History of Impactors—The First 110 Years

Abstract

This history of impactors detailed in this article covers the time span from 1860 to 1970. The origin of the inertial impactor was in the time period from 1860 to 1870, and the very first impactors were essentially the same as they are today-a jet of particle-laden air impinging on a plate. Impactors have a history of going through spurts of development. In the 1800s, impactors allowed researchers for the very first time to quickly collect particles and inspect them under a microscope to study the relationship between dust and disease. This was an exciting time for researchers, and these early impactors were used extensively. The next spurt of development was about 1920, when impactors were rediscovered in the form of konimeters, dust counters, and impingers, which were considerably more advanced than the impactors of the 1800s and were used extensively for determining the dust concentrations to which industrial workers were exposed. These instruments were used in different forms until the mid 1940s when the cascade impactor was developed. The discovery of the cascade impactor, along with extensive theoretical analysis of jet impaction in the early 1950s, led to much activity in cascade impactor development. In 1970, with the help of finite difference techniques and high-speed computers, a parametric study of impactors was made which unlocked nearly all of the secrets of how to design an impactor. From 1970 forward, the design of impactors became rather routine, and numerous impactors of all shapes and sizes for all manner of purposes were designed and built.

Impactor Apparatus for the Study of Particle Rebound: Relative Humidity and Capillary Forces

“…Early studies of impactor performance noted that not all particles colliding with a plate adhered (Pouchet 1860;Marple 2004). Particles of sufficient kinetic energy to overcome the adhesive interactions at the surface rebounded (Dahneke 1971;Winkler 1974).…”

Aerosol Science and Technology: History and Reviews

“…Conventional impactors were introduced in 1860 (Marple, 2004); thus, the virtual impactor, which was introduced in the 1960s, is a relatively new type of inertial size separator. Despite its relative newness, the virtual impactor has proved to be very useful as both a particle classifier and a particle concentrator.…”

“…The impactor stage shown in the center of this figure is the same in all of these impactors; other design criteria are the cause for the wide variety of designs. These impactors include (1) the micro-orifice uniform deposit impactor (MOUDI) that uses micro-orifice nozzles to collect particles as small as 0.056 µm and rotation of the impaction plates to obtain a uniform deposit on the impaction plate (Marple, 1978;Marple & McCormack, 1983;Marple et al, 1991); (2) the nano-MOUDI that adds three smaller cut stages to the MOUDI (Marple & Olson, 1999); (3) the Marple, Spengler, and Turner (MST) PM 2.5 and PM 10 indoor air sampler (Marple et al, 1987); (4) the Marple personal cascade impactor (MPCI) (Rubow et al, 1987); (5) the micro-environmental monitor (MEM), an indoor impactor/filter sampler with cut sizes of 10 or 2.5 µm and operates at 10 l/min; (6) the respirable impactor (RI), a single-stage impactor that has either American Conference of Governmental Industrial Hygienists (ACGIH) or British Medical Research Council (BMRC) respirable cuts at flow rates of either 2 or 30 L/min (Marple, 1978;Marple & McCormack, 1983); (7) the personal dust aerosol sampler (PDAS), a 2 L/min personal sampler with a respirable cut cyclone first stage and 0.8 µm cut impactor second stage to separate coal dust particles from diesel exhaust particles in dieselized coal mines (Marple et al, 1995b); (8) the Marple-Miller impactor (MMI), built as either a 30 or 60 L/min cascade impactor for the pharmaceutical industry (Marple et al, 1995a); (9) the nextgeneration pharmaceutical impactor (NGI), a cascade impactor that operates at any flow rate from 15 to 100 L/min (Marple et al, 2003a(Marple et al, , 2003b(Marple et al, , 2004; and (10) the personal environmental monitor (PEM), a two-stage impactor/ filter sampler that operates from 2 to 10 L/min and has cut sizes of 1.0, 2.5, or 10 µm. Five of these impactors, the MOUDI, the nano-MOUDI, the MPCI, the PEM, and the NGI are widely used and deserve some explanation.…”

Use of Virtual Impactor (VI) Technology in Biological Aerosol Detection

“…This review will attempt to focus on the role played by VI technologies in solving problems associated with biological detection. It is assumed that the reader will have familiarity with VI as previously reviewed by Marple (2004). Having an understanding of naturally occurring bioaerosols and their transport characteristics in nature as reviewed by Jones and Harrison (2004) is helpful.…”