficiency curves rise monotonically from zero to 100% efficiency. However, with uncoated steel plates, the efficiency curves rise up to 20 or 50% and then drop. The peak efficiency of stages is very sensitive to jet velocity and to some extent to particle size. The use of glass fiber filters as collection surface minimizes bounce, but modifies the collection characteristics. Some Whatman filter papers are unsatisfactory as collection surfaces.