A personal dust spectrometer for aerodynamically classifying and collecting sub-fractions of inspirable dust, has an entry which has an entry efficiency approximating that of the human head during inhalation, and a cascade impactor comprising a stack of stages each having a flat element and a peripheral wall and gas exit holes. A connector enables a gas sampling pump to be attached to draw air through the entry and through the cascade impactor. A filter is desirably used to collect the smallest dust particles. All the dust entering the device is collected and is measurable.

This invention is directed to a high pressure drop cascade impactor wherein the particles do not bounce from the collection plate; to a method for designing said impactor; a method for calculating and determining the particle size distribution of an aerosol wherein the particle size may have a Stokes (aerodynamic) diameter as small as 10 nanometers; and, to a method of manufacturing such an impactor.

A high pressure drop cascade impactor wherein particles do not bounce from the collection plate; to a method for designing said impactor; a method for calculating and determing the particle size distribution of an aerosol wherein the particle size may have a Stokes (aerodynamic) diameter as small as 10 nanometers; and, to a method of manufacturing such an impactor. Particles drawn through the impactor exhibit substantially no reentrainment, or bounce, from the collection of surfaces. The impactor eliminates turbulence near the entrances to the jet holes by rounding the edges of the jet holes. This is accomplished on the small holes by means of electropolishing. The impactor is capable of capturing particles as small as 10 nanometers Stokes (aerodynamic) diameter.

Air containing entrained particulate matter is directed through a plurality of parallel, narrow, vertically oriented impactor slots of an inlet element toward an adjacently located, relatively large, dust impaction surface preferably covered with an adhesive material. The air flow turns over the impaction surface, leaving behind the relatively larger particles according to the human thoracic separation system and passes through two elongate exhaust apertures defining the outer bounds of the impaction collection surface to pass through divergent passages which slow down and distribute the air flow, with entrained smaller particles, over a fine filter element that separates the fine particles from the air. The elongate exhaust apertures defining the impaction collection surface are spaced apart by a distance greater than the lengths of elongate impactor slots in the inlet element and are oriented to be normal thereto. By appropriate selection of dimensions and the number of impactor slots air flow through the inlet element is provided a nonuniform velocity distribution with the lower velocities being obtained near the center of the impactor slots, in order to separate out particles larger than a certain predetermined size on the impaction collection surface. The impaction collection surface, even in a moderately sized apparatus, is thus relatively large and permits the prolonged sampling of air for periods extending to four weeks.

A particle collector and fractionator having a 360.degree. omnidirectional gas inlet slit is disclosed herein. The collector and fractionator generally comprises a top and bottom fractionating member, each of which has a set of concentric, annular ring projections which are complementary to the other set. The ring projections form channels in the top and bottom members. The collector has at least one standoff for fastening together and spacing the top and bottom fractionating members. The concentric, annular ring projections form rectangular-shaped slits, when viewed in a cross-section. The slits, formed as they are by the ring-like projections, define a gas flow path from the omnidirectional gas inlet slit to a centrally disposed gas outlet port. Particles are collected and fractionated in the channel portions of the concentric, annular ring-like projections whenever particle laden gas flows into the gas flow path and out through the centrally disposed gas port. The minimum aerodynamic size of the particles collected and fractionated may be selected by adjusting the stand-offs so as to vary the cross-sectional area of the gas flow path, which in turn increases or decreases the velocity of a stream of particle laden gas flowing through the path. The cross-sectional areas may all be adjusted simultaneously by the use of the stand-offs.