Development and evaluation of a compact, highly efficient coarse particle concentrator for toxicological studies

Abstract

A high-efficiency coarse-mode particle concentrator (CPC) has been developed and evaluated in the laboratory as well as validated in the field experiments at the University of Southern California, in Los Angeles, CA, and in Bilthoven, the Netherlands. The CPC operates with a total intake flow of 1000 LPM. The minor flow rate, containing the concentrated coarse-mode particles (2.5-10 μm), can be adjusted from 33 to 120 LPM in order to enrich ambient coarse PM concentrations by a factor of 8-30, depending on the desirable exposure level and flow rate needed. The laboratory evaluation of the virtual impactors at 3 minor flow rates (3.3, 7, and 10 LPM, respectively) indicated that extremely efficient concentration enrichment was obtained for 2.5-10 μm particles. In the field tests, the CPC operated at a minor flow rate of 33 LPM and the mass obtained was compared to the mass collected by a reference sampler, a (rotating) micro-orifice uniform deposit impactor (MOUDI), which sampled at 30 LPM. Concentration enrichment factors in the range of 26 to 30 were achieved based on particle mass, sulfate, and nitrate as well as selected trace element and metal concentrations (Al, Si, Ca, Fe, K, Mn, Cu, Zn, Ti). CPC and MOUDI concentrations were highly correlated for all species, with R2 in the range of 0.74 to 0.89. The use of round (compared to rectangular geometry) nozzle virtual impactors in the CPC results in a high concentration efficiency, which reduces the CPC size as well as the power requirement that is required for its operation. The compact size of the CPC makes it readily transportable to desired locations for exposure to coarse-mode particles derived from different sources and thus of a varying chemical composition.