Real-time measurement of nano-agglomerate and aggregate mass and surface area concentrations with a prototype instrument

A prototype instrument was developed to measure geometric surface area (GSA) concentrations and mass or volume concentrations for agglomerated or aggregated particles at a time resolution of 1 s. It couples a diffusion charger with two sets of electrostatic precipitators and electrometers to monitor two current signals synchronously. In this way, we refined the measurements with a weighted-sum method. Initially, we tested the ability to distinguish different particle morphologies. Subsequently, theoretical volume and GSA measurements of single agglomerates and aggregates were performed to calibrate the instrumental sensitivity for particle sizes. Experimental results with polydisperse silver particles indicated that a diffusion charger coupled with a differential mobility analyzer and a condensation particle counter could identify particle shapes having different fractal dimensions. Above all, the instrument could be used to measure GSA, volume, or mass concentrations of both agglomerates and aggregates in real time. A favorable comparison with results obtained with a scanning mobility particle sizer suggested great potential for commercial applications.