AAAR 31st Annual Conference
October 8-12, 2012
Hyatt Regency Minneapolis
Minneapolis, Minnesota, USA
Abstract View
Validating a Centrifugal Particle Mass Analyzer and Differential Mobility Spectrometer System for Mass-Mobility Measurements
Tyler Johnson, Jonathan Symonds, JASON OLFERT, University of Alberta
Abstract Number: 699 Working Group: Instrumentation and Methods
Abstract Many different methods measure the mass mobility of individual nano-particles such as the Aerosol Particle Mass (APM) analyzer and Centrifugal Particle Mass Analyzer (CPMA). However, the traditional setup of these instruments with a Differential Mobility Analyzer (DMA) and Condensation Particle Counter (CPC) require each mass setpoint to be scanned, limiting their application to steady state measurements.
This limitation can be overcome by using a Differential Mobility Spectrometer (DMS), replacing the DMA-CPMA-CPC with a CPMA-DMS system. Since the DMS measures real-time aerosol size distributions, transient mass mobility measurements can be completed for each CPMA mass setpoint.
This concept was verified by measuring the mass mobility of aerosolized lube oil using both a DMA-CPMA-CPC and a CPMA-DMS system. To increase sizing accuracy the DMS was modified by disabling the aerosol charger and lowering the sample and sheath flow rates. In a normal DMS the uncertainty, largely due to charging efficiency and its dependence on particle morphology, would have been 10% in particle size or 31% in effective particle density. By size calibrating the modified DMS with a DMA and applying a post-processing algorithm to correct the DMS results for multiply charged particles an uncertainty of 4-5% in particle size or 13-17% in effective particle density was achieved. These values were calculated using a 8% CPMA mass setpoint uncertainty and a 3% DMA mobility size uncertainty. Using the above values a 12% uncertainty in effective particle density for the DMA-CPMA-CPC system was determined.
The lube oil effective density results from the DMA-CPMA-CPC and CPMA-DMS systems were found to agree within error. Therefore, the CPMA-DMS can be used for mass mobility measurements, but at the cost of higher uncertainties compared to a DMA-CPMA-CPC system.