Practical Considerations for Tandem Aerosol Classifier Measurements: The Effect of Scan Time, Resolution, and Calibration on Effective Density Accuracy
Morteza Kiasadegh, Timothy Sipkens, Jonathan Symonds, JASON S. OLFERT, University of Alberta
Abstract Number: 92
Working Group: Instrumentation and Methods
Abstract
This study systematically investigates the influence of resolution, measurement time, and calibration method on the accuracy of tandem aerosol classifier measurements of effective density. We investigate tandem combinations of the centrifugal particle mass analyzer (CPMA), aerodynamic aerosol classifier (AAC) and differential mobility analyzer (DMA), where the downstream classifier is a scanning instrument (scanning DMA (SMPS) or scanning AAC (SASS)). The impact of scan time depends on the classifier and its flow rate. For low-flow measurements (0.3 LPM) with a TSI 3776 particle counter, scan times greater than 2.4 and 5.1 minutes per size decade should be used for the SMPS and AAC, respectively. For high-flow measurements (1.5 LPM), scan times greater than 0.3 and 2.4 minutes per decade should be used for the SMPS and AAC, respectively. Measurements at lower resolutions (mass resolution of Rm = 2, and mobility or relaxation time resolution of Rs = 7) introduce significant errors. Conversely, medium (Rm = 6, Rs = 18) and high-resolution (Rm = 15, Rt = 45) settings produce nearly the same result. Using a high sample flow or high resolution enhances effective density accuracy but leads to a notably narrower measurement range. By determining the effective density of a spherical particle with a known material density (e.g., DOS), a calibration factor can be derived by comparing the measured density to the actual material density for each particle diameter. This allows for more robust instrument calibration. Using calibration, it was found that particles densities could be measured within ~5–7% of the actual material density. These findings demonstrate that using a scanning downstream classifier can yield accurate effective density measurements in a relatively short time if the tandem system is configured appropriately.