| abstract |
Environmental monitoring of atmospheric air is facilitated by a single stage virtual impactor (11) for separating an inlet flow (Q O ) having particulate contaminants into a coarse particle flow (Q 1 ) and a fine particle flow (Q 2 ) to enable collection of such particles on different filters (19a, 19b) for separate analysis. An inlet particle acceleration nozzle (28) and coarse particle collection probe member (37) having a virtual impaction opening (41) are aligned along a single axis (13) and spaced apart to define a flow separation region (14) at which the fine particle flow (Q 2 ) is drawn radially outward into a chamber (21) while the coarse particle flow (Q 1 ) enters the virtual impaction opening (41). Symmetrical outlet means (47) for the chamber (21) provide flow symmetry at the separation region (14) to assure precise separation of particles about a cutpoint size and to minimize losses by wall impaction and gravitational settling. Impulse defocusing means (42) in the probe member (37) provides uniform coarse particle deposition on the filter (19a) to aid analysis. Particle losses of less than 1% for particles in the 0 to 20 micron range may be realized. |