High-volume Impactor for Sampling Fine and Coarse Particles

Final design, calibration, and field testing have been completed for a new 1.13 m³/min (40 cfm) High-volume Virtual Impactor (HVVI). Field tests have demonstrated that the new classifier/collector works well as an accessory to the existing PM10 Size Selective Inlet high-volume samplers. The HVVI provides two fractions of PM10 mass, both of which are collected by filtration. The fine fraction (0-2.5 μm aero. dia.) Is collected on the standard 20.3 × 25.4 cm (8- × 10-in) high-volume filter; the coarse fraction (2.5-10 μm aero. dia.) is collected on a 5.1 × 15.2 cm (2- × 6-in) filter. Coarse flow through the receiver tubes is limited to 0.057 m³/min (2 cfm), 5 percent of the total flow.

The operating pressure drop across the HVVI stages Is sufficiently high to make changes In pressure across the collection filters Insignificant. The HVVI filter holder assembly facilitates loading/ unloading samples in the laboratory, thus eliminating damage due to handling filters in the field. Size separation characteristics of the HVVI agree well with those for the 16.7 L/min commercially available dichotomous sampler with the 50 percent effectiveness (cut-point) occurring at 2.5 μm. Applying laboratory-determined particle losses to the typical ambient particle mass size distribution described In Federal Register 49, 40 CFR, Part 53, Table D-3, the HVVI fine fraction total mass loss is less than 0.8 percent for liquid particles and less than 0.1 percent for solid particles; coarse fraction total mass loss is less than 2.5 percent for liquid particles, and less than 0.2 percent for solid particles.