Practical considerations for measuring effective density: Operational tradeoffs in resolution, characteristic scan time, and calibration

This study investigates the key parameters influencing tandem measurements of effective density for low-volatility spherical particles and examines the impact of instrument resolution on the operational range of different tandem configurations. Three tandem setups were evaluated using a differential mobility analyzer (DMA), a Centrifugal Particle Mass Analyzer (CPMA), and an Aerodynamic Aerosol Classifier (AAC). To enable fast measurements, the downstream classifier was used as a scanning instrument, either a Scanning Mobility Particle Sizer (SMPS) or a Scanning Aerodynamic Size Spectrometer (SASS). The effects of instrument resolution on the operational range and measurement accuracy were assessed using three resolution settings. Data were collected for mass set points ranging from 0.05 fg to 5 fg and aerodynamic diameter set points from 50 nm to 500 nm with aerosol flow rates of 0.3 L/min (low-flow mode) and 1.5 L/min (high-flow mode). The results indicate that the characteristic scan time (CST) required for accurate measurements depends on the flow mode and the downstream classifier, with longer CST required in low-flow mode and for the SASS compared to the TSI 3082 SMPS. Additionally, the medium-resolution setup provides the best balance between accuracy and range for effective density measurements. Furthermore, calibrating the effective density of Santovac particles using the measured DOS effective density improves measurement accuracy. The conclusions apply to spherical, low-volatility particles (50–500 nm) measured with the instruments in this study, while the framework and procedures are broadly applicable to other tandem configurations and aerosol types.