Development of a Two-Stage Virtual Impactor System for High Concentration Enrichment of Ultrafine, PM_2.5, and Coarse Particulate Matter

Abstract

A two-stage particle concentration enrichment system was developed to provide highly concentrated particles at low flow rates, for applications in areas such as toxicity studies of particulate matter (PM) as well as for increasing the signal-to-noise ratio in online particle sampling instruments. The current system is an extension of the Versatile Aerosol Concentration Enrichment System (VACES) developed at University of Southern California and operates by placing a second-stage miniature virtual impactor (VI) downstream of the VACES. Particles are sequentially enriched through each stage. Laboratory evaluations were conducted using various types of polydisperse particles to simulate typical ambient PM components as well as monodisperse polystyrene latex (PSL) particles. The system's configuration was tested by adjusting the intermediate flow rate, which is the intake flow of the second-stage VI (or minor flow of the first-stage VIs), for which 15 L/min was determined to be optimal in terms of maximizing the overall concentration enrichment. Particle size distributions before and after concentration enrichment were compared using a scanning mobility particle sizer. Overall, our results indicate that the sampled particles were relative consistently enriched by factors of 100-120 (i.e., a concentration enrichment efficiency 75-85% of the ideal value) based on both PM mass and number concentrations, and along with similar physical properties of the size distribution (i.e., mode, median). Continuous and time-integrated field tests using urban ambient PM also showed consistent enrichment factors (by Received 31 July 2012; accepted 20 October 2012. This study was funded by the National Institutes of Health through Grant #1566G HB474, and the Environmental Protection Agency through Grants/Awards #1566G HB474 and #RD-83374301-0 to the University of Southern California (USC). The research described herein has not been subjected to the agency's required peer and policy review and therefore does not necessarily reflect the views of the agency, and no official endorsement should be inferred. The authors would like to thank Dr. Junfeng Zhang (USC Keck School of Medicine) for his assistance in the chemical analysis.Address correspondence to Constantinos Sioutas, Department of Civil and Environmental Engineering, University of Southern California, 3620 S. Vermont Ave., KAP210, M/C 2531, Los Angeles, CA 90089, USA. E-mail: sioutas@usc.edu roughly 100-120 times) for number and mass concentrations, black carbon, and PM-bound polycyclic aromatic hydrocarbons.

Toxicity of aged gasoline exhaust particles to normal and diseased airway epithelia

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Versatile aerosol concentration enrichment system (VACES) operating as a cloud condensation nuclei (CCN) concentrator: development and laboratory characterization

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