AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
A Two-Stage Versatile Aerosol Concentration Enrichment System (VACES) for Very High Concentration of Ultrafine, PM2.5 and Coarse PM
DONGBIN WANG, Winnie Kam, Kalam Cheung, Payam Pakbin, Constantinos Sioutas, University of Southern California
Abstract Number: 680 Working Group: Instrumentation and Methods
Abstract A two-stage aerosol concentration enrichment system was developed to provide highly concentrated aerosols at a 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 on-line particle sampling instruments. The current system is a modification of the Versatile Aerosol Concentration Enrichment System (VACES) (Kim et al. 2001) and operates by placing a second-stage miniature virtual impactor (VI) after the first-stage VIs to generate an aerosol that is sequentially enriched through each stage. With a total inlet flow of 200 LPM and a final minor flow of 1.5 LPM, the theoretical enrichment factor is approximately 130.
Laboratory evaluations were conducted using various types of polydisperse aerosols to simulate the ambient PM (ammonium sulfate, ammonium nitrate, adipic acid and glutaric acid) and monodisperse polystyrene latex (PSL) particles for 100, 300, 400 nano-meter and 1 micro-meter. System configuration was tested by adjusting the intermediate flow, which is the inlet flow rate of the second-stage VI or minor flow of the first-stage VIs, of which we determined 15 LPM to be optimal. The number and mass concentration in different particle size ranges were compared using a Scanning Mobility Particle Sizer (SMPS) before and after enrichment to determine size distribution. Overall, results indicate that the aerosol is consistently enriched by factors of 100-120 (thus at an efficiency of 75-85% of the ideal value) based on both PM mass and number concentration, and without substantially altering the particle size distribution. Efficiency curves to determine the 50% cutpoint of the second-stage VI were also performed. Continuous field tests using urban ambient PM also show consistent enrichment (by roughly 110-120) for number and mass concentration, black carbon and EC/OC.