The Cascade Impactor: An Instrument for Sampling Coarse Aerosols

TLDR

The study introduces the Cascade Impactor, an instrument designed to sample windborne and stationary aerosols—including fogs, clouds, sprays, dust, pollen, and spores—and outlines new methods for handling volatile droplets and analyzing the collected samples. The device uses four progressively finer jets that impact glass slides in series, separating aerosols into size‑graded fractions for microscopic analysis, and the authors derive a general parameter for jet impaction efficiency via dimensional analysis. The Cascade Impactor achieves peak sampling efficiency for particles 50 µm–1.5 µm, and its size‑grading enables detailed microscopic examination and approximate size‑distribution estimates without individual particle sizing.

Abstract

A new instrument is described which will sample windborne and stationary aerosols such as natural fogs and clouds, fine sprays, insecticidal mists, coarse dusts, pollen and spores, etc. By means of four progressively finer jets impinging on glass slides in series the sample is split up into size-graded fractions in a form suitable for microscopic analysis. The greatest efficiency of sampling is achieved for particles in the range 50 μ-1.5μ diameter. The size-grading greatly facilitates the detailed microscopic examination of heterogeneous samples and in some cases enables approximate size-distributions to be obtained by bulk estimations of the samples without the need for microscopic sizing. Experimental results for the efficiency of jets in impacting particles are correlated by dimensional analysis, and a parameter of general applicability for estimating impaction efficiencies of jets is derived. Descriptions are given of new methods of dealing with volatile droplets and of analysing the samples.