Measuring the effective density, porosity, and refractive index of carbonaceous particles by tandem aerosol techniques

Abstract

The physical properties of carbonaceous aerosol particles are often of interest but are difficult to determine from a single measurement. In this study, we used tandem aerosol measurement techniques to measure the effective physical properties, namely the effective density, porosity, and effective complex refractive index of spheroid aggregated and porous carbonaceous aerosol particles. An in-flight measurement system, composed of a differential mobility analyzer (DMA) followed by either an aerosol particle mass analyzer (APM) or a laser particle counter-pulse height analyzer (LPC–PHA), was constructed and used to examine shape-controlled and porosity-controlled carbonaceous particles produced by a spray-drying process. The effective density and porosity were inferred from tandem measurements in which particles were first mobility-classified by the DMA and subsequently mass classified in the APM. The effective refractive index of the particles was inferred from tandem DMA–LPC–PHA measurements in conjunction with Mie Theory. The measured effective density and porosity of the carbonaceous particles ranged from 695.0 to 1399.9 kg/cm 3 and 15.2% to 64.3%, respectively. Furthermore, the real and imaginary parts of the effective complex refractive index were between 1.430 and 1.736 and between 0.035 and 0.125, respectively. Both the real and imaginary parts decreased with increasing particle porosity.