A skimmer device for concentrating an aerosol from a flowing gas stream, having an inlet with inlet aperture and inlet raceway, an outlet with virtual impact void and collector channel, and bulk flow divertors symmetrically disposed on either side of the long axis of flow, further characterized in that the downstream walls of the bulk flow divertors are concavedly curved and reverse the direction of bulk flow. In section, the four channels or passages of the “skimmer” thus form a “crossed tee” with concavedly contoured lateral arms curving back around. The lateral flow channels are for diverting the bulk flow into exhaust chimney spaces, and the chimney spaces are positioned proximate to the inlet element and anterior to the collection channel. In operation, the bulk flow streamlines are thereby folded more than 90 degrees away from the long axis of flow on the laterally disposed concave walls of the bulk flow channels. While counterintuitive, this was found using computational fluid dynamics (CFD) and experimentation to dramatically reduce wall separation and related instabilities and to improve particle recoveries. Large two-dimensional arrays of closely stacked inlet and skimmer elements are thus achieved by fitting the chimneys into spaces between parallel inlet elements. The interlinked problems of flow instability, manufacturability of arrays, and scale-up of chimney cross-sectional area to equalize pressure differentials in the bulk flow diverter exhaust ducts, particularly in two-dimensional arrays at high throughput, are uniquely solved with this geometry.